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Author Topic: Tail for turning flying wing  (Read 23334 times)

Offline Dennis Toth

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Tail for turning flying wing
« on: December 05, 2013, 03:50:56 PM »
Guys,
Just thinking about a fun ship for next summer was wondering how much separation from the trailing edge does a full flying elevator need to be to effectively act as a turning control as apposed to acting first as a high lift device then adding the turning moment. There was a discussion about why flying wings like the Fierce Arrow don't stunt smoothly. The general consensus was that with the "elevator" on the trailing edge it didn't actually turn the wing, it first acts like a high lift flap then finally pitches the wing over.

So thinking about it, looking back at the Voodoo wing it seemed to turn really good without being touchy with the short tail booms.  How close to the trailing edge could you be and get a true elevator control?

Best,        DennisT

Offline Howard Rush

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Re: Tail for turning flying wing
« Reply #1 on: December 05, 2013, 05:54:08 PM »
The general consensus was that with the "elevator" on the trailing edge it didn't actually turn the wing, it first acts like a high lift flap then finally pitches the wing over.

One problem with these fora is that you can get a consensus that's wrong. That one certainly makes no sense.  A flap on the back of the wing will give pitching moment to turn the airplane in the same direction as an elevator further back deflected in the same direction.  The main problem with something like a T-Square or Fierce Arrow is that the flap makes the pressure gradient on the low pressure side of the wing worse, causing the wing to stall at less lift than it would otherwise.  There are other problems caused by having a tail that's too short that aren't related to whether the surface is connected to the wing. They've been listed here several times.  Search on "pitch rate" or "downwash", for example.  
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Offline Howard Rush

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Re: Tail for turning flying wing
« Reply #2 on: December 05, 2013, 05:54:59 PM »
I'm willing to bet it depends entirely on the wing, airfoil, wing loading, etc as no two are alike enough to give a definite answer .

I've been wondering what I can do for easy money.
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Offline Serge_Krauss

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Re: Tail for turning flying wing
« Reply #3 on: December 05, 2013, 06:21:56 PM »
I'm interested in this answer too, although I seriously doubt that anyone really knows at these sizes, since the purposes and expectations of flying wings often get confused. I've spent many years researching the history of tailless and semi-tailless aircraft, in the process learning some of their quirks and theory, but I can't answer this one.

I know that Wild Bill and friends built his various families of "-cats" and "-Arrows" with some variation in their pitch controls. I've seen pictures of slotted elevators, pivotted somewhat like stabilators as well as all-flying and hinged configs. Unfortunately about the time we were ready to get into this discussion, he passed away. I was (and will be again be) working on a very unorthodox configuration that calls for a close-coupled control like that. So I too would like to hear from anyone who's experimented with them. I pretty much decided to do a raised stab with perhaps a pivoted, rather than hinged section for adjustability to air direction. To that end I looked at some near-surface flow directions at lower RN's, but not much seemed reliable or applicable, and the asymmetry bothered me. That's why I wonder what the flow is like near a chordwise/on-line "slot". I'd like a good turn, without the combat-like control sensitivity. My experience and analytical skills aren't up to the task either.

Anyone have knowledge or experience here?

We will probably end up just trying something.

Offline Jim Thomerson

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Re: Tail for turning flying wing
« Reply #4 on: December 05, 2013, 07:10:54 PM »
Get plans and laser cut ribs from Walter Umland, and build an Agile Arrow.  i consider it the best stunt airplane I have ever flown.  I've only flown my own airplanes, so it may not be the best in the world. H^^

Here is the appropriate website. http://www.builtrightflyright.com/New_Web_Pgs/kits/AgileArrow/AgileArrow.htm

Offline Howard Rush

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Re: Tail for turning flying wing
« Reply #5 on: December 05, 2013, 08:35:42 PM »
I know that Wild Bill and friends built his various families of "-cats" and "-Arrows" with some variation in their pitch controls. I've seen pictures of slotted elevators, pivotted somewhat like stabilators as well as all-flying and hinged configs.

I saw Fierce Arrows in their heyday and always thought they were cool.  He said that the "balanced" elevator was better than the simple hinged one on earlier Fierce Arrows.  I don't know whether that was because air flowed through the slot and stuck to the wing better or that the balanced elevator had less hinge moment. 

I don't think stability and control characteristics will change much with Reynolds number. 
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Offline Ted Fancher

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Re: Tail for turning flying wing
« Reply #6 on: December 05, 2013, 09:16:35 PM »
I can remember as kids my big brother Gary and I used to take surviving wings from crashed "Veco" stunters like Smoothies and make flying wings out of them by installing motor mounts in the leading edge and using the flaps as "elevators".  They all flew but I've no recollection of the "quality" of their performance.  It is very likely that, at the time, I wasn't aware there was a "quality" quotient!

In my advance, more informed years, I find myself pretty much in agreement with Mr. Rush.

To which I could add...

When as a mini-adult around 1966 I decided to start flying stunt for the big bucks after moving to California I installed flaps on my very nice flying Mathis Coyote because I knew that, to be a "competitive" stunt ship, it needed to have flaps.  Absolutely killed the turn rate...thus my introduction to "adverse" (with respect to desired pitch/turn rate) pitching moments and the birth of my more or less organized pursuit of stunt ship design.

Ted

Offline Dennis Moritz

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Re: Tail for turning flying wing
« Reply #7 on: December 05, 2013, 09:25:03 PM »
I saw a Fierce Arrow fly at the last Brodak. Judged it in Classic. It looked as tho it swiveled some side to side when hitting corners. Better than OK round maneuvers seemed possible. Corners not so good.

Offline Dennis Toth

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Re: Tail for turning flying wing
« Reply #8 on: December 06, 2013, 11:28:12 AM »
Seems the flying wing for stunt is fascinating because of the potential lower weight and simpler build. I remember a discussion about the "Arrow" and that's were the idea that the TE elevator didn't achieve the best rotation came from and that separate pitch and lift surfaces were better. But perhaps the layout of the Arrow is not optimum for this type of stunter. Some other layouts like Larry S's Werewolf and Red R's Stuntwing might with some separation of the control surface have better corners.

Best,         DennisT 

Offline Tim Wescott

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Re: Tail for turning flying wing
« Reply #9 on: December 06, 2013, 11:58:20 AM »
The general consensus was that with the "elevator" on the trailing edge it didn't actually turn the wing, it first acts like a high lift flap then finally pitches the wing over.

One problem with these fora is that you can get a consensus that's wrong. That one certainly makes no sense.  A flap on the back of the wing will give pitching moment to turn the airplane in the same direction as an elevator further back deflected in the same direction.

I don't think it's as wrong as you're making it out to be, Howard.  It's poorly stated and it implies a chronological relation (first less lift, then pitching) where one doesn't exist, but IMHO it's kinda right.  An upwards-deflected trailing edge flap on a wing is going to both rob the wing of some lift and add some positive lifting moment (or add negative lift and positive lifting moment, if you want to think in engineering terms).  This will happen at the same time.  Careful tracking of the aircraft CG may show it actually going down before it goes up, depending on how long it takes to respond to the pitching moment -- but that's another matter.

An elevator that's back there a ways, and deflected TE up is going to do the same thing -- it's going to rob some lift from the airframe, and add some positive lifting moment.  It's just that the farther back you put it, the less lift its going to rob as it contributes that positive lifting moment.

I suspect that the 'reason'* that we put our tails where we do, with the balance between stabilizer area and elevator that we do, is because it offers a reasonable compromise between turning ability and nice straight lines when you want them.  A full-flying stab will probably give you lots of the turn you want, but get right in the way of the straight lines.

* 'reason' put in quotes, because the reason most of us do most stunt design features is because it worked well when Paul Walker, or Ted Fancher, or George Aldrich, or whoever, did it.
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Offline Brett Buck

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Re: Tail for turning flying wing
« Reply #10 on: December 06, 2013, 12:46:59 PM »
I don't think it's as wrong as you're making it out to be, Howard.  It's poorly stated and it implies a chronological relation (first less lift, then pitching) where one doesn't exist, but IMHO it's kinda right.  An upwards-deflected trailing edge flap on a wing is going to both rob the wing of some lift and add some positive lifting moment (or add negative lift and positive lifting moment, if you want to think in engineering terms). 

   I think what it does in the transient case is vaguely interesting, but the problem really is that you are pitching it one way and putting in camber the other way. An extreme example was seen in an airplane Bob Hazle built for VSC, where not only was the trailing edge hinged, it was a compound elevator with 2 segments. It was reported to be nearly unflyable because of the pitch one way, lift the other way effect. As small deflections it seemed as if the controls were reversed, and at large deflections it went the way it was intended.

    I am pretty sure that the offset hinge Fierce Arrow worked about like a typical combat airplane, just with an exceptionally short boom. The version with the conventional hinges definitely had the "wrong way" problem.

    Brett

Offline Howard Rush

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Re: Tail for turning flying wing
« Reply #11 on: December 06, 2013, 02:13:43 PM »
An elevator that's back there a ways, and deflected TE up is going to do the same thing -- it's going to rob some lift from the airframe, and add some positive lifting moment.  It's just that the farther back you put it, the less lift its going to rob as it contributes that positive lifting moment.

You seem to be looking at the problem as if the wing and elevator are independent with their effects superposed.  Yes, there's the problem of the stab lifting one way and the wing lifting the other, and there's the nonminimum phase issue-- up elevator makes the airplane go down before it goes up--but the main reason that flying wing control line airplanes suck is that the air on the upper side of the wing (for up elevator) has to flow from a low pressure at the front of the wing to a high pressure at the back and comes to a stop along the way. 
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Offline Howard Rush

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Re: Tail for turning flying wing
« Reply #12 on: December 06, 2013, 02:23:04 PM »
The version with the conventional hinges definitely had the "wrong way" problem.

Negative direct lift control?  Could be.  I suspect that more likely is the extremely narrow CG range at which such a plane is flyable.  All the more reason I should build a Fierce Arrow.

If the transient negative lift is of the whole dadgum wing, rather than just the elevator, maybe so, but flying wings don't have much pitch moment of inertia, so I'd think the transient wouldn't last long.  This calls for a Fierce Arrow with a barbell that can be used to adjust moment of inertia.
« Last Edit: December 06, 2013, 02:41:41 PM by Howard Rush »
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Offline Howard Rush

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Re: Tail for turning flying wing
« Reply #13 on: December 06, 2013, 03:08:42 PM »
   I think what it does in the transient case is vaguely interesting, but the problem really is that you are pitching it one way and putting in camber the other way...As small deflections it seemed as if the controls were reversed, and at large deflections it went the way it was intended.

For steady state then, wouldn't this mean that lift goes up faster relative to pitching moment for small flap deflections than it does for large deflections?  I looked into using XFoil to see if this happens (and having the satisfaction of proving myself massively full of you-know-what) but it looks like one would have to make a bunch of runs at different flap deflections, then plot the raw data for Cl and Cm as a function of flap deflection.  One could do this at different Reynolds numbers to see if that has an effect as Serge suggests.  Maybe later.  I should be working on a stunt plane and typing up contest results now.   
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Offline Brett Buck

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Re: Tail for turning flying wing
« Reply #14 on: December 06, 2013, 04:06:30 PM »
Maybe later.  I should be working on a stunt plane and typing up contest results now.   

    Yes to the first.  The second is a nice-to-have and everybody is glad you do it, but is not going to affect your participation in Poland.

    Brett

Offline phil c

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Re: Tail for turning flying wing
« Reply #15 on: December 06, 2013, 06:41:33 PM »
The Fierce Arrow series all have significant problems doing sharp turns.  It seems to mostly be the problem of the large elevator flap killing some lift from the wing, the large flap needs a lot of torque to move so it needs a large bellcrank, the short couple between the elevator and wing makes the plane very sensitive to balance point, and  the large elevator and close couple to the wing can result in a "death dive" if you don't fly it with a very gentle touch trying to do low, inside, corners of a sharp radius(square loops, eights, etc.). If you bleed off too much speed before corner three, corner four ends up barely clearing the ground.

If you want to find a good flying wing design look at F2D.  There are two popular styles-  The Beliaev style with a sharply tapered wing and a small conventional stabilator ~1.5-2in. behind hinged to an ~2 in. span rectangular extension faired into the wing.

The other is the Wakkerman layout.  A similar span wing, but with a curved, elliptical trailing edge and a conventional elevator mounted on a rectangular extension about 3-4 in. wide and ~20% of the span.

Both perform very well.  The Wakkerman layout is reminiscent of "Red" Reinhardt's extended Stuntwing.  For the guys really into it each planform is tweaked to an individual's preferences for balance, responsiveness, and controllability.  When you see video of someone doing reverse wingovers with 5-10 ft pullouts while looking at his toes they have the performance and control pretty well nailed.

The main difference is the Beliaev style is a bit more responsive starting and stopping maneuvers.  The Wakkerman has a bit softer response and tends to be a bit more pointable.

If you want to scale something like this up to 1000 sq.in. or so it would be best to use Wild Bill's procedures that he laid down in his American Aircraft Modeler articles and Model Airplane News columns in the late 60's/ 70's.
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Offline Brett Buck

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Re: Tail for turning flying wing
« Reply #16 on: December 07, 2013, 12:31:33 AM »
Here's a side view of the aforementioned wing, and a front view of the aforementioned Bob Hazle.

    The "pitch around faster crowd" should know - this airplane is barely controllable.

     While we are at it, Ted asked this one a long time ago, but it's relevant here, for the same reason - which way should the flap go on a canard? If you get it wrong, it's worse than having no flap at all.

    Brett


Offline Dennis Moritz

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Re: Tail for turning flying wing
« Reply #17 on: December 07, 2013, 02:36:39 AM »
Combat wings can do astonishing corners when trimmed to preference and flown by an excellent pilot. Reverse wingovers at speed break at as close to a true 90 degrees as I have seen. It also appears to be possible to do the pattern in half the conventional space. Or a third. But these planes need to be flown fast, far as I can tell. When slowed down they mush.

Offline Serge_Krauss

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Re: Tail for turning flying wing
« Reply #18 on: December 07, 2013, 11:53:04 AM »
It's certainly been hinted at a lot here, but I don't think it has actually been written out in this thread. So I'll just say it. The "Fierce Arrow" has two disadvantages over the Red Reinhardt and Jim Thomerson designs:

1) It is very short coupled.

2) It is highly swept.

The first requires higher control forces acting over a small distance and gives less c.g. range. The second should, I'd think, present yaw-roll couple problems, more spanwise flow, and perhaps tip stall tendencies.

At VSC 14, there was the then latest iteration of the "Fierce Arrow" and some discussion. I asked Bill why he didn't just reverse things to get the control surfaces further from the a.c. He was quite aware of the advantages, but responded simply, "But then it wouldn't be a 'Fierce Arrow.'"

SK

Offline Dennis Adamisin

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Re: Tail for turning flying wing
« Reply #19 on: December 08, 2013, 08:21:59 AM »
Hmmmmm, how about a "whale tail" (Reinhart Stunt Wing) layout, but for the elevator, use the double-slotted arrangement that Wesley Dick designed for his flaps???   VD~
« Last Edit: December 08, 2013, 09:54:49 AM by Dennis Adamisin »
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Offline Chris Wilson

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Re: Tail for turning flying wing
« Reply #20 on: December 08, 2013, 10:16:35 PM »

     While we are at it, Ted asked this one a long time ago, but it's relevant here, for the same reason - which way should the flap go on a canard? If you get it wrong, it's worse than having no flap at all.

    Brett


Ok, I will bite - "which way should the flap go on a a canard?"

Synchronized to move in the same direction as the fore plane or opposed to it?

(By the way, that is a genuine question.)
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Offline Brett Buck

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Re: Tail for turning flying wing
« Reply #21 on: December 09, 2013, 01:22:32 AM »
Ok, I will bite - "which way should the flap go on a a canard?"

Synchronized to move in the same direction as the fore plane or opposed to it?

(By the way, that is a genuine question.)

   One of those two, for sure!  A corollary question is whether or not using flaps, even moving in the right direction, is better than no flaps at all

     Brett

Offline Dave_Trible

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Re: Tail for turning flying wing
« Reply #22 on: December 09, 2013, 07:54:31 AM »
This is interesting.  An easy way to find out is to build a simple sheet 1/2a where all control options can be set at the flying field and go try it.  I had one 1/2a canard as a kid.  It flew a decent level flight with a noticeable nose up, and was very sluggish to respond to control.  It's pretty hard to keep these from being too nose heavy.  My guess would be that flaps would more take over and function like a regular elevator while overpowering what the canard was doing.  Maybe somebody will try that 1/2a and show us.

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Offline Howard Rush

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Re: Tail for turning flying wing
« Reply #23 on: December 09, 2013, 03:35:45 PM »
I think you can make a canard stunter that has the flaps move the right way (same way as the canard surface) without artificial stability augmentation.  I started work on such a stunter in 1977, but got distracted.  I'll get back to it, but not until next September at least.
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Offline phil c

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Re: Tail for turning flying wing
« Reply #24 on: December 09, 2013, 05:57:46 PM »
A friend got me to test fly the Dick Sarpolus design that appeared in Flying Models some years ago.  The engine is mounted between booms on the front of a stubby fuselage.  Not a super stunter, but more of a souped up Ringmaster.  We discovered a few things.  As originally built the controls were hooked up as a canard, both flaps moved the same direction to get more lift.  VERY strange.  Under power it was very stable until you moved the controls.  Then it tended to mush and suddenly go into a loop.  As soon as the motor quite it handled and landed predictably and smoothly.  Obviously the prop wash on the flaps over powered the canard, up to a point.

Next, locked the flaps in place.  It flew fine and was stable and controllable.  Much like a Ringmaster, but a little better.

Finally, hooked up the flaps to move opposite the wing.  It flew OK, but didn't turn as tight.

Regards the picture- the combined flap/elevator is about 4-5 times as wide as it needs to be.  If you glue the forward portion solidly in place it will be something like Reinhardt's Stuntwing, or a Wakkerman F2D.  it'll fly better, but the elevator is still about twice as wide as needed.  Might have a CG problem with all the paraphernalia behind the balance point.
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Offline Chris Wilson

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Re: Tail for turning flying wing
« Reply #25 on: December 09, 2013, 07:04:45 PM »
Thanks for the info Phil and the  model sounds like the 'Wild Goose'.
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Offline Brett Buck

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Re: Tail for turning flying wing
« Reply #26 on: December 10, 2013, 10:40:41 AM »
I think you can make a canard stunter that has the flaps move the right way (same way as the canard surface) without artificial stability augmentation. 

      Howard tangentially refers to the fact that you want a big canard to overcome the fact that the CG is well ahead of the lift vector from the wing, however, the bigger the canard, the further forward the CG has to go, making the adverse pitch moment worse, meaning you need a bigger canard. This continues until the canard is bigger than the wing, say, 4x as big.

    The solution is to make the flaps move the wrong way (canard down, flap up), however, that puts you in the same situation as Bob Hazle had, and to a lesser extent, the Fierce Arrow - you are trying to do an outside loop in a Piper Cub, with the camber in the wrong direction. You would do better with no flaps.

     You really want the CG to be near the CP, so that creating large amounts of lift does not try to pitch you in the wrong direction, and a canard does not do that. The CG has to be way ahead of the lift vector from the wing to make it stable. The most recent go-around on canards was when it was suggested that if you put the CG at around the CP of the wing, how great it would maneuver. Which it will, even without control input, unless you do something odd.

   Note that there are other unfortunate issues, like, the CG is in the wrong place for the leadouts to come out the wing.

     Brett

     

Offline Howard Rush

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Re: Tail for turning flying wing
« Reply #27 on: December 10, 2013, 11:58:16 AM »
No, I was thinking of an actual canard where the little wing is in front.  There's one sorta obvious way to do that, and another way that's less pure.  Think of ways to get pitching moment from a canard without Cmα or lift from flaps without pitching moment.
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Offline Brett Buck

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Re: Tail for turning flying wing
« Reply #28 on: December 10, 2013, 03:49:01 PM »
No, I was thinking of an actual canard where the little wing is in front.  There's one sorta obvious way to do that, and another way that's less pure.  Think of ways to get pitching moment from a canard without Cmα or lift from flaps without pitching moment.

   With or without flaps, or without pitching moments from the wing airfoil alone,  I think I still see ~60 lbs of lift centered on a point 6"+ behind the CG, pitching the airplane the wrong way. You have to make the canard big enough or the long enough to create something like 50-60 ft-lbs of torque, 30 ft-lb just to stay level. That the canard lift helps rather than hurts is the supposed advantage.  But that also makes you move the CG forward to maintain stability.

    If you try putting the CG on the CP of the wing, (also with or without flaps), it won't be passively stable unless you let the canard free-float, and then put in reflex like a flying wing.

    I suppose I do not have sufficient imagination, so you will have to spell it out for me.

 
     I have a rocket glider with a free-floating canard, so it's stable and has no lift or pitching moment in the ballistic boost, and then the canard is locked down when it is supposed to glide. Works pretty well, when the explosive-driven piston that locks the canard doesn't blow the entire front end off.

    Brett

Offline jim gilmore

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Re: Tail for turning flying wing
« Reply #29 on: December 10, 2013, 04:10:41 PM »
Putting an elevator on the trailing edge of the wing all depends on the size of the elevator you add and how much movement you give it.
Too much movement you have a speed brake. Not enough movement your just going to climb and dive.
Also one of the big problems with canards is that with insufficient power the canard will stall first. and the plane is then very stable for level flight. Since it cannot rotate beyond a certain stable point.

Offline Howard Rush

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Re: Tail for turning flying wing
« Reply #30 on: December 10, 2013, 05:05:35 PM »
I suppose I do not have sufficient imagination, so you will have to spell it out for me.

Looks like you do.  Floating the canard is the main trick.  Also, if you have a high aspect ratio wing with enough sweep, flaps on part of it are far enough forward not to fight the canard.  I made a hand launched glider that gave me the impression that the flaps would work.  I worked with a guy from Kawasaki who gave me some stuff on the Shinden from WW2.  It looked kinda like a Long-EZE.  The drawings appeared to show a floating canard.  I put a overfloating rudder on the front of an RC glider once.  Its main effect was adding drag.
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Offline Brett Buck

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Re: Tail for turning flying wing
« Reply #31 on: December 10, 2013, 05:35:00 PM »
Edmonds ECEE Thunder. Canard elevator floats on ascent. The ejection charge pushes a balsa piston forward and jams a horn on the elevator into a stop, while a port that is uncovered by the piston movement vents the pressure. This locks the elevator into a position with a bit of "up" canard, then it glides gently to earth.  Unless it doesn't, and it blows the nose (which has a butt-joint right in that area) off. It's very stable without the canard and the nose, just like lawn dart.

    In your stunt version, how to you control it with the canard floating?  Use a pushrod with a huge amount of slop?

     Brett

« Last Edit: December 10, 2013, 08:04:06 PM by Brett Buck »

Offline Howard Rush

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Re: Tail for turning flying wing
« Reply #32 on: December 10, 2013, 06:45:39 PM »
That's a cool glider.  Who thought it up?

You can control the canard with a tab on the back, but I'd use a stabilator (for some of the same reasons one would use it with a wing).  The mechanism is a little challenging.  The forward rudder on the RC glider was for stability, with no control hookup, and was driven by a weather vane with linkage to drive the rudder in the same direction as the vane, but with a bigger angle.   
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Offline Brett Buck

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Re: Tail for turning flying wing
« Reply #33 on: December 10, 2013, 08:03:34 PM »
That's a cool glider.  Who thought it up?

   A guy named Rob Edmonds sells this one. He has some interesting ideas about trimming boost-gliders, but this one works very reliably aside from the nose-blowing-off issue. I can tell you, launching a large rocket glider like this one can lead to some nervous moments because of you get something wrong, you end up looping a 12-ounce under power into the crowd at 200 mph. Selling a kit for it, and hoping that rocket guys can reliably put it together and have success, takes some good engineering. You ought to see some of the workmanship at a rocket launch, not pretty.

    They are all laser-cut, and he recommends that no one even try to sand the edges round, just leave the burn marks.

    When I first went back to flying rockets (after about a 15 year layoff), I took a bunch of boost-gliders to a club launch with about 100 or so people. I was the hit of the day, because no one there had ever seen one fly safely. They called every one of them a heads-up launch because the LSO was scared. Even after I boosted one to about 500 feet, had it circle perfectly over the pad for about 2 minutes, and then catching it about 10 feet from the launcher. Later I had one hit the launcher.
  

Quote
You can control the canard with a tab on the back, but I'd use a stabilator (for some of the same reasons one would use it with a wing).  The mechanism is a little challenging.  The forward rudder on the RC glider was for stability, with no control hookup, and was driven by a weather vane with linkage to drive the rudder in the same direction as the vane, but with a bigger angle.  

    I could figure out how to make the canard actuate, I just can't see how you make it free-float the rest of the time.

      Brett

this gives a sense of scale:

« Last Edit: December 10, 2013, 08:30:09 PM by Brett Buck »

Offline Douglas Ames

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Re: Tail for turning flying wing
« Reply #34 on: December 12, 2013, 11:12:43 PM »
Guys,
Just thinking about a fun ship for next summer was wondering how much separation from the trailing edge does a full flying elevator need to be to effectively act as a turning control as apposed to acting first as a high lift device then adding the turning moment. There was a discussion about why flying wings like the Fierce Arrow don't stunt smoothly. The general consensus was that with the "elevator" on the trailing edge it didn't actually turn the wing, it first acts like a high lift flap then finally pitches the wing over.

So thinking about it, looking back at the Voodoo wing it seemed to turn really good without being touchy with the short tail booms.  How close to the trailing edge could you be and get a true elevator control?

Best,        DennisT

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Offline Douglas Ames

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Re: Tail for turning flying wing
« Reply #35 on: December 12, 2013, 11:36:22 PM »
No, I was thinking of an actual canard where the little wing is in front.  There's one sorta obvious way to do that, and another way that's less pure.  Think of ways to get pitching moment from a canard without Cmα or lift from flaps without pitching moment.

Why not a forward mounted stabilator? (not a fixed canard w/ elevator!)

Why not coordinated leading edge flaps? (A simple "OR gate" shaped LE that pivots and is linked with the TE flaps.)
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Offline phil c

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Re: Tail for turning flying wing
« Reply #36 on: December 13, 2013, 06:20:31 PM »
So thinking about it, looking back at the Voodoo wing it seemed to turn really good without being touchy with the short tail booms.  How close to the trailing edge could you be and get a true elevator control?

Best,        DennisT

The VooDoo turned pretty well if the balance point and the stabilator movement were trimmed properly for a specific speed range.  If you got it trimmed for a plain bearing ST and then bolted on a G-21 it would suddenly turn like a tank- nose heavy and not enough control power to move the stabilator at a higher speed.
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Offline Howard Rush

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Re: Tail for turning flying wing
« Reply #37 on: December 13, 2013, 07:21:01 PM »
Why not a forward mounted stabilator? (not a fixed canard w/ elevator!)

I think so.

Why not coordinated leading edge flaps? (A simple "OR gate" shaped LE that pivots and is linked with the TE flaps.)

That sounds interesting.  Cool description.  Do you suppose it would be stable or would it get stuck in full deflection?
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Offline Brett Buck

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Re: Tail for turning flying wing
« Reply #38 on: December 13, 2013, 09:36:32 PM »
So thinking about it, looking back at the Voodoo wing it seemed to turn really good without being touchy with the short tail booms.  How close to the trailing edge could you be and get a true elevator control?

Best,        DennisT

The VooDoo turned pretty well if the balance point and the stabilator movement were trimmed properly for a specific speed range.  If you got it trimmed for a plain bearing ST and then bolted on a G-21 it would suddenly turn like a tank- nose heavy and not enough control power to move the stabilator at a higher speed.

  Thats because the tail volume was very small, so the CG range was correspondingly small. I can easily guess what happened if you got it 1/16" too far aft, too.

    Brett

Offline Dave_Trible

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Re: Tail for turning flying wing
« Reply #39 on: December 15, 2013, 06:54:40 AM »
Being an old combat flier from 'those' days I will say that the Voo Doo was a great airplane for its time as was the Vampire which I favored ( thank you Riley).  As we went on though the thinner wing and shorter tail gave it a great speed but a little short in turn.  There were some extended boom versions versions that were better, getting the tail back for more leverage.  These were an attempt to get them more current with Howard's Nemisis and the Bosta and the like.  The Winder attempted to do it with a long span.  'Turn' happened with the Guillotine which used a bigger area, flaps and the Nobler wing rib at the cost of a little speed.  Our theory was that even if our aponent was a little faster we were in a sphere so he couldn't get away from us.  And dare him try to follow us down low!  A short couple will make the airplane more tame on the controls unless you push the CG back to dangerous places which would mean lead fishing sinkers bolted to the booms like we did on the VooDoo.

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Offline Dennis Toth

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Re: Tail for turning flying wing
« Reply #40 on: December 18, 2013, 06:36:20 PM »
Interesting stuff but still want to know how far away from the TE does the stabilator need to be 1/4", 1/2"?

Second, does the combo layout with the wide center section and narrow outer wing layout smooth the turn?

Best,          DennisT

Offline Howard Rush

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Re: Tail for turning flying wing
« Reply #41 on: December 18, 2013, 06:54:49 PM »
For a stunt plane?  Maybe 18" and not enough, respectively. 
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Offline Mark Scarborough

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Re: Tail for turning flying wing
« Reply #42 on: December 19, 2013, 11:21:56 AM »
      Howard tangentially refers to the fact that you want a big canard to overcome the fact that the CG is well ahead of the lift vector from the wing, however, the bigger the canard, the further forward the CG has to go, making the adverse pitch moment worse, meaning you need a bigger canard. This continues until the canard is bigger than the wing, say, 4x as big.

   
     
so,, what your saying is that my new Impact derivative is actually a Canard with the correct proportioned canard wing,, ;)
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Offline Ted Fancher

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Re: Tail for turning flying wing
« Reply #43 on: December 21, 2013, 10:02:00 AM »
so,, what your saying is that my new Impact derivative is actually a Canard with the correct proportioned canard wing,, ;)

Sounds right to me!

Offline Ted Fancher

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Re: Tail for turning flying wing
« Reply #44 on: December 21, 2013, 10:10:50 AM »
look at it this way...

When was the last time you saw a canard entered in a full scale aerobatic event...let alone a competitive one??

Ted

p.s. This excludes, of course, those canards the canard surface of which is 4X the area of the "wing".  Mark's canard Impact for instance.

Offline Brett Buck

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Re: Tail for turning flying wing
« Reply #45 on: December 21, 2013, 12:44:13 PM »
look at it this way...
p.s. This excludes, of course, those canards the canard surface of which is 4X the area of the "wing".  Mark's canard Impact for instance.

   25+ years, finally I get the clear win for our side! What do I get?

    Seriously, I have no doubt that you could make a canard that would turn tightly enough, even without flaps, rendering the question of which way the move moot. The other issues (like lining up the leadouts properly with the CG and many others) are probably a bigger issue than how tight it turns. The value of the canard found on full-scale aircraft in steady-state cruising flight is not particularly important for a stunt plane. The purported value of the canard for a stunt plane is that the lift and drag associated with control "helps" instead of hurts, but we aren't close to running out of lift anyway, and you can solve the drag problem with the little bent wire sticking out the side of the engine.

     Brett

Offline Ted Fancher

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Re: Tail for turning flying wing
« Reply #46 on: December 21, 2013, 11:30:27 PM »
I pretty much agree with everything Brett has said...no big surprise!

For Control Line purposes I think you could probably design a canard stunter that would work very well under a specific set of conditions.  The CG, by definition, must be pretty far ahead of the center of lift of the main plane (the big wing in back).  For that "given" set of more or less ideal conditions you could then compute a canard size and distance from the CL to a provide adequate pitch capability to fly well.

Unfortunately, stunt contest conditions seldom provide a predictably ideal set of conditions.  As conditions change...primarily wind velocity...the extended distance between the CG and the CL will become an issue as the airplane accelerates and decelerates as the wind vector changes throughout the hemisphere of flight.  As the airplane speed up or slows down while maneuvering the distance between the two forces will have a dramatic effect on the the control input necessary to maintain the desired (necessary according to the rule book) rate of pitch (and, therefore, g forces) change.  As the airplane flies faster the moment between the CG and the CL will increase and try to open up the loop/corner radius and vice versa when it slows down.  Control input to maintain concentricity and maneuver size will have to be varied quite dramatically throughout any maneuver that is exposed to acceleration or deceleration due to the winds (or, for that matter, other factors).

One of the primary advances "conventional" stunt ships have made in their 70 or so year history has been the realization by designers that the tail needs to be large enough to allow a CG location as close as possible to the CL of the main plane (the wing).  The closer the two are to one another the less the control inputs to retain a given rate of pitch will change as the airplane speeds up and slows down while maneuvering in modest or greater winds.  The conventional configuration allows the two to be essentially co-located as long as the tail is large enough to allow stability with the CG that far aft.

A canard configuration, on the other hand, hasn't that luxury and, to be stable and flyable, the CG will always be well forward of the CL and increased G forces while maneuvering will always demand greater control deflection during acceleration and vice versa.

I think....

Ted

Offline Chris Wilson

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Re: Tail for turning flying wing
« Reply #47 on: January 01, 2014, 03:05:28 PM »
Just a quick question here -
If all the wing planforms are contributing to the total lift (as in both the canard and the main have individual centres of lift that combine to lift the aircraft) then surely the combined CL (or neutral point) is approaching the CG far more closely than is described in most texts?

Thanks.

(See pic below, how close does one want the CG to the NP anyway?)
« Last Edit: January 01, 2014, 04:24:48 PM by Chris Wilson »
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Offline Serge_Krauss

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Re: Tail for turning flying wing
« Reply #48 on: January 04, 2014, 06:47:06 AM »
Chris-

I don't fully understand the question, I guess, but I'll try to contribute. Is your illustration from an R/C Proving Grounds calculator? I think I've seen it before, but I don't have a direct link to it. If so, there are a couple things to look out for. First, their static margin expectations are more attuned to R/C and full-sized aircraft, whose c.g.'s are significantly behind those used in CL. Also, the N.P. locations are based on a simpified analysis that I did not fully "get" and which also actually depends on vertical aft-wing placement and a lot more. I have pretty well given up on reasonable analyses, but there are some out there, including good papers from Stanford aeronautical. Anyway, their N.P. is not necessarily accurate, and for sure, you don't want to locate it as though the aft wing is as efficient as the forward one.

Here's what I think I know about Canard's in general (and agree with Ted for stunt). Not only is the "main" wing less efficient, due to down wash from the canard, but for reasons of longitudinal stability and stall behaviour, the canard must be more heavily loaded. The main wing ends up unable to use its entire lifting capacity. So the canard loses its intuitively apparent advantages and is less efficient in overall function than an aft tail. If computer aided control/stability is employed, then it becomes about as efficient as an aft-tailed plane.

From this cursory "analysis", I'd conclude that you'll want the c.g. further ahead of the plane's NP than shown, but that the NP may be a bit off anyway. These on-line calculators are great for wings, but probably not too sophisticated regarding aircraft NP's. I think they're great for normal stunt configurations, coupled with our normal rules of thumb, but we don't really have that luxury with canards. We already have the wing and tail a.c. approximations to deal with - the assumption that all points on a wing lift equally. We adjust for this, but it's tougher when you couple them together and then add a smaller lifting surface that compromises the larger.

So you may be correct about their proximity in this mathematical model, but the facts that it is an approximation applied to approximations, and that our c.g.'s are placed forward of their R/C predictions, makes the analysis harder. In reality, the NP may indeed be further forward than predicted (especially when predicted by assuming equal lifting ability per unit area, front and rear), but so is the CL c.g. and shifted c.g. needed to load the canard surface more heavily. Some reading and further researching are probably in order!

SK

Offline Chris Wilson

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Re: Tail for turning flying wing
« Reply #49 on: January 05, 2014, 04:26:58 PM »
Thanks for the reply Serge and please accept that I have since gone back into the archives here and read much of Ted's and Brett's previous words of wisdom.

It was just that I was having trouble reconciling why there would be such a great distance between the CL and the NP when the NP really can be considered as the rear most point the CG can exist with any hope of stability - but as you say models are different.

(I think someone has said in the past that this information should be 'stickied.')

Good stuff, thanks.
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Offline phil c

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Re: Tail for turning flying wing
« Reply #50 on: January 06, 2014, 08:57:27 PM »
Chris, I think you interpreted the graphic you showed correctly, and the R/CPG calculator gives a reasonable notion of where the CG and Neutral Point should be.

The neutral point calculation has to be simplified when working just with the wing and stab(or canard).  It is a theoretical, or modelled, point where the plane has NO stability- i.e. no negative or positive pitching moments at all.  Of course a simplified model can't get all the aerodynamics right so it doesn't account for the fuselage/rudder, or relative positions of the surfaces which might interact under some conditions. But it would be a useful comparison with where R/CPG puts the CG and NP on a typical stunt plane.  A modern stunter with a 25% stab will have the NP some 10% further rearward than the CG.

A C/L plane becomes unflyable long before the CG gets near the NP.  The last time I did the calculation for a combat plane I think the useable CG was at about 15% of chord and the NP about 28%.
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Offline Serge_Krauss

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Re: Tail for turning flying wing
« Reply #51 on: January 07, 2014, 10:28:16 PM »
A year or so ago, on paper, I made up a simple mythical "Hershey-Bar" winged and tailed conventional stunter with modern numbers to compare where that calculator chose the best c.g. position, using their suggested static margins. These, as c.g.'s in some texts on full-sized aircraft, were quite a bit behind our rearmost (25% MAC) ones. It does appear that we need ours further forward than those in R/C, FF, and full-sized planes. Our CL SM's are greater than their suggested range. What I said about canards is readily agreed upon in the literature, and it appears in practice that CL canards have c.g.'s ahead of where their builders expected to place them.

Offline phil c

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Re: Tail for turning flying wing
« Reply #52 on: January 14, 2014, 07:51:34 PM »
Interesting stuff but still want to know how far away from the TE does the stabilator need to be 1/4", 1/2"?

Second, does the combo layout with the wide center section and narrow outer wing layout smooth the turn?

Best,          DennisT

Since even I didn't really answer you Dennnis, try this.  Airfoils are typically measured by their chord.  So placing the stabilator at least one chord length behind the wing should be enough that any pressure effects from it(which will be pretty small since it's lightly loaded) won't interfere with the wing.  Minimal "reverse airfoil" effects that happen to a Fierce Arrow.  To keep the control loads down and improve power off handling I'd go with a stabilator with a 20% or so higher aspect ratio than the wing and no more than 2 in. wide.  You can go wider if it has some overhand ahead of the pivot, but don't go over 10% or so of the area.

Phil C
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Offline RC Storick

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Re: Tail for turning flying wing
« Reply #53 on: January 21, 2014, 03:41:12 PM »
Tail moment and tail area are not independent items. Generally speaking, for a given amount of pitch or yaw stability, there is a linear relationship between static stability (how strongly the plane wants to return to its trimmed position) and either tail area or tail moment. That means that if you double the tail are or double the tail moment, you get double the static stability.

For dynamic stability (the ability to damp out oscillations), the relationship for tail area is linear (as above), but there is a squared relationship for tail moment arm. In other words, if you double the tail moment arm you get FOUR times the dynamic stability.

You can trade these off against each other; i.e: if you increase the tail area you can reduce the tail moment and vice versa.

So we should make all our models with enormous tail moments and tiny tail surfaces, right? Well, not quite. As you make the tail longer, the weight of the tail surfaces decrease, but the weight of the tail boom increases. the same is true for whetted area of the tail surfaces vs. the tailboom. Of particular importance to models, as the tail surfaces get smaller, so do their Reynolds numbers and/or span, hurting both their drag and their effectiveness. BTW, this is one of the lesser-recognized advantages of V-tails. By concentrating the total area into two surfaces instead of three, the span and/or chord of those surfaces is improved.

Longer tails also move mass further from the C/G, which hurts control and stability. This may also mean making the nose longer in order to minimize weight required to balance the model. Since surface area ahead of the C/G is de-stabilizing, you end up paying double in this regard for the longer tail.

As far as numbers go, there are quite a few methods, most of them complicated. The simplest on is probably the method of "volume coefficients".

Imagine that you had many, many years of experience designing models of a certain type. Because of that experience you could estimate with a fair degree of accuracy what size tail assembly a new model would require, right? Now, what if there was a way to attach numbers to all the major factors affecting stability, and a formula to combine those numbers into an overall "effectiveness" result. You could quickly calculate the "effectiveness" numbers for existing successful designs, and use those to determine the appropriate size tail for your new designs. In effect, the formula would allow you to utilize the results of the experience of all designers in the accumulated history of that type of aircraft.

The method of volume coefficients is a way to do exactly that. We take the measure of the dominant parameters influencing pitch or yaw stability through a formula, the result of which is a measure of that model's relative tail proportions. Since the numbers just happen to have cubic dimensions the way the formula works out, we call them "volume" coefficients.

For the horizontal tail (pitch stability), the pertinent parameters are the Mean Aerodynamic Chord (MAC) of the wing, the wing area, the horizontal tail area, and the tail moment arm as measured from the aerodynamic center (AC) of the wing to the AC of the tail, parallel to the fuselage. For our purposes the MAC is the chord of the surface is where the area of the panel outboard of the MAC equals the area inboard of that chord. You can assume that the aerodynamic center (AC) is located on the MAC, 25% of the chord back from the leading edge. Since more moment arm and more tail area makes the model more stable, we multiply those together. Since more wing area and more wing chord make the model less stable, we divide by those. The resulting formula for horizontal tail volume coefficient (Vht) is:

           (horizontal tail area x hor. tail moment arm)
     Vht = ---------------------------------------------
                       (wing area x wing MAC)


For vertical tail volume coefficient (Vvt) the formula is similar, except we use semispan of the wing (i.e.: half the wingspan) instead of MAC. The formula is:

           (vertical tail area x vert. tail moment arm)
     Vvt =  ------------------------------------------
                   (wing area x wing semispan)



Find some models with good stability and handling similar to the one you're working on, calculate their volume coefficients, then use those as a guideline for designing your model. V-tails are a more complicated than this, but volume coefficients are a starting point.

You have to use these numbers with some care, since there can be some other factors involved. For example, poly 2-ch vs. ailerons, the use of flaps vs. no flaps, relatively heavy wingtips vs. light wingtips, large model vs. small model, multi engine vs. single engine vs. no engine, can all effect the final results. The effects of local airflow during certain types of maneuvers can also complicate the picture. Be careful when comparing models that are not very similar in their design and intended use to the one you're designing.

As far as tail moment arm, the ratio of tail moment to tail area used in the baseline models you compared yours to are a good starting point. Ultimately the length of the tail is a structural engineering question. If you can design a long tail while still keeping mass and whetted area of the tailboom low, a long tail moment can be very effective. The Monarch series is one very successful example of this.  

Don Stackhouse @ DJ Aerotech
EDIT:for credit



Here is the eyeball engineering way. Half span of wing is stab length and volume is determined by model weight. Just what I do. But I am no Picky-sist. Of course sometimes I don't use a jig and draw rib templates with a French curve and a dozen other off the wall things.
« Last Edit: January 24, 2014, 11:27:35 PM by Robert Storick »
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Offline Howard Rush

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Re: Tail for turning flying wing
« Reply #54 on: January 21, 2014, 05:37:03 PM »

It appears that you use "moment" and "moment arm" interchangeably.  Both have conventional definitions, which differ.  What do you mean by "moment"?

You say that dynamic stability is a function of tail moment arm squared, then just disregard that and say,

Now, what if there was a way to attach numbers to all the major factors affecting stability, and a formula to combine those numbers into an overall "effectiveness" result. You could quickly calculate the "effectiveness" numbers for existing successful designs, and use those to determine the appropriate size tail for your new designs. In effect, the formula would allow you to utilize the results of the experience of all designers in the accumulated history of that type of aircraft.

The method of volume coefficients is a way to do exactly that.

Well, it's not.  It's what stunt people have passed down through the generations, but it's crude even statically, and isn't of much help in understanding or improving flying characteristics.  Better alternatives are copying something that works, experimenting, or looking in an actual stability and control textbook.
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Offline Igor Burger

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Re: Tail for turning flying wing
« Reply #55 on: January 22, 2014, 01:34:05 AM »
The effects of local airflow during certain types of maneuvers can also complicate the picture.

An that is reason, why it is not well applicable for aerobatic models

Since more wing area and more wing chord make the model less stable, we divide by those. The resulting formula for horizontal tail volume coefficient (Vht) is:

           (horizontal tail area x hor. tail moment arm)
     Vht = ---------------------------------------------
                       (wing area x wing MAC)


And this is also not so on C/L models, where we have CG fron of AC of wing, so larger wing does not make it less stable :- ))

we have simply another rules for areas and it's distribution. (fuselage side area also counts if you are speaking about rudder, or vertical side area)

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Re: Tail for turning flying wing
« Reply #56 on: January 22, 2014, 01:58:05 PM »
I have found on the models that I built and tested, plus others I have flown that more chord makes them more stable, not less stable. The trick is to have just the right amount of chord to span ..ie  Aspect Ratio.  This is especially true high higher winds and turbulence

Randy

Offline Howard Rush

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Re: Tail for turning flying wing
« Reply #57 on: January 22, 2014, 03:57:53 PM »
Sparky didn't write the stuff in reply 54 before the last paragraph.  It comes from http://www.djaerotech.com/dj_askjd/dj_questions/formula.html and was used without attribution.  Based on the last paragraph, I presume that Sparky quoted the DJ stuff as an example of how he wouldn't go about designing an airplane.  Looks like we all agree with him.
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Offline RC Storick

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Re: Tail for turning flying wing
« Reply #58 on: January 24, 2014, 11:18:32 PM »
No Howard I didn't write it
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Offline Serge_Krauss

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Re: Tail for turning flying wing
« Reply #59 on: January 25, 2014, 09:43:55 PM »
I haven't commented recently, because this thing (the related thread too) was being approached from so many perspectives, and criticisms of "absolutes" are easy, but require too much verbage to qualify otherwise. I will say though that we do not all entirely agree on that last statement. The basics we use to create a reasonable model, even CFD and some data on low-RN flow I'm not sure anyone has, are also based on simplifying assumptions. The main one behind MAC and a.c. is certainly one with which we must deal from experience of what works and what we like (static margin, how it 'feels', etc.). The TVC may be a bit less "precise", but I do think it to be useful - just as "Ted's Rule" is useful. You may not stretch it too far, without possibly unfortunate consequences, but in comparing planes and trying to choose changes to a design (within it's basic concept), you should be able use it profitably. You just must temper it with some compensation for things like Frank Zaic's "circular airflow" concept, inertial effects, or other effects you have found to limit it's use. But even here, when any extreme becomes unreasonable, the TVC concept can help one adjust away from it. I don't write that off at all.

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Offline Dennis Toth

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Re: Tail for turning flying wing
« Reply #60 on: February 01, 2014, 03:41:18 PM »
OK, we seem to have established that putting the elevator on the trailing edge of a flying wing will result is not so smooth maneuvers. Canards look funny and may still be difficult to get smooth maneuvers with. I still like the idea of a wing layout with the higher aspect outer panels and low aspect center. I think moving the elevator off the TE a small amount could help with the wing first moving as a high lift then turning. I also think if one couples a small front stabilator that works as a couple with the rear elevator would pivot the wing and help the maneuver shape. I'm thinking the front stabilator is positioned half way ish between the LE and the engine. The great thing about this hobby/sport is that we can develop by cut and try without risking much.

Best,       DennisT

Offline Howard Rush

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Re: Tail for turning flying wing
« Reply #61 on: February 01, 2014, 03:56:52 PM »
The great thing about this hobby/sport is that we can develop by cut and try without risking much.

And we don't have to get the boss's approval.
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Offline phil c

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Re: Tail for turning flying wing
« Reply #62 on: February 07, 2014, 09:04:36 PM »
Hey Dennis, adding a small forward stabilator/elevator will help the plane turn faster.  It'll also make it less stable, so you'll have some cut and try building to do to find a workable combination.  The biggest diffculty, to me, would be finding a place in the forward fuselage to put the hardware and getting it connected properly.
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Offline Trostle

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Re: Tail for turning flying wing
« Reply #63 on: February 08, 2014, 02:28:39 PM »
Hey Dennis, adding a small forward stabilator/elevator will help the plane turn faster.  It'll also make it less stable, so you'll have some cut and try building to do to find a workable combination.  The biggest diffculty, to me, would be finding a place in the forward fuselage to put the hardware and getting it connected properly.

Well, Dennis Adamisin had a stunt model at the Nats with a small canard fairly close to the propeller.  He got an award for technical innovation.  I think the award was sponsored by Jack Sheeks.  It should show up in the Stunt News archives somewhere.

Keith

Offline MikeyPratt

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Re: Tail for turning flying wing
« Reply #64 on: July 08, 2015, 02:19:54 PM »
Hmmmmm, how about a "whale tail" (Reinhart Stunt Wing) layout, but for the elevator, use the double-slotted arrangement that Wesley Dick designed for his flaps???   VD~



Hi There Guy’s,
I just found this post and thought I would comment on it.  I’ve built and flown Fierce Arrow’s and the Fierce Arrow 400’s with some, flying better than others (that’s for sure), But, I still liked the way they looked, different and way cool.   

A number of years ago I wanted to build a flying wing with better performance than the old Fierce Arrow.  I spent a number of hours on the phone talking (and emails) with Bill talking about the FA and FA 400 about which one he liked the best and why it was designed that way it was.  He said there was an article he had written telling to move the elevator hinge line aft and install an elevator counter balance to the leading edge of the elevator (same as the FA 400).  Bill’s reasoning for this was it equalized the pressure difference between the upper and lower airfoil and to promote a better turn rate.

I think Bill was right, but I also think there is more to this as well.  My thinking is that the counter balance adds more effective area to the elevator in a turn.   Also, the counter balance increases drag in a hard turn because it protrudes below or above the trailing edges in turns, depending on the direction of the turn.  I don’t have any hard data or wind tunnel testing to prove or disprove any of this, just my feelings.     

Biased on previous experience with the Fierce Arrows models I built, there were a number of things I wanted to improve on.  The first issue was yawing in hard turns.  This was the biggest problem and needed to be addressed mainly because it made the whole pattern look sloppy and way out of trim.

There was a slow turn response at the beginning of the square corners and very soft corners on the tops of the hourglass. Take off’s, landings were good and rounds and level flight were always easy and smooth.

I added an adjustable lead-out guide and adjustable tip weight box to the Fierce Arrow and I went to work from there.  I always felt it was just a matter of getting the C.G., tip weight, and the lead-out position correct and all these little problems would go away.  After a few gallons of fuel, that helped cured a lot of the problems but it still had a few funny wiggles in different parts of the pattern.  Then I moved the lead-outs in front of the leading edge about ½” to 1” and things started looking up and performance was much better. Still, my thinking was that excessive wing sweep was holding the performance back.  It was always way to stable and there was no quick cure for that except designing and building a new model the Delta Force.


Later,
Mikey

Offline Ted Fancher

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Re: Tail for turning flying wing
« Reply #65 on: July 08, 2015, 04:08:08 PM »
A friend got me to test fly the Dick Sarpolus design that appeared in Flying Models some years ago.  The engine is mounted between booms on the front of a stubby fuselage.  Not a super stunter, but more of a souped up Ringmaster.  We discovered a few things.  As originally built the controls were hooked up as a canard, both flaps moved the same direction to get more lift.  VERY strange.  Under power it was very stable until you moved the controls.  Then it tended to mush and suddenly go into a loop.  As soon as the motor quite it handled and landed predictably and smoothly.  Obviously the prop wash on the flaps over powered the canard, up to a point.

Next, locked the flaps in place.  It flew fine and was stable and controllable.  Much like a Ringmaster, but a little better.

Finally, hooked up the flaps to move opposite the wing.  It flew OK, but didn't turn as tight.

Regards the picture- the combined flap/elevator is about 4-5 times as wide as it needs to be.  If you glue the forward portion solidly in place it will be something like Reinhardt's Stuntwing, or a Wakkerman F2D.  it'll fly better, but the elevator is still about twice as wide as needed.  Might have a CG problem with all the paraphernalia behind the balance point.

A question I would have had was what happened to airflow into the prop disc when the canard surface was displaced and did some degree of up/down P factor result?

Offline phil c

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Re: Tail for turning flying wing
« Reply #66 on: August 04, 2015, 04:24:15 PM »
 Based on the results with the Sarpolus design p-factor didn't seem to be a factor(pun intended).  The problems appeared to be all due to the front flap(elevator) and the flaps on the wing fighting each other.  With the wing flaps fixed it flew much like any other plane.  It couldn't turn sharp enough(wing loading) for p-factor or precession to rear its head and make a yaw.  This is not a highly tuned stunter.  I expect with a lower wing loading and more power and probably some other tweaks to the design you might see the more subtle trim issues.
phil Cartier

Offline Dennis Toth

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Re: Tail for turning flying wing
« Reply #67 on: September 17, 2015, 04:23:49 PM »
Mikey,
I also like the idea of the flying wing platform, your information is very interesting. I wonder if the small nose canard similar to what  Dennis Adamisin used working in tandem with the balanced elevator would help the corner issue. I also think you need lots and lots of power on a light weight, small diameter, low pitch/high rpm, wood prop set up. This would address the yaw issue along with your more forward leadout position. I'm wondering if a thinner, wider blade prop could give reasonably strong pull up top. I would also propose flying it faster say 58 - 60 rather then normal 53 mph stunt and put it out on longer lines.

The other question is how much of a gap between the trailing edge of the "wing" and full flying type elevator would you need to get positive pitch control without the first high lift effect then the turn - 1/2"?

Just some thoughts.

Best,       DennisT
« Last Edit: September 26, 2015, 06:40:56 AM by Dennis Toth »


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