Author Topic: Designing Plans?? (Read 4094 times)

GWH · « **on:** December 29, 2006, 10:03:18 AM »

I am looking to start creating my own designs and experimenting.

I know we can only go so far per say. All our planes have a similar look. But where do you start?

I use AutoCad everyday. it is my chosen profession LOL. But, I have only tinkered with planes. Mainly 1/2A stuff and they fly well.

So, I need to know about airfoils and fuselage dimensions etc etc. Such as, what is a good sized fuselage, wingspan, wing area, tail feather combo for say a .40 piped to .51piped sized aircraft. Like the lengths and all

I have searched on the net. I understand flight theory and concepts. I cant draw ribs to save my life lol. The leading edge gets me everytime. Any Help? books? sites? programs? etc etc

Thanks for reading
Happy New Year

Randy Powell · « **Reply #1 on:** December 29, 2006, 10:53:22 AM »

Easiest is to pick out a couple of successful designs and study those. Say an Impact and SV-11 or Trivial Pursuit. Compare various design aspects such as areas, taper, airfoils and moments along with side area. Then decide what aspects are important (to you) and start tinkering. Staying within such parameters, the plane will fly when you're done and you can then evaluate your efforts to decide what, if anything, needs to change.

Clancy Arnold · « **Reply #2 on:** December 29, 2006, 12:28:18 PM »

If you are serious about airfoil designs, the best thing is to read or buy a copy of:

Theory Of Wing Sections by Ira H. Abbott and Albert E Von Doenhoff
available from Dover Publications, Inc.
180 Varick Street
New York N. Y. 10014

It includes a vast array of airfoil data in coordinate dimensions so Auto Cad should be compatible. Lift, drag and other factors are addressed also.

Clancy

John Miller · « **Reply #3 on:** December 29, 2006, 01:03:00 PM »

Good advice has been given here. Since you're already CAD proficient, (are any of us really??) you're ahaed of the game. So much of design is compromise. What I deem acceptable for a 40 sized engine, is usually flown with a much larger powerplant. This is a correct principle, as none of our designs really utilize all the power available from the engine.

Here are the basics to stunt design that will get you a good flyable design almost everytime.

Nose moment, enough for the size tank you'll need for the engine.

Tail moment, enough to balance the plane with the intended engine and tank, without having to add trim weight. A sub caveat is at least 14 inches hingeline to hingeline, flap to elevator. up to about 18 inches max.

Center line of the airfoil, about 1 to 1.5 inches below the thrustline. go to the lower numbers with bigger, heavier, engines.

center line of stab, About 1 to 1.5 inches above wing centerline, to maintain a good geometry for control symetry .

Wing area, enough to acieve a wing loading of about 13 sq inche to the ounce of design weight. This can vary due to aspect ratios, and percentaqge of thickness. Higher, more, square inches to the ounce is usually good.

Stab and elevator area, About 24 to 28% of the wing area.

Flap area percentage, usually 20 to 23% is a good number.

Elevator to fixed stab area percentage, usually no more than 50-50. You actually get more going to 40% elevators.

Airfoils that work well. NACA 4 digit airfoils, na63a modified by moving the high point forward to about 25%. Thickness, 16 to 22%.

Everything else is optional and part of the designers desires.

I've found that a good airfoil program is invaluable. There are several good ones available. I personally use Compufoils pro 3D.

Mark Scarborough · « **Reply #4 on:** December 29, 2006, 01:17:18 PM »

As an addendum, you may try Ted Fanchers two part article on the design of the Imitation in Model Aviation. It is available online on the AMA web site. It covers a vast array of information regarding the interelationships of design elements.

Gordon Tarbell · « **Reply #5 on:** December 29, 2006, 08:59:59 PM »

Why would having horizontal stab /elevator ratio of 60/40 be more desirable than 50/50 or even 40/60% ? I figured if the elevator was larger than the stab, less movement would be needed and less drag produced. I have also been trying to figure a way of building a flying tail or stabilator style hoizontal flying surface to replace the elevator /horzintal stab combo.

John Miller · « **Reply #6 on:** December 30, 2006, 10:59:04 AM »

Gordon, A good question, which I can't answer as precisly as I would like to. But, let me try to give my own eplanation as to why I believe the way I do.

First, I believe that the greatest amount of drag is produced elsewhere during a hard turn, and that some extra drag at the rear of the plane may be beneficial in stabalizing during the turn.

Secondly, with larger stab elevators, the need for large areas of elevator diminishes. Consider the stock Flight streak, or the fact that one cure for taming a stalling turn with a Ringmaster is to reduce the span of the elevator.

Thirdly, Planes I've flown using this percentage, 40/60%, or even greater exhibit a quicker recovery into level flight, more like a snap into level. A personal experience, for sure, but noticable to me.

Lastly, Fully flying stabs can be especially effective, and require much less deflection, and producing less drag, for a given radii of turn, hence their use in events requiring high speed and blasing turns, such as Combat. I just don't believe that the benfits actually apply to stunt designs as our requirements are different. I know they will work, seen them applied, but don't personally believe such a system will offer a better solution than the one I believe in.

I could be wrong, been wrong before, but so far my experience has been positive. I would commend you for your pursuit of knowlege, and would encourage you to continue your experiments.

John Miller

John Miller · « **Reply #7 on:** December 30, 2006, 11:01:27 AM »

Quote from: John Miller on December 30, 2006, 10:59:04 AM

Gordon, A good question, which I can't answer as precisly as I would like to. But, let me try to give my own explanation as to why I believe the way I do.

First, I believe that the greatest amount of drag is produced elsewhere during a hard turn, and that some extra drag at the rear of the plane may be beneficial in stabalizing during the turn.

Secondly, with larger stab elevators, the need for large areas of elevator diminishes. Consider the stock Flight streak, or the fact that one cure for taming a stalling turn with a Ringmaster is to reduce the span of the elevator.

Thirdly, Planes I've flown using this percentage, 40/60%, or even greater exhibit a quicker recovery into level flight, more like a snap into level. A personal experience, for sure, but noticable to me.

Lastly, Fully flying stabs can be especially effective, and require much less deflection, and producing less drag, for a given radii of turn, hence their use in events requiring high speed and blasing turns, such as Combat. I just don't believe that the benfits actually apply to stunt designs as our requirements are different. I know they will work, seen them applied, but don't personally believe such a system will offer a better solution than the one I believe in.

I could be wrong, been wrong before, but so far my experience has been positive. I would commend you for your pursuit of knowlege, and would encourage you to continue your experiments.

John Miller

John Miller · « **Reply #8 on:** December 30, 2006, 11:02:14 AM »

Quote from: John Miller on December 30, 2006, 11:01:27 AM

Whoops

Gordon Tarbell · « **Reply #9 on:** December 30, 2006, 06:53:13 PM »

If I understand what you are saying, I might be heading towards too much of a good thing. And that level of too much is different for each flyer. And thanks for the reply, I probablyshould have started this as a new thread instead of burrying it deep in this thread.

GWH · « **Reply #10 on:** December 30, 2006, 07:58:27 PM »

No need Gordon....It is good here. I will learn with ya. Lets keep it going.

So, i would think that having less or a balanced stab/elevator combo of 50/50 has more effect. My thinking is 60/40 causing more deflection in a given turn. and 40/60 pushes the envelope or having maybe to much control. Hence having to open/close handle to tame the plane.

So, huuummmm?? what about some odd combos? such as: 55/45; 45/55; or 30/70 etc etc...

I am thinking the flying stab: would really be a waste of building as the turn radius increases with less handle movement....But then a again a "flick" of the handle to get into the turn maybe work??

if my thinking is correct here: more elevator % would equal more drag into the turn and cause wobble...I corrected that very issue on my twister(modified) by closing the handle leads.

Gordon Tarbell · « **Reply #11 on:** December 30, 2006, 08:39:40 PM »

I like the idea of a fully flying tail with the fulcrum(pivot point) forward of center. Let's say the cord length is 5" ,have the fulcrum 2" back from the leading edge of the stabilator. By experimenting with the placement of the fulcrum I think that you would see deffinate increases in control effort for the pilot as the pivot point moves forward and a decrease as it is shifted to the rear. Sort of power steering effect. Do to my level of flying ability (not that great) I find I fly better with a fast reacting plane. I tried flying a freinds plane set up with slow controls that he does rather well with and it feels like I have to give it my all to get it to turn. Most people that have flown my planes think the controls are too fast and tell me to narrow my handle spacing. For now slow controls don't work for me that is why I am delving into this idea of stabilators or larger elevators. I know I am not breaking new ground. I would like to find a set of plans for a stunt ship that used a stabilator or flying tail set up to see how it was constructed and use it as a spring board to more learning.

Paul Smith · « **Reply #12 on:** December 31, 2006, 01:04:49 PM »

Quote from: gordon tarbell on December 30, 2006, 08:39:40 PM

I like the idea of a fully flying tail with the fulcrum(pivot point) forward of center. Let's say the cord length is 5" ,have the fulcrum 2" back from the leading edge of the stabilator. By experimenting with the placement of the fulcrum I think that you would see deffinate increases in control effort for the pilot as the pivot point moves forward and a decrease as it is shifted to the rear.

I've thought about stabilators on stunters quite a bit. They work fine on twin-boom combat planes where the stab is all one piece. The problem on a stunter is how to rig the two sides of the tailplane on opposite sides of the body without having the linkage either flimsy of weighting a ton.

Jim Thomerson · « **Reply #13 on:** December 31, 2006, 07:03:42 PM »

It has been said, and there is some truth to it, that all stunt airplanes are just more or less modified Noblers. And in fact, I have seen some nice flying Noblers. So maybe just get a set of original Nobler plans from Bodak and start modifying. Seriously, any widely flown modern airplane is pretty good and could serve as a starting point. Back in the 80's I did a full fuselage airplane; a couple of iterations, starting with Sig Twister plan and a red pencil. Wasn't too shabby.

John Miller · « **Reply #14 on:** January 01, 2007, 01:57:00 PM »

Gordon and Gary.

Experimentation is a powerful incentive to design. Notice though that the top pilots stick to some proven designs, or continue to build iterations of the same design. Modifying a small detail here and there as they strive for that perfect package. It's also important to note that design elements being close to optimum, will often lose to the more experienced pilots flying a less developed design. In other words practise and familiarity with the plane is usually better than most of the designing we can do. Over the years since this "sport" of competitive Cl Aerobatics began, many well seasoned experimentors/designers, have worked out the basic numbers to a point that most of what we can do now has already been done. The exception being the use of modern composits with stregnths and reliabilities undreamed of 50 years ago.

I'm not trying to discourage anyone, rather trying to encourage exploring paths that will reward us with the most bang for the time spent.

In the case of fully flying stabilators versus the standard style, and for now, we'll stick to 50-50 as far as proportions go, The amount of successes have not been good for the stunt event, compared to the performances with it for Combat. In Combat, the desire is for high speed, with the least amount of speed scrubbing DURING hI-G, high speed, turns. Normally there are several ways to get this type of performance. One of the best, in my opinion, is the combination that uses enough of a low wing loading with an airfoil that is rather stall resistant at the speeds used, combined with a tolerance for a further aft CG, while still maintaining control, and a fully flying stab, with the fulcrum near the leading edge of the stab-elevator.

Combat planes designed to this standard are fast enough in the level, but resist slowing during the turns and will literally "chew up" an opponent during manuevers. They have the reserve to out fly their opponents at the time when their opponents are at their worst, as far as flying ability goes. This is a great advantage, and the design is a large part of the equation. But this is not neccessarily the optimum setup for Stunt.

Most modern Stunters are designed to fly at about 55 mph, compared to well over 100 mph in combat. We need to optomise the hard turns within our speed envelope. Not only do we need to create the look of a square turn, but it must nuetralize, and lock in level flight effortlessy, or at least appear to do so.

I believe that the Flying stab, when we look at our requiements, isn't going to perform all our requirements as well as the normal stab-elevator will.
Partly, I believe we may actually benefit from a small increase in drag during maximum deflections, with slightly better stability during the turn. That extra drag acts in a similar fashion as the tails on an arrow, and I believe this helps in taming down wiggles at the rear during hard turns.

This should also help to create the look of a square turn, balancing the lift-drag from the wing-flaps, with drag-lift in the opposite direction at the tail-plane. Since the tail plane is smaller, when nuetralized, it should regain it's composure, Flying level, sooner than the wing and help snap and lock the plane into level flight.

So, how does having less percentage of elevator make this better? I believe that during the turn, the elevator may deploy dlightly higher to make the same force, but not substantially enough so that there's a huge increase in drag over the 50-50 setup. The advantage, to my mind, comes when the controls are nuetralized. Since more area is already at nuetral, the level seems to lock in , sort of a snap and lock. inhancing the look of, and actual quality, of the turn.

I was looking at several designs, and noticed that many of our modern designs use less than 50% area for the elevators.

Now, having said all the above, There are likely to be other opinions, and I know that there are those who have the training and ability better explain these theories than I. Hopefully they will add to this discussion.

Mark Scarborough · « **Reply #15 on:** January 01, 2007, 03:38:47 PM »

At the risk of sounding repetative, Ted Fanchers arrticle on designing the Imitation covers these design choices in depth both the reasons and implications. It is neccesary reading. It will also answer virtually every question that has been asked in this thread.

Gordon Tarbell · « **Reply #16 on:** January 01, 2007, 06:35:17 PM »

John I do not at all feel your info to be discouraging. I was hoping that someone would step up and shine more light on this and that is what you did. I know people have mentioned an article by Ted Fancher, where can I read it? And John I understand what you are saying in the previous post and it makes alot of sense. I see a little more of the big picture now.

Howard Rush · « **Reply #17 on:** January 02, 2007, 02:24:26 AM »

I wouldn't hinge the stabilator farther aft than 25% chord. The stabilator will be unstable if it's hinged any farther back: it will tend to jump toward full up or full down. You can try to balance this instability with the flaps, but I bet you won't be happy with that combination.

Gordon Tarbell · « **Reply #18 on:** January 02, 2007, 06:34:30 AM »

I knew their was a point of instability but wasn't sure how far back that point would be. I remember back in the early 70's when I was working on getting my pilots license,the Cherokees that we used as trainers used a stabilator set up . That is what gave me the idea to try it. That and the fact that it was also used on the f-86 Sabre. I have read of one or two classic era plane designs that incorporated this feature, and I would like to get the plans to see how it was connected to the plane. I know I should just spend more time flyng and improving my skills with available designs that are proven , I am always thinking 'what if '.

Howard Rush · « **Reply #19 on:** January 02, 2007, 09:49:29 AM »

The neutral point is theoretically 25%. It's pretty close to that in practice. The Cherokee hinge, as I remember, is aft of that, but the elevator is hinged to the stabilizer so the elevator travels in the same direction as the stabilizer, but faster. This arrangement is stable, but probably requires that there be no slop in the linkage and maybe requires a damper.

The stabilator is out of fashion for stunt. I don't know why that is, but maybe you'll find out.

Trostle · « **Reply #20 on:** January 02, 2007, 10:48:49 AM »

Quote from: Howard Rush on January 02, 2007, 09:49:29 AM

(snip)

The stabilator is out of fashion for stunt. I don't know why that is, but maybe you'll find out.

I think the consensus of those who have tried an all flying stabilator on a stunt ship is that the models do not groove and are difficult to make a good track in the maneuvers. That was my impression when I tried one many years ago when admittedly, I did not know much about the stunt pattern. But as a student in aeronautical engineering in 1960, I thought I would try it and set the world on fire with this great innovative thought. My pivot point was at 25%. The airplane would go through the maneuvers, but it was not comfortable. I do know tht it did not fly nearly as well as any other conventional model that I built around that basic configuration. That is pretty much the same report from those who have tried them that has appeared over the years on these forums when the question of all flying stabilators has come up. They work on combat ships, but those airplanes are performing in an entirely different environment.

This is not to say that there may be some design configuration that could be found that would give the pilot exactly what he is looking for and have an airplane that would perform extremely well as a potent CLPA model. Any effort to find such a configuration is to be applauded and respected. From my experience and based on what has been written over the years, such an effort is as productive as chasing shadows.

Keith Trostle

phil c · « **Reply #21 on:** January 02, 2007, 11:01:47 AM »

Gordon, for more than you ever wanted to know about designing CL planes, dig out Wild Bill Netzeband's three articles on the subject from the old American Aircraft Modleler(I think the first is on the PAMPA website), and then dig out his columns on the subject in Model Airplane News in the late 60's, early 70's. He covers everything in great detail, including how to figure out the control loads so the plane comes close to feeling like you want it too.

For airfoils, figure out how to import a text file into AUTO Cad to produce a shape or polyline. Profili(an Italian program) has a ton of airfoils in it and will export the coordinates as text files. (http://www.profili2.com/eng/default.htm). Coordinates are also available from the NASA website and some programs to generate NACA series airfoils.

As far as stabilators, I use one on my Streak 2000 design. It is a front-hinged stabilator with about 10% of the wing area. With the plane properly balanced and the right control throw, it corners and grooves as well as any conventional design stab. The big big problem with a stabilator for a typical stunter though is designing and building the hinge mechanism. The Streak 2000 design would not scale up well and requires that the stabilator be one piece, behind the fuse, which limits the design quite a bit.

Trostle · « **Reply #22 on:** January 03, 2007, 12:15:12 AM »

Quote from: phil c on January 02, 2007, 11:01:47 AM

(clip)

As far as stabilators, I use one on my Streak 2000 design. It is a front-hinged stabilator with about 10% of the wing area. With the plane properly balanced and the right control throw, it corners and grooves as well as any conventional design stab.

(clip

Phil,

I would be interested on the configuration, size and overall design of your Streak 2000. If this is something that has been published, I must apologize that I am not familiar with it. I would like to know if you feel if your design with a stabilator provides any advantage in feel, flying ability, ease of control, accurately flying corners, flying particularly sharp corners, ease of sizing and shaping of your maneuvers or any other benefit that you could describe.

Please do not misunderstand and read this as being sarcastic in any way. I know that all flying stabilators have been tried on many occasions over many years, at least dating back to the Detroiters and Bob Dailey (sp), who developed the I-Beam construction. Though they might have appeared, I am not familiar with any design that has placed in the top 20 at the Nats for the past 20 or 30 years (if ever). There may be reasons for this, but I doubt if one of those reasons is that no top flyers ever tried it.

Again, I am not trying to discourage anyone from exploring the possibilities of using a stabilator on a CLPA design. There might be something out there that might just be the next big thing in our event, right there behind tuned pipes, electrics, 4-strokes, the Rabe Rudder, adjustable everything, better tank technology, better construction techniques, composite materials, better engines, boost tabs (maybe should not yet be on this list), better props, and the list goes on and hopefully will never stop growing.

Dick Fowler · « **Reply #23 on:** January 03, 2007, 05:15:21 PM »

I feel the biggest problem to overcome would be sensitivity in control deflection using a stabilator. Unlike conventional stab/elevator controls, the Angle of Attack (AoA) of the stabilator is a 1:1 function of control horn deflection angle. Conventional designs produce ratios of less than 1:1 (not linear) dependent on stab to elevator chord ratios.

The guys at the field are flying a design that uses stabilators (can't remember the name right now) but four of the five planes hunt. They have tried all sorts of fixes including CG changes, slop in the linkage all to no avail. Nobody knows why the one doesn't hunt!

Gordon Tarbell · « **Reply #24 on:** January 03, 2007, 07:55:27 PM »

In an earlier post Phil listed some articles that are mandatory reading on stunt design. Since I don't have 50 years of back issues of several model publications how do I get copies of these and others like them ? Can I down load copies from a web site or can I purchase them from some where? Also when buying plans for older planes is there a place that shows photos of the planes and offers copies of the build article?

John Miller · « **Reply #25 on:** January 03, 2007, 08:20:00 PM »

Gordon, check with the AMA. They bought all the plans from John Ponds estate, and have published a ton of designs over the years. They also offer reprints of many articls from the past.

John Miller

Mark Scarborough · « **Reply #26 on:** January 03, 2007, 10:29:10 PM »

Gordon, the Fancher articles on the Imitation was Printed in Model Aviation magazine as I recall. It is avalailable on the AMA website if you are a member, its in the archives. It is a free download. When I get a chance I will try to find the reference. email me and I will give you the reference.

phil c · « **Reply #27 on:** January 04, 2007, 10:33:34 AM »

Quote from: Trostle on January 03, 2007, 12:15:12 AM

Phil,

I would be interested on the configuration, size and overall design of your Streak 2000. If this is something that has been published, I must apologize that I am not familiar with it. I would like to know if you feel if your design with a stabilator provides any advantage in feel, flying ability, ease of control, accurately flying corners, flying particularly sharp corners, ease of sizing and shaping of your maneuvers or any other benefit that you could describe.

No problem Keith. There is a picture on my homepage, http://home.earthlink.net/~philcartier
The Streak is a flapless, 500 sq.in. stunt trainer. As far as I can tell, there are virtually no performance advantages to a stabilator over a conventional stab/elevator. I've tried both on similar planes and if the design is good and the balance point and control travel are correct they fly the same.

There is a difference in trimming. A stabilator plane is much easier to trim to fly over a wider CG range. Within limits, you don't need to add nose or tail weight. Just dial in more or less elevator. A stab/elevator has a limited amount of adjustment range. Anything over 25 deg. or so of elevator doesn't help the plane turn but just adds drag. So if the CG is a bit too forward you can easily run into a situation where you simply can't get any more elevator.

The biggest problem with a stabilator on a larger plane is the blasted hinge. It has to have very little slop, free movement, long-wearing, and strong. The combat style hinge doesn't scale up well. Just sitting here thinking, a jet-styled stunter with a fairly wide rear fuse might be a good candidate. The bearings could be spaced out a couple inches and be simple plastic bushings on an arrowshaft. F-15 here we come!

Trostle · « **Reply #28 on:** January 04, 2007, 03:24:27 PM »

Quote from: phil c on January 04, 2007, 10:33:34 AM

(clip)

The biggest problem with a stabilator on a larger plane is the blasted hinge. It has to have very little slop, free movement, long-wearing, and strong. The combat style hinge doesn't scale up well. Just sitting here thinking, a jet-styled stunter with a fairly wide rear fuse might be a good candidate. The bearings could be spaced out a couple inches and be simple plastic bushings on an arrowshaft. F-15 here we come!

Phil,

I understand about the structural problems posed by an all flying stab with its single pivot point hung on the side of the fuselage. I also understand the problem you suggest with scaling up the configuration used on the combat ships. One thing that can help with this situation and is made possible because we do not have a jet engine blowing through the fuselage where we have our control mechanism. What I found was needed is to put a bar some logical distance from the pivot point that rigidly ties the two stabilators together. This adds considerable stiffness to the entire stabilator assembly. There has to be a slot in the sides of the fuselage for this bar up and down as the stabilator is moved, but given the angles necessary for the stabilator to move (probably no more than 10-degrees) that slot on the fuselage sides does not need to be very long, depending on how far it is from the pivot point. Maybe you have already worked this out, but before a designer starts down the road for a stabilator, this is one thought to take into consideration. With this bar, you do not need a particularly wide fuselage to hold the hinging mechanism, it just needs to be as rigid as the rear of any good stunt ship and be strong enough to hold the bearings for that pivot.

Also, by your description of what you have used on your design, your stabilator hinges at the leading edge, much like used on most current combat ships. Have you tried moving the pivot point rearward so that you have some aerodynamic balancing? As has been suggested here and elsewhere, that pivot point should not be further aft than 25% of the area of the stabilator. In fact, I would think a more reasonable location for our application would be around 15%, plus or minus a small amount.

RC Storick · « **Reply #29 on:** January 05, 2007, 05:40:37 PM »

Quote from: Trostle on January 04, 2007, 03:24:27 PM

I understand about the structural problems posed by an all flying stab with its single pivot point hung on the side of the fuselage. I also understand the problem you suggest with scaling up the configuration used on the combat ships. One thing that can help with this situation and is made possible because we do not have a jet engine blowing through the fuselage where we have our control mechanism. What I found was needed is to put a bar some logical distance from the pivot point that rigidly ties the two stabilators together. This adds considerable stiffness to the entire stabilator assembly. There has to be a slot in the sides of the fuselage for this bar up and down as the stabilator is moved, but given the angles necessary for the stabilator to move (probably no more than 10-degrees) that slot on the fuselage sides does not need to be very long, depending on how far it is from the pivot point. Maybe you have already worked this out, but before a designer starts down the road for a stabilator, this is one thought to take into consideration. With this bar, you do not need a particularly wide fuselage to hold the hinging mechanism, it just needs to be as rigid as the rear of any good stunt ship and be strong enough to hold the bearings for that pivot.

Also, by your description of what you have used on your design, your stabilator hinges at the leading edge, much like used on most current combat ships. Have you tried moving the pivot point rearward so that you have some aerodynamic balancing? As has been suggested here and elsewhere, that pivot point should not be further aft than 25% of the area of the stabilator. In fact, I would think a more reasonable location for our application would be around 15%, plus or minus a small amount.

Keith I could be wrong on this but is it right that full pivot stabs are no good. You ask why do I say that? I have built a few test planes and the ones I tried had no glide path. Any deflection in the stabalator causes the air brake effect. When the tail quits flying the glide is killed. Am I wrong on this as I had it attached at 50%?

Trostle · « **Reply #30 on:** January 05, 2007, 11:22:20 PM »

Quote from: Robert Storick on January 05, 2007, 05:40:37 PM

Keith I could be wrong on this but is it right that full pivot stabs are no good. You ask why do I say that? I have built a few test planes and the ones I tried had no glide path. Any deflection in the stabalator causes the air brake effect. When the tail quits flying the glide is killed. Am I wrong on this as I had it attached at 50%?

Robert,

With the concern that I am being redundant to what has previously been written here and on other threads, perhaps in other forums, I will try to answer what I understand to be your question.

I am sure that you have seen some posts here where people claim to have flown a stunt ship with an all flying horizontal tail or stabilator and have reported that they fly just fine. (When I read something like that, I wonder what they are comparing it to. Sometimes I think such statements are similar to those who write that their 40 ounce Ringmaster "flies just fine". But there is a huge difference between a 40 ounce Ringmaster that "flies just fine" compared to a truly competitive, top 20, fully trimmed stunt ship.) I think that most that have experimented with this configuration have found that no advantage is to be gained, and in fact, as you have found, these models have less than desirable performance. As I have mentioned, there may be some magic formula yet to be found with this concept that could be the really next big thing in our design evolution of these airplanes. That has not yet been found. Also, as I have mentioned, we have not seen any stabilator equipped model in the finals at the Nats. There must be a reason for that, and it is certainly not that top fliers have never tried them.

To say that a stabilator equipped stunt ship is "no good" may be an extreme statement. I think it is fair to say that they offer no improvement, and as you have found may degrade the performance of your stunt ship. One of the problems you may have encountered with your design is the pivot point if indeed yours was at 50% of the tail area. As Howard Rush suggested, unless there is some sort of dampening that might be found on full scale aircraft with all flying stabilizers, that 50% pivot point will create a lot of unwanted problems. The 50% pivot creates unwanted aerodynamic forces resulting in the control surface to move off center or forcing the surface to move on its own accord, more than your intended input. This will happen no matter how tight your linkages are or how sound your hinges are. I think the conventional wisdom is that the pivot should not be further aft than 25% of the area. The Combat guys often put the pivot at the leading edge of the all moving stab. When a combat design does not use a leading edge pivot point, there is generally far less than 25% of the area forward of the pivot point. (It might also be pointed out that the combat flyers are not too concerned about any precision tracking of their model after a square turn.)

On your models, if you feel that any deflection of the stabilator in the glide acts like an airbrake, I would suggest that the 50% pivot point is causing the surface to deflect more than you transmitted at the handle, causing control responses that you never intended.

Keith Trostle

phil c · « **Reply #31 on:** January 06, 2007, 08:04:42 AM »

Quote from: Trostle on January 04, 2007, 03:24:27 PM

Phil,

I understand about the structural problems posed by an all flying stab with its single pivot point hung on the side of the fuselage. I also understand the problem you suggest with scaling up the configuration used on the combat ships. One thing that can help with this situation and is made possible because we do not have a jet engine blowing through the fuselage where we have our control mechanism. What I found was needed is to put a bar some logical distance from the pivot point that rigidly ties the two stabilators together. This adds considerable stiffness to the entire stabilator assembly. There has to be a slot in the sides of the fuselage for this bar up and down as the stabilator is moved, but given the angles necessary for the stabilator to move (probably no more than 10-degrees) that slot on the fuselage sides does not need to be very long, depending on how far it is from the pivot point. Maybe you have already worked this out, but before a designer starts down the road for a stabilator, this is one thought to take into consideration. With this bar, you do not need a particularly wide fuselage to hold the hinging mechanism, it just needs to be as rigid as the rear of any good stunt ship and be strong enough to hold the bearings for that pivot.

Also, by your description of what you have used on your design, your stabilator hinges at the leading edge, much like used on most current combat ships. Have you tried moving the pivot point rearward so that you have some aerodynamic balancing? As has been suggested here and elsewhere, that pivot point should not be further aft than 25% of the area of the stabilator. In fact, I would think a more reasonable location for our application would be around 15%, plus or minus a small amount.

Keith, by my experience, on a combat plane putting 10-15% of the stab area ahead of the pivot is good. It allows moving the balance point further forward without making the control loads too high. On the balance, it is more work to build and repair.

The second rod between the two stab halves is a good idea. The RC pattern guys do this. When I tried prototyping this kind of setup for control line the problem was not that the rear of the fuse wasn't strong enough. The bearings weren't far enough apart and the tips of the stab looked like they would move too much. The RC guys may be able to accept this. They are flying much larger maneuvers. Again, from combat experience, it doesn't take much slop in the hinge to start affecting what happens during control reversals. Intersections go all to pot when the stab is flopping around.

Howard Rush · « **Reply #32 on:** January 06, 2007, 09:36:48 PM »

I copied the way I hinged stabs on my Rushpuppy combat planes from Phil. I don't remember how far back his hinge was, but mine was at about 17% chord. Phil can hit a seven-foot moving target with his airplane quite precisely. I have been rather disappointed at his precision on several occasions.

Jim Pollock · « **Reply #33 on:** January 06, 2007, 09:56:41 PM »

All,

I think there is value in a stabalator if you can get it hinged and built well enough, however, I think that a conventional stab/elevator is much easier to produce and will yeild very close to the same result the stabalator provides - Therefore, why make you building job that much harder for nearly no return? That's my assessment of why stabalators are not in wide use today.

Jim Pollock

Gordon Tarbell · « **Reply #34 on:** January 07, 2007, 06:29:06 AM »

F-14 Tomcat, Piper Cherokee, F-18 Hornet, many arcraft old and modern use this set up or a version of it. I agree that it is alot of effort for possibly little gain. I was hoping someone knew of a stunt ship in the past 50 years that used this setup so I could see how they incorporated it in the construction. I just wanted a starting point. I seem to recall while looking through a plans list of a 60's era stunter with a stabilator but now I can't find it.

Jim Pollock · « **Reply #35 on:** January 07, 2007, 06:45:21 AM »

Gordon,

How about 57 years, yes, Bob Dailey's 1949 Nats winning airplane had a stabalator - according to the Nuts and Bolts article in Stunt News his was hinged at about 33%. The Nuts airplane was a nearly direct copy of that airplane except I believe it was hinged at somewhat less than 50%, quite sensitive setups that could possibly reach aerodynamic lock-up with too much control input. The Bolts airplane had a conventional stab/elevator setup.

Jim Pollock

Clayton Smith · « **Reply #36 on:** January 07, 2007, 08:24:16 AM »

Regarding stabilators or flying stabs on stunt planes. Here is a photo taken today of the prototype TEOSAWKI. Note the counterbalanced flying stab. The turbulator strips are a recent change giving added transition stability. Extremely smooth linear control.

This plane has something over 1500 flights since built six years ago. This is the only TEOSAWKI having the flying stab. All TEOSAWKI's sold to customers have had a conventional built up stab/elevator at their choice.

Many stunt flyers have declared the TEOSAWKI a combat plane. Call it what you choose, it has proved itself in the CLPA contest records.

L0U CRANE · « **Reply #37 on:** April 03, 2007, 05:34:33 PM »

For a while in the early 1980's I developed several all-flying stabilator stunters. They flew well, but had the problems several have mentioned...

I set the hinge-line at 20% (Stab)MAC, to provide some positive neutral-restoring force. It seemed adequate. I used a tie between sides to reduce 'chatter' on the root. The trailing edge overhung the fuselage tail end, so the tie went there. For a stable base, the center section was around 2" wide, with a full width brass tube for the main joiner between sides.

As I said, they flew well, except, as John Miller has been trying to convince doubters, for stunt we need a stabilizer to help us track out of a turn or corner neatly. That fixed piece in front of the conventionally hinged elevator is called what?

Right!

And the best trimmed of my experiments required full-time attention to where it was going. There was no such thing as a "groove" straight or curving. Got to be a bit of a nuisance - you couldn't relax anywhere.

I also used proportionally smaller total tail area and quite small +/- angles - see the '30°-elevator equivalent AoA' sketches above - and had one model stall the entire tail during a windy day flight, at the bottom of the hourglass. Well, I was able to salvage the engine..

It can be done, but things are so much simpler the other, proven way. Small tail stunters look wrong these days, even if they fly well. Why bother? There's no practical advantage.

phil c · « **Reply #38 on:** April 05, 2007, 11:05:04 AM »

Lou, the tail on a combat plane is usually called a stabilator, for good reason. It performs exactly the same functions as the stab/elevator on a conventional setup. The fixed surface on a conventional setup doesn't have any extra stabilizing function, by itself. It's part of the tail surfaces, and the air sees the whole sheebang. It doesn't care a bit where the hinge is located, as far as stability goes.

Since you mention that you used a smaller than usual stab and quite small movement, that is a good indication that the plane was tail heavy, and possibly the amount of counterbalance(20%) was too much. Both of those things would make the plane tend to wander off course and not track well. When the balance point and the stab travel are adjusted correctly there is no difference between a stab/elevator and a stabilator that I've ever seen. Even with flaps. I think Bigiron was putting flaps on slow combat ships equipped with stabilators. They flew fine.

When a plane with a stabilator stalls the stab, you get hexagonal loops. Happens when the plane is noseheavy. When a plane flys into the ground on the fourth corner of the hourglass it's because it either runs out of lift, the controls get stiff from airspeed and you can't move them fast enough, or the pilot just plain mis-estimates where the turn has to start.