Aug 12, 2015, 08:27 PM
Caution: Noob in training
Australia, QLD, Redbank Plains
Joined Jun 2007
1,018 Posts
Discussion
Aileron as pseudo rudder?

I posed this question in the Durafly Vampire thread but didn't get any answers as to whether it would work or not

The Durafly Vampire doesn't have a rudder (or rudders, as it's twin boom), but reading one user's description of using asymmetrical aileron throws to help with this got me wondering whether moving a single aileron would act as a pseudo-rudder as it were?
ie., instead of moving the ailerons in opposite directions for a bank, will moving only one aileron result in a rudder-ish behaviour, or will it just be a badly performed bank?

My TX is capable of all sorts of weird and wonderful mixing, so I can "easily" have both normal aileron operation and a possible pseudo-rudder mixed in.

RoryG's original post that sparked the thought, note the differential in the up and down values, and I've bolded his main comment
Quote:
 Originally Posted by RoryG I've got some info on my blog page here, but the throws I use are: Ailerons: low rate 7mm up / 4mm down; high rate 10mm up / 6mm down Elevator: 10mm up / down Spoilerons: ailerons 10mm up; elevator 4mm down I tend to fly in low rate most of the time, the ailerons are *very* responsive and don't need much travel. I find the differential really helps as the bird has no rudder. Hope this helps, Rory

Here's my original query based on the above:
Quote:
 I'll have plenty of questions, but one that presented itself after reading RoryG's post/blog, is whether mixing rudder into the ailerons would work as a pseudo-rudder? I always fly with rudder (started with 6ch helis, so it's second nature), and I think I'll feel a bit lost without one! My vague idea is this, based on RoryG's asymetrical aileron throws; if for example I set the ailerons to +/- 4mm, and then mixed rudder to ONLY give an increase in the positive of up to an extra 3mm, would this give a pseudo-rudder in that one side drags more rather than increases roll, sort of a skid-steer? eg. full right aileron, no rudder => left: -4mm, right: +4mm full right aileron, full right rudder => left: -4mm, right: +7mm full right aileron, full left rudder => left: -1mm, right: +4mm Is that clear as mud?
Last edited by RoGuE_StreaK; Aug 12, 2015 at 08:32 PM.
 Aug 12, 2015, 11:03 PM B for Bruce The 'Wack, BC, Canada Joined Oct 2002 13,966 Posts Spoilerons is an option. A number of aircraft use spoilers for combined roll and yaw from one control. Many airliners use small spoiler movements for small corrective inputs because it provides drag for some yaw at the same time. A few aircraft have no actual ailerons. Just spoilers on the outer wings that are used differentialy for roll control. So it's certainly possible. Will aileron surfaces work for this? Yes and no. They are not actually spoilers that rise from the wing so they don't work quite the same. And they don't give you yaw with no roll. You're going to get roll with either ailerons used as spoilerons or from true spoilers used for roll/yaw combined control. So are they a replacement for rudders? Nope. As for your mixed up rudder and ailerons issue? It's not going to work at all like you think. It'll just act like some differential aileron. Even if you set the ailerons up with 110% throw in one direction and 0% in the other so you have 110% full on differential it's still going to produce a combined roll with yaw. And roll will be the primary reaction. You simply can't replace the rudders with single surface ailerons. Now if you do like the B-2 and use split drag rudders then you CAN produce a pure yaw with no roll. But it's a draggy way to do so compared to installing proper rudders.
 Aug 12, 2015, 11:53 PM Caution: Noob in training Australia, QLD, Redbank Plains Joined Jun 2007 1,018 Posts Hmmm, I not so much expected it to replace rudders, I think I expected that there would be a roll element involved, I guess I'm asking whether it would be a workable way of introducing some controllable yaw without extra hardware mods? Would almost exclusively be for banking turns, just wanting a semi-controllable way of bringing the tail inline, or inversely skidding the tail in the opposite direction... you know, do a little dance, make a little love, and just generally get down tonight I wouldn't expect to be doing flat yawing. So if you allow for added roll, would you expect a smidgen of yaw control to be introduced, or is it a useless/dangerous occupation? RE: spoilerons, I'm looking at those for landing (if we are talking the same spoileron, ie. upwards flaperons), as the vamp is apparently a very glidey bird, sometimes a little too much so for landings. Hoping to maiden this weekend, so I might start with standard settings and perhaps set some switches up to try bringing in different mixes once she's (hopefully) proven to be flying right.
 Aug 13, 2015, 09:21 AM An itch?. Scratch build. South Wales U.K. Joined Mar 2003 16,381 Posts A rudder controls yaw, ailerons control roll. Some of the flying wing guys are using drag rudders for yaw control. Basically like a split horizontally aileron opening up and down at the same time.
 Aug 13, 2015, 11:11 AM treefinder SE MI Joined Oct 2004 11,514 Posts Rogue: what you are (correctly) labeling as asymmetrical aileron movements is more commonly called Aileron differential. It is when the aileron going up travels farther than the aileron going down. Generally a set amount is put into the plane mechanically (by changing the angle of the control wires in plan view, particularly effective with a single aileron servo) or by programming the differential into the radio. Your idea to tie a variable amount of differential to the rudder stick is an interesting variation of the theme. I suspect it would take getting used to, but I could see how it might work in aiding turns. I have a 42" Blubaby (high wing monoplane) that had a problem with adverse yaw when I flew with a KFM3 aileron wing. It would roll, but not turn well with just aileron/elevator unless I added a lot of rudder (like full travel). I got on RCG and asked about it, got the tip to add differential and changed the location of aileron servo to make a 90 degree angle between the two control wires in Plan View. That solved the problem, she now dips the inside wing quite nicely and rolls into the turn. Interestingly she also rolls quite axially as well. The way it works as you probably have already learned, is that the greater movement of inside aileron drops the inside wing in a turn, thereby aiding the turn. On a high wing plane it really helps, on a mid wing or low wing, it isn't as effective, but they don't generally need it as much either. Here's a video showing how she flys with that wing and differential: http://www.rcgroups.com/forums/showp...03&postcount=1 Last edited by springer; Aug 13, 2015 at 11:16 AM.
 Aug 13, 2015, 05:23 PM Caution: Noob in training Australia, QLD, Redbank Plains Joined Jun 2007 1,018 Posts Thanks guys, yeah I guess you could term it variable differential, or dynamic differential, or something like that I might try it with a few different mixer setups, built-in differential vs variable, and see if it's usable or not in this case. The full-scale Vampire does have rudders, and some have added them to the Durafly, but if I can get a bit of yaw control without having to resort to major mods then that should make me happy
 Aug 14, 2015, 08:37 AM Registered User Joined May 2010 54 Posts "Oh, and then there's the Ercoupe. It uses conventional ailerons with a massive amount of differential and NO RUDDERS AT ALL." Ercoupes have rudders, which are coupled to the ailerons, so most of them have no rudder control (a few of the later ones do have rudder pedals). They have a complicated system which moves each of the two rudders a different amount.
 Aug 14, 2015, 09:23 AM B for Bruce The 'Wack, BC, Canada Joined Oct 2002 13,966 Posts Oops, my bad. I recalled a flying buddy that also flew a full size Ercoupe talking about the no rudder pedals and I guess I jumped to the wrong assumption while finishing off my post.
 Aug 14, 2015, 02:47 PM An itch?. Scratch build. South Wales U.K. Joined Mar 2003 16,381 Posts A 'differential' aileron would need to cause drag, but not much roll, if you intend using it as a yaw control. Doesn't the down going aileron cause more adverse yaw ?, that's why we dial in differential aileron, 'more up than down', to reduce yaw. Isn't there a danger that to get the yaw, it could seriously hamper the roll control, or even aileron roll causing excessive yaw if you tamper with the existing ailerons ? Wouldn't just adding a micro servo operating one rudder be simpler and give better reliability.
 Aug 14, 2015, 05:47 PM Registered User Joined Oct 2004 3,345 Posts A way to further enhance aileron differential would be to use Frise ailerons. These are hinged on the top surface, an little back from the aileron leading edge. When deflected downwards the aileron leading edge moves into a recess in the wing, but when deflected upwards the leading edge drops down in the high pressure airstream on the wing bottom surface, effectively acting like an airbrake and providing additional drag.
Aug 15, 2015, 02:52 AM
Registered User
New Zealand, Canterbury, Christchurch
Joined Jun 2008
402 Posts
Hi Brandano,

I don't mean to sound pedantic but the ailerons you describe aren't actually Frise Ailerons. It's a fairly common misconception in the model aeroplane world and even full size.

Frise ailerons are bottom hinged behind the trailing edge, the up going aileron LE protrudes into the airstream a bit but that's designed to work as a balance horn reducing the effort required to deflect the ailerons more than to help with adverse yaw.

The down going aileron forms a slot allowing high pressure air from the wing undersurface to flow over the top of the aileron. This allows the aileron to produce more lift with less deflection and therefore drag, and makes it less likely to stall. You can get away with the sin of picking up a wing with aileron at the stall with Frise ailerons.

Interestingly enough Frise ailerons on their own don't do much for adverse yaw, experiments with having the LE protrude further into the air flow just caused excessive drag and flutter.

Frise ailerons with a bit of differential are quite good in this respect though.

The ailerons you describe work in a similar manner but without all the advantages and finesse of the Frise ones. I bet they are cheaper and lighter to build though which is why they are superior in some situations, at least that seems to be what Cessna and Piper have decided. Could be patent issues too maybe.

Dave H

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Aug 15, 2015, 06:56 AM
Registered User
Joined Apr 2006
5,587 Posts
I totally agree with the above 2 posts. As confirmation, when the B-2 was first publicly revealed, my neighbor in Seattle did not believe it could fly. So I took the top-view photo from the newspaper and made a small paper model, using cambered and complexly twisted wings. It flew very well and I even flew it at Boeing for my engineer friends there. So when WhiteWings AG [with whom I'd worked before, providing them with some other diecut coverstock glider designs] asked me for a B-2 I told them I could give them one.

However, since no normal person could be expected to accurately reproduce the complex curves of my original P.OP. model on a flat coverstock plane, I basically used what the fullsize B-2 does. That is, the ailerons on the B-2 are well inboard of the tips, the outer control surfaces are rudders! Ailerons on the tips would adversely twist the wing tips but the drag-rudders are symmetrical and do not, apparently open all the time except for stealth mode in my understanding.

With this semi-official knowledge acquired from an expert in the program I used the drag rudders on my diecut toy coverstock design as:

1. yaw stabilizers by keeping them split and open, with the lower surface flat with the wing [which is stiffer than the fullsize B-2]

2. horizontal stabs [fixed elevators], with the locking tab for the folded-over "ruddervator" significantly protruding below the wing to both increase the drag-rudder effect while reducing the asymmetrical elevator effect.

This simple "ruddervator" design allowed fixed drag, elevator and aileron effects without the necessity of users finding and KEEPING the surfaces exactly bent.

The final item [which I produced and sold to WhiteWings] flew well, but of course not so well as my original cambered & twisted-wing design, with maybe 80% of its L/D [stable glide from shoulder height launch of 40ft, vs 50+ft. for the original]

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Aug 15, 2015, 08:28 AM
treefinder
SE MI
Joined Oct 2004
11,514 Posts
Quote:
 Originally Posted by RoGuE_StreaK Hmmm, I not so much expected it to replace rudders, I think I expected that there would be a roll element involved, I guess I'm asking whether it would be a workable way of introducing some controllable yaw without extra hardware mods? Would almost exclusively be for banking turns, just wanting a semi-controllable way of bringing the tail inline, or inversely skidding the tail in the opposite direction... you know, do a little dance, make a little love, and just generally get down tonight I wouldn't expect to be doing flat yawing. So if you allow for added roll, would you expect a smidgen of yaw control to be introduced, or is it a useless/dangerous occupation? RE: spoilerons, I'm looking at those for landing (if we are talking the same spoileron, ie. upwards flaperons), as the vamp is apparently a very glidey bird, sometimes a little too much so for landings. Hoping to maiden this weekend, so I might start with standard settings and perhaps set some switches up to try bringing in different mixes once she's (hopefully) proven to be flying right.
Based on the above, your second post, i think your plan to program variable aileron differential will do what you want. My experience with adding differential on low & mid wingers is that it aids in turning by both increasing roll (dropping the inside wing faster than without differential) and yawing the plane slightly into the turn roughly similar to adding a bit of rudder. What it won't do is reverse rudder, as the yaw function is directionally coupled with the roll function. I think your idea is cool, and will try it myself. I've built several wings and a couple tailless biplanes flying with elevons. I programmed 10% differential (if i recall correctly) to a switch, and can tell the difference in turning ease/smoothness, but being able to dynamically add or reduce it via rudder will be interesting!