V-TAIL OR CANARD LSA/BURT RUTAN.

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tu16
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Re: V-TAIL OR CANARD LSA/BURT RUTAN.

Post by tu16 »

tl-3000pilot wrote:... as well as a design that incorporated the V-Tail design, much like the V-Tail Bonanza. Just make it work and beneficial somehow.

Imagine a sleek high-wing, such as the P-2008 with a V-Tail or Canard or even both...
I'm pretty sure V-tail in canard configuration would be silghtly redundant (as a third+ lifting surface). As far as V-, T-, H-, "crucifix" etc. tailplans - aerodynamically they are pretty much equivalent (after counting all slight differences). In the end it all boils down to preferences in construction and aesthetics. It is said V-tails do produce higher torsion loads on a tailboom. Bonanza piilots were often complaining of "hunting" yaw motion in a turbulence.

Nevertheless here it is (almost in LSA specs) :) :
Image

Crew: One pilot
Capacity: 1 passenger
Length: 17 ft 10 in (5.44 m)
Wingspan: 19 ft 3 in (5.86 m)
Height: 5 ft 5 in (1.65 m)
Wing area: 83 ft2 (7.7 m2)
Empty weight: 610 lb (277 kg)
Gross weight: 1,125 lb (510 kg)
Powerplant: 1 × Continental A65 horizontally-opposed four-cylinder piston engine, 65 hp (49 kW)
1 × Continental O200 horizontally-opposed four-cylinder piston engine, 100 hp ( kW)
Performance

Maximum speed: 120 mph (193 km/h)
Cruise speed: 110 mph ( km/h)
Range: 450 miles (725 km)

http://en.wikipedia.org/wiki/Davis_DA-2
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drseti
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Re: V-TAIL OR CANARD LSA/BURT RUTAN.

Post by drseti »

tu16 wrote:Bonanza piilots were often complaining of "hunting" yaw motion in a turbulence.
As a longtime (30 year) Beechcraft owner, and former director of the Beech Aero Club, I feel a bit qualified to address this.

The Dutch roll tendency of the V-tail Bonanza is also found in the conventional tail model 33 and 36 Beeches, the straight tail Model 23 and 24 Baby Beeches, and in fact all the short-coipled Beech designs. It is not a function of the V-tail configuration, but since over 10,000 V bonanzas were produced, it became closely associated with them in many pilots' minds.
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tl-3000pilot
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Re: V-TAIL OR CANARD LSA/BURT RUTAN.

Post by tl-3000pilot »

tu16 wrote:
tl-3000pilot wrote:... as well as a design that incorporated the V-Tail design, much like the V-Tail Bonanza. Just make it work and beneficial somehow.

Imagine a sleek high-wing, such as the P-2008 with a V-Tail or Canard or even both...
I'm pretty sure V-tail in canard configuration would be silghtly redundant (as a third+ lifting surface). As far as V-, T-, H-, "crucifix" etc. tailplans - aerodynamically they are pretty much equivalent (after counting all slight differences). In the end it all boils down to preferences in construction and aesthetics. It is said V-tails do produce higher torsion loads on a tailboom. Bonanza piilots were often complaining of "hunting" yaw motion in a turbulence.

Nevertheless here it is (almost in LSA specs) :) :
Image

Wow, designed in the 60's!

Nice!

Thank you for sharing! :D

tl-3000pilot.

Crew: One pilot
Capacity: 1 passenger
Length: 17 ft 10 in (5.44 m)
Wingspan: 19 ft 3 in (5.86 m)
Height: 5 ft 5 in (1.65 m)
Wing area: 83 ft2 (7.7 m2)
Empty weight: 610 lb (277 kg)
Gross weight: 1,125 lb (510 kg)
Powerplant: 1 × Continental A65 horizontally-opposed four-cylinder piston engine, 65 hp (49 kW)
1 × Continental O200 horizontally-opposed four-cylinder piston engine, 100 hp ( kW)
Performance

Maximum speed: 120 mph (193 km/h)
Cruise speed: 110 mph ( km/h)
Range: 450 miles (725 km)

http://en.wikipedia.org/wiki/Davis_DA-2
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zaitcev
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Re: V-TAIL OR CANARD LSA/BURT RUTAN.

Post by zaitcev »

tl-3000pilot wrote:I still think it would be neat to see an LSA design that incorporated the appropriate canard set-up, as well as a design that incorporated the V-Tail design, much like the V-Tail Bonanza.
Sonex comes in both conventional and V-tail versions. The company says that there's essentially no discernable difference in handling or performance between the two, and builders select the configuration purely for looks.
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Re: V-TAIL OR CANARD LSA/BURT RUTAN.

Post by FastEddieB »

zaitcev wrote:
FastEddieB wrote:I think the logic is that the conventional arrangement is inherently inefficient. Why? With the CG ahead of the center of lift of the main wing, the horizontal stabilizer has to provide a down force.
Not true. All that's required for the static stability is for the main wing fly at larger angle of attack than the tail. The tail may be lifting. In fact it is in most of the pemitted loadings of original V35. I heard you could easily load a 172 like that, although I did not verify it myself.
I'd be interested in specifics here.

It goes against everything I've learned, and taught, about aircraft longitudinal stability.

I cannot think of a single plane I've flown where the acceptable CG range was not ahead of the center of lift.

The typical textbook case here:

Image

It does seem that...

1) If the center of gravity is ahead of the center of lift, then there MUST be a nose-down moment associated with the lift, which MUST be countered by a tail down force, and,

2) If the tail was lifting, then pitch diversion from level flight would be exaggerated - hence unstable. Nose goes up, speed goes down, tail lifts less, nose goes up more, and so on. Or nose goes down, speed goes up, tail lifts more, nose goes down more, and so on - the word is divergent.

I know there are military fighters that are inherently unstable and "stabilized" electronically in the name of maneuverability.

Anyway, if I'm wrong on any of the above, educate me!
Last edited by FastEddieB on Wed May 15, 2013 7:16 am, edited 1 time in total.
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tu16
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Re: V-TAIL OR CANARD LSA/BURT RUTAN.

Post by tu16 »

FastEddieB wrote: ....Anyway, if I'm wrong on any of the above, educate me!
I've found this post from the thread I recommended above quite enlightning : it contains graphs for Cessna 172.

http://www.avcanada.ca/forums2/viewtopi ... 39#p810939

It appears that at the nominal CG zero-tail-lift (and hence, minimum drag) trim is at 100kts. Tail is lifting at slower speeds, and downlifting at higher speeds.
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zaitcev
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Re: V-TAIL OR CANARD LSA/BURT RUTAN.

Post by zaitcev »

FastEddieB wrote:2) If the tail was lifting, then pitch diversion from level flight would be exaggerated - hence unstable.
Tu16 has dealt with the calculations. But for those who do not trust the math, here's what Denker writes about it:
Another misconception that is more nearly true is the notion that the center of mass of the whole airplane has to be ahead of the center of lift of the wing alone. This condition will occur if the tail is producing a negative amount of lift. As we have seen, this is possible, but not necessary.

Here’s an explicit example. I’ve actually done the following experiment:

* I took a Cessna 172 Skyhawk and put a couple of large pilots in the front seats, with no luggage and no other passengers. That meant the center of mass was right at the front of the envelope, so the tail had to produce considerable negative lift in order to maintain equilibrium. There was lots and lots of angle of attack stability.
* I took the same Skyhawk and put a small pilot in the front seat, a moderately large mad scientist in the back seat, and 120 pounds of luggage in the rear cargo area. That put the center of mass right at the rear of the envelope, so the tail had to produce considerable positive lift in order to maintain equilibrium. The airplane still had plenty of stability. (As far as the pilot could tell, it was just as stable as it ever was.)

The easiest way to determine whether the tail lift is positive or negative is to observe the direction of motion of the tip vortices, as discussed in section 3.12. To observe the vortices, I attached a streamer of yarn, about half a yard long, to each tip of the horizontal tail, at the trailing edge. The streamer gets caught in the vortex, so its unattached end flops around in a circle. When the tail is producing positive lift, the circular motion is in the direction shown by the green “circulation” arrows in figure 3.27, i.e. downward on the inboard side. When the tail is producing negative lift, the direction of motion is the other way, i.e. upward on the inboard side.
See http://www.av8n.com/how/htm/aoastab.htm ... -stability
tl-3000pilot
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Re: V-TAIL OR CANARD LSA/BURT RUTAN.

Post by tl-3000pilot »

http://www.youtube.com/watch?v=5eSFqGyK ... =endscreen

Look at what I found.

Would love to hear some thoughts and opinions please.

Thanks!

tl-3000.

p.s. If the above link does not work, please type "todds tips canards" on youtube.
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