Endgame II Build - Restarted

[Ken Culbertson]

Recently, unless I post in the main forum, I get virtually zero responses to a question or the thread just gets deleted by the "Phantom Thread Snatcher".  So, I will repost my question here and, even if it is to just "go pound sand", I would like some advice.

From my other thread:
I got sidetracked but I am back and working on the canard.  It is not 100% but I solved the control problem today.  Seems that the logarithmic I used reversed the controls and I would need to put the horn on the bottom of the canard.  Since the pushrod did not want to go through the battery I had to go to the top and add a reversing lever under the turtledeck. I will mock the linkage up tomorrow to make sure it works but I am heading into uncharted waters when it comes to size, throw and the pivot point.  What I am planning is a 13" x 3" canard with a pivot point around 30%.  It will be about 2" behind the prop and about 1/4" above the thrust line.

I don't plan on much movement.  Approximately 1/2" deflection at the TE.  That will be adjustable.  I have a choice to use either a hinged "elevator" layout or a "flying" type.  Whole point is to counter the down pitch from the flaps and up the effectiveness of the elevator.  I am also cutious how placing the canard in the prop blast will affect the wake.

Ken

[john e. holliday]

My experience with canards has the prop behind the canard.  Also with it needs a moving surface behind the wing that works in opposite direction or a nose gear to keep the nose up until air speed is attained.  Another thing is the CG(center of gravity will be further ahead of normal aircraft.  If you do a search you should be able to find pics of my two canards.   They both will do the pattern when engine is set right.

[Tim Wescott]

Pitcher?  Is this a "total" canard, with the main wing as the rear surface, or a 3-surface plane, with wing, tail, and canard?

[Ken Culbertson]

Pitcher?  Is this a "total" canard, with the main wing as the rear surface, or a 3-surface plane, with wing, tail, and canard?

Three surfaces.  The proposed Canard is about 5" x 3" on each side of the nose and quite close to the prop.  It will be easy to disconnect if it turns out to be a brain fart.  I need to get some advice on the pivot location more than anything.  How much in front, how much in back.  Too close to the LE and I will create control loads I don't want or even worse flutter, and too far back it will probably make the plane track like a drunken sailor.  My other concern is the effect on the propwash being so close to the prop.  If it works it will make trimming level flight not dependent on the elevator...or not.  Sometimes we try things just to see if we can do it.  This may be one of those times BUT if somebody out there has built this mouse trap and it wasn't a better one, I will not waste my time proving him right.

It is "ready to install".  Just waiting on the horns I have ordered from Russell so I only have a couple of months to decide.
A rough sketch is attached.  It is an earlier drawing and I think the canard will end up about 10% smaller and closer to the nose.

Ken

[Tim Wescott]

Someone has built this mousetrap, and you commented on the thread!  https://stunthanger.com/smf/stunt-design/three-surface-stunter/msg563418/#msg563418

Remember that there'll be loads on the spar -- I think I'd make a carbon-fiber thingie that goes around the motor and has stub spars on it, to which the front surface's spars attach or continue.

If you do take my suggestion on the CF ring thingie, allow me to additionally suggest that you make the panels removable -- this will allow you to experiment with areas, aspect ratios, control ratios, weird asymmetrical airfoils, etc.

If it's right up against the prop you'll have extra prop noise.  It may or may not be worthwhile to use cambered airfoils, arranged to straighten the air from prop -- this may actually add some useful thrust, by converting some of the slipstream's rotary momentum into backward momentum.  If you don't want to build a separate set of panels to try this, you can try tweaking the control surfaces.

The best CG position will change.  Build a chuck glider and try it out.  Use up some of that scrap balsa that's too heavy to build stunters with.  Try it without the front surface, and again with.  You probably want to adjust it for a fast glide, instead of the best HLG performance -- so build in some tail incidence.  Adjust for the same sort of glide with & without the front surface, and note how much you need to change the CG to get it -- that'll be a first cut at how much you'll need to change the CG for the full sized plane.

[Tim Wescott]

Here's proof that I take my own advise about chuck gliders when thinking about weird planforms.

That's a 3/13 scale Impact wing, BTW.  And the same-scaled (very rough) Legacy horizontal surface.  It balances between 1/2" and 1" in front of the wing LE, which translates to 2" to 4" for the real deal, should I take the spare parts I have lying around and make a weird airplane out of them.

[Paul Walker]

If your front canard is a full pivoting surface, I would be sure the pivot is no further aft that 25% of MAC. Going to further art will cause flutter of that surface, and that is likely not good.  I know from experience that this will happen!

[Tim Wescott]

If your front canard is a full pivoting surface, I would be sure the pivot is no further aft that 25% of MAC. Going to further art will cause flutter of that surface, and that is likely not good.  I know from experience that this will happen!

I would expect that if you really got it wrong you'd get stick snatch.

One way or another, either a very scary ride or one that ends with splat!.

[john e. holliday]

Years ago there was plane designed that had three flying surfaces like your drawing.  The front surface had the nmoving surface and the rear had a moving surface, th main had no moving surfaces.  I think it was called Witch-a-way.  I don't think it caught on.

[Ken Culbertson]

Installed the Canard.  Removable panels and independently adjustable.



Ken

[Paul Walker]

Based on your video  the pivot is very far aft. Beware!

[Brett Buck]

Based on your video  the pivot is very far aft. Beware!

     It is right on the edge, at best - maybe the sweep is sufficient to move the 1/4 chord line back enough.

     I would also be concerned about it going hard-over from the propwash before or shortly after release.
 
     Brett

[Ken Culbertson]

Based on your video  the pivot is very far aft. Beware!

I can make new ones if it turns out that it is.  It is at 20% MAC.  3" chord at fuselage tapering to 2" at the tip.  Pivot is 1/2" in at 3" from the fuselage and at the LE at the tip.  LE taper doesn't show very well in the video.  If you think it might be too far back it would be simple to add another 1/2" to the TE.  That would make it 17% MAC with 28% at the fuselage.  You can bet that the first flight will be SHORT!   If this works at all I plan to experiment with various sizes and shapes.  If it turns out to be a brain fart, it is all removable through the battery compartment hatch.   Unless I get some ideas from others that have tried something similar, my initial movement is going to be 1/2 the movement of the flaps (which are logarithmic) except linear.  The amount of up/down movement will be adjustable.

Ken

Brett:  Before I add more to the aft I am going to post a picture of one of the paddles removed so You can see the taper better.  You raise a point I had not considered in that MAC may not be the right place to measure for the pivot.  I have used flying stabs on sailplanes at 20% for the pivot and they can fly considerably faster than we do but they don't have to deal with propwash.  You can bet this will be tested on the ground with a full run up of the motor.

It is this kind of stuff that makes this hobby so much fun.

[Ken Culbertson]

Here is one of the Canards detached.  One pix shows adding 1/2" to the TE.  The area behind the pivot is 4x that of what is in front.  Maybe it is time for the Rabe treatment.  Stick it out the window at 55mph! ... ...

Ken

https://www.youtube.com/shorts/FyMLCxjmuzM

Not your grandfather's control system.  Bellcrank and logarithmic controls courtesy of Mark Wood.  Smoothest controls I have ever had.  High hopes.

[Paul Walker]

Yes, it looks different when detached.
Good luck.

[Ken Culbertson]

Yes, it looks different when detached.
Good luck.

Thanks!  Even if it turns out to be a dud it has been worth the adventure.

Ken