Velocity continues it's twin canard development

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nerobro

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Those 75% power numbers show that the rutan plane is at a higher power setting, or richer fueling than the velocity is.

The numbers there don't make sense. Unless the defiant is a brick.
 

Jan Carlsson

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320hp X ,75 = 240hp
240 X ,45 / 6 = 18 gal/h

16 / 240 X 6 = ,4

cubic rooth of 0,75 = ,9085

188 X ,9085 = 170,8 Kts

200 X ,9085 = 181,7 kts

So 75% of what and at what altitude?
 

Mac790

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The numbers there don't make sense. Unless the defiant is a brick.

Of course those numbers don't make sense. Same as comparing apples to oranges don't make sense either. There are some similarities between those planes (like between apple and orange), but there are more differences.

First, Defiant is fixed gear airplane, Velocity retract gear one, if someone thinks it really doesn't matter, take a look at Waiter LongEze. He replaced his fixed gear configuration with retract gears, at low altitude he gained 10kts, however at higher difference is marginal.

Second, Defiant is 25+ years old design, built with moldless technology/method, Velocity molded technology/method.

Third aerodynamics, however despite I said previously that Velocity has bulky fuselage, but compared to that Defiant is closer to the brick actually. Just take a look at fuselage shape, and cowling especially rear one, arrrgghhh

So if anyone want to compare those planes, I would say, replace fixed gear with retract ones, reshape fuselage, change cowling shape, use blended winglets, and use molded approach instead of moldless one. After all those changes I bet that Defiant is going to be 10-15 kts faster.

Seb
 

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Detego

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... Of course those numbers don't make sense.
... Same as comparing apples to oranges don't make sense either.
... There are some similarities between those planes (like between apple and orange), but there are more differences.



I'm showing TWO types of TWINS with SIMILAR configurations. Your MILEAGE may vary!

http://www.homebuiltairplanes.com/f...its-twin-canard-development-2.html#post155077



... First, Defiant is fixed gear airplane, Velocity retract gear
... if someone thinks it really doesn't matter, take a look at
Waiter LongEze.
... with retract gears, at low altitude he gained 10kts, however at higher difference is marginal.

"At FL180, I only seen a 2 kt improvement, but lost about 5 gallons of fuel and about 100 lbs of useful load." Plus the cost of the Retracts.
http://www.iflyez.com/LongEZRetrofitReport.shtml

Flying at Sea Level is difficult for me, as the water keeps getting in my way.
 
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Jan Carlsson

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One reason that make holland a great country for gliding, can fly below SL. make long glides, when thermal is gone.
 

Mac790

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Flying at Sea Level is difficult for me, as the water keeps getting in my way.

:gig: I think that you could call now, to all those engines/airplanes producers, and tell them that they shouldn't give any specification for sea level (power, climb rate, speed, etc), because nobody beside people in Holland flies so low. But because you have PHD in AE (and I assume that you already know it), I'll take it as a joke.


There were also papers for Cozy's, I don't have time to look for it now, here is just a short presentation by Marc Zeitlin http://www.cozybuilders.org/Oshkosh_Presentations/2009_Zeitlin-Soup_To_Nuts.pdf page 17 for potential influence of different mods.

Seb
 
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nerobro

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Of course those numbers don't make sense. Same as comparing apples to oranges don't make sense either. There are some similarities between those planes (like between apple and orange), but there are more differences.
75% power is 75% power. Both planes should be using about the same amount of fuel. They aren't.

As for apples to apples. Both planes are, canard designs, twin engine, with the same engine, with the same number of passengers. That's pretty apples to apples.

What else doesn't make sense, is the plane with the greater frontal area, and higher weight, is climbing faster on one engine. That... doesn't make a whole lot of sense to me. I'm not saying it's impossible just unlikely.
 

Mac790

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As for apples to apples. Both planes are, canard designs, twin engine, with the same engine, with the same number of passengers. That's pretty apples to apples.
Seems that you guys took this apples vs oranges part too seriously. Just to finish it, last sentence in relation to it. There are some similarities between apples and oranges, but there are also differences, I see probably more differences between those two airframes (retract vs fixed, etc) than you guys, but that might vary.

75% power is 75% power. Both planes should be using about the same amount of fuel. They aren't.

What else doesn't make sense, is the plane with the greater frontal area, and higher weight, is climbing faster on one engine. That... doesn't make a whole lot of sense to me. I'm not saying it's impossible just unlikely.

First I don't know where are those numbers from, I've seen different ones, for example single-engine climb rate for Defiant 390 feet/min not 310. Cruise for Velocity V-twin 170 kts, not 185 kts, etc. Which numbers are the real one, I don't know. So for this reason entire discussion is a little bit pointless in my opinion, I just think that Defiant push-pull configuration might be a better idea, for twin canard.

On the other hand, from those two Defiant is closer to a brick. I don't know what is your sentence "the plane with greater frontal area" based on. What's really count is the equivalent of flat plate area http://www.homebuiltairplanes.com/f...uivalent-flat-plate-areas-various-planes.html
I believe it's much larger for Defiant (fixed gears, brick a like shape, terrible rear cowling, etc) So if we have two airplanes A and B, lets say that both have same Lift (without going into details), same horsepower, but plane A has 2.8 ft^2 and plane B 3.2 ft^2, for me it's sure that plane B is going to be slower, and have worse climb rate, higher D for same L, means lower L/D. But like I said without exact numbers this discussion is fruit less.

Seb
 
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wsimpso1

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Anytime you put the prop in the back, it is in the sinusoidally varying downwash of the wing, which automatically makes the prop efficiency go down. That was why the Beech Starship was not as good a performer as it should have been. There was a bunch of work done with propellers to get it to contract speed in the first place.

Did anyone notice that the Velocity folks are still using submerged inlets for engine cooling. At least they show as frontal area so they have a chance...

Burt came up with the Defiant as a poor man's twin and a pretty safe one at that. Originally it had fixed props, which made engine out procedures bone-head easy. But fixed props meant either lousy take-off and climb performance or run out of revs in cruise depending upon your prop pitch. When he started experimenting with constant speed props, well, engine out procedures became more complicated and bordered on the procedures that make staying alive in a conventional twin so difficult. In addition, the Defiant had a bad feature from C337's - you tended to not notice right away when the aft engine dropped off line.

So, put two aft, and you get lousy efficiency on both. They give you asymmetric thrust in an engine out case, so you are almost in the same boat as a conventional twin for emergency procedures. And with the very short vertical tail arm, I wonder if it has enough yaw damping.

You guys are not even mentioning Burt's progression. After the Defiant and Starship, Burt designed and built the Catbird, with phenomenal speed range. Yeah, it was a three surface, but they sequentially removed more and more of the canard. In the end it is flying with the left side canard only, with the right side gone. So much for the important features of aft engines and canards. Then Burt designed and built the best configuration for a twin, with dual fuselages, both engines on the front, the tail in the back, and a phenomenal boost in all performance topics.

The only reason no one is discussing building a Boomerang is because the total market for new piston twins is minuscule. So why is Velocity playing with one? Maybe they thought it would be a straightforward stretch of what they do now...

Billski
 

nerobro

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First I don't know where are those numbers from,
Four posts up, or something like that. Here's the link: http://www.homebuiltairplanes.com/f...its-twin-canard-development-2.html#post155077

I've seen different ones, for example single-engine climb rate for Defiant 390 feet/min not 310. Cruise for Velocity V-twin 170 kts, not 185 kts, etc. Which numbers are the real one, I don't know. So for this reason entire discussion is a little bit pointless in my opinion, I just think that Defiant push-pull configuration might be a better idea, for twin canard.
See, that makes a lot more sense. I wasn't favoring either airplane in my "this makes no sense" post. I was calling the numbers into question.

On the other hand, from those two Defiant is closer to a brick. I don't know what is your sentence "the plane with greater frontal area" based on. What's really count is the equivalent of flat plate area http://www.homebuiltairplanes.com/f...uivalent-flat-plate-areas-various-planes.html
I believe it's much larger for Defiant (fixed gears, brick a like shape, terrible rear cowling, etc)
My use of the word "brick" was a joke, I was trying to point out that the numbers seemed very wrong to me. Neither airplane is an aerodynamic mess. The reason I stated the velocity has a greater frontal area (and I can check it... but I'm pretty sure i'm on the money here) is the rutan doesn't give passengers any extra space, and the defiant has no engine nacelles to deal with on the wings.

I think both planes are quite good designs. The Velocity even avoids the starship problem, with the divergent tunnel on top of the wing. Speaking of starships....

Anytime you put the prop in the back, it is in the sinusoidally varying downwash of the wing, which automatically makes the prop efficiency go down. That was why the Beech Starship was not as good a performer as it should have been. There was a bunch of work done with propellers to get it to contract speed in the first place.
It's probably best not to try to point at any one issue with the starship. The list of what was wrong with the plane is longer than what they got right. The engine pods and fuselsage made a divergant duct, causing flow separation at all speeds. It's not unlike carrying a parachute in there. The plane was massively overweight, and that alone would have slowed the plane down.

Burt came up with the Defiant as a poor man's twin and a pretty safe one at that. Originally it had fixed props, which made engine out procedures bone-head easy.
I had forgotten about the fixed pitch props.
 

autoreply

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because nobody beside people in Holland flies so low.
Israel (dead sea), US (Death valley), the Cradle of mankind (something depression, Ethiopia) etc ;)

So, put two aft, and you get lousy efficiency on both. They give you asymmetric thrust in an engine out case, so you are almost in the same boat as a conventional twin for emergency procedures. And with the very short vertical tail arm, I wonder if it has enough yaw damping.
A big advantage is that the running engine blows the fin straight, much like in the Cri-Cri, such that you need less rudder than with a conventional twin.
 

Grelly

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A big advantage is that the running engine blows the fin straight, much like in the Cri-Cri, such that you need less rudder than with a conventional twin.

True, but the downside is that rudder authority varies depending on throttle setting.
 
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