Jet Design Report - EAA Chapter 1514

Transcription

EAA Chapter 1514
Jet Design Team Project Wrap-Up
February 20, 2013
By Willard White
Contents
Beginnings:.....................................................3
Engine:............................................................5
Wing:..............................................................7
Weight and Balance:......................................10
Specifications and Performance:...................16
Summary and Conclusions:..........................20
EAA Chapter 1514 - Jet Design Project Wrap Up - Page 2
Beginnings:
For the last two and a half years, our small but tenacious group of EAA-ers has been working on
a design for a small (tiny) jet airplane. Our organizational meeting was attempted before the
regular Chapter 330 meeting at Briar Patch on 18 Sept. 2010. The word attempted pretty much
describes the pandemonium that occurred when our meeting was continuously interrupted by
arriving members who didn't realize a meeting was in progress. Disorganized as it seemed, we
did reach consensus on several important aspects of our project for the next 2½ years. We set
the guidelines for the brainstorming style of our meetings. We agreed to design an airplane for
two people. We managed to reach consensus on a turbo-jet engine manufactured in the Czech
Republic.
Our second attempt at a meeting occurred at Lovezzola’s Pizza. Again, it was chaos as early
arriving members interrupted our meeting, which was rather informal to begin with – and, again,
we managed to reach consensus on basic characteristics of our project. After some spirited
discussion about engine location, we agreed to locate the engine behind the aft wing-spar with
the exhaust pipe exiting beneath a stinger type tail boom. Significantly, we abandoned the idea
of conducting our meetings concurrently with Chapter meetings.
Our third meeting was at Signature Aviation at KSAV. We set some basic specifications and
performance objectives:
Stall speed less than 60 knots
1,200 lb. Maximum Gross Takeoff weight
480 lb. empty weight
FAR 23 Normal Category structure; +3.8 and – 1.52g
Cruise speed: 217 knots at 10,000'
Range: 350 nm with two on board, 500 nm with pilot only
We began to appreciate the size of our task and agreed to meet every other Tuesday, except
when it conflicted with Chapter meetings.
Our fourth and every subsequent meeting were at SheltAir at KSAV. By then, we had decided
on side-by-side seating and had sized the wing.
Engine:
The Prvni Brnnska Strojirna (PBS) TJ100 engine
Once we decided on a jet engine, the choice of engine was easy. The TJ 100 turbojet, at 247
pounds thrust, was a bit small for our application, but there simply wasn't anything else
available. The good news was that it was physically small at 10.4 inches in diameter and 25
inches long including tail pipe; it weighed only 43 pounds including fuel pump and
starter/generator.
The engine is basically a design from the fifties which uses a single shaft with a centrifugal
compressor, updated with a digital fuel controller which uses phase width modulation to control
the speed of the fuel pump. Good news; the digital fuel controller takes care of starting and
all limitations, simplifying engine management for the pilot. Bad news; the simple, dated
engine design yields a specific fuel consumption of 1.09 pounds of fuel per pound of thrust.
This limitation drove a lot of the choices we had to make. For example, the 40 pounds of thrust
at idle and the slow (by piston engine standards) spool-up required a powerful flap which
allowed three degree approaches to be flown at approximately half throttle to allow for glide
path control with throttle and immediate go-around capability.
Wing:
The wing developed over nearly a year and a half of debate and self-education. We settled on
the AS5045 profile, a computer generated airfoil with approximately 50% laminar flow and the
following characteristics:
15% thick
Cl max of 1.5 (with Aspect Ratio of 8)
L/D of 20 at Re of 6 million (Cruise)
Cl max of 1.5 at Re of 2 million (Climb)
Moment index of -.06 at cruise
The planform evolved into 60.5 square feet with an Aspect Ratio of 8:1, so the span was 22 feet
and the average chord is 2.75 feet. The taper ratio is 0.5. Dihedral is 5 degrees and the twist
is 1.5 degrees. Flat wrap lofting techniques are used to assure a smooth flat skin. We could
have achieved a 60K stall speed with a smaller wing, but we needed the wing volume to carry
adequate fuel. Stall speed is 57K.
The structure of the wing consumed at least 8 months of our time. I can't begin to illustrate the
process in the space available.
Weight and Balance:
Specifications and Performance:
Jet Specifications 33
January 13, 2013
Low wing conventional monoplane with retractable landing gear, side by side seating, and wet
wing. The engine is located behind the aft wing-spar and beneath a tail boom. The wing,
tail-boom and tail surfaces are aluminum construction, the fuselage is constructed of carbon fiber
and foam. Cockpit access is by forward tilting canopy, the combing is approximately 28 inches
above the ground.
Stall speed: 57K
Estimated takeoff distance at sea level, 1,200 lbs.: 1,200 ft.
Estimated rate of climb at 5,000 ft. MSL: 1,000 fpm at 150 KITA
Wetted area: 285 sq. ft.
Equivalent Flap Plate area: 1.14 sq. ft. (Using P-51 drag coefficient; .004)
Estimated cruise performance: see chart
Altitude
Rho:
%SL
KTAS
T&D#
FF#
NM/LB
1000
0.00176
74
233
160
176
1.32
18000
0.00136
57
247
140
154
1.6
24000
0.0011
46
246
116
128
1.93
Engine: TS100A
250 lb. Installed thrust (270 lb. uninstalled)
Airfoil: AS5045
Wing area: 60.5 sq. ft.
Wing span: 22 ft.
Dihedral: 5 degrees
Sweep: 8 degrees at .25c
Aspect Ratio: 8:1
Taper Ratio: 0.5
Twist: 0 degrees
Flap/Chord: .25
Flap/span: .62
Flap travel: 0 to 60 degrees
1.09 SFC
Length: 17' 2”
Cockpit width: 42 in.
Horizontal tail arm: 87.2 in.
Horizontal tail area: 13.9 sq. ft. (Horiz. tail volume coefficient: .6)
Vertical tail arm: 95.6 in.
Vertical tail area: 7.5 sq. ft. (Vert. tail volume coefficient: .045)
Maximum Ramp Wt.: 1,210 lb. MGTOW: 1,200
BEW (target): 480 lb.
Fuel capacity: 75 gal. (500 lb.)
Allowable CG travel: 103.9 to 109.0 in. (25 to 35% MAC)
Location of major components:
FS 0 is 109.3 inches ahead of .25 MAC
Wing: CG at FS 114.2 FWD spar at .285 MAC, AFT spar at .70 MAC
Fuselage: FS 84.4 (tube frame)
Firewall/Aft bulkhead at FS 116
Horizontal tail: FS 197.4
Vertical tail: FS 191.3
Tail boom: FS 144.75 Engine: FS127.0
MLG: FS 113.0, BL 42
NLG: FS 38.25
Battery: FS 46.0
Seats: FS 94.3 to 100.3
Fuel: FS 107.0
Main spar is located at .285c and aft spar is at .75c.
Flap and aileron hinge lines are at .8c.
Composite cockpit section, showing the forward pivoting canopy and the center inlet
Composite materials were chosen for the cockpit to allow laminar flow over the majority of the
cabin. Composites have some potential for weight saving also. The retracting nose wheel was
relocated six inches to the left of centerline to allow the intake duct to be straight. The nose wheel
is castering; steering is with individual wheel brakes. The cockpit is 65 inches long to accommodate a pilot 6 foot 2 inches tall.
After 2 ½ years, the decision was made to change the intake configuration from two wing-root
intakes to a single F-86 style nose inlet. We weren't comfortable with our estimates of momentum
loss due to the required two 90 degree bends in the intake. The space besides the occupants sides
(the console area) was largely wasted so we abandoned the twin wing root intakes for the single,
straight-to-the-engine configuration. We estimate the installed static thrust is 250 lb., from 270
lbs. uninstalled. At cruise, the dynamic pressure is about ¾ PSI at 10,000 feet.
Aileron and elevator control is by side stick controllers which actuate the controls thru cables,
push-pull tubes and torque tubes. Flaps and ailerons are mounted on concentric torque tubes (the
aileron tube fits inside the flap tube). This was necessitated by the wet wing design, which was
necessitated by the high fuel consumption of the engine. The Grumman American Yankee has a
similar design.
The wheels are Beringer JA-02 4:00 x 5”. The brakes have 144,000 ft. lb. Rejected takeoff
capacity, the main wheels, tires, axles and brakes weigh 8 pounds each, the nose landing gear
(4:00 x 5”) wheel, tire and axle weighs 6.3 lbs. The landing gear is manually retracted by a lever
in the cockpit, thru a series of cables and pulleys patterned after (and scaled up from) the BD5.
Summary and Conclusions:
Problems:
Our lack of a draftsman was a major obstacle, one we never really overcame. Swaid purchased
a sophisticated drawing and modeling program and I dusted off my ten year old Turbocad but
we never really produced “buildable” drawings. A second problem, more subtle but still a major
problem was our own knowledge. That is to say our personal experience led us to expect our
airplane to have certain characteristics. This single engine jet, being like no other airplane
before it, was new and different – very different. Every individual in the group had to change
their long held beliefs at some point.
Lessons Learned:
The early decisions are the critical decisions: For example the decisions to design an airplane
for two people, and the engine choice were the two choices that drove the development. We put
the two place capacity decision behind us the first week, but the engine, more specifically the
fuel consumption of the engine, influenced nearly every subsequent decision.
The “brainstorming” approach to designing an airplane was successful beyond our expectations.
No one person on the team had the entire repertoire of experience, knowledge and tenacity to
accomplish what we accomplished together. Our meetings would resemble pandemonium to an
observer, yet the final result was impressive. As discussions progressed good solutions naturally
floated to the top and were adopted. Our respect for each other, and for another's opinion, was
at the root of our success. We intend to carry this approach over to our next project.
Thanks to participants and contributors
Sharath Gudla
Allen Jackson
Tom Keith
Bill Leftwich
Bob MacDonald
Doug McKissack
Varun Nare
Raj Narisetti
Swaid Rahn
Vin Sharma
Esteban Villa
Willard White
Ed Wischmeyer
Gene Yarbrough

Jet Design Report - EAA Chapter 1514

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