Twisted wing panel with correction tab - loss of lift?

[Dennis Toth]

I acquired a ship that had the outboard wing panel with a built-in twist up. I added a tab/wedge under the outboard wing to level the wing. This worked but the ship seemed to be doing rather large loops (65 - 70deg ish). I was wondering if the area with the tab/wedge was just coming along for the ride and not contributing to carrying any weight through the maneuvers?

Best,   DennisT

[Dave Hull]

Here's my simple take:

--The drag goes up due to the inefficient airfoil; and
--The maximum available lift goes down due to the inefficient airfoil and the spanwise elements fighting each other. In other words, the zero lift line is not constant spanwise.

I believe a simple way to visualize this is to take sections thru the wing every few inches. Forget what it is supposed to look like, just draw how it is, and then align the sections with the waterline of the plane at zero lift. At small angles, some of the sections with the warp will not be in a favorable position to provide any lift. Depending on how it is warped, this may be upright or inverted. To really visualize this, you need a good diagram of an asymmetrical wing section that shows the chord line and also the zero lift line. The AOA should be measured from the zero lift line. A few years back, there was a diagram in Model Aviation that accompanied an article that was trying to explain this--but it didn't have enough detail to get much right. In other words, good enough to explain to your 10 year old as long as you didn't expect him to understand because the theory was missing. I suspect that you'd find the best diagram and explanation in Abbott and Von Doenhoff, The Theory of Wing Sections, but I don't have it in front of me right now.

In your example, I would expect that inside loops would be softer for sure, and probably outsides as well. You didn't say how much of the span was affected by the warp, and if you placed the wedge over the entire affected area. I would have tried that approach--after I gave up trying to straighten the wing.

Wing twist may be included on full size aircraft for stability. It's how a plank flying wing achieves pitch stability beyond using a reflexed airfoil that attempts to limit the movement of the center of pressure with angle of attack.  It is also common to use washout in the wingtip to keep the tip from stalling first and creating snaproll problems. (They also may use a turbulator on the inboard section to force it to stall first for the same reason.)

The Divot

[Howard Rush]

I was wondering how to visualize the effect of a trim tab on a warped wing.  I think one could come pretty close by doing something similar to the stuff I posted here on wing asymmetry awhile back.  It would reduce max lift, but the most annoying effect would be the wandering around of the spanwise center of pressure with angle of attack.  At best, you’d always have the wrong amount of tip weight.

This is an example of the engineering principle that other people’s disciplines are linear.   Hence EEs put trim tabs on their stunt planes and Bob Carver and Norm McFadden rolled their eyes at my assertion that op amps are perfect.

As for reflexed airfoils stabilizing flying wings, yes, I’d always read that, including in textbooks, but it’s based on an unnecessarily ambiguous definition of stability.  A reflexed airfoil gives a positive Cm, allowing a flying wing to be trimmed at a forward CG, but it don’t do @#$% for dCm/d alpha.

[Dave Hull]

"This is an example of the engineering principle that other people’s disciplines are linear."

Boy, that one really hit the mark. One of my favorites was when an EE tried to explain to me (a mechanical engineer) how ball bearings work because he was worried that I didn't appreciate proper sizing and selection, etc. He wasn't really sure what the difference between a shield and a seal was. He was an excellent high voltage power supply designer, though....

[Chuck_Smith]

Dave. you can make a trim tab work but it will have two effects that are "unbecoming" to a good flying stunt ship.

First, it will be speed sensitive. That means it's effect will change throughout a manuever.

Second, it will change the neutral point for the control forces. For example: if you put a downward tab on either flap, as the lines go slack the elevator will want to move to the down position. This will manifest itself as a tracking issue on a windy day when you may have light line tension in certain maneuvers.

Chuck

[Chuck_Smith]

"This is an example of the engineering principle that other people’s disciplines are linear."

Boy, that one really hit the mark. One of my favorites was when an EE tried to explain to me (a mechanical engineer) how ball bearings work because he was worried that I didn't appreciate proper sizing and selection, etc. He wasn't really sure what the difference between a shield and a seal was. He was an excellent high voltage power supply designer, though....

Or a ME trying to explain a tilting pad & sleeve bearing to an aero guy! 

Howard - interestingly, a flying wing doesn't require a reflexed airfoil if the wing sweep is correct. Ask the guys at Northrop. I was fascinated by the Northrop wings as an undergrad and studied them rigorously. I even have pieces of the B35 that crashed here in my desk as I type, along with some simple balsa gliders I built back in the day to prove the inherent stability of swept-wing tailless aircraft.  You can toss them like a Frisbee and they almost instantly settle in to level flight. Also got some cool B2 memorabilia laying around here somewhere.

[Serge_Krauss]

Chuck - just a FWIW...

The earliest successful swept-wing tailless aircraft (non-Zanonia-leaf types), as you probably know, were those of then Lieutenant J.W. Dunne.  His wings achieved lift and stability configured as very thin sections wrapped about imaginary cones and cylinders, which created camber and wash-out needed on swept wings. He used to send these paper-airplane ideas to his friend H.G. Wells around 1903-8. Anyway his planes were among the earliest to fly in England. Full sized gliders were successful around 1906, and by 1910 he had achieved reliable powered flight with his "D-5." It was in that year that he made a famous flight demonstration in which he piloted the D-5, with virtually no experience (he had a heart condition), taking both hands off the stick to write each maneuver on a piece of paper given to him by Griffith Brewer of the Royal aeronautical Society and then descended with both hands in the air until just before flaring for landing. Representatives of the R.A.S. and Orville Wright witnessed the demonstration.

So, with an extremely thin but cambered wing, he built the first successful single-swept tailless plane. Starling Burgess used his patents to build several Dunne types in America during the war, improving the wing sections and adapting them to use as sea planes. However, WW I increased the performance of what became conventional (aft-tailed) aircraft immensely,  leaving his designs behind. As we know, Lippisch, Hill, the Hortens and Northrop, among others, later built high-performance swept-wing tailless aircraft, and other low-aspect-ratio sorts also flew successfully. But none illustrated your statement better than Dunne's, whose wings had arcs for camber.

The pictures (my scanner needs replacing) below are from the "Aeronautical Journal" (later the 'Journal of the Royal Aeronautical Society') and "Flight."  'just an historical footnote.

SK

[Tim Wescott]

"This is an example of the engineering principle that other people’s disciplines are linear."

Boy, that one really hit the mark. One of my favorites was when an EE tried to explain to me (a mechanical engineer) how ball bearings work because he was worried that I didn't appreciate proper sizing and selection, etc. He wasn't really sure what the difference between a shield and a seal was. He was an excellent high voltage power supply designer, though....

Ball bearings work because I tell the ME's why they need to make the changes I'm asking for, then they laugh at me and go off and make totally different changes, and the assembly ends up working the way I wanted it to.

[Chuck_Smith]

Serge,

Very cool stuff. I did a lot of research on the Horton Bros., including getting to see the Ho 229 years ago. I was at the Udvar-Hazy Center a few years back and to my surprise, in the restoration center sat the 229!  After languishing at Silver Hill for so many decades it's hopefully finally going to get the spa treatment it deserves.

When I was an undergrad I was sure flying wings had to be the way to go. Later on I got enlightened enough to understand their limitations. Heck, even birds have tails, If tailless was better evolution would have favored the pterosaurs, lol!

Chuck

[Serge_Krauss]

Hi, Chuck -

Wow, I envy you for having been able to look in on that project! When I saw the Ho IX (8-229) at Silver Hill (1980's), it was in awful shape and getting no TLC. 'glad to hear some version of it will fly again. My material indicates that the Ho. IX V-2 seemed to fly well, until one was carelessly flown and destroyed. Tailless aircraft do fit in some niches, especially now that fly-by-wire can make lethal versions safe, but they have often not fit assigned tasks. The Horten "bell-shaped" lift distribution might have let Northrop get by Mr. Symington with the bombers.

[Chuck_Smith]

Hi, Chuck -

Wow, I envy you for having been able to look in on that project! When I saw the Ho IX (8-229) at Silver Hill (1980's), it was in awful shape and getting no TLC. 'glad to hear some version of it will fly again. My material indicates that the Ho. IX V-2 seemed to fly well, until one was carelessly flown and destroyed. Tailless aircraft do fit in some niches, especially now that fly-by-wire can make lethal versions safe, but they have often not fit assigned tasks. The Horten "bell-shaped" lift distribution might have let Northrop get by Mr. Symington with the bombers.

Northrop YB49 had two fatal flaws.  First, the autopilot couldn't keep it stable enough in yaw for accurate bombing with the dumb bombs its era and

second, the B47 was MUCH faster and destroyed the speed records of the YB49.

Now Loyal Wingman, that's some interesting new tech.

[Dan McEntee]

Hi, Chuck -

Wow, I envy you for having been able to look in on that project! When I saw the Ho IX (8-229) at Silver Hill (1980's), it was in awful shape and getting no TLC. 'glad to hear some version of it will fly again. My material indicates that the Ho. IX V-2 seemed to fly well, until one was carelessly flown and destroyed. Tailless aircraft do fit in some niches, especially now that fly-by-wire can make lethal versions safe, but they have often not fit assigned tasks. The Horten "bell-shaped" lift distribution might have let Northrop get by Mr. Symington with the bombers.

     I have always been fond of flying wings, and built gliders in that configuration as a kid, and hope to some more in retirement. I have read a little about how hard Sen. Stuart Symington worked to get the Northrop Flying Wing eliminated from the bomber competition in the early 50's. Some where in my collection of stuff is some newspaper clipping of the time that I found by accident in some books or magazines I bought. I need to find those again some time!  Symington represented my area here in St. Louis, MO and as I remember it, Symington fought hard for Convair because a fledgling little aircraft manufacturer back home in St. Louis called McDonnell Aircraft was a subcontractor for Convair in those days. Then when the B-36 was chosen, he went as far as to make sure that ALL of the existing YB-49 airframes be destroyed so they could never fly again. I understand that there was a lot of back room dealings and hard nosed politicking going on about that. i also saw an interesting interview with Bob Cardenas, who I think was chief test pilot on the YB-49 at the time. After making a record setting cross country flight from California to Washington DC, the crew left the aircraft alone and unguarded to attend some ceremonies and a dinner. They were to fly back the California and attempt to break their own record as a demonstration of the aircrafts efficiency. Shortly after take off they developed some engine problems and upon making an emergency landing, discovered some empty oil tanks. He stopped short of claiming sabotage, but said there was no real reason for the tanks to be dry, and that he regretted leaving the airplane alone in Washington!  I think all that stuff could make a great movie plot!
  Type at you later,
   Dan McEntee

[Chuck_Smith]

     I have always been fond of flying wings, and built gliders in that configuration as a kid, and hope to some more in retirement. I have read a little about how hard Sen. Stuart Symington worked to get the Northrop Flying Wing eliminated from the bomber competition in the early 50's. Some where in my collection of stuff is some newspaper clipping of the time that I found by accident in some books or magazines I bought. I need to find those again some time!  Symington represented my area here in St. Louis, MO and as I remember it, Symington fought hard for Convair because a fledgling little aircraft manufacturer back home in St. Louis called McDonnell Aircraft was a subcontractor for Convair in those days. Then when the B-36 was chosen, he went as far as to make sure that ALL of the existing YB-49 airframes be destroyed so they could never fly again. I understand that there was a lot of back room dealings and hard nosed politicking going on about that. i also saw an interesting interview with Bob Cardenas, who I think was chief test pilot on the YB-49 at the time. After making a record setting cross country flight from California to Washington DC, the crew left the aircraft alone and unguarded to attend some ceremonies and a dinner. They were to fly back the California and attempt to break their own record as a demonstration of the aircrafts efficiency. Shortly after take off they developed some engine problems and upon making an emergency landing, discovered some empty oil tanks. He stopped short of claiming sabotage, but said there was no real reason for the tanks to be dry, and that he regretted leaving the airplane alone in Washington!  I think all that stuff could make a great movie plot!
  Type at you later,
   Dan McEntee

I've seen and read some of the interviews but in reality, the YB49 was a flawed concept and merely an attempt to keep the funding from the YB35 going as an interesting science experiment. There was no way that thick flying wing was going to be relevant in the jet age and transonic flight for bombers.

The B47 was 100mph faster and cruised at a higher speed than the YB49 could muster flat out.  It was more stable and a better bomber. Heck, they were operational into the 70's.

And don't forget the B52 was coming down the pike in 1952. That's still the gold standard.

Even the B2 was only an experiment in low RCS and a symptom of the Reagan era love of throwing money at defense programs like Star Wars or the F117 (how long did they last?)

[Serge_Krauss]

Thanks for the input, Dan. I knew about the efforts to get the B-36 chosen. I understand that it had many problems, but did not know/remember the conflicts of interest.

Chuck, thanks too. I would comment though that I don't see the lack of jet power as a "flaw," since the plane was developed to be implemented during the prop age and have a huge range at speeds near those of then current fighters. When development/contracts lagged and the war ended, the jet age caught up with them. Jets ruined the range advantage. The reason I mentioned the Horten lift distribution is that it could provide "pro-verse" yaw (I think that NASA's Al Bowers coined that term; I heard it first from him), which would have cured the yaw problems, perhaps at a drag penalty. I have read varied assessments of the seriousness of the yaw problem, some saying that it was minor. Pitch steadiness was addressed among Northrop's patents, and if these were not sufficient to have cured the problems (I read that they were still to be implemented),  I wonder whether among the multitudinous Sperry patents there might have been a solution. Northrop patents in auto-stability devices were prominent, if I remember right without going through them.

[phil c]

I acquired a ship that had the outboard wing panel with a built-in twist up. I added a tab/wedge under the outboard wing to level the wing. This worked but the ship seemed to be doing rather large loops (65 - 70deg ish). I was wondering if the area with the tab/wedge was just coming along for the ride and not contributing to carrying any weight through the maneuvers?

Best,   DennisT

The description is a bit foggy.  A "Twisted up" right wing usually refers to the trailing edge being higher than the leading edge, rolling the wing to the right.
You can't make a twisted wing into a  straight wing with tabs.  Small warps can be counteracted by putting a tab on the top of the left wingtip in this case making it have a better balance of lift.

The only way to really sort things out is to twist the right wing straight until it balances with the left wing.  If it's already crashed.  Build a new wing.

[Trostle]

Something to consider:  Put equal size trim tabs on the TE of both wings, both to counter the warp in the one wing.  Will help neutralize the drag of just one trim tab on one wing.

Keith

[Scientifiction .]

I find if you set it on a packed plank , outdoors over a few nights , with a board with a few packers / spacers etc , and a car battery or suchlike on it , the moisture cycles free it off & hold it set .

A nasty one , take it equal opposite twist , as itll ' come back ' a way over a week or so . GENERALLY  ' Butrate ' dope in excess & huridly  has a bearing on the cause . Can take years to ' gas off ' fully .

[Tim Wescott]

I find if you set it on a packed plank , outdoors over a few nights , with a board with a few packers / spacers etc , and a car battery or suchlike on it , the moisture cycles free it off & hold it set .

A nasty one , take it equal opposite twist , as itll ' come back ' a way over a week or so . GENERALLY  ' Butrate ' dope in excess & huridly  has a bearing on the cause . Can take years to ' gas off ' fully .

That sounds like a good thing to try.  It certainly works on bare balsa -- whether to turn straight wood into bent, by storing it wrong, or to turn bent wood into straight, by storing it really flat for several months.

[phil c]

     I have always been fond of flying wings, and built gliders in that configuration as a kid, and hope to some more in retirement. I

It's sad to see that air combat doesn't just occur in wars.  Just like today. the political conflicts can be just as dangerous.
The current election is wrapping up with a lot of vote count raggeling.  Very few nominees will be able to claim clear cut victories.
Regardless of the law there is too much monkey business going on.

[Brett Buck]

Even the B2 was only an experiment in low RCS and a symptom of the Reagan era love of throwing money at defense programs like Star Wars or the F117 (how long did they last?)

     I don't know, my part of it was designed for a mean mission duration of 7 years, started fielding it in 1994, sounds like 4x to me, and with no clear end in sight.

    Another ex post facto defense expert...

    Brett