Wren 44 Gold

Transcription

Wren 44 Gold

Wren 44 Gold
45N Kerosene starting Turbine
Engine and warranty
Features:
Compact but tough
Extremely short overall length
10lbs (4.5kg) thrust @ 195,000rpm
Only 0.3lbs (0.15kg) idle thrust
Integral protective FOD screen
High duty precision bearings
Inconel combustion system
Fast kerosene starting system
Sturdy high quality anodised case
3 piece pre-shaped anodised mounting
Copyright Wren Turbines 2012
Introduction to the Wren 44 Gold.
Features:
High thrust to weight ratio.
Small physical size – extremely short length enhances install options.
Integral high quality FOD screen and starter mounting.
Neat new rotateable, low current kerosene ignitor,
Solid stainless steel bearing carrier system.
High precision ceramic bearings.
Inconel combustion chamber for long service life.
High quality anodised case for excellent service life and superb finish.
Xicoy 107k ecu
Hausl ZP25M14 magnetically coupled fuel pump
50 hour service interval.
History
In the early years of jet flying during the 80’s and 90’s the i/c engine ducted fan ruled the
roost. Although noisy and heavy this was the closest modellers could get to real jet flying. At
the beginning of 2001 all this changed. Wren Turbines were the first manufacturer of small
gas turbines to release a small engine to replace these old fan engines. First came the Wren
54 which was intended to replace a 90’ size ducted fan and here we present the Wren 44 to
replace the 45’ size ducted fan.
The Wren 44 was first released to eager model flyers back in 2003 with a rating of 7lbs thrust
and hand start only. The engine has not stood still during this time. Successive
improvements and enhancements – onboard start in 2004, full autostart capability in 2006,
increase in thrust to 8lbs in 2006, and a new standard in miniature turbines – the Gold
standard in 2007 with a massive increase in power to 10lbs thrust following a complete
redesign of the engine and accessories.
Since 2007 the engine has formed the basis of the Wren 44 Turboprop and in 2008 the Wren
44 Helicopter greatly increasing the numbers supplied.
In 2010 we reworked the bearing supports to include a new stainless steel front preload for
smoother easier running and introduced a long life “mini-plug” to replace the standard
glowplug for a ceramic element for ignition purposes. In 2011 we introduced a new
development requested for a long time by flyers – kerosene starting. The successful
introduction of kero-start marks a turning point for many. The limitations of fiddly gas
cannisters and cold day troubles with ignition can now be eliminated. A new miniature burner
born after a long period of development enables all the benefits of kero starting but without
the current drain or bulky burner components of other systems. A new smaller ECU and well
engineered fuel pump completes this new package.
This new system eliminates on-board gas tanks, gas restrictors and all the extra accessories
required to support a gas system and replaces them with just an additional valve to control
flow to the new burner. Installation is simple with very few components making the 44 Gold
thrust engine a delightfully easy installation and a real powerhouse for the jet enthusiast.
Propane start remains popular with many users and there are no plans to discontinue this as
long as demand lasts.
Description
The engine is a single shaft turbo-jet with high pressure centrifugal compressor and single
stage axial turbine. A precision aluminium diffuser system gives a wide operating margin able
to cope with large pressure and temperature extremes. A high quality stainless steel shaft
Wren 44 Gold TurboJet Engine
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tunnel supports the two precision ceramic bearings with a gentle preload, allowing very free
running and low operating loads.
The reliable Inconel combustion chamber has been retained and offers long service life and
low weight penalty. The 44 Gold uses the solid and reliable Xicoy 107k ECU, which offers
over-current protection and excellent engine control functionality for fuss free operation. The
ECU can be set up for gas start, kero start or manual start all in the same unit.
The Wren kerosene-start burner is compact with user replaceable parts (not built it out of
reach) – not that this is likely to be needed as the element has a voltage range equivalent to
the 2S LiPo battery supplying the ecu – making it almost impossible to overdrive it. The
element has extremely fast heat-up time and generates a strong healthy pilot burn making
the start process rapid, consistent and fuss free. The main body is rotatable ensuring the
feed pipe always finishes in the required position – no need for packing washers or kinked
pipework here. The low installed height is a huge bonus for those with limited room in the
engine compartment.
All this and of course, the as-standard Wren quality which customers know and expect make
the Wren 44 Gold the ideal first choice for jet enthusiasts looking for quite a bit more than the
usual in their turbine choice. We are confident customers will find it easy to use and enjoy its
sparkling performance.
Wren 44 Gold
The name “Wren 44” refers to the original diameter of the compressor wheel, was 44mm, –
now 46mm. The name has always been associated with this small engine so we retained it
even though the dimension it referred to has changed.
The engine has a 75mm diameter case size
and is just 215mm long from tip of starter to end
of exhaust making this one of the smallest
engines in this thrust class available. This short
length is made possible by making extensive
use of our experience in designing short
combustion chambers that work well and are
fuel efficient.
The engine weighs just 660g (1.45lbs) including
the integral ECU screen / starter mounting. For
this class of engine, a modified tea strainer
really is not the answer, nor do we expect customers to pay extra for such an essential
accessory. The integral FOD screen is in keeping with our ethos of safety and performance
for our customers. The starter is the well proven Wren bendix style clutch and fully ball-raced
280BB motor for long life.
An inline fuel filter is fitted under the FOD screen to protect the fuel and lubrication system.
The engine uses a hall-type magnetic rpm pickup to sense engine rotating speed. The
sensor picks up the rotating magnetic field from a small bar magnet fitted inside the spinner
nut.
The rpm pickup under the FOD screen is sensitive to stray external magnetic fields so it is
advisable to keep devices capable of producing interference away from the sensor.
The engine connections also include the power cable for the starter and kerosene igniter
plug. These are locally terminated and reach the ECU via a lead supplied with the engine.
The fuel and igniter supply to the engine is via the 3mm Festo fittings on the pipes (clear)
extending from the FOD screen and the igniter body.
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On kero start engines a propane system is not fitted to the
engine. A propane start engine may be subsequently
converted to kero-start by simply plugging the propane inlet.
A conversion to propane-start from a kero-start engine will
require the relevant propane equipment installing.
A three piece engine mount is supplied which allows the
lower section to be retained in the airframe so the engine is
cradled in position before being secured by the two upper straps.
The main fuel supply to the engine is controlled via a small solenoid valve.
The fuel supply to the kerosene igniter is delivered to the engine via a solenoid valve which
controls the flow by pulsing rapidly on and off. The resulting flow is set by an easily
accessible value set in the ECU. See the settings section for the default values used. On the
propane start engine, the propane supply uses a similar solenoid valve, followed by a screwdown flow restrictor to preset the gas flow as required for the engine.
Sabb Viggen and 44 Gold of Franz Leitner
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Wren 44 Gold Gas Turbine, Mechanical Description
The Wren 44 Gold miniature gas turbine is the latest in the line of Wren 75mm (3”) diameter
miniature gas turbines. The engine is a single shaft turbojet comprising of single stage
centrifugal compressor and single stage axial turbine.
The compressor is a 12 vane retro-curved pattern offering
high pressure rise with wide operating envelope and freedom
from surge. The diffuser system comprises a one piece
machined assembly with eleven vanes combining a wedge
style front vane with integral side vane.
The diffuser is enclosed by a front plate combined with the
engine air intake offering strength and rigidity with good
aerodynamic characteristics and high flow capacity. This
system offers minimal parts count with maximum repeatability and service.
The turbine rotor assembly is dynamically balanced to below
0.03g/mm and is carried by two angular contact high speed, high
precision ceramic bearings housed in a high quality stainless shaft
tunnel. The bearings are lightly preloaded using wave springs to a
load of just 5N allowing very free rotor running, minimal torque
requirement for starting and long bearing life. The bearings are
lubricated and cooled by a small bleed-off from the main fuel
pressure line. Lubricating oil is mixed at 5% to the fuel to provide
lubrication as the fuel alone has little lubrication qualities.
The combustion chamber is of annular pattern with all hot
contact surfaces of Inconel 600 for freedom from distortion and
erosion for the lifetime of the engine. The chamber also
benefits from a circulation ring to allow correct combustion to
be attained in a much shorter than standard pattern. This
results overall in a shorter and more compact engine. The fuel
vapour conversion is via six vapourizer tubes of special pattern
fed by stainless injectors mounted in a brass manifold. The
combustor is fitted with a twin outlet gas injector (on gas start
engines) for even and controlled pre-heating, minimising
distortion of the guide vane and endowing the engine with
clean quick starting characteristics.
The 17 blade guide vane is cast from a multi-part pattern
made at Wren and is in ANC5C, a high temperature
furnace grade alloy ideally suited to operating in this
environment. The turbine is a 23 blade wheel made from a
Wren wax pattern and is vacuum cast in Inconel 713C to
full aerospace certification for maximum safety and life.
The contoured exhaust cone is machined from solid
stainless steel for strength and safety and is designed to
safely contain any blade failure of turbine for whatever
reason at any rpm.
The engine casing is machined from solid anodised
aluminium for rigidity and accuracy and is complimented at
the front end by a machined anodised starter housing with integral stainless steel meshed
fod screen to protect the engine from accidental ingress of potentially damaging particles and
inquisitive fingers. A high pressure 15 micron fuel filter is fitted in the fuel pressure line as
protection from potentially harmful fuel contamination getting to the engine.
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The engine starter is a high speed ballraced electric motor driving a miniature bendix-type
clutch assembly retained in the off position by a magnetic ring to the motor casing. The drive
is transmitted through a small replaceable neoprene O-ring. The motor, clutch assembly and
O-ring are easily accessed by simply slackening the three grub screws and withdrawing the
complete starter.
The Electronic Control Unit (ECU) is a closed loop system using a magnetic hall-effect
sensor to detect rotating speed of the rotor via a small magnet fitted into the aluminium
compressor securing nut. A type “K” inconel sheathed thermocouple inserted into the
exhaust cone measures exhaust gas temperature and this is read by the ECU to ensure
operation is within limits set.
All screws used on the engine are in stainless steel and of the cap head pattern for ease of
access and a locking compound is used on all critical screws. All pipework is secured to the
engine via 3mm quick release industry standard fittings. Pipework for all services is via high
flexibility 3mm polypropylene fuelproof tubing.
Safety Notes.
Wren Turbines are active members of BMFA (British Model Flying Association) and fully
endorse the BMFA code of practice for operating gas turbines. The BMFA also provides
insurance cover for modellers in the UK. This Code of Practice may be accessed from the
Gas Turbine Builders Association (GTBA) website on www.gtba.co.uk The GTBA is the
BMFA advisory body for model gas turbines.
Failsafe. Please read carefully the notes on setting the failsafe on your radio to ensure safe
operation in event of interference or loss of signal.
It is advised always to have a CO2 or similar gas-type fire extinguisher with you when running
the engine – you never know when an emergency will strike and it is best to be prepared. If
you need to extinguish an onboard fire you should point the extinguisher into the front of the
engine and not in through the turbine end as this may simply blow the flame into the model.
Always ensure, when running a gas turbine that you keep spectators at least 10m (30ft) clear
of the area to the side and rear of the engine as you would a propeller engine, as although a
broken turbine is extremely rare it is still technically possible and it is better to be safe.
When running the engine you should stand in front, or in front and to one side of the engine,
and not to the side for the reason above.
Always wear ear defenders when running the engine as gas turbines have a high intensity
noise level close to the engine that can impair your hearing
in time.
Never try to improve/speed up the starting of the engine by
spraying ignition agents into the engine – a dangerous
flashback fire may result and you will in any case never
improve the starting this way.
This engine is not a toy and can cause bodily harm to you or
others if misused. The engine may not be used for purposes
of powering a vehicle or craft to propell a human being.
It is your responsibility as owner, to ensure safe, careful and
considerate operation of your engine at all times, and in
accordance with the manufacturers instructions.
If you sell or give away this engine, please pass these
instructions to the new owner.
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This engine must only be run firmly attached to a secure and sturdy engine test stand or
model installation where the model is suitably restrained. The thrust generated is
considerable and mountings must be sufficient to withstand such forces. Use appropriate
screws and lock-nuts. The engine must never be run held in the hand or clamped in a vice.
This engine is an internal combustion gas turbine engine which generates large quantities of
heat – ensure the mountings and installation are appropriate for operation at these elevated
temperatures.
During operation and for a time afterwards there are parts of the engine which are hot
enough to cause serious burns – do not touch any part of the engine until it has cooled to
room temperature.
Always operate your engine in open air away from confined spaces as the engine exhaust
contains gases which can cause asphyxiation and nuisance from smells.
The exhaust gases are very hot (up to 700’C) on leaving the engine and can cause burns to
skin or damage to objects close to it – keep exhausts clear of anything which is affected by
such heat.
This engine must not be used near flammable gases, liquid or materials.
Always keep a CO2 fire extinguisher close by when operating this engine.
Turbine fuel is poisonous. Keep it away from the mouth and eyes and from contact with skin.
Always store it in a marked container and out of reach to children.
Turbine fuel has a relatively high flash-point but in certain circumstances (ie if allowed to
contact hot surfaces) can be highly flammable or even explosive. Keep it away from heat and
sources of combustion.
Starting propane, if used, is highly flammable and must be used with extreme care. Maintain
canister and fittings in good leak-proof condition. Protect from sunlight and prevent exposure
to temperatures exceeding 50’C. Keep out of reach of children. Discard used canisters in a
safe place and do not puncture or incinerate, even when empty. Avoid deliberate inhalation.
If used, ensure propane gas only is supplied the engine, liquid propane must not be allowed
to pass into the engine. Propane supply must be disconnected until ready for immediate use.
Propane is heavier than air and can fill a model if allowed to leak unchecked, and become a
potential explosion hazard.
Continual failed kerosene starting or excessive priming of the fuel system can cause excess
fuel to build up in the engine chamber which can cause flaming on eventual ignition. If fuel
excess is suspected the only way to drain the engine is to tip the engine forward and allow
the fuel to exit through the fod screen and mop up with a rag. It is no use tipping the engine
with the exhaust downwards as excess fuel will not be released due to the ngv being
mounted forward of the engine rear.
Turbine oil can be are hazardous to health and must not be allowed to come into contact with
skin, mouth, eyes or through ingestion, accidental or otherwise. Take care when decanting
and ensure any spillage is wiped away immediately and clean any affected area with warm
soapy water. Wash hands and any affected part immediately after any contact.
Turbine oil can discolour or affect certain paint finishes as may be used. Take precautions to
prevent spillage. Do not discard or allow any spillage to run into drains.
If removing the kero-start plug to test it, keep fingers or bare skin away from possible burn
from the glowing element – use a metal tool or appropriate insulation. The igniter body heats
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to a high temperature very quickly and could cause severe burns if allowed to contact the
skin.
As operator, it is your responsibility to ensure any spectators (especially small children) or
helpers are kept well away from the engine whilst it is operating. The safest position to
operate the engine is directly in front. The area inline and to the rear of the turbine is the
most dangerous area and you must keep well clear of this.
Keep all spectators away from the side and rear of the engine to a distance of at least 10mtrs
(30ft) radius, as shown. If operating from a pit area take special care as safety distances are
often difficult to maintain. Consider the high engine noise level when spectators are around
and do not use high throttle levels in these circumstances.
Keep all helpers close by and brief them fully on their duties before starting the engine. One
helper should carry out the role of fireman. Ensure they are aware of what to do in event of
emergency and where to position the extinguisher if required.
Wren 44 Gold package contents
The engine package contains the following:
This Operators Manual
Wren 44 Gold engine
3 piece engine mounting
Xicoy ECU
Data Terminal
Fuel pump
Solenoid valve (2-off), c/w 3mm quick
release fittings
Propane flow control (on propane start
engines)
4-core, engine to ECU power cable
Battery/pump to ECU cable 0.3m
7.4v LiPo battery (capacities vary)
1m clear 3mm pipe
1m green 3mm pipe
0.3m 3.1mm (1/8”) internal Tygon
Rx signal cable
(Spare/additional cables and pipes available on request)
LiPo battery.
A 2-cell LiPo battery pack is supplied with the engine. The precise capacity may vary
(according to supply) but it will always be a two cell of at least 1800mAh and a “C” rating of at
least 20. The “C” rating is the number of multiples of the nominal capacity that the battery
may deliver in short bursts, without damage. With a C rating of 20 and a capacity of
1800mAh the battery should be able to supply 20x1800mA=36,000mA or 36A for short time
during the start cycle without significantly dropping the output voltage.
The actual amount of power consumed during a typical kero-start and cooldown is around
60mAh, so the battery supplied should be easily capable of five or six good starts and flights
without problems. It is good policy to monitor the amount charge required to recharge the
battery to be sure and to monitor the battery health. The kerosene-start system uses a low
resistance heating element to ignite the kerosene in addition to driving the engine through
the starter motor. This makes a large demand on the battery, so a high C rating is imperative
to successful starts.
Always disconnect the battery from the ECU before charging. Charging with battery
connected to ECU can destroy the ECU and this will not be covered by the warranty. Charge
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the pack with a charger especially set up for LiPo batteries. Chargers for any other batteries
MUST NOT be used and can cause the battery to destruct. A larger capacity pack can be
substituted if required. After the flying session is finished, disconnect the battery to prevent it
from irreversible damage caused by deep discharging.
Fuel.
The engine is designed to run on Jet A or Jet A1 or low sulphur paraffin such as is available
at airfields and DIY stores or at filling stations from the pump. A system of decanting the fuel
safely into the fuel tank must be arranged. Do not use open-top fuel tanks which could fall
over or be unstable when filled. When decanting fuel, take precautions to ensure no solid
particles or water droplets are carried over into your fuel tank – use an effective filter system.
Note that it is common for water to collect in the bottom of fuel containers – ensure this
cannot be sucked into the fuel system by regular visual checks. If necessary, drain the
contents and discard the water residue in a safe and responsible manner.
Note that jet fuels and oils should not be allowed to come into skin contact so wear suitable
gloves and take extra care when handling.
Oil.
To this fuel must be added 5% of a suitable oil, ie a mixture of around 20:1 fuel to oil.
Suitable oils are turbine oils such as Mobil JetOil, Aeroshell 500/550 and Exxon 2380. Other
oils specifically for use in turbine engines and which will mix readily with the fuel and stay
mixed, may also be used, for example
Castrol TT 2 stroke motor cycle oil has been used very successfully.
At Wren we use Mobil DTE Light, a clear non hazardous hydraulic oil which requires no
special handling precautions and generates no carcinogenic vapours when used in the
engine, plus has no significant environmental impact. Its only real disadvantage is it is only
available in large 20ltr drums but of course friends can club together and get a good supply
in the one container. Mobil DTE Light is available from the larger tool and hardware
suppliers.
Setting up the engine
The engine and its accessories have already been set up and run at least three times so
experienced modellers may proceed and install the engine directly to their airplane. Pay
heed to the notes on intake requirements and mounting.
For less experienced modellers it is suggested to set the engine up on a test-stand and to
familiarise themselves with starting and running the engine before installing in a model. A
three-piece mounting strap is supplied and this should be strongly attached to a pair of
timber battens screwed to a base-board. The two top straps must fit securely on the engine
to prevent the casing sliding.
The various components can be temporarily secured to the baseboard, but be careful not to
allow any cables or pipes to run close to the engine intake where they might be sucked
against the FOD screen. Remember, this engine produces 4.5kg (10lbs) of thrust and it can
push over the test stand unless it is very secure.
Setting up in the model
Intake considerations.
The Wren 44 Gold consumes a considerable volume of air and the intake area must be large
enough. The mass flow of the engine is approximately 0.13kg/sec - just over 100ltrs per
second and all this must pass through the intake and exhaust system.
The minimum size for a square inlet is 50mm x 50mm or 2” x 2”. A single circular opening
would need to be approximately 75mm (3”) diameter to have the same area. This inlet area
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can be achieved through a number of openings but need to be uncluttered and free of
internal restrictions especially in the immediate area of the engine intake grille.
25mm
If a tailpipe is required then you can use the 44 version. You must leave a gap of 25mm (1”)
between the end of the engine exhaust nozzle and start of the tailpipe bellmouth. This
ensures adequate secondary air can be induced into the tailpipe and enable a small increase
in throughput to be achieved without causing restriction in the airflow of the engine.
Too small a gap can cause reduced thrust, excessive running temperature and unstable
running. Too large a gap can allow overspill of the exhaust around the edges of the
bellmouth.
Pipes are available in single and twin wall. Standard lengths are 420mm (16.5”) and 620mm
(24.4”).
Engine mounting detail
6 holes Ø3
The Wren 44 is supplied with a
3-piece engine mount enabling
customers to provide a secure
and stable fixing point into their
model.
The mount can be fixed into
place with six #6 woodscrews or
M4 bolts into a suitable hard
point on the airframe. This
mount acts as a cradle for the
engine to enable it to sit into
position whilst the services are
connected without needing to
support the engine weight.
The upper section of the
mounting can then be used to
secure the engine into place.
c WREN Turbines
The
drawing
shows
the
mounting arrangement from
above and looking at the engine
from the exhaust nozzle end
(end view). The engine may also
be mounted inverted if required.
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Wicked looking 44 powered “Scorpion” by Eric Rantec seen at Jet Power 2010.
Fuel system
Small turbines need a consistent fuel supply where no air bubbles can be allowed into the
suction side of the fuel pump. Any such bubbles will allow the pump to cavitate (ie stop
pumping momentarily) and the engine will stop, resulting in a flameout. The small pump used
has a very high suction level and for this reason we must insist no filters, connectors, valves
or shut-off taps are placed in the suction line. The only thing that should be fitted between is
a UAT (Air Trap) – see below.
The ideal fuel system will have a fuel tank with around 1200ml (40oz) to 1500ml (50oz)
capacity, a weighted pickup clunk and an air trap such as the “Ultimate Air Trap” (UAT) by
BVM models and similar. Capacity of the UAT should be around 115ml / 4oz.
The UAT is like a small fuel tank that fits between the main fuel tank and the fuel pump. The
feed line out of the UAT is in the centre so as long as there is fuel in the UAT no air can enter
the fuel line to the pump. The UAT is constantly replenished by the main tank until the main
tank level falls too low and air will finally enter. Obviously you need to have landed safely
before this point is reached so use your transmitter timer carefully. Mount the UAT at an
angle from vertical, so that the two pipe fittings are at the highest point.
The UAT has a bladder in the form of a filter so will provide a degree of debris protection but
the filling of the main tank is done through the UAT so in time debris will build up in the fuel
tank and cause problems, so ALWAYS filter carefully the fuel going into the tank when
refuelling.
Vent
Fill point
Fuel Pump
Fuel Tank
Air Trap
Recommended fuel system for Wren 44 Gold installations (not to scale)
Keep the fuel pump close to the UAT and keep the fuel line from the main tank to the UAT as
short as you can.
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Connect the Outlet (bladder part) of the UAT to the suction side of the pump using Tygon
tube – seen below with blue locking cap. Use a small (20mm -3/4”) piece of 4mm tube
pushed onto the pump inlet nipple and push the Tygon over it to form a tight joint.
Push Tygon tube over the inlet pipe of the UAT (either of the
two clear pipe connections shown left) and connect the
other end to the fuel outlet of your tank. If the tank outlet is
of 3.1mm (1/8”) brass tube, then use another small piece of
4mm clear to sleeve it before pushing the Tygon over it.
These two pipes are critical to the safe and reliable
operation of your engine so take extra care to be sure they
are perfect.
Use a short length of Tygon to connect the remaining
connection - the “Fill” point of your UAT and leave the free
end accessible. This free end must have a perfect blanking
plug fitted. This pipe is used to back-fill your fuel system – the aim is to fill the UAT and
backflow to your tank via this route so all air can be purged from the fuel system as it fills.
Aim to completely remove all trapped air by angling the plane as you refuel so that the air
travels into the tank and out through the tank vent.
Lastly, a small piece of Tygon should be used as a tank vent pipe, which should be fitted to
allow air into the tank as the fuel level lowers.
A successful fuel system will show only a small size air pocket in the UAT as the tank level
lowers. If you land and find a large or increasing air pocket then you must look for an inward
air leak either in your tank or the pipework to the UAT, as the fuel system will be unreliable.
Do NOT use tie wraps anywhere on your fuel system as they distort the pipe into a “D” shape
which will let in air or leak.
Two of the very popular small Czech
Savex L39’s (www.savex.cz) owned by
Paul Gray and Joe Cannella with
daughter Theresa Cannella for scale.
The aircraft are virtually ready-built and
available in a range of colour schemes.
They are exceptionally easy to fly and
are particularly good off grass strips.
Excellent Schreiner F-18 seen at the
July 2005 Wren 2005 open day.
Turbine version of an electric ducted
fan ARTF kit.
Page 12
Performance.
Jet engine performance varies according to atmospheric conditions so the figures we quote
are for a “standard day” and on most days we correct the readings we get to reflect standard
day performance. There will always be small differences between the thrust of engines
because they are designed to run to a specific max rpm, and no two engines are identical,
however hard we try. Full-size engines suffer from the same problem and so are set up to
run to a specified thrust, the engine rpm would be set to achieve the specification by raising
or lowering the max rpm. This is impractical for engines in our size so we just aim for the
highest spec’ possible with each engine.
Because of these differences we use the term “nominal” – which means ”normally” in our
case.
Nominal Performance figures for the Wren 44 Gold.
Max RPM
Max thrust
Idle speed
Idle thrust
EGT idle
EGT max
Fuel consumption at max
Fuel consumption at idle
195,000rpm.
4.5kg (10lbs)
55,000rpm
0.13kg
(0.3Lb)
450-550’C
600-700’C
170ml/min (6oz/min)
25ml/min (0.8oz/min)
Specifications:
Weight engine only
660g
(1.45lbs)
Weight ancillaries ex. battery 140gms
(4.9oz)
Weight inc. ancillaries
800gms
(1.75Lbs)
Length o/a inc. FOD screen 215mm
(8.5”)
Diameter
75mm
(3”)
Standard cabling distance between engine and ECU - 305mm (12”) (Alternatives available)
ECU battery
2-cell LiPo 7.4v, min 1800mAh 20C (capacities vary)
A larger capacity 2-cell LiPo battery may be substituted for longer running time and to help
with aircraft CofG corrections, but ensure its C rating is 20 or more.
Useful measures:
Bearing lubrication flow
Oil content
Oil type
Starter motor
Igniter
Rpm pickup
Exhaust temp’ probe
7.6% total fuel flow
5%, 20:1 fuel – oil
Turbine oils, quality 2-cycle oils or Mobil DTE Light
Multiplex 280BB ballraced 3-pole motor c/w Wren bendix clutch
Wren ceramic kerostart element, 6.9v operation, 20W
Magnetic hall effect sensor, ∅3mmx3mm magnet fitted across
end of compressor nut
K-type, Inconel sheath, 1.5mm inserted min 6mm into exhaust
Engine servicing interval
50hrs runtime – bearing service.
Page 13
Wren 44 kerosene start schematic
Pump
Igniter
Valve
Igniter Plug
Fuel tank
Fuel
Valve
Starter
motor
Temp sensor
RPM sensor
STARTER
GLOW
Data
Terminal
PUMP
BATTERY
KERO VALVE
7.4V
2cell
LiPo
GAS VALVE
Xicoy Fadec
Au-107K ECU
Receiver
RPM
Throttle signal
Throttle In
TEMP
System Components:
44 Gold Engine
Xicoy AU-107K ECU pre-programmed
3-wire type Data Terminal
Hausl ZP25M14 magnetically coupled fuel pump
Two valves c/w 3mm push-in fittings, (brass type)
Wren kero burner
3mm ptfe burner feed pipe and inline connector
3mm T or Y connector
3mm fuel piping
2-cell LiPo 1800mAh, 20C rating battery
Xicoy AU-107K ECU showing plug locations.
See text overleaf for details on what plugs in where.
Page 14
Quick start installation, mechanical:
Position the fuel pump, ECU and valves. Place valves as
close to engine as possible.
Rotate the burner feed into the direction to suit your install
before tightening.
Fit plug cap to burner nipple, carefully.
Connect inline 3mm fitting to end of burner ptfe tube.
Connect a short (20mm) 4mm tube onto fuel pump inlet and longer 3mm tube to outlet.
Push on Tygon feed pipe from UAT (Air Trap) onto 4mm pump tube.
Fitting and removing tube from the quick release fittings
This almost seems a pointless note but it is surprising how many people have not used these
fittings before. To fit tube to the fitting, ensure the end of the tube is cut perfectly square
using a sharp knife – not side cutter pliers.
Apply a very thin smear of regular axle or silicon grease to the last few mm of tube and with a
slight turning action push the tube fully home into the fitting. A light tug on the tube will
confirm it is properly fitted.
To release the tube, hold the fitting firmly in the fingers of one hand and using the finger and
thumb of the other hand, push on the blue outer ring and gently pull out the tube from the
fitting using the remaining fingers.
Just pulling hard on the tube is sure to damage the retainer in the fitting and stretch the tube
and make the fitting hold the tube even tighter - so don’t!
Connecting up – continued
Position Y connector close to valve inlets and
connect pump outlet to Y inlet with 3mm tube.
Connect Y outlets to each valve with 3mm tube.
Connect one valve output to engine fuel inlet with
3mm tube.
Page 15
Connect the other valve output to the burner feed fitting with 3mm tube.
A fuel shut-off tap is not essential on an autostart engine as the solenoid valves provide this
function as soon as powered down, but where local regulations require or personal
requirements dictate it, a tap can be fitted in the delivery line of the pump before the “Y”
fitting, (suitable taps available from Wren).
An in-line 15um fuel filter is fitted in the fuel feed to the
engine under the green FOD guard. It is covered in clear
heatshrink to prevent possible electrical noise by
rubbing. It is rare for this filter to need cleaning but if this
is required it must be refitted back in the same
orientation (the turned ring indicates the output) – else
any debris remaining will travel straight into the engine in
event of fitting it back to front.
Connections in the fuel system should be kept spotlessly clean to eliminate the possibility of
contaminants entering the system. This can cause sticking valves, stalled fuel pumps and
blocked filters and igniters. Debris entering the engine can cause hot spots, ruined bearings
and poor running, requiring major repair. Cleanliness is truly next to godliness in this respect!
A common failure complaint is the result of tiny pieces of the yellow “Tygon” fuel feed tube
getting into the suction side of the fuel pump and jamming the gears. This is why it is good
practice to fit a piece of fuel tube over the barb before the Tygon. Always check the barb is
clear of Tygon bits if you have to disconnect the suction pipe.
If you do get a stalled pump through bits getting in, do not disassemble the pump but clear
the obstruction by disconnecting it from the ECU and running it in reverse whilst connected to
a supply of clean fuel on the output side. If the pump is opened it will not be covered by the
warranty.
IMPORTANT. If the engine needs to be returned for servicing or to transfer between
aircraft, keep the fuel and igniter plug lines blanked off to prevent contamination.
Quick start installation - electrical:
Refer to the picture of the ECU on previous page for plug locations.
Plug burner valve to the 2-pin socket marked as “Gas valve” on ECU (see top left).
Plug engine fuel valve to adjacent 2-pin socket marked “Fuel valve” (extreme top left), note –
this label is on side of ECU.
Plug in the receiver throttle signal wire from receiver to the plug marked “Throttle input” (see
bottom right).
Plug in the engine rpm sensor to the 3-pin plug marked “RPM sensor” (bottom right).
Plug in the engine temperature probe to the 3-pin plug marked “Thermocouple” (bottom
right).
Plug in the glow/starter cable from the engine, using extension if fitted, (see top right).
Plug in the battery/pump cable (top left). Leave the battery end unconnected at this stage.
Plug in the data terminal (bottom left). A standard servo type extension cable can be fitted to
the model to allow convenient access, if required.
Page 16
Setting up ECU (Engine Control Unit)
Remove all rates, mixes and throttle travel settings in the transmitter. The setup assumes the
use of a transmitter with manual trims.
Digital trims and Throttle-Cut function.
If you have a transmitter with digital trims you can simulate the trim up/down function using
the “Throttle Cut” switch, which is usually a function switched through a toggle switch
mounted on the transmitter (must not be spring loaded). Consult your radio manual for this
function. Setting the ECU using the “Throttle Cut” function is done in the same way except
that when “trim-up” is required you switch the “Throttle Cut” to off, and when trim-down is
required, you switch to “Throttle Cut” on.
For initial testing the normal digital trims can be used if you don’t want to have to explore the
“Throttle Cut” function just yet. The trim up/down function is used to switch the engine to
“ready to start” and “off”, and would not normally be used to vary the idle rpm. Note - some
transmitters may need throttle reversing - see later. As the display does not photograph well
we have reproduced the display readings as a green box.
Turn on the transmitter and receiver. On power-up the Trim Low
T=020’C
screen should come on and after a few seconds
RPM 00000
PW 000
should stabilise to the opening screen and should
show as right: (If the temp’’ probe is not connected it will show as 0’C). “T” = ambient temp’.
There are four buttons on the display. The buttons
are:▼▲-+.To scroll through the different screens use
▼▲. The buttons - + are used to change the values
stored.
Start
Press the Up button (▲) and scroll through the menus
until you find the one showing:
Transmitter
adjust
Info
Run
Radio
Enter
Press the minus (-) button and the screen will change to:
Press the + button to enter the radio setup screen. You should then see this screen:
Stick Up
Trim Up
(Full power)
On your transmitter,
place the throttle stick and trim to maximum and press the
+ button to set the value into the ECU.
The screen will now
change to:
Stick Down
Trim Down
(Stop)
Move the throttle trim (or switch the “engine cut” switch to
on) and throttle stick back to zero and again press the +
button.
The display will now
change to:
Stick Down
Trim Up
(Idle)
Page 17
Leaving the throttle stick in the minimum position, raise the throttle trim to the max position or
switch “Engine Cut” switch to off, and again press the + button.
The display should
then show:
Thrust curve:
LINEAR
Lower trim to zero. Now switch off the receiver.
Turn the receiver on again, if you have done all the steps
correctly the opening screen will show “Trim Low” and if
you raise your trim to full it should change to “Ready” and
a blue led will light on the ECU. If not, you will need to
reverse the throttle channel on your transmitter and repeat the radio setup.
This completes your radio set-up. It should only need doing again if the radio settings are
changed or installation moved to another radio but it is worth rechecking periodically.
Failsafe function
The ECU checks the incoming throttle channel pulses from the receiver to ensure they are
between the limits set when the transmitter setup was carried out. If a signal arrives outside this
range or is corrupted the failsafe function is enabled.
The failsafe function will stop the engine in the event of loss of radio link or continued radio
interference that masks the normal signal, but will allow the engine to continue to operate in the
case of short glitches. The system works with PCM, PPM and IPD systems.
VERY IMPORTANT - The radio must be set to shut the engine off in event of loss of valid
signal. If the receiver is set to “hold” the failsafe in the ECU will be prevented from
operating. As default the FADEC ECU supplied with this engine is set to do the following:
Operation is as follows:
ECU will tolerate loss or corrupted radio signal for up to 0.5 sec’s.
If loss or corrupted signal continues beyond 0.5 seconds the ECU will command the engine to go
to 10% thrust.
If the error condition continues for a further 1.5 seconds the ECU will shut the engine off.
This system allows the engine to fly through minor interruptions of signal or glitches, thus
avoiding the engine shutting off unnecessarily, while maintaining the safety of automatic
shutdown in cases of loss or corruption of radio link.
IMPORTANT
ALWAYS PROGRAMME THE RECEIVER FAILSAFE TO SHUT OFF THE ENGINE
NEVER FLY A TURBINE AIRCRAFT WITH THE RECEIVER FAILSAFE SET TO “HOLD” AS
IT WILL PREVENT THE ENGINE FROM BEING SHUT DOWN IN A FAILSAFE SITUATION.
Page 18
John Wright’s Savex F-16, designed especially for the Wren 44. This model is a genuine ‘pocket
rocket’!
Setting up to run engine
Turn on the receiver and verify the screen shows a reading.
Go into the 3rd screen and enter the “RADIO” menu and perform the transmitter setup if not
already completed as above.
Connect the LiPo battery.
Priming the fuel system - new installation
The next job is to prime the fuel system to ensure it is full before a start.
This is very important with a kero-start system as the burner needs to have a little kerosene in
the body to absorb some of the heat and prevent the element from overheating. Successive
attempts at starting with no fuel present in the burner can cause damage.
Ensure trim and stick are at zero. Go into “INFO” menu and go down the entries until you get
to “test” functions. Find “Test/Prime Pump”. Press “On” button to turn on fuel pump and
watch fuel travel along from the tank to the engine. Press “Off” to stop.
Go further down “INFO” menu to “Prime Burner On Off”. Press “On” button and watch fuel
travel to burner, then press “Off” to stop. Do not prime longer as you risk pouring fuel into the
engine which will cause a flaming start. Small bubbles in the pipes at this stage will not
prevent a start but may delay it.
Place the engine/plane into a suitable place and prepare for a start. Use helper if required to
restrain model.
Position fire extinguisher – if you get into trouble place trim down, stick down immediately to
halt the start. Then energise the starter by raising the stick to full to spin the engine up to
clear.
If you have a fire, position C02 extinguisher nozzle at engine intake and use short bursts to
put out.
Page 19
This section deals with engine running
At this point it is assumed the engine and its accessories are properly installed and connected up
as described in the various sections.
If a tailpipe is fitted it is secured in position with the recommended 25-30mm distance between
exhaust outlet and bellmouth.
Running the engine.
Once you have completed the priming of the burner and main fuel line you can prepare for an
engine run:
Check all leads and pipes are in the correct position and properly connected.
Position it in a suitable place in a well ventilated area, preferably outside and clear of any likely
hazards.
Secure your test stand or get someone to restrain the aircraft firmly – at the front end.
Ensure your fire extinguisher is in position and easily to hand.
Brief all onlookers about the requirement for minimum safe distances and indicate the correct
place to stand – including yourself.
Check the danger area is clear before making an engine start.
Starting the engine
Turn on transmitter and receiver.
Plug in display - screen shows “Trim Low”
To initiate the start, raise trim to full, ((led in ECU lights and screen shows “Ready”). Place
stick to full and back down quickly. (Holding the stick at full will spin engine at full power –
can be used to cool down from a previous hot start or run)
Starter will spin engine briefly and then power igniter (screen shows “Glow Test” then “Burner
On”).
Note - to initiate start without spinning engine raise trim to full, raise stick half way and back
down.
Igniter will heat and after some seconds starter will spin engine slowly, pump will turn on
slowly, igniter valve ticking. If pump does not come on raise “pump power ignition kero” until
it does.
You should hear a pop and combustion starts in engine and temperature rise on the display.
(Screen shows “Preheat”)
After some seconds engine speed will increase, valve pulsing will speed up and the main fuel
valve begin to open and engine begins accelerating towards idle. (Screen shows
“Switchover” then “Fuel Ramp”). If engine stops at switchover, increase “pump start point”
until it continues through the start. (sometimes needs to be “50” or more)
During the acceleration, burner turns off at 20,000rpm, as soon as “fuel ramp begins”.
Starter turns off as engine passes 30,000rpm.
Page 20
Engine arrives at 55,000rpm - idle, (screen shows “Running”).
You now have control of engine via throttle stick.
At any time the start can be terminated by lowering stick and trim to zero. The throttle stick
can then be used to switch the starter to clear the engine.
Throttle response
Once the engine is back at idle you can operate the throttle stick. Over a period of about five
seconds, raise the throttle to full and the rpm should increase to close to 195,000rpm. Lower the
throttle back to idle and the engine should run back to idle. The ECU needs this cycle to learn the
throttle stick position to rpm match and it is good practice to do this at the beginning of all engine
runs.
Once the ECU has successfully learned the high rpm position you can now explore the response
time of the engine. Note the stick position relates directly to the engine thrust, 1/2 stick = 1/2
thrust, 3/4 stick = ¾ thrust and so on. If you find you need a more gentle response, if you enter
the RUN menu, there is a setting for throttle response –“acceleration delay”, raise the number by
3 or 4 if you want it a bit slower or vice-versa to speed it up. Beware of going too quick as the
engine may struggle to pick up if you try to make it accelerate too fast.
Great little L39 of John Wright. Only 9Lbs all up weight makes for a lively performance and great combination!
After running.
After running or flight, raise rpm to 100,000rpm for five seconds and lower stick and trim to
zero for cooling.
ECU will spin engine in short bursts until the temp reading goes below 100’C where it will
stop. If temp rises above 100’C again ECU will spin the engine again until below 100’C.
Once cooling is complete display shows “Stop”.
You can turn off receiver and transmitter and disconnect LiPo battery, if this is the last run for
a while, or you need to recharge.
Never recharge a LiPo whilst installed in a model.
Page 21
Settings used in ECU.
A Wren supplied kerostart engine package will already be adjusted for optimum ECU and
pumps settings and should need little or no attention, so do not fiddle with the settings. As
the fuel pump wears it may be necessary to adjust settings – see later.
Please note, no two installations will be truly identical so do not swap settings with a
colleague with a similar engine as they will most likely not be compatible.
If the fuel pump is replaced, new settings may be required as no two pumps have precisely
the same characteristics.
A problems checksheet follows in the next couple of pages. It lists common faults and the
likely cures and hopefully will solve your problem quickly. Please use the checksheet before
calling us – it is there to help you to save time trouble and expense.
If you find something not covered then of course mail us with a description and we will try to
help you: [email protected]
ECU default values and adjusted settings:
Item:
Initial value:
Pump start point
030-50
Pump start ramp
004
Glow power
6.9v
Low battery volts
6.0v
Starter power at ignition
060
Starter power at fuel ramp
075
RPM point 100% starter power
25,000
RPM starter off
30,000
RPM reconnect starter
27,000
RPM Ignition kero
7,000
Pump power ignition kero
35-50
Engine min flow %
55-65
EGT end preheat ‘C
180’C
RPM preheat kero
12,000
RPM fuel ramp kero
20,000
Preheat fuel
60
Ignition timeout secs
25.5
Your values:
*Items highlighted adjusted for fine tuning* DO NOT TWIDDLE WITHOUT REASON
Page 22
Problems Checklist:
The usual problems associated with a kerostart installation can be narrowed to just two key
items – the “Pump Start Point” and the “Pump Power Ignition Kero”. Both of these can be
trialled with the same number and are adjusted to suit each fuel pump fitted to the system.
A tight or new pump will benefit from some running-in before fitting and this helps to settle
the gears etc. The values may need to be raised considerably to get the initial settings to get
the pump going. As the fuel pump loosens in service the values for these functions may then
need reducing by a few points to make a start less aggressive.
Symptom
No reading on ECU
display unit
Transmitter stick
down/trim up reads
“StickLo”
Temp’ reading
incorrect or “0”
Temp’ reading
shows lower or
negative figure on
ignition
No rpm indicated
when engine is
spun
Problem
RX not switched on or RX
battery discharged
Verify connection and charge if
necessary
Display not connected
properly
Display malfunction
ECU problem
Ensure that display is plugged in
the correct orientation
Throttle channel needs
reversing,
Reverse channel on Tx
(Futaba’s often need this)
Thermocouple not
connected to ECU
Verify connection
Contact Wren
Contact Wren
ECU problem
Thermocouple failure
Contact Wren
Thermocouple plug
inserted wrong way round
Ensure connector matches the
label on the ECU
Rpm sensor plug inserted
incorrectly
Rpm sensor lead
broken/chafed
Rpm sensor malfunction
ECU problem
Ensure connector matches the
label on the ECU
Glow power set too low
Kerosene does not
ignite
Action
Poor glow at igniter
Plug partially blown
ECU battery low
Burner fuel too low
Burner valve not operating
No kerosene
ignition
Pump not turning
ECU shows
“GlowBad”
Element blown / open
circuit
Contact Wren
Remove source of chafing and
repair/replace
Contact Wren
Contact Wren
Check at least 6.8v in start
menu - Glowpower
Check connections / earth
Replace element
Charge
Increase burner fuel
(Pump Power Ignition
Kero)
Check valve inserted
correctly into ecu
Check pump for correct
operation (use
“TEST/Prime PUMP” in
INFO)
Replace element (call
Wren for service
replacement)
We present above some of the usual things encountered in the hope they clear up any
problems you might see.
The checklists are listed in the order in which problems may be encountered, ie setup and
starting.
Page 23
It is not intended in this supplement to cover normal running problems as these would
already be covered in the respective operators manuals.
A detailed manual covering all the kerostart functions is available to download from Xicoy
Electronica SL on www.xicoy.com
Be sure to ask for the V10 kerostart manual (there is a choice of gas start too).
Checklist cont.
Symptom
Fuel pump not
running
No or little temp’
rise on ignition
Pump runs but no
fuel delivered
No or little rpm
increase as fuel
enters
Problem
Pump not connected
Pump jammed with
foreign object
Action
Check wiring
Investigate operation and
rectify (disconnect, run
backwards to clear)
No drive from ECU
Contact Wren
Insufficient burner fuel
Increase Pump Power
Ignition Kero
Temp’ probe not inserted
into exhaust cone
Insert 6mm
Fuel not reaching tank
pick-up
Pump fault
burner solenoid not
opening
Insufficient revs on starter
motor
Clutch slipping
Air in fuel line
Check clunk for blockage.
Ensure fuel like is not
kinked
Check solenoid operation
Check wiring to ECU
Recharge ECU battery
Replace O-ring
Purge fuel lines and retry
Trim down/shut off fuel immediately
Residual fuel in engine
Excessive flaming
“Engine min flow” % too
high
Insufficient revs on starter
Starter motor
weak/inoperative
Spin engine “dry” for 5
seconds to clear
Reduce 2 points and retry
Recharge ECU battery
Contact Wren
“Pump Start Point “ too high
Lower by 2 points and retry
Engine malfunction
Return to dealer
Normal problem until ECU settles down
Engine overshoots
at idle
Engine slows or is
stopped during
start
Aggressive starting
Clear excess / lower Pump Start
Ramp by 2 points and retry
Air in fuel line causes late but
rapid start-up
ECU will correct itself and settle
down
“Overtemp’” is detected by ECU
and shutdown if temp’ has run
over 800’C due to long hot start,
low start battery or air in fuel
line.
Cool off and restart
Wild rpm reading
Interference to rpm pickup by
burner wiring (usually), find and
move. Check starter/burner
wires are well twisted.
Page 24
Igniter System.
The igniter is a five part assembly
which consists of:
A ceramic heater element mounted in a
stainless steel heater body,
A brass connecting pin to provide a
contact with the plug cap,
A stainless steel outer body to provide
a fuel connection to the heater body.
An aluminium gland nut to secure the fuel pipe onto the burner body.
O-rings fitted above and below the body.
A feature of the Wren burner assembly is the swivelling outer body which allows the fuel
feeder pipe to be rotated to the optimum direction for the installation and not dictated by the
plug hole screw threads in the engine like some others.
The heater element housing is user replaceable, therefore it is not required to replace the
entire burner assembly if the element goes faulty, like some manufacturers. The faulty heater
housing can be returned to Wren for element service and then returned and retained as a
spare part, to further reduce running costs.
To provide the swivel feature, the heater housing is sealed into the outer body by two heat
resisting O-rings sized to be a close fit when screwed into the plug hole on the engine. When
refitting a very light smear of silicon grease or “Vaseline” will help ensure the swivel feature
does not damage the O-rings.
NOTE: In event of coking (carbon build-up) of the element into the housing it is technically
possible for the user to access the heater element by removing it from the heater housing
and scraping away any coke deposit. It should be noted however, that in event of the
element being jammed-in, the element is often broken and ruined by the act of undoing the
retaining collar so should never be done if the element is still serviceable. The engine
warranty will not cover a broken element.
Please note, all the items used in the kerostart system are available as individual spares – no
need to buy a whole new unit.
The ceramic burner element is regarded as a long life component but as with all electrical
devices can decide to give up without warning.
If the screw-in centre section of the kero igniter is returned to us we can refit a new element
for a small charge.
Alternatively you can buy an extra one for holding as a spare in your flightbox so you never
need to lose a flight due to an expired element!
Page 25
Care and Maintenance
The engine, like most mechanical machines will appreciate being kept clean and dry. Keep
the intake clear from ingress of grass, fluff and all the other small bits the engine will “find”
from around itself while running. The engine has no consumable parts in the accepted sense
of the word, however the rotor bearings will eventually wear and become noisy.
We recommend a service interval of 50 hrs.
Be careful to ensure your ECU battery is kept well charged in order that the engine is always
started briskly and properly cooled down after a run. After flying is completed for the day,
disconnect the ECU battery from the ECU. Failing to do this may cause the battery to
discharge beyond the level to which it can be recovered. If this occurs the only option is a
replacement battery. Warranty will not cover a deep discharged battery.
General check-points:
Ensure that the ECU battery has sufficient charge before flying. Note the amount of charge
required after a flight/run to recharge the battery and take this away from the battery
capacity. Example if a previously fully charged battery requires 400ma to recharge and
battery capacity = 1800mAh, 1800-400 = 1400. This would indicate it should be safe to make
a second and possibly a third flight but then the battery would require recharging (always
remove from plane to recharge).
Always aim to leave at least 700mAh reserve. If in doubt, charge before each flight. LiPo’s do
not mind this and it will not harm their capacity. If don’t want to charge at the flying field then
fit a larger capacity battery or get a second battery which you can swap in after flight(s).
Keep the rpm pickup clear of stray magnetic sources such as fuel pump, solenoid valves,
igniter cable, or servos, as the magnetic field generated can upset the rpm reading.
Note, the igniter and starter wires are deliberately twisted tightly together to minimise
stray interference. Do not straighten them out in the belief this will “neaten” your
installation.
Do not fly with the display unit attached to the ECU as this is a potential source of
interference.
You must set-up the ECU with your radio before it will operate correctly, so do this first.
Only prime the fuel system once. If the lines are still full there is no need to repeat this.
If this is your first turbine, we recommend you set-up and confirm the operation of your
Auto-start installation on the test-stand, before installing into your model.
The ECU is pre-programmed to suit all Wren44 engines. The settings have been found
suitable for most installations. The only adjustment to running you may wish to employ is to
change the acceleration/decelleration rate to allow for hot conditions where the acceleration
may not be as smooth as before. This setting is held in the “RUN” menu. This should solve
the problem.
Remember the engine has already been run and the ECU adjusted to optimum conditions
with the fuel pump supplied – it should therefore only require setting to your radio and it
should then run perfectly.
Please do this before making any adjustments as in our experience unnecessary adjustment
of the ECU settings will only add problems to an otherwise perfect set-up.
Page 26
Exhaust temp.
At all times the temp should remain well below the value set in the main menu. If the engine
goes over this value the ECU will reduce the fuel pump power until the overheat has passed.
It is quite normal to have very short term high temp spikes of a couple of seconds, but longer
than this can result in overheating of the engine and the ECU may shut the engine down, and
the cause should be investigated.
Kerosene Burner Settings
The kerosene burner has been carefully set up to start easily and reliably. Please do not
jump in and change ANYTHING of the settings unless there is a very good reason for doing
so. If a friend has a similar engine DO NOT copy their settings in the belief it will make your
starts better/faster/easier. More likely it will result in you failing to get a start of any kind.
Fitted a new igniter element?
If the element or igniter is replaced the power setting may need adjusting to achieve correct
operation. All elements are slightly different resistance so each has to be programmed to run
on different voltage. However, once set there is no need to change.
If fitting a replacement igniter, set the glowpower voltage initially to 6.6v and initiate a start in
the normal way. If the engine only smokes and the igniter does not pop into normal operation
then the power may need increasing slightly. Raise the voltage to 6.8v and make a second
start.
Adjusting pump starting voltage:
Pump start point. If it appears there is too much flow at the middle of the start then reduce
the “Pump Start Point” value in the “Start” menu by 2 or 3 points and try a start again after
allowing the engine to go cold. The important thing is at the start the pump must turn
continuously otherwise the combustor will fail to keep going and the temperature rise will be
too low to complete the start and will just make smoke. Only reduce the pump starting
voltage if you are sure the pump starts too fast.
Please note: coking or carbonising of the element
Continual attempts at starting can carbon or “coke” up the igniter. The construction of the
igniter is such that the tip where the heater is exposed is surrounded by a very narrow gap
through which the starter fuel passes, causing it to flash into flame. During each start (the
first 5 seconds) the element will heat up to glow to orange hot and any fuel in this area will
turn to carbon and burn off. Successive attempts to start will build up this carbon very quickly
and may prevent further starts happening at all.
If a start is followed by a normal run or flight, ie several runs up to full power, the hot fuel and
pressure present in the combustion chamber will wash the element clean each time leaving it
in perfect condition for the next run.
SO, please do not keep starting the engine just to watch it get to idle and then shut down as
it may eventually fail to start at all, due to coke build-up and the low engine speed will not be
enough to keep the element clean. The cure is a start and a really good run to clean up the
element.
We welcome feedback on this product or this set of operating instructions. Please let us
know if you have any problems but check they are not already covered by the manual and/or
checklist above.
Page 27
Repair.
Before returning the engine or ancillary equipment for service or repair, please contact Wren
Turbines Ltd or Wren Turbines USA in the USA, to agree action and costs.
In the USA and Canada:
Wren Turbines USA
1027 Southampton Drive
Decatur
Indiana
46733
Ron Ballard.
Telephone: 260-724-8936
Cell: 260-701-8936
Website: http://www.wrenturbinesusa.com
email: [email protected]
Rest of World:
Wren Turbines Ltd
Unit 19, Century Park Network Centre
Manvers
Rotherham
S63 5DE
UK
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Page 28

Wren 44 Gold

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