daven

My Feedback: (1)

I know this may sound a little crazy, but has anyone built a quickee with a full flying stab?

I think I got a pretty good idea about how it can be done, but will the advantages outweight the negatives?

Can you move the tail in small enough (accurate) enough movements to be effective for precision racing?

Will the gap at the fuze/tail joint cause more drag than an actual moving surface?

Thanks Al, you've kept me up 2 nights in a row thinking about this!

diggs_74

Well, if a 1" movable surface at 3/16" deflection is what you're using now imagine a 4" movable surface..... If my math is correct you would be looking at 3/64" of throw... You might have to run digital servos

HighPlains

My Feedback: (1)

Dave,

I agree that it is a crazy idea. Oddly enough, though for a variety of reasons, I think you would gain more by changing the angle of attack of the wing instead, and having a fixed stab. You would need to pivot very close to the center of pressure.

Bob

ALbert.S

I got the idea a long time ago when I got this accessory pack of stuff from Kraft. It had the parts for making a flying stab included. We were going so slow then I figured it wouldn't make much difference. Then I saw the piece about the Sabre and the Mig and Chuck Yaeger said the advantage the Sabre had was it's flying stab.At the performance level that the 428 class is at who knows. My guess is that it.s going to help mostley in the turns

IRLJR

My Feedback: (37)

Daven
My best friend and racing partner, Fran Mitchell, has been doing r&d with flying stab Q-500's for several years. We have built and flown both V and T-Tail versions with great success. We have found that both versions require digital servo's for precise centering.
The T-Tail version is the easiest to build, and also offers the advantage of having the stab out of the wing-wash. While not nessessarily faster in the straight away, the flying stab definately turns with less loss of speed.
These planes typically fly with TT 40's at the NEPRO races, but they have also been test flown with a Nelson.
Give it a try--
IRL

diggs_74

Assuming you're planning to try this on a Seeker fuse I wonder about having room for the linkage and mechanics involved.... There isn't exactly a lot of room back there... The pivot point is one thing but what about the anchor points front and rear and the slots for those anchors to slide in..... I think it would be cool as hell but I just can't see where it's going to all fit without some major changes to the usable area in the back of the fuse... Just my .02 worth.

banktoturn

Dave,

You would definitely want small throws, and I think you could, and should,
arrange that mechanically, so that you could have most of the range of motion
available on the servo end.

There are a few drag tradeoffs. One is the gap at the joint with the fuselage.
I wonder whether a clever builder could mount each half of the stabilizer on
a plate which is flush with the side of the fuselage, and rotates with the flying
stab. Friction would be your #1 enemy in this scenario, and you would
definitely want the pivit to be near, and a little ahead of, the aerodynamic
center of the stab. Another drag issue is that a cambered lifting surface is
a lower drag way to generate lift than an uncambered one, and an elevator
gives the stab camber when it is deflected. This means that a symmetric
flying stab should give lower drag only if it is operated at fairly near zero lift.
This means that the CG should be set as near to the aerodynamic
center of the main wing as possible, so that the stab generates as little lift as
possible. Of course, this is useful for limiting drag from any kind of stab, but
could be more important for a flying stab. This won't be enough in turns,
though, because you need the stab to generate lift then. The tradeoff in
turns is a question of whether the relative inefficiency of generating the
needed lift with an uncambered surface is balanced by the lack of a 'dirty'
elevator. I don't know the answer, but I will do a little cruising on the web
when I get a chance.

As long as you're thinking outside the box, what about flaps on the main
wing for turns? You could mix in a little flap with elevator. There are a
few possible benefits: It could reduce the angle of attack of the whole
airframe during turns, it could shift the lift distribution toward the wing
root, which would reduce the bending moment at the wing root, allowing
lighter building, and it could make the distribution of lift along the span
more nearly elliptical, which minimizes induced drag. Just a thought.

banktoturn

aseaholm

My Feedback: (1)

Ooh, ooh, ooh, finally something I know a little about…

I have been running full flying stabs on my combat design for 3 years now. Granted, they’re flying around at about 75 mph, not 175 mph, but here’s a few things I’ve learned.

1) CG range is greatly reduced. CG doesn’t work behind 25% MAC. You can’t load the tail up with a 30%+ CG location like you can with a fixed tail.

2) The plan form of the flying stab makes a big difference on responsiveness and linear feel of control inputs.

3) You can fly with very little surface area. I currently run 30 sq. inches of horizontal full flying stab area on a 72� span wing with 550 sq inches of wing area. They turn on a dime and finished 1 & 2 at the NATS this year. Glote, glote, glote, just don’t ask if I was 1 or 2… []

4) The pivot point for the tail should intersect the aerodynamic center AC of the flying stab or be slightly forward of the AC. If you get the pivot behind the AC, look out.

Here’s the simple attachment I use. It’s a brass busing an a 5/32� solid glass rod.



I’ve thought about how a full flying stab might work on a Q500. If you can get the torsional stiffness up enough I think you could do some cool things with intersection drag. Like the image below.

You could use a 3/16� OD hollow carbon tube as the spar and pivot. Reinforce the inside of the fuse with 1/64� ply. Drill a hole through the sides and insert brass tubes on each fuse side for your bushing. You could drill a hole through the carbon tube and use a 4/40 bolt for your control horn. Probably need a little extra material around hole so the tube didn’t split. This wouldn’t be tough. See I have given this a little thought…

It might not be ultra practical, but it makes for interesting forum discussions…

daven

My Feedback: (1)

If I decided to try it, it would be with a conventional tail. V-tail could be a nightmare.

diggs_74

Hmmmm, I see... I was thinking fighter jet style stab with the guides in the front and rear of the pivot point, not just a piviot point... I guess the real trick then is to make the fuse stong enough at that point.... Very interesting for sure...

HighPlains

My Feedback: (1)

Well, I don’t know who banktoturn is, but he makes some very good points. I have read a number of his posts over the past months and while I don’t think he races, he knows aerodynamics. So I tend to agree that there would little to no benefit from a drag standpoint with the flying tail. If you refer back to my earlier post, you will see I suggested that changing the angle of attack of the wing might provide greater benefits without saying why. Banktoturn briefly brushes across the reason with his out of the box thinking, namely to reduce the angle of attack of the entire airframe during the turns. I’ll let you guys speculate why this might actually provide an advantage over conventional design. Two dead Nelson plugs to whom ever come up with the correct rational.

js3

My Feedback: (3)

Bob,

Would it be that a higher AOA means more lift, which means more drag? Or at a lesser AOA the airfoil has a better chance of staying within its drag bucket?

HighPlains

My Feedback: (1)

Increasing the AOA of a wing does increase lift. That’s what happens when you give up elevator. The AOA doesn’t change much from level flight on a quickie to a tight turn. It’s in the range of 5-7 degrees in the turn if my estimates are correct. What I am suggesting is to control pitch by changing the angle of incidence of the wing and leaving the stabilizer completely fixed. Remember, about 30% of the heat is flown in the turns. I’ll up the offer to three dead Nelson plugs to anyone that comes up with why this might offer an advantage over traditional design.

This offer excludes from anybody from the Denver area.

js3

My Feedback: (3)

Ok Bob, I think I have it now. Too bad you won't let me answer. I could really use those three dead plugs!

PylonWorld

Bob,

Does this variable incidence wing have coupled panels, or is each half independent and able to control the roll as well as pitch axis?

StegallHobbies

Bob,

Does this variable incidence wing have coupled panels, or is each half independent and able to control the roll as well as pitch axis?

HighPlains

My Feedback: (1)

Don,

The glider guiders did something like this with independent panels for roll and coupled for pitch years ago. But I think they gave up on it because of weight/strength issues. I think they also had issues with adverse yaw when rolling without a pitch change. I would couple them and use small ailerons for roll where you can use differential action. There was a 50’s Navy Jet that popped up the entire wing for landing, so that the fuselage was relatively flat, while the wing was working at an AOA that put it close to stall at landing speeds.

DHG

My Feedback: (7)

Dave,

Make it a T tail. Mount the main pivot pin and a secondary alignment pin on a large bellcrank, sandwiched inside the fin. Plug the stab halves onto those pins. The lower end of the bellcrank would be long enough to reduce the throw and also engage the elevator pushrod in a straight shot down the fuse. This eliminates the biggest problem with flying stabs (too much throw/slop) and with T-tails (difficulty in routing the elevator pushrod), all at once.

Oh, and it also makes the airplane easier to transport. I'm 3 for 3.

Bob,

And of course the reason for changing the AOA of the wing instead of pitching the whole fuselage up and down is that the fuselage has less drag when it's aligned with the slipstream.

Too bad I'm ineligible for the prize ... but then, when it comes to dead plugs, I'm independently wealthy.

Mr. Pro Bono Bozo

Bozarth

My Feedback: (15)

I know where you can find 5 or 6 good plugs...20 or so feet from the edge of Airpark Elite's runway. Why? I was throwing them there left and right thinking I was burning out plugs when I finally realized my ni-starter had a short in it.

mini-DHG

garys

Bob, I know you're cheap, so go ahead and keep your three dead plugs. Your reasoning as to why it may be an advantage to change in the AoA of the wing is because the fuse would still be flying at roughly 0 AoA, campared to the 5-7 degrees that your estimating is needed for the wing in the turns....

oops...i guess I missed DG's post....oh well...at least you got off paying out dead plugs..

HighPlains

My Feedback: (1)

Gary, Duane, and John,

Yes, having the fuselage not trying to act like a wing should cut the drag quite a bit, as it's aspect ratio is so low. There are of course other compelling reasons as well. I think that there is not much more that can be done for speed on the straight-a-way, except coming out of the turns carrying more speed. (Actually, there is alway more that can be done to increase speed.) I did some experiments recently that convinced me of this.

So I have thought about this for a few more days, and what is required is finding out the true angle of attack required. This could be rather exciting, since I would just jack up the leading edge of the wing a few degrees and test fly. Be sure to set up the elevator with a bunch of throw in the down direction.

In an airplane, you might not want the wing incidence change to do all the work, so if it takes 6 degrees to do the turn radius, perhaps the wing should do 4 degrees, and an elevator pitch for the other two.

Although a "blended flaps" design might help get the elliptical lift distribution that gives the lowest drag, (similar to washout used sometimes in the past), it would also tend to give problems with the airfoil "pitching moment" and require more stab loading. But you could washout a wing, and use flaps that remove the twist from the section closest to the fuselage for the straight-a-way.

Over all though, I still like the incidence change concept. Can it be built and make weight? Perhaps.

banktoturn

HighPlains,

I agree with most of what you say, but I don't know that changing the incidence
of the whole wing would end up being the best solution. When you deploy flaps,
you do several things. One of them is to increase incidence. Another is to increase
camber, which can help you keep the wing operating in the drag bucket. Another,
as we've discussed, is to make the lift distribution more nearly elliptical, while also
reducing the maximum bending moment at the root. I really like the idea of using
flaps to get an elliptical lift distribution, as it is an elegant way to kind of 'beat the
system', while still using the mandated constant chord planform. Yet another is
to give the wing some washout, although tip stall is probably not a problem for
Q500 planes.

As you say, I don't race myself, so I'd love to hear how it goes if you build &
fly the variable incidence wing.

banktoturn