Belly Canard Flap on STOL airplane

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Victor Bravo

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The belly flap canard is far more problematic in my opinion than what it will give you. Although this is not what you asked for directly, I have a completely different idea to arrive at the result you want (we specialize in this here on HBA :) )

First, add roll spoiler/brakes at the 20% chord line on the outer 2 feet of each wing that are slaved to the upward-moving flaperon (the spoiler only comes up when that flaperon comes up).

Second, adjust the flap function of the flaperon control to allow 25% greater flap deflection downward, by adding another flap position.

Third, modify the horizontal tail mounting system to use a Piper Cub or Cessna 180 style jackscrew, where you can move the leading edge of the horizontal tail down by a couple of inches.

The extra flap deflection will inrcease lift and drag, giving you the ability to take off and land shorter. The spoiler/brakes will give you additional roll control at ultra-low speed, and deal with any adverse yaw issues, and counteract the (likely) control reversal in the aileron circuit at these high AoA's. The trim-able tail will deal with the extra nose-down pitching moment that the flap deflection will certainly cause.
 
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pictsidhe

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Jul 15, 2014
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7,377
Location
North Carolina
Lower Cm airfoils and reduced flap deflection on a sesquiplane conversion? If you have moved the Cg a bit with a jumbo engine, you can tweak the stability by putting the new lower wing forward a bit. I like VBs tail mod. With the canard, you'd need to lower the CLmax of the main wing to avoid deep stall. With a small canard, that could actually raise stall speed.
 

ZenithDriver

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Dec 17, 2019
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Seattle, WA
Original poster here. I thank you all for your comments...some have given my positive food for thought. However, the natural flow of the discussion has gotten away a bit from my original proposal. A couple of simple bullets below may steer us back in that direction....or not ;)

  • One baseline groundrule is that I am not looking to massively alter this well designed little airplane. Engine changes, swing wings, and adjustable tailplanes are indeed an interesting discussions, but out of bounds for this winter project. I am hoping to do something I can play with and experiment, but then remove if it does no seem viable or worthwhile.
  • Perhaps I should not have mentioned the word "canard" in this proposed modification. I am not proposing a pitch control device forward of the CG, rather a forward mounted flap. The flap would be deployable, but the concept would be to only use it when the aft wing mounted flaps were deployed to balance their nose down pitching moment (as I initially describe in the .PPT slides
  • One perfectly valid point that has been brought up is the stall response with a fwd mounted flap that is additionally mounted in the propeller slip stream. This airplane does have a large and very effective elevator,. Therefore it is hard to imagine, given the length of the tail moment arm relative to the fwd flap, that a situation could develop where the nose could not be lowered in the stall. However, that is certainly a sobering thought and merits some consideration and later....careful flight testing.
Here are a couple of pictures to re-clarify the proposal

upload_2019-12-26_8-9-58.png

upload_2019-12-26_8-11-50.png

Elevator

upload_2019-12-26_8-15-23.png

Elevator
 

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flyrite

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Joined
Mar 22, 2015
Messages
55
Location
lyons, ga. in the usa
Original poster here. I thank you all for your comments...some have given my positive food for thought. However, the natural flow of the discussion has gotten away a bit from my original proposal. A couple of simple bullets below may steer us back in that direction....or not ;)

  • One baseline groundrule is that I am not looking to massively alter this well designed little airplane. Engine changes, swing wings, and adjustable tailplanes are indeed an interesting discussions, but out of bounds for this winter project. I am hoping to do something I can play with and experiment, but then remove if it does no seem viable or worthwhile.
  • Perhaps I should not have mentioned the word "canard" in this proposed modification. I am not proposing a pitch control device forward of the CG, rather a forward mounted flap. The flap would be deployable, but the concept would be to only use it when the aft wing mounted flaps were deployed to balance their nose down pitching moment (as I initially describe in the .PPT slides
  • One perfectly valid point that has been brought up is the stall response with a fwd mounted flap that is additionally mounted in the propeller slip stream. This airplane does have a large and very effective elevator,. Therefore it is hard to imagine, given the length of the tail moment arm relative to the fwd flap, that a situation could develop where the nose could not be lowered in the stall. However, that is certainly a sobering thought and merits some consideration and later....careful flight testing.
Here are a couple of pictures to re-clarify the proposal

View attachment 91513

View attachment 91514

Elevator

View attachment 91516

Elevator

Explain to me again, why what I have on the bottom of my plane is not exactly what you are talking about?


https://photos.google.com/share/AF1QipMbyQVVxzQ2ANLHgGnOO0rTpUffWifmbBsYNkNcXaewDVthFqG3xWogSs4l8xuJiQ/photo/AF1QipPRfjR4lEJfEpBDSYSdFmNXdIGWzRyML8VcjtaD?key=UV9lbjFIYmRqUUxnSTNfRTR0Nk9ORWNVWlRDdTVn
 

pictsidhe

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Joined
Jul 15, 2014
Messages
7,377
Location
North Carolina
Original poster here. I thank you all for your comments...some have given my positive food for thought. However, the natural flow of the discussion has gotten away a bit from my original proposal. A couple of simple bullets below may steer us back in that direction....or not ;)

  • One baseline groundrule is that I am not looking to massively alter this well designed little airplane. Engine changes, swing wings, and adjustable tailplanes are indeed an interesting discussions, but out of bounds for this winter project. I am hoping to do something I can play with and experiment, but then remove if it does no seem viable or worthwhile.
  • Perhaps I should not have mentioned the word "canard" in this proposed modification. I am not proposing a pitch control device forward of the CG, rather a forward mounted flap. The flap would be deployable, but the concept would be to only use it when the aft wing mounted flaps were deployed to balance their nose down pitching moment (as I initially describe in the .PPT slides
  • One perfectly valid point that has been brought up is the stall response with a fwd mounted flap that is additionally mounted in the propeller slip stream. This airplane does have a large and very effective elevator,. Therefore it is hard to imagine, given the length of the tail moment arm relative to the fwd flap, that a situation could develop where the nose could not be lowered in the stall. However, that is certainly a sobering thought and merits some consideration and later....careful flight testing.
Here are a couple of pictures to re-clarify the proposal

View attachment 91513

View attachment 91514

Elevator

View attachment 91516

Elevator
It doesn't matter what you call it, it is surface mounted well in front of the cg and will reduce the stability. If you still want to go ahead, calculate the stability change it will cause, then mimic that in flight testing by SLOWLY moving your cg aft with weight in the tail before you do any aero mods. If your calculations show that it puts stability below that of max standard aft cg, you might want to think of another plan.

It might be a simple mod to perform, but it is a major aerodynamic mod, and should be carefully evaluated.
 
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Victor Bravo

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Joined
Jul 30, 2014
Messages
7,078
Location
KWHP, Los Angeles CA, USA
Explain to me again, why what I have on the bottom of my plane is not exactly what you are talking about?
The difference is he wants to mount it forward of the CG and you mounted it at the CG. Yours is designed to add drag and lift without changing the pitch trim, and his is designed to add drag and lift with changing the pitch trim.
 

flyrite

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Joined
Mar 22, 2015
Messages
55
Location
lyons, ga. in the usa
The difference is he wants to mount it forward of the CG and you mounted it at the CG. Yours is designed to add drag and lift without changing the pitch trim, and his is designed to add drag and lift with changing the pitch trim.
I believe any flap mounted on the bottom on or forward of the center of lift will provide the cancellation of the pitching he’s desiring. Mine sure does. Without the bellyflap, My plane has the nose down pitch any plane does, Once the bellyflap is mounted it cancels it completely without the need to re-trim. Hands off 40 to 45 approach all the way to touch down.
Obviously the more forward of the CL he mounts it the more effect it will have.
 

Jonny o

Member
Joined
Oct 31, 2015
Messages
5
Location
Fairbanks, AK USA
Gentlemen,

1.
One thing not yet mentioned is that, on any airplane, the front wing causes the wing aft of it to fly in downwash ( lower "relative" angle of attack ).
This helps a conventional airplane because you want the tail in downwash to help trim issues. On a canard, the front wing is causing part of the wing behind it to be at a lower relative angle of attack and make LESS lift. If the canard has a span of 8 feet, then around 6 feet of the main wing will be producing LESS lift than if the canard was not there. This is part of the effect called Circulation. The canard on the Wren 182 is causing some of the main wing to produce LESS lift. You can't just look at parts. You have to look at the whole picture.

2.
It would be interesting to mount the Swamp Monster on a gimble to get data on which way the moment of the belly flap is actually pushing. It is mounted around 4 feet BELOW the neutral point of the aircraft. Not in front and not behind. No doubt, it is making a great deal of drag, and drag in the right place can be good.

Picture a pendulum hanging down, 4 feet, into a slip stream, with just the belly flap (drag) mounted on the end. The result would be an aft moment (force ) and therefore if it was connected to an airplane; a nose down pitching moment, which is the opposite of what Zenithdriver needs.

Enjoy your day,

Jonny
 
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