Airplane design.

Just as a friendly challenge to anyone foolish enough...
Design an airplane within the 254 pound weight limit.

IFR or not? Does it have to be able to fly into known icing?



Ben Hallert
PP-ASEL - http://hallert.net/cozy/

("Richard Lamb" wrote)
Design an airplane within the 254 pound weight limit.

Clean sheet of paper.
254 pounds empty weight.
Your choice of engines, design, materials.

Where would you start?


Cri-Cri type
Twin diesels - torque, torque, torque
Wings that rock - "control wing" "free wing"

http://www.flyingflea.org/docs/SprattControlwing.htm

http://www.airandspacemagazine.com/ASM/Mag/Index/1995/DJ/ssfw.html

Original CriCri's weighed approx 150lbs, that included two 9hp engines. 150
lbs - total!

150 lbs - (15# engine + 15# engine) = 120 lbs - 20 lbs other stuff = 100 lbs
of plane building material.

So I'm thinking ...how much would (guessing) 60lbs of Titanium cost?


Montblackium

In article . net, Richard Lamb
says...

Just as a friendly challenge to anyone foolish enough...

Design an airplane within the 254 pound weight limit.

Clean sheet of paper.
254 pounds empty weight.
Your choice of engines, design, materials.

Where would you start?

I for one have done it www.cgsaviation.com/hawkultra.htm and so have
others.Mine not also meets the 254 # but the stall speed and top speed criteria
set by the feds in part 103-7. Although I don't think this is the style of plane
the original questioner had in mind. Weight is relative and on this end of the
spectrum alum sheet gets heavy as a build material.Especially if it's over .020.

The Hummel plane is all alum and can carry a 200# guy has a fairly good sized
wing, so it's not a rocket at landing.But it still tips the scales at almost
300# empty.

It's an interesting challenge something us Ultralight guys have had to work with
for about 25 years. One thing I did was to not design to the 170# FAA pilot
since most pilots I know and and those I see at airshows haven't been 170# since
8th grade ,that includes me as well :-)So your design should use 200# -220# for
the design criteria. Good luck.

See ya

Chuck S

"Stuart Grey" wrote in message
. ..

I put into Raymer's spreadsheet a few things like 619 mile range, max
speed 160 mph, payload weight of 1190 lbs, wing taper ratio 1.0 and I get
a whopping gross weight of 4322 pounds, not the 3000 pounds of the Murphy
Moose. The engine suggested by the spreadsheet was also huge.

Well, that's a bit of a disconnect. I got similar disconnects when I put
in sizing data from other airplanes. The Raymer spreadsheet gives much
heavier designs. What's with that?

Q1) Is this because the Raymer book recommends overbuilding so that the
typical home designer doesn't have the engineering skill to make it
lighter?

Q2) Are there any better books out there?

Please be kind. I'm a very sensitive fellow. (HA!)


I've only given Raymer's book a cursory look, but I wouldn't say he's overly
conservative. I do believe he assumes an effort to meet the intent, if not
the letter, of Part 23. That could introduce significantly more
"conservatism" than some kit makers have put into their designs. Would that
make up the difference you cite? Maybe, but probably not.

I expect a big factor in the difference is the basic assumptions made
regarding manufacturing materials and design. Aircraft design is a lesson
in compromise. Change one thing and it ripples thru affecting a dozen other
things. The fact is most a/c designs start out too heavy, too slow, and not
enough payload or performance.

Then the real work starts. Find a few little things to reduce drag. That
can give you a few extra knots or let you cut a few HP. Cut that HP and you
save structure and engine weight. With less to haul around, you can reduce
your fuel tanks and save some more weight or trade it for payload, and so
on...

I'd consider Raymer's numbers a starting point. The Murphy is one possible
end point. Give the same starting point to a Van or a Rutan, and you'll
have a different end point.

There are other books out there. They're different. Better is a very
subjective term.

Gerry

Gerry Caron wrote:
"Stuart Grey" wrote in message
. ..

I put into Raymer's spreadsheet a few things like 619 mile range, max
speed 160 mph, payload weight of 1190 lbs, wing taper ratio 1.0 and I get
a whopping gross weight of 4322 pounds, not the 3000 pounds of the Murphy
Moose. The engine suggested by the spreadsheet was also huge.

Well, that's a bit of a disconnect. I got similar disconnects when I put
in sizing data from other airplanes. The Raymer spreadsheet gives much
heavier designs. What's with that?

Q1) Is this because the Raymer book recommends overbuilding so that the
typical home designer doesn't have the engineering skill to make it
lighter?

Q2) Are there any better books out there?

Please be kind. I'm a very sensitive fellow. (HA!)



I've only given Raymer's book a cursory look, but I wouldn't say he's overly
conservative. I do believe he assumes an effort to meet the intent, if not
the letter, of Part 23. That could introduce significantly more
"conservatism" than some kit makers have put into their designs. Would that
make up the difference you cite? Maybe, but probably not.

I expect a big factor in the difference is the basic assumptions made
regarding manufacturing materials and design. Aircraft design is a lesson
in compromise. Change one thing and it ripples thru affecting a dozen other
things. The fact is most a/c designs start out too heavy, too slow, and not
enough payload or performance.

Then the real work starts. Find a few little things to reduce drag. That
can give you a few extra knots or let you cut a few HP. Cut that HP and you
save structure and engine weight. With less to haul around, you can reduce
your fuel tanks and save some more weight or trade it for payload, and so
on...

I'd consider Raymer's numbers a starting point. The Murphy is one possible
end point. Give the same starting point to a Van or a Rutan, and you'll
have a different end point.

There are other books out there. They're different. Better is a very
subjective term.

Gerry


It's interesting in that the methods used are based on existing designs
for a rough estimate. If you use the wrong class of airplanes for your
parameter selection, you don't get the numbers you expect. My problem
was that I used a parameter that was not close to the type of plane I
was targeting.

Aircraft design seems to be an iterative process; you guess the weight,
design to a given weight, look at how much the structure weighs, and
then try again. You can't design the structure without knowing the
weight, you don't know how much the structure weighs until you design
it. Chicken and egg thing. For this reason, they use regression analysis
of existing working designs.

Stuart Grey wrote:

Aircraft design seems to be an iterative process.....
Chicken and egg thing. For this reason, they use regression analysis
of existing working designs.

Correct. This is a good thing, if you know what you're doing, because
it lets you easily determine what a new airplane is going to look like,
weigh, etc. On the other hand, you never get breakthroughs by using
this method, since whatever you design will be very similar to what's
come before.

I have found, since I started working at Scaled last September, that we
use a mix of "do it just like that" and "don't do it anything like
that", depending upon need :-).

--
Marc J. Zeitlin
http://www.cozybuilders.org/
Copyright (c) 2006

"Marc J. Zeitlin" wrote

I have found, since I started working at Scaled last September, that we
use a mix of "do it just like that" and "don't do it anything like that",
depending upon need :-).
\
Cool stuff going on at Scaled; I would love to be qualified, and to get a
chance to work there.

I know you have posted what you do there, but I have forgotten. What is it,
again, if you would?

That philosophy you posted above, about says it all, huh? g
--
Jim in NC

Morgans wrote:

I know you have posted what you do there, but I have forgotten.
What is it, again, if you would?

I don't think that I have - maybe you're confusing me with someone else,
but I don't know who that might be - Scaled is not a big place :-).

I'm a mechanical/aeronautical engineer. I design stuff. Sometimes I
build it, too, and test it :-).

--
Marc J. Zeitlin
http://www.cozybuilders.org/
Copyright (c) 2006