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Old Dec 17, 2010, 09:58 PM
Jets are for kids-of all ages
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Right at touchdown, with the nose slightly higher than the main, a gust (5-7kts) hit and it popped straight up in the air nose almost vertical. I hit the power it started to pull away at maybe 10 feet and the wind was blowing it right into the spectator area. Being more inclined to demolish the plane than my bank account through a lawsuit, I pushed the nose down and it went almost right into the pilot barracade. Yuo can see in the picture where it hit, I was just on the backside of the barracade and my wife and club freinds were about 20 feet behind that. So I sacrificed it for safety. I'll build another one this time out of foam board again. Those really fly good and they are durable.
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Old Dec 18, 2010, 06:50 AM
What could possibly go wrong?
nickchud's Avatar
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Do you think foam board would survive that sort of thing better than Depron, Roger?

Nick
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Old Dec 18, 2010, 07:43 AM
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THat sort of behavior sounds almost like the wing stalled before the canard.
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Old Dec 20, 2010, 07:05 AM
What could possibly go wrong?
nickchud's Avatar
Market Harborough
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canards landing..

The only compulsory aerobatic maneuver.

I'm coming to the conclusion that, whilst I use a high alpha to slow down, a point arrives where I usually do that for too long until I stall the canard. With a forward CG, this results in a more or less gentle nose-dive instead of a landing.
Canards Landing (3 min 55 sec)


Or just accept that I have to land a little faster and hope that I can find a smooth patch in that field!
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Old Dec 20, 2010, 07:11 AM
What could possibly go wrong?
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I met up with Charles at the weekend for some good old Southern Hospitality. His collection of planes is very, very inspiring. Perfect craftsmanship and all of them in spotless, ready to fly condition.

Many thanks Charles!

Nick
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Old Dec 20, 2010, 08:29 AM
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Nick, an interesting and instructive collection of videos. There wasn't much sound on some of the clips but it seemed to me that mostly you were landing with power off. The result of this is that you end up trying to control both the attitude of the plane and the descent rate with the elevator stick - which is always going to be a challenge.

The answer is to use the elevator solely to maintain the aircraft in the desired attitude and use the throttle to regulate the descent rate. From what I saw at Chilliwack, this is lesson two in the Ivan flying school of smooth landings, lesson one being to make sure you have no more elevator deflection than you really need.

Just a thought.

Trevor
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Old Dec 20, 2010, 09:36 AM
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Regarding the comment at the end of the video, that "as the speed bleeds off, we need to push the nose down to keep from stalling", that suggests a too-far-aft C/G, resulting in insufficient static pitch stability. If the plane's C/G is far enough forward, then as the speed bleeds off, it will put the nose down all by itself. It's only if your static pitch stability is nearly neutral (because the C/G is at, or nearly at the Neutral Point) that you will need to make the correction yourself.
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Old Dec 20, 2010, 02:24 PM
What could possibly go wrong?
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Trevor
Quote:
There wasn't much sound on some of the clips but it seemed to me that mostly you were landing with power off.
Thanks for your help. I took the sound off to remove the barking dog. The reason I left it on for the final, Starship landing was to show that I was trying to keep the high attitude by adding a little throttle. I think I added too much and found the plane starting to rise again. Then I cut the throttle and down went the nose.

Don
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If the plane's C/G is far enough forward, then as the speed bleeds off, it will put the nose down all by itself.
Thanks to you too. 'Trouble is, the nose goes down by itself alright, but it keeps going down into the gentle nose-dive before the elevator authority comes back. The model with the most consistent good landings is the Polar Duck, which has the least static margin of all, pretty close to zero. The other difference about that one is the canard chord, which is 20% more than the others, while it's AR is much less.

Possibly, the neutral point of the Polar Duck is affected one way or the other by the shape of the fuse or the very small rear elevator. I have guessed (sorry!) that they will cancel each other out at least to the nearest 5mm. I avoid cutting the throttle all the way on that one because I want to avoid the pitch-up effect of drag from the prop. That prop is inevitably going to have more pitch effect either way than any of the other models.

Living and learning, hopefully.

Nick
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Old Dec 20, 2010, 04:03 PM
Jets are for kids-of all ages
Florida, USA
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Quote:
Originally Posted by Trevorh View Post
Nick, an interesting and instructive collection of videos. There wasn't much sound on some of the clips but it seemed to me that mostly you were landing with power off. The result of this is that you end up trying to control both the attitude of the plane and the descent rate with the elevator stick - which is always going to be a challenge.

The answer is to use the elevator solely to maintain the aircraft in the desired attitude and use the throttle to regulate the descent rate. From what I saw at Chilliwack, this is lesson two in the Ivan flying school of smooth landings, lesson one being to make sure you have no more elevator deflection than you really need.

Just a thought.

Trevor

I agree with the statement of pitch for attitude , power for altitude. Here is a video from about 2 years ago with one of my early and best canard planes. This one did great touch and goes.

http://www.youtube.com/watch?v=hJoJLWr3YTs

turn up the sound and you can hear the power fluctuations for altitude control.

Roger
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Old Dec 20, 2010, 04:41 PM
What could possibly go wrong?
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Nice Video Roger! and a lovely plane.

I was wondering if my problem was due to the Rutan style wings requiring more speed than the Delta Duck style wings, especially the narrow chord canards.

Partly, I suffer from trying to land on small patches of rough ground. Trevor will confirm that I can land planes with low stall speed and plenty of approach space. I mean the Ivan Pettigrew Minicat on the reservoir. I don't think it should be called a Minicat. It's an 84" Catalina, called that because he also designed a bigger one.

cheers

Nick
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Old Dec 20, 2010, 05:37 PM
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Originally Posted by nickchud View Post
...Don
Thanks to you too. 'Trouble is, the nose goes down by itself alright, but it keeps going down into the gentle nose-dive before the elevator authority comes back.
So, your canard is very close to stall at the point where you cut the throttle, and ineffective until you regain some speed?

Quote:
The model with the most consistent good landings is the Polar Duck, which has the least static margin of all, pretty close to zero.
And therefore the greatest elevator authority, all other things being equal.

Quote:
The other difference about that one is the canard chord, which is 20% more than the others, while it's AR is much less.
An airfoil stalls at a particular lift coefficient. Reducing aspect ratio reduces the dCl/d-alpha (i.e.: lift curve slope), so it takes more angle of attack to get it to the lift coefficient where it stalls. Lower aspect ratios also tend to make the stall more gentle and less well-defined.

Quote:
Possibly, the neutral point of the Polar Duck is affected one way or the other by the shape of the fuse or the very small rear elevator.
It's possible, particularly the rear elevator, which would tend to move the NP aft.

Quote:
I have guessed (sorry!) that they will cancel each other out at least to the nearest 5mm. I avoid cutting the throttle all the way on that one because I want to avoid the pitch-up effect of drag from the prop.
Are you speaking of that specific plane? Because above you stated that the nose goes down when you cut the throttle.

On an aft prop like that, there is the effect of the high thrust line. However there is also the factor of the blanking of airflow over the wing by the prop. This would also tend to cause a pitch-up, in addition to the nose-up effect of the high thrust line.

We ran into this effect on our Roakill Series Northrop XB-35 model. The four props spread across a large portion of the trailing edge of the wing, in particuar the area containing the elevators, would blank the airflow in that area. This did cause some pitch-down when the throttle was cut, but the main effect was to make the elevators almost totally ineffective, making a flair for touchdown essentially impossible. We found that keeping the throttle stick at about 25% all the way down final approach and touchdown fixed the problem.

Quote:
That prop is inevitably going to have more pitch effect either way than any of the other models...
But most of the principles will still be the same, and still apply to all of them, just not necessarily to the same degree.

I do get the impression from all of the above that the trouble may be that you are making throttle changes that are too large and too abrupt. It might help to set up for a longer final approach, then get the plane established on a stable, steady descent, with slow, smooth throttle corrections as needed to keep the approach angle steady, while holding the pitch attitude constant with the elevators. The other thing is to not try for a full-stall landing, fly it on with some airspeed and control.

On full-scale aircraft it's fairly common in zero wind to fly the landing pattern at 1.3 times the stall speed, 1.2 times Vstall on final approach, and 1.1 times on "short final" just before touchdown. In the wind they add some to that for safety margin. ON twins, the standard method is to fly final approach at the best single-engine rate of climb airspeed, so they are all set for a go-around if one engine quits on final. On mst large, heavy and/or complex aircraft, they do not try for a full-stal landing, they "wheel" it on with some power and speed. If you do want to make a full-stall landing, flair the plane into level flight just inches off the ground, then easy the throttle off while holding the pitch attitude steady with the elevators, and let the plane settle the last few inches.,

The point is that in all cases, they FLY the plane on with some margin for error and enough speed for good control response, rather than hanging it on the hairy edge of a stall all the way down final approach, then trying to make it plop onto the ground at the end.
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Old Dec 20, 2010, 05:54 PM
What could possibly go wrong?
nickchud's Avatar
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Don
Quote:
The point is that in all cases, they FLY the plane on with some margin for error and enough speed for good control response, rather than hanging it on the hairy edge of a stall all the way down final approach, then trying to make it plop onto the ground at the end.
That's exactly what I've been trying to do because of the need to land in small patches of rough ground. There's no doubt that the Delta Duck in its different incarnations manages that better than the Rutan wingplan.
Quote:
An airfoil stalls at a particular lift coefficient. Reducing aspect ratio reduces the dCl/d-alpha (i.e.: lift curve slope), so it takes more angle of attack to get it to the lift coefficient where it stalls. Lower aspect ratios also tend to make the stall more gentle and less well-defined.
My point is, for STOL, short stumpy canards are best, yes?

Nick
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Old Dec 20, 2010, 06:23 PM
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Quote:
Originally Posted by nickchud View Post
Don
That's exactly what I've been trying to do because of the need to land in small patches of rough ground. There's no doubt that the Delta Duck in its different incarnations manages that better than the Rutan wingplan.
My point is, for STOL, short stumpy canards are best, yes?

Nick
Stall characteristics are one point, but the other point is that short, stumpy canards, and also short, stumpy wings, have lousy aerodynamic efficiency in comparison to the typical Rutan layout. For STOL operations you need a truly horrible L/D in landing mode, but the ability to quickly clean that up and/or enough power that you can go immediately into a steep climb in case of a go-around.

However, you do need something that will do a steep, slow approach but with enough surplus speed to do a decent flair for touchdown (unless you want to have landing gear with shock strut travel in the same league as a Navy carrier plane), and no need to accelerate from the final approach speed to go back into a steep climb. That means carrying some speed on final, AND designing for a slow climb speed. It also means that you really can't rely on flaps to reduce your stall speed much, just use them to make massive amounts of drag. If they substantially reduce your stall and final approach speeds, then you will have to dive to regain speed before you can retract them and "clean up" the plane for a go-around.
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Old Dec 20, 2010, 08:33 PM
What could possibly go wrong?
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Don
Quote:
(unless you want to have landing gear with shock strut travel in the same league as a Navy carrier plane)
Tried that. Skids/floats seem to work better.

Power at these weights is not a problem, though I agree with you about the 5x5 prop. Lousy aerodynamic efficiency seems to be also not a problem. I get a wide range of speed and maneuverability. The dog gets plenty of exercise.

So, the future is.... use a proper runway for my Starship etc and use my Polaris with the Delta Duck wing and the short stumpy canard for the rough field.

How's that?

Nick
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Old Dec 20, 2010, 08:37 PM
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Sounds like a plan!
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