Aeronautical Engineering Help needed

"David Lednicer" wrote in message
...
Rich S. wrote:

All's I know is that my elliptical-winged Emeraude (same wing area &
airfoil) is a LOT more efficient than those Hershey-bar RV wings! And I
holler "Nyahh Nyahh" at every one that passes me.

Most wings with elliptical planforms also have twist, to improve stall
performance. This twist changes the loading, resulting in a non-optimal
loading.

The Emeraude *does* have a bunch of wash-out. If that wasn't there, would it
be a fast-cruzin', snap-rollin' beast?

Rich S.

On Mon, 05 Jan 2004 09:04:20 -0800, David Lednicer
wrote:

:
:
:Ed Wischmeyer wrote:
:To get
:low induced drag, you need the sum of all lifting surfaces to have an
:elliptical lift distribution.
:
: Lemme display my ignorance here. I always thought that the elliptical
: lift distribution minimized wingtiptip effects. That being the case
: (ignoring the wake of the canard for the moment), then each wing should
: have an elliptical lift distribution. When you toss in the wake effects,
: is having the sum of all lifting surfaces give you an elliptical
: distribution a handy approximation, or is it what you really want from
: first prinicples?
:
:The canard usually has a much smaller span than the main wing. Subtract
:its elliptical load from the overall elliptical sum and you end up with
:a really wierd load distribution on the aft wing.

It's much worse than that. The winglets create much more lift at the
wingtips than you'd normally get, while serving double duty as
vertical stabs. And you have to add up all the lift into a single
system, and see how the entire thing is loaded.

It's true that if you fly a perfectly point designed canard off it's
point, it will be worse than a perfectly point designed conventional
configuration flown the same amount off it's point. For example, the
Solitare has a terrific L/D - if it's flying in a straight line. Load
up the canard to thermal and it's a dog. But if we're trying to make
sweeping statements about one configuration always being better than
another, the difference is small enough to be overwhelmed by the
details of the execution.

Besides, I don't like looking through a prop.

"Bill Daniels" wrote:

For me, the Solitaire drove the final nail in the canard's coffin. In
addition to poor aerodynamics, canards have poor TO and landing performance,
suffer from FOD, and have a notably worse safety record than conventional
airplanes. They are an all-round bad idea.

"Poor aerodynamic performance"? Hardly. Canard aircraft hold several
FAI recognized world records in altitude, speed, and range. A canard
holds the CAFE Challenge efficiency record and will likely have a lock
on it for years to come. Canards have been flown to numerous
first-place race wins and high race placings in competitions against
non-canard designs. Notably worse safety record"? That claim is
false as well.

The true tradeoffs of canard vs. non-canard aircraft are well
understood, at least among the informed, let's not muddy the waters
with misinformation from those with an obvious anti-canard bias.

David O -- http://www.AirplaneZone.com

David Lednicer wrote:

The canard usually has a much smaller span than the main wing. Subtract
its elliptical load from the overall elliptical sum and you end up with
a really wierd load distribution on the aft wing.

Your mistake is your false premise that an "overall elliptical sum" is
either necessary for efficiency or desirable in such canard aircraft.
But let's put aside your curious CFD-based musings for the moment and
instead look to the real-world. The simple fact is that the
normalized cruise and range performance of homebuilt canard aircraft
vs. non-canard aircraft belie your claim of substantial inherent drag
inefficiencies. As one poster correctly noted, the theoretical drag
differences between the two types are so small that it is execution
that accounts for any realized performance difference.

Canard aircraft hold several FAI recognized world records in altitude,
speed, and range. A canard holds the CAFE Challenge efficiency record
and will likely have a lock on it for years to come. Canards have
been flown to numerous first-place race wins and high race placings in
competitions against non-canard designs. Here are the placings from
just one such race, http://www.AirplaneZone.com/race.html

David O --- http://www.AirplaneZone.com

For me, the Solitaire drove the final nail in the canard's coffin. In
addition to poor aerodynamics, canards have poor TO and landing performance,
suffer from FOD, and have a notably worse safety record than conventional
airplanes. They are an all-round bad idea.

"Poor aerodynamic performance"? Hardly. Canard aircraft hold several
FAI recognized world records in altitude, speed, and range. A canard
holds the CAFE Challenge efficiency record and will likely have a lock
on it for years to come. Canards have been flown to numerous
first-place race wins and high race placings in competitions against
non-canard designs. Notably worse safety record"? That claim is
false as well.

The true tradeoffs of canard vs. non-canard aircraft are well
understood, at least among the informed, let's not muddy the waters
with misinformation from those with an obvious anti-canard bias.

David O -- http://www.AirplaneZone.com
+++++++++++++++++++++++++++++++++++++++++++

Hell, I even like canards....
when a Lycoming is in the back seat.

P.S.
Apologies to Mr. Graham's Mazda. )


Barnyard BOb --

Canard aircraft hold several FAI recognized world records in altitude,
speed, and range. A canard holds the CAFE Challenge efficiency record
and will likely have a lock on it for years to come. Canards have
been flown to numerous first-place race wins and high race placings in
competitions against non-canard designs.

That's not engineering analysis, that rhetoric trying to impress and to
win an argument. Can we go back to lift distributions, please?

Ed Wischmeyer

David O wrote:
Your mistake is your false premise that an "overall elliptical sum" is
either necessary for efficiency or desirable in such canard aircraft.
But let's put aside your curious CFD-based musings for the moment and
instead look to the real-world. The simple fact is that the
normalized cruise and range performance of homebuilt canard aircraft
vs. non-canard aircraft belie your claim of substantial inherent drag
inefficiencies. As one poster correctly noted, the theoretical drag
differences between the two types are so small that it is execution
that accounts for any realized performance difference.

How about dropping the ax you are grinding and learning some basic aero?
The "overall elliptical sum" is NOT a false premise. It is also a
"CFD-based musing". This dates back to the 1920s and people like
Ludwing Prandtl and Max Munk. Your arguments are ancedotal. Mine are
engineering based.

Canard aircraft hold several FAI recognized world records in altitude,
speed, and range. A canard holds the CAFE Challenge efficiency record
and will likely have a lock on it for years to come. Canards have
been flown to numerous first-place race wins and high race placings in
competitions against non-canard designs. Here are the placings from
just one such race, http://www.AirplaneZone.com/race.html

Show me a canard Reno racer that has ever won a race.

Show me a canard Reno racer that has ever won a race.


isnt that like trying to compare a high mileage compact car to a dragster?

take care

Blll

David O wrote:
Hold it right there, pilgrim. Your premise, which forms the basis for
your entire post, fails the practicality test. When people talk about
the cruise range for aircraft such as a Long EZ or an RV-4, they are
not talking about lumbering along "near or at L/D max" (about 70 kt in
both the Long EZ and the RV-4). Rather, they are talking about the
range at cruise speeds (65% and 75% power at altitude). In a like
manor, the cruise range for piston powered aircraft is typically
specified at 65% and 75% power at altitude, not throttled way back to
max L/D speeds. In truth, the actual cruise range for the Long EZ and
RV-4 are practically identical given the same engine and same fuel
load. That's the difference between reality and an argument based
upon an inappropriate premise and CFD "analysis". The previous
poster's comment that "if you want good range don't choose a canard"
remains laughably absurd in both theory and practice, and his
subsequent post reveals his considerable grudge ax -- no surprise
there.

1) I purposely said "long range", not range. For long range, you do
slow down to near L/D max. This is not the result of a 'CFD
"analysis"', this is basic aero. I never mentioned CFD in my post - it
is just one tool that I use in my work.

2) For cruise range like you talk about, you're right, the Long EZ is
actually better than an RV-6. This is due to the Long EZ's low zero
lift drag and reasonable induced drag efficiency.

3) Calling me "Pilgrim" is technically incorrect. My mother's family
came to the Puritan Bay Colony ten years (1632) after the Mayflower
landed (1622).

As for the Voyager, it didn't lumber along "near or at L/D max"
either. The average speed was 122 mph. I find your claim that a
non-canard Voyager would have had better range quite suspect. One
simply can not make such a determination by punching in a few what-if
scenarios into a CFD program, especially for such a highly specialized
aircraft. For example, the Voyager's canard forms a structural box
with the booms and the main wing. Remove the canard and you would
have to add significant structural weight elsewhere to obtain the same
airframe strength.

1) No, the Voyager didn't lumber around near or at L/D max. Early in
the flight, it did, but then Dick got impatient. Average L/D on the
flight was near 22. My analysis (which has nothing to do with CFD)
shows the airplane to have a max L/D, at the average flight condition,
closer to 26.

2) Stop grinding your ax - I don't just "punch in a few what-if
scenarios into a CFD program". For highly specialized aircraft, CFD is
the only way to get a handle on such things as the stability and control
(Burt used a very crude code called Tanwing to design the VariEze,
Voyager, Long EZ, etc.). However, you need to do a lot more than run a
CFD code to analyze an aircraft.

3) Your average speed for Voyager is incorrect. They covered 24,986.73
statute miles in 216 hours, 3 minutes and 44 seconds. This works out to
115.6 mph ground speed. I have been told that this is a pretty good
approximation of the average true airspeed.

4) Yes, the Voyager benefited from the structural layout. However, it
is not the only way to skin the cat.

If a non-canard "Voyager" would indeed have greater range then I will
believe it when I hear it from Burt Rutan himself. I expect that any
realized range difference, one way or the other, would be quite small.
Yes, the new Rutan designed GlobalFlyer will not be a canard
configuration. That design choice, however, could be based solely on
the wishes Fossett/Branson rather than on technical considerations.
The authoritative answer to these questions will come in time but
certainly not here in Usenet (unless Burt himself decides to chime in
as in the old days).

Oh, so only Burt knows anything about designing airplanes. I guess the
rest of us aero engineers might as well go quit and go home. My
firsthnad experience is that Burt is a very skillful designer, but there
are many designers, equally skillful, who get little or no press.

Ooops, I meant to say 'It is also NOT a "CFD-based musing".'