AA5BY

Our group is investigating a summer competition using foam gliders from Walmart or Hobby Lobby converted to two ch RC. They will be piggy backed aloft to a prescribed altitude and released and longest time aloft wins. The only requirements are the 54" one design airframe and two channels. Control is the choice of the builder as well as adding di or polyhedral.

The immediate task is to build the first and test for adequate strength to endure the launch ride. In an effort to keep it simple, I'm wondering if elevons (on the wings) would provide enough pitch control on what is otherwise a conventional air frame, given that flying will require light air and not a lot of pitch control will be needed if the plane is otherwise in good trim.

Any thoughts?

BMatthews

That's an interesting concept and not the sort of thing that comes instantly to mind.

Ailerons on the wing change the lift by altering both the camber and angle of incidence of the resulting airfoil when deflected. So angling both "flaperons" or "elevons" down at the same SHOULD lead to an elevator like nose upward pitch. In this regard they would function much like wingerons where the whole panel shifts for roll and pitch.

Two things to consider on the prototype that will be built to try this. One is that you want to use full span flaperons or elevons so that the whole wing changes camber. Otherwise if only outboard "conventional" aileron like surfaces are used the pitching action will be damped by the fixed portion of the wing panels. Also using full span controls of this style will avoid any tip stalling issues with using "up" elevon inputs at lower speeds. Using nose up inputs may still result in the whole wing stalling but at least it'll do so evenly. Secondly because you're only moving a part of the wing you'll want the full span strip surfaces to be wider than what we normally use for only strip ailerons. I'd say you want the flaperons to be more like 15% or more of the wing chord. That way it'll tend to produce something closer to the an adequite amount of pitching action.

Some years back I built a 2 meter glider with full span flaperons. I had a regular elevator as well but I do recall that deflecting the flaperons down did make the nose pitch up quite noticably which took noticable amounts of down trim to counteract. The flaperons were in the 12 to 15% of the chord size range. So it's more than likely that a similar "elevons only" modifiction to your glider would allow for basic flying. Only actual flight testing would determine if it was enough to do loops and other similar stuff to show that it truly acts like having a separate elevator. But for setting the basic flight trim and general flying tasks I suspect it would be fine.

countilaw

The LOWERING of "flaberons", flaps or Elevons will pitch the nose down. Not up. The LOWERING of the elevator will also pitch the nose DOWN.

EXAMPLE: Upon landing, the flaps are lowered and the added lift pitches the nose down. If lowering the flaps pitched the nose UP it would put the aircraft in a stall.


Frank

AA5BY

Thanks for the thoughtful reply and insights. My experience in this area is limited to my Ultra Stick Lite that allows throwing the mix switch and coupling the elevators and flaps (opposite movement) for more pitch control perhaps 20-30% more so even with good size flaps, the pitch control is certainly far less than would be afforded by elevators.

My new radio has a additional trims one of which provides for trimming ailerons up and down, which doing so usually requires a corresponding elevator trim... so there is little doubt that elevons in that config would provide some pitch control... the question as always is adequacy.

My freeflight guru friend is suspicious that without any dihedral, the pitch control needs will be more demanding than afforded by such a config. Another config would be to put the elevons on the tail where no doubt pitch control would be adequate, but would roll authority be adequate... again he thinks unlikely to wit I tend to agree on not enough surface and not enough lever arm with them inboard.

What I've concluded to do... is to mount three servos two on conventional ailerons and one on elevator with the first task to determine the airworthiness of the glider for launch. I've used two inch wide strapping tape top and bottom spars and it firmed the wings up a great deal to the point I think it'll be ok. I've added 1.25" strip ailerons and have yet to do the elevator.

This config can test a wing elevon config by then setting it up for three ch with the elevator for back up authority.

The answer will be interesting.

AA5BY

Frank... are you sure. My planes that have flaps require down trim mix to trim out the couple unless my memory has gone totally.

Lnewqban

Can you simply increase the dihedral and use rudder to bank?

If I remember correctly, those foam planes have a sweep back wing, which is equivalent to the conventional dihedral and conversions to RC have been successfully done without adding ailerons.

Check this search out:

http://search.rcuniverse.com/search....hwhere=subject

AA5BY

Thanks for the link to some good reading. Looks like all attempts were E-power conversions, not the way we are going. Our wish is to convert to RC glider for some summer competition made possible by the advent of altitude telemetry to get fairly equal altitude launches.

Yes, the plane has swept back wings and dihedral could be added with little effort. The frame is fragile but firms up pretty good with strapping tape spars added to the wings and a popsickle stick joining spar.

countilaw

Iam sure AA5BY, The first time I applied flaps on one of my pattern planes, it startled the heck out of me. The nose dropped and I thought I was losing it, so I gave up elevator and the plane pitched up. So the next time i applied flaps and let off the elevator and started my flare over again. The flaps provided a lot more lift at the slower speed and the last thing you want is the nose pitching up further.

With the nose dropping, you have basically started your decent over again and you again have a lot more elevator to use. The added lift behind the CG pushes the nose down.

Frank

AA5BY

I was wrong about the swept wing.... this glider has TE taper and straight LE.

As to how a plane pitches with aileron up/down, I'll know fairly soon on how it does with this design. I'll likely finish construction today and if WX permits test tomorrow.

The config is full length elevons with them trimming down for up pitch. It will have as well an elevator (at least for testing) which can be switched in/out by mix switch.

Lnewqban

Wingtip dihedral versus V dihedral could help in keeping the structural integrity of the center of the wing.

You may find helpful some of these articles on free flight:

http://pensacolafreeflight.org/page5/page5.html

AA5BY

It is done except some buttoning of securing balancing weight and wires and final gluing of wings into fuselage. Wing area is 351 sq in and weight is 9 oz for 3.7 oz/sq ft loading. CG is 1.93" aft LE for abt 30% mac. Btw it required 10 cents (pennies) to balance. If elevators are not needed, it will lighten up a good bit as the elevator servo is somewhat aft with wire linkages and these offset by 2-3 pennies.

The config does use three ch, with two for elevons and one for elevator. The elevator is switchable in and out with the mix switch to test possibility of not needing, which would simplify RC conversions.

I'll report back after testing on whether elevons offer enough pitch control.

Just remembered I need to check to see if the elevator trim will follow the mix as it is plugged into the rudder port on a 4ch RX.

Tried to upload a pic... server not taking it... will try another route and provide link in a short.

[link=http://pages.suddenlink.net/arlyn/P0003345.JPG]Walmart Glider[/link]

AA5BY

Well.... I was right the first time... it does have some sweep... abt 1.5" worth and it does have a little dihedral. I'd not inserted the wings fully to keep from getting them loose when gluing so really couldn't tell exactly what was. They are now glued and show the sweep and dihedral.

That means my CG position needed corrected and running the numbers yields 2 7/16" aft the LE at root. I've taken four cents back off.

The only remaining work is gluing the horizontal stab, which I've decided to do after hand launch trials. It fits rather tight and will stay in place for some initial testing and allow setting the stab incidence to suit. That might get done this PM.

BMatthews

Frank, pitching up or down or not at all with flaps depends on the flap arrangement as well as the planform of the model. It also depends a lot on if the flaps are full span flaperons or if they are conventional flaps with separate outboard ailerons. And to add to the mix the percentage of the chord used by the flaps will play a part. Oh, and the tail moment length. So all in all the answer is "it depends".

On two out of the three models where I've played with flaps two of them responded with a strong nose up action from deploying flaps. On the third they didn't do anything. This last one was an ARF with narrow strip ailerons that I had set up the controls to act as flaperons just to try them out. The narrow roughly 7% width resulted in no detectable pitch change and no detectable gain in lift. I guess I'm lucky that they even worked as ailerons.

The other two were/are sailplanes. In both cases the roughly 18 to 20% chord width flaperons and flaps resulted in a fairly strong nose up response to flaps going down. One used mixed in down elevator and the other I just stuff in some forward stick manually.

The fact that your pattern model responded the other way suggests to me that there was something a trifle different or extreme in how the flaps were set up.

nh4clo4

My Feedback: (33)

Just a thought, make the elevators elevons, Some smaller models do that to eliminate the weight and complexity of ailerons.

Those gliders have enough stability and dihedral to fly without controls. The wings are not very stiff, and any extra weight or controls may make it worse.
Ed

AA5BY

That was my first thought with some concern about adequate roll authority and I may try that config eventually. At the moment, what is needed is for the guys to see that it can be successfully launched and fly so the conservative approach was taken for now.

You are correct in that the wings and even the tail boom need strengthening and that has been done with packing tape... it actually seems to have stiffened well. The weakest issue is possibly the wing joining dependent strictly on foam so two popsicle sticks were added as wing joining spars.

Part of the fun will be seeing the various configurations used.

Another pic of the setup.
[link=http://pages.suddenlink.net/arlyn/P0003346.JPG]Glider mounted to launch plane[/link]

BMatthews

That option really only works on models that are flying wings, deltas or use short span wings such as semi scale jet fighter style wings with wide spaced stabilizers. Otherwise the natural damping of the wings fight the roll effect from the elevons very strongly. In the case of the foam glider that AA5BY is using the roll authourity would more than likely be rather dismal as the wings are more than high enough an aspect ratio to fight the roll from tail surfaces and reduce the control effect to far below what would be acceptable.

ARUP

SIG had a sailplane that had fixed tail surfaces. The wings rotated about their axis for pitch and roll control. It was called the 'Samuri' or something like that. Is this concept adaptable to what you have in mind with the foam gliders? A carbon rod in an aluminum tube might be the ticket!

AA5BY

Very interesting. That would be one way of getting the surface area that BMatthews suggested would be needed to get pitch authority at the wings.

BMatthews

Wingerons do work very well both for roll and pitch. But adapting the wings to pivot requires a rather well designed center pivoting system be produced and integrated into the model. I'd suggest that it would cause far more trouble than just adding flaperons that work on the elevator and aileron channels.

What would be there and which is open for experimentation would be the potential for adding a LOT of drag by using larger pitch control inputs with a flaperon. Theres a very real issue with airflow separation at the hinge line when the deflection angles get to be more than a few degrees. And the hinge line on a full span flaperon is a LOT longer than a separate elevator. So it would be worth doing a model like you did where you have the option of going either way.

Of course with the liberties taken with the molded foam model as the core of the project it's open to wonder if the model would see the difference. And many plank style wings fly just fine with full span elevons. So perhaps I'm stuck thinking about how many angels fit on the head of a pin....

AA5BY

Finally got a light air day to test the glider launch and its flight. First, the little cheap foam glider with a little reinforcing tape survives piggy back launches with no evident problems and actually flies quite well. By the third flight it was in balance for prolonged flight.

As promised, a report on the use of elevons for pitch control. We never got to the point of switching out the elevators to see if adequate pitch control would be provided by elevons because the elevons were producing too much drag and limiting flight time. Flight endurance was greatly extended by going elevator only for pitch control. Pitch control was only slightly greater when combined with the large elevons having considerable throw and was quite adequate with the very small elevators only. Simple conclusion... far too much drag was produced with them.

It is also likely that strip ailerons produce too much drag for such a light foam glider. They caused opposite yaw. Some of that was likely because the wing TE is fat and the ailerons didn't comply to the foil thickness and were tape hinged on the bottom. The down aileron would likely be far more drag producing than the up and on a long wing had too much lever arm couple and induced the opposite yaw. More likely the better route is to trade ailerons for rudder.

Very briefly, in only lower 70s temperatures, after getting the glider in trim, it produced 5-10 min flights when released at 750 ft. It is anticipated that when temps heat up... prolonged flights can be achieved.

The good news was the launching was successful and the guys gave a thumbs up to the one design competition and are committed to a RC conversion.

charlie111

I thought they called it a Stabilator.The Whole (Elevator)  moved?Not just the Rear piece of the Horizontal Stabilizer.Glad to Hear you cut down on Drag and ext. your Flight Time.You Must Tow it with another Plane and release it?

AA5BY

The configuration that was opted for is conventional elevators, which are quite small but seemingly effective. The glider is launched piggy back using a cradle and release mechanism.

The first one has strip ailerons but one of the guys currently converting will be using rudder and we'll see how that compares.

We've not tried towing. The server wasn't working the last time a pic was tried... trying again.

alasdair

It certainly does depend. Not only on the size and spanwise extent of the flaps, but also on the tail area (as a % of the wing area) and also on the tail height. I made this observation inof my jet column in AMI magazine a while back.
Models like my Composite-ARF Lightning or the Ultra Bandit that Ali Machinchy and Raul Lozano flew at Florida Jets need a little down elevator trim (Ali says 8%) with flaps. Check out the photos and you can see that the low mounted tailplane is in line with the wing. Raise the tail up a bit and you get away with little or no trim change, as has been done on the Tomahawk Futura that Ali and others flew at Florida Jets this year. Place the tail even higher, as on the L-39 Czech trainer, and you need up trim. Malcolm Harris says that on his 1/6 scale L-39 from Global Jet Club he has 3 mm of up elevator with full flap, mixed in proportionally throughout the flap range.

I have seen photos and video of a model called "Tizzy" in the UK that had fixed tail surfaces and was controlled solely by elevons. Up elevon pitched the nose up, I believe. But on other configurations it could pitch the nose down. On some models, like my Falcon 120 the pitch effect of flaps is virtually neutral, so I would never recommend elevons as a primary pitch control without an extensive analysis of their overall effects on all parts of the aircraft.

AA5BY

An aside....this evening the CG of the glider was checked following the flight testing and balancing done yesterday and I'll once again have to give kudos to the aeronautical calculator. It had projected a CG at 2.58" aft of LE at root and that is exactly where the CG produced the best glide endurance.

Also noted was subtle changes have large effects on a light airframe. Glide endurance went way up when following slight balance changes.

alasdair

which CG calculator did you use?