Aerodynamic Balancing

[Ken Culbertson]

I have reread Dave's article link below from an old thread.  Typical of everything I do, the stab configuration I an considering is the only one not listed in his testing and results.  I am considering adding balancing tabs (aerodynamic balancing) to an airfoiled stab.  A "C1" in the article.  I have had them on two planes in the past, a Spitfire and a Chipmunk but that was so long ago that I am amazed I even remember.

I am assuming that they will improve cornering but will it be at the cost of the other characteristics or will it add to them and if I go ahead will the square Chipmunk style or the angled spitfire tab be better.

Also, that article is 20 years old.  Have we learned anything since then that makes it any different today?

Thanks - Ken

https://stunthanger.com/smf/open-forum/copy-of-the-david-fitzgerald-article-'de-tails'-from-the-marapr-98-stunt-news/msg511851/#msg511851

[Allan Leonard]

Are you expecting the elevator to be a little heavy on the handle? Interesting.

[Ken Culbertson]

Are you expecting the elevator to be a little heavy on the handle? Interesting.

Yup, that and curiosity.  If they reduce control pressure and improve cornering then why are so few fliers using them except on semi-scale like the Spitfire?  If the consensus is they are a good thing then I will add them. 

ken

[Vitalis Pilkionis]

This is the model of chinese pilot Jun Yang, who ended 5th at 2016 WC in Perth, Australia. As you can see it had quite a big balancing tabs on elevators.


Regards,
Vitalis P

[Ken Culbertson]

This is the model of chinese pilot Jun Yang, who ended 5th at 2016 WC in Perth, Australia. As you can see it had quite a big balancing tabs on elevators.


Regards,
Vitalis P

Your picture did not come through.  I was able to find a YouTube of his flight.  The plane does corner well.
Thanks - ken

[Steve Helmick]

Since the flaps cause most of the control pressure (putting your model closer to the much feared "Netzeband Wall"), I'd think it makes more sense to start there. Howard did his "servo tabs" for awhile...looked cool, but neither Howard or Paul (who sometimes takes a flight on Howard's planes) will say that it definitely helps...or not. IMO, the aero balance tabs on the end of the Chimpunk (sic) elevators are likely to be a PITB, plus add weight aft of the CG, and get broken off at an inconvenient time. I seem to recall somebody saying that these tend to make the "stop the corner NOW" worse. I think that's more important, as long as you don't get too close to that Netzeband Wall.

I wouldn't do it! I would look very closely at what Paul has detailed on his recent stabilizer LE shape. I think it starts as 1/2" thick per the Impact (for structural stiffness, which is crucial) and has a very sharp LE over the front 7/8" from memory. He may have posted this info here on SH or SSW, but I seem to recall it from facebook in the Alberta Controline Flying Club website hosted by Bruce Perry. There's a lot of excellent info posted there, for all skill levels. I honestly don't know how to do a search or look for archives there. Fun place, too. Unfortunately, I think you may need to join facebook. But all the big guys are there, including Chris Cox.        Except Howard, who doesn't do facebook. Possibly Mary Lou won't allow it.  Steve

PS: I am barely a user of facebook. I joined only to use the ACFC site. Then the PAMPA and NFFS sites  came along. Unfortunately, one of my fishing buddies seems to spend all his spare time on there, mostly forwarding AOC and USMC stuff. Lookout for hot babes wanting to be "friends" with you. I'm not sure what their reasoning is, but DON'T just accept "friends" without investigating them. Look at their page and "about". If there is nothing there regarding who they are, where they are, where they work, and what sort of model airplanes they fly, 86 their request!   

[Steve Helmick]

This is the model of chinese pilot Jun Yang, who ended 5th at 2016 WC in Perth, Australia. As you can see it had quite a big balancing tabs on elevators.


Regards,
Vitalis P

Probably the file size is over 1,000kb? I have found previously that the title of a file adds onto the file size and is not included in the total shown when you put the cursor on the file icon. Not logical, but there it is.    Steve

[M Spencer]

Having used these on a good few planes ,

Im thinking they ( Elevator ' Ears'  ) give a more ' finger tip ' style of control , in calm conditions .

In Severe steady winds or turbulent bumpy air , they ' steady up ' control input ,
and maybe even ' downhill ' in loops , around the 3 - 4 O'Clock posn. , help it conter gusts ,
as in it blows into / holds - the turn . Rather than the gust opening the turn .

All have been on thinish  Airfoiled Tailplanes. Elevators Actually . 'V'ee ones - Triangular even .
Nose Follows Stab. Conture- section - airfoil . BUT ; Mine generally have inlaid 1/16 ply , main grain  longitudeinally.
at the center of the sheet .

I.E. for a 1/4 Sht. ( or 3/8 , 1/2 etc etc . ) a razor saw then hacksaw blade , on the centerline . Almost as the first opperation , on ' The Blank
Maybe a folded fresh sandpaper through  , or on a ruler . Ea side . Elev on bench . . You can do it later. of course . Last thing even .

These dont really help you in unflyable conditions a lot . Still the G 51 71 Oz Spitfire , in a Gen U Wine 20 Kt. ( or 25 ) Steadyish wind
with only the odd hole blowing through , the 25 was a 15 to 25 ' lighter ' wind , as it wasnt the glued to the ground cold ocean air ,

' The .018 Laystrate would twang and shiver on the square bottom corners , and be stretching across the way through the bottoms , Sq. & Round . So I consider they do help keep the plane on track . Along with the Heavy Pushrod ( 1 1/2 Oz. - as a ' dampener ' ) and the ' Y '
reversed bellcrank where one line is a anchor & ' the operating ' line is less loaded thus more dialable .
As youre hanging on both hands , at times , in those conditions . Kicking the heels into the deck to avoid sliding on the damp grass / earth ,
and leaning back away .  ( Bellcrank just a enlarged to 4 in. Brodack pattern . so  10 mm negative leadout ofset to mounting bolt )
The Ship Itself .

Later fitted Irvine 40 & 10 x 4 three blade , in an endevour to stabilse in big howling roters of wind . ( The Field was adacent a Yacht Club ).
On the third flight , going like blazes , ' That Funny Noise ' in the engine , was the pushrod end , where it'd cracked . As it pulled inverted out of the 2nd wingover corner hard- broke , nosed down , lifted , and , . . . noseded down . And ploughed a trench .
Detaching much of the outer wing .
A further 20 minutes with a disc grinder , due to spruce spars 7 ply reinforcing / gear mounts etc . to cleanly remove the then diheadraled wing. From the undamaged fuse . Anyway , this is its replacement wing . The Same . Another new , in the corner of the shed. Unused as yet.
And a Aerodynamically Balanced Tailplane Assy. on the shelf. Amougst others . The De H 88 & Mosq. hadem too.

[M Spencer]

NOW ;

Increased Airfolw = Inreased Load across the End of The Tailplane . And Elevator . So they NEED TO BE STIFF .

Most Wood in that was Stiffer  than you blokes'd used . Typically 7 - 11 Lb Ft . Still tho , the Complete finished Fuse And Empenage weighed 11 Oz. AFTER the Wing had been ' Removed ' . Sans Pushrod . 

Tailplane & Flaps were some 1/4  New Gunea Jungle Wood close grained dense stiff quater grain . & still not that heavy .
Better bening resitance than 3/8 or 1/2 4 - 6 Lb wood . AND Twist Resistance .

Which Brings Us To , ' SLOTTED TIPS ' .

Those on the Hurricane , Typhoon ( Shown ) and Tempest , The 1/8' Dia L.E. Rad of the Elevator Extensions ( at the outer ends )
which are 1/2 in extra chord thus  just on 9/16 Fwd. of the Hinge , only start to protrude above the tailplane surface ,
Near Full Deflection .
Obviously in the Sqare ( And Emergency  ) Corners .

Acting as ' a Slot ' Or Similarly to Blown Control Surfaces .



You can just about se them here , when its ' enlarged ' .

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I believe , under severe loading , they ' Hold ' The airflow stabler . thus help control authority . If the whole bleddy things stiff .
( otherwise its liable to start walking , twisting , shifting , & jumping . Locationally ! )

Thus the Aerodynamic Balances , which is wot we ARE dicussing ? ? , Act Similarly . As well .
And have similar constructional requirements .

A bit of soft spanwise grain 1/4 Sht tacked on & monocoated , isnt really likely to be up to much , there . 

[Howard Rush]

Steve’s got it. Flaps are bigger and operate farther from their float position in turns than do the elevators. I’d suspect them to be the main contributors to hinge moment. PJ and I used servo tabs to reduce flap hinge moment. That works, but I came across an old NACA report that showed them being most effective near neutral, which isn’t what we’d want. They probably don’t benefit an airplane with adequate bellcrank movement. Igor’s system is good about giving you leverage over hinge moment at high flap deflections. That’s what’s in my current dog. I might try servo tabs again if I can figure out some linkage that gives them less (or even opposite) travel near neutral.

Putting some control surface area in front of the hinge line is appealing because it’s light, easy to do, and doesn’t add friction, but it can cause evil, as it did on a particularly dumb application by me in 1961.

Another way to look at aerodynamic balance is that for an airplane that needs ballast to get to the “sweet spot” Ken was discussing, aerodynamic balance would reduce the amount of ballast needed.

[Vitalis Pilkionis]

Your picture did not come through.  I was able to find a YouTube of his flight.  The plane does corner well.
Thanks - ken

I'v managed to attach pictures only today. I am sorry, guys, SH server is a bit slow recently.

Regards,
Vitalis P.

[Ken Culbertson]

I might try servo tabs again if I can figure out some linkage that gives them less (or even opposite) travel near neutral.

Putting some control surface area in front of the hinge line is appealing because it’s light, easy to do, and doesn’t add friction, but it can cause evil, as it did on a particularly dumb application by me in 1961.

Taken to extreme the "flying stab" used on full scale aircraft is probably the most efficient.  I messed around with that concept in the late 60's with mixed results.  Pivot point too far forward and the force was worse, too far aft and you got flutter and an exercise in rebuilding.  It did produce superior turns but was totally uncontrollable.  Never tried the servo tabs, in fact this is the first time I have heard of anybody using them.  Seems like I missed out on all the fun stuff.

So, the question becomes, since both appear to work, why is no body using them?  I can think of only two reasons, one that they are difficult to build and the other is that the same effect can be achieved by simpler means.

Ken

[FLOYD CARTER]

Check the stabs on combat planes.  Hinged at L.E., so no "tab effect".  No need for dynamic balancing as long as line tension provides enough bellcrank force to move the elevator against air resistance.

My Hurricane stunter had elevator tabs, but not sure if it did anything.

[Howard Rush]

So, the question becomes, since both appear to work, why is no body using them? 

I think we've given some general reasons why nobody is using them and have come to the point of diminishing returns on detail.

People are, however, as you saw above.  Here's an example I saw at the NW Regionals Saturday:

[Curare]

I'm assuming I'm looking at a Profile Edge 540, so in that instance is it fidelity to scale or aerodymanic sorcery that sees them on there?

[M Spencer]

You could put lead in the nose of them , so they were statically balanced , weight wise . Like a prop about its axis .

The big contemplation has me believing the aerodynamic balance , if adequate area ,
Like the ' locked in ' bit -
has the CONTROLS more ' locked in ' .
Thus a steady hand is required , as the plane will more redilly act on the controls .
Thus deviates from path more redilly . So its less ' locked in ' to the groove , than without them .

Id still maintain Fast Hand Luke could more redilly maintain course - through the manouvers , in gusty / turbulent air , with them .
Though the Average Joe isnt a Grand Prix driver , and may not be ' on it ' sufficently to benefit . In Fact theyd be detrimental , like touchy steering on a overloaded dilevery van .

[Russell Bond]

How about having the elevator hinge-line tapered forwards same as what some people do on the flap hinge-line? 
What would that do and has anybody tried it to see what happens?

[PJ Rowland]

Howard.. I semi solved the problem around neutral by gearing the flap tab to be VERY low gear. At 2mm deflection + and - the tab hardly moved..
It got to the point where you would gear down so far the few times in a tight corner you did get good response sort of outweighted the silly things it would to to trim in certain spots..

Added weight...

I finally decided to no bother using them in the last ship.

I was doing tests of back to back fixing them and engage.. Its such a minor minor feel difference when geared low..

Geared high do cause trim issues in roll and yaw .. I would twst trimming them at different throw angles to eachother..

Again.. if I really felt like there were signifigant gains id keep going.. but with stiff flaps and solid control systems / engines im not convinced " stick pressure" is real enough to bother to "counterbalance"

I do think out of trim models can exhibit bad stick pressure..