Aeronautical Engineering Help needed

"Cy Galley" wrote:

I thought the round the world non-stop Voyager was a canard... Guess I am
wrong! GRIN

Interestingly, though, the Scaled Composites design for the
Fossett/Branson solo effort will apparently not be a canard.

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

I've got to disagree with your assertion that canards are good for
range. I worked on the Voyager, Starship, Triumph, Catbird, ATTT, Ares
and JetCruzer, plus I've analyzed the VariViggen, VariEze, Long EZ,
Solitaire, Defiant, Predator, Quickie, Q2 and Dragonfly post-facto.

To get long range, you want to fly at a speed slower than maximum, near
or at the best L/D point. This involves flying at a higher lift
coefficient and the induced drag becomes more important here. To get
low induced drag, you need the sum of all lifting surfaces to have an
elliptical lift distribution. The canard will by itself be nearly
elliptically loaded. The aft wing, of greater span, will then need a
hole in its lift distribution inboard to accomodate the canard's
loading. This means that the inboard aft wing will be carrying little,
if any, loading. However, it will physically be there, causing profile
drag - a horse that is eating, but not pulling. Even worse, on a
canard, you want the fuel on the CG, so as it is used, the CG won't
shift. This means real big strakes on the aft wing usually. Thus, the
part of the wing contributing profile drag, but no lift, gets even
bigger. For a given L, the D has now been forced to get much bigger,
clobbering L/D.

The induced drag efficiency ("e") of the Voyager was around .5, as
opposed to .75-.8 on conventional configurations. Simply put, the
Voyager could have gone around the world with less fuel if it had been
conventionally configured. The reason that the Voyager is in the
Smithsonian is that Dick, Jeana, Burt and the rest of the crew created
an airplane and performed a mission that no one had ever performed, plus
many had dreamed of.

Yes, the Long EZ has good range. However, a conventionally configured
aircraft of the same GW, with the same engine and fuel quantity would
have longer range. For the same L, the D would be lower.

"David Lednicer" wrote in message
...
I've got to disagree with your assertion that canards are good for
range. I worked on the Voyager, Starship, Triumph, Catbird, ATTT, Ares
and JetCruzer, plus I've analyzed the VariViggen, VariEze, Long EZ,
Solitaire, Defiant, Predator, Quickie, Q2 and Dragonfly post-facto.

To get long range, you want to fly at a speed slower than maximum, near
or at the best L/D point. This involves flying at a higher lift
coefficient and the induced drag becomes more important here. To get
low induced drag, you need the sum of all lifting surfaces to have an
elliptical lift distribution. The canard will by itself be nearly
elliptically loaded. The aft wing, of greater span, will then need a
hole in its lift distribution inboard to accomodate the canard's
loading. This means that the inboard aft wing will be carrying little,
if any, loading. However, it will physically be there, causing profile
drag - a horse that is eating, but not pulling. Even worse, on a
canard, you want the fuel on the CG, so as it is used, the CG won't
shift. This means real big strakes on the aft wing usually. Thus, the
part of the wing contributing profile drag, but no lift, gets even
bigger. For a given L, the D has now been forced to get much bigger,
clobbering L/D.

The induced drag efficiency ("e") of the Voyager was around .5, as
opposed to .75-.8 on conventional configurations. Simply put, the
Voyager could have gone around the world with less fuel if it had been
conventionally configured. The reason that the Voyager is in the
Smithsonian is that Dick, Jeana, Burt and the rest of the crew created
an airplane and performed a mission that no one had ever performed, plus
many had dreamed of.

Yes, the Long EZ has good range. However, a conventionally configured
aircraft of the same GW, with the same engine and fuel quantity would
have longer range. For the same L, the D would be lower.

Absolutely agree.

Burt Rutan once designed a canard sailplane where L/D is paramount called
the Solitaire. It was a miserable failure. Conventional designs of the
same span, weight and general fit and finish, had much more performance.
(And, if powered, would have more range.) In a sailplane, there is nowhere
for the designer to hide - aerodynamic problems are plain for all to see.
More power and less weight can hide aerodynamic problems in powered
aircraft, but not in a sailplane.

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.

Bill Daniels

David Lednicer wrote:

The induced drag efficiency ("e") of the Voyager was around .5, as
opposed to .75-.8 on conventional configurations. Simply put, the
Voyager could have gone around the world with less fuel if it had been
conventionally configured.

Great post, thanks. Why'd they choose a canard configuration?
Were their aero estimates optimistic or was there some other
reason for the canard?

Dave 'trim drag' Hyde

1) I'm not sure I'd list the JetCruzer in my vita

Actually, we were called in late in the game and helped fix it so that
it could be certified. So, I guess its not that embarassing. BTW - I
forgot to mention the CIL Eagle in the list. I helped design that one,
but didn't take part in the fixing in that case.

2) What about all the wetted area and weight that a conventional configuration
drags around in the big empty tailcone?

Its hard to do a one-on-one comparison, but the Starship and King Air
are pretty close. Swet on the Starship was 1695 feet^2. The King Air
200 is 1522 feet^2.

David Lednicer wrote:

To get long range, you want to fly at a speed slower than maximum, near
or at the best L/D point.

snip

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.

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.

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).

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

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?

thanks

Ed Wischmeyer
currently building the C-frame table for the RV-10 project

"Ed Wischmeyer" wrote in message
...

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?

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.

Rich "Who me? Disgruntled? Nahhh." S.

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.

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.