I am considering the GP Extra300 .40 size and I have heard several threads including losses due to tip stalling. I think I understand the need to not induce too much up elevator at slower speeds but is there anything you can do to a kit in the building process to limit exposure to this problem? Without increasing wing area, is there a modification that has been successful in decreasing this nasty occurance?

do not induce too much elevator at ANY speed. Make sure the CG is CORRECT. Even if it's specified at some point behind 25% MAC, I would still start at 25%.

You can always build the wing with a little washout in it. That is, the tip of the wing is nose down compared to the root. This will help prevent tip stall by allowing the root to stall first.

Dr.1

GP has a tab-n-lock system for positioning ribs (so a flat symetrical wing is built); is there a preferred way to induce this washout so just the right amount of nose-down outer rib is produced?

Washout will make the wing root stall before the wing tip. This will make the plane easier to fly - UPRIGHT. When inverted, the tip stall problem will be WORSE with built-in washout, and as mentioned in post #2, this type of aircraft can stall at any speed with enough elevator deflection.

It depends on what type of flying you are going to do with the Extra. It is designed to be symmetrical; to fly upright/inverted/knife edge without problems. Building in washout might ruin some of the flight characteristics when it comes to aerobatics. Outside loops, or negative G maneuvers in general, can be a problem.

another trick is to be sure to sand the leading edge very carefully, making extra sure that it is round and the radius is as large as possible. You can let the radius tighten up near the wing root then the root will stall B4 the tip. Also, when covering, make the outside half of the wing all one color with no trim strips, letters, or other roughness that would trip the boundary layer.

Another thing: wipe off all the hanger dust before you fly it...that's why they de-ice airliners before they take off.

Actually, tripping the boundary layer to turbulent flow could help prevent flow separation. You could use turbulators on the outer half of the wing (strips of map tape or glued-on monofilament line just back from the leading edge on both top and bottom).
It couldn't hurt but still might not solve the problem.
Allan

An old trick was to glue about 6 to 10 inches of 1/4" balsa triangle stock to the leading edge, at the root. This sharpens the L.E., causing it to stall first and "hardest" at the root, instead of at one tip or the other. Mooneys and Cherokees are examples of full-scale airplanes that employ this trick.

Now here's a new trick, from the age of computer radios. I'm assuming your area of greatest concern is the landing. (For aerobatics, you'll be higher and have more time to save it, plus it's nice to have the ability to snap-roll easily on cue, whether upright or inverted.) For landing, all you really want is for the wheels to hit the runway first -- preferably at about the same time. So try this:

Use two separate servos for the ailerons, and rig your radio's "Flaperon" function so that you have a landing mode. That would be a slight amount of down flaperon (call it 1/8" to 1/4" deflection, measured at the T.E.) and a slight amount of up-elevator trim (call it 1/16" to 1/8", fine-tuned through flight testing) to compensate for the nose-down pitch that the flaperons will cause. On the JR systems, you'll be activating the flap switch and also the flap-elevator mix ("F-E" mix) function. So for landing, all you need to do is hit your flap switch before entering the pattern, and carry a couple of clicks of throttle until just before touchdown. The glide will be steep and slow.

For this to work, your ailerons have to end short of the tip. You can easily modify the kit if it's designed with "strip" ailerons; you'll just have to increase the total throw a little bit to make them as effective as they were before. I'd say make the ailerons end at least 3-4 inches inboard of the tip. What happens is, you'll hit the landing switch, then the inner part of the wing will take a slightly increased angle of attack due to the drooping of the ailerons. The tips, which aren't affected by the landing switch, remain at their original angle of attack. The difference between the two is washout ... now you see it, now you don't!

Very interesting.... I believe the ailerons are out to about an inch from the tips.... I will give the plans the "once over" on this when it gets here..... I like the idea; just wonder how much computer I need to learn. I fly with the Futaba 6XA. Also, I wonder what the wing loading would be with an aileron in each wing? Something to think about.

The extra servo adds 1-1/2 oz maybe to the plane.. out of the 80 oz plus weight, it's of no significance.
THE most important thing to do with this type of plane is to keep the landing speed higher than normal.
That alone will keep it out of the tip-stall area.

The best aerobatic planes are inherently unstable. I still have a Yellow Cap 10 B., well actually on my third one. It will do two lomcevecs pivoting on the wing, one on top of the other then go into a knifedge spin,if you hold the same controls in, with the wing perfectly vertical and the fuse spinning around it. Never had another plane come even close to the aerobatics. Yet when you put the flaps down for landing it's a *****cat.

One fix not mentioned -and the most important one
sand every part -reduce every part to minimum weight - seriously
The real problem has NOTHING to do with airfoils at this size
the real culprit is simply weight
At this size it is simply impossible to make the plane as light as required for really good low speed performance.
Sorry about that - but that is the real problem

Certainly less weight is better but to say that this is the ONLY issue is patently absurd.
This isn't one of your little foamies, Dick.
Allan

You apparantly think I only fly foamies --
Not so - I am familiar with this particular model
It is very difficult to get weight in line with it's size.
Also - I am more firmly than ever , convinced that weight is the prime cause of problems like this
You can twist in tip mods - add flaps -etc.,
None of this will make any notable difference .
If the model is straight and balanced -then speed will keep it controllable .
Slow it down and it will trip you up.
Theory is fine -and I do understand the theories put forth.
In this case tho - we are caught with simply a high wing loading.
You might want to go to Kirby Chandless'web site and look at the comments made by the team on wing design.
The info there is very applicable to models .
As for the foamies
Did you ever try them ?
They can provide a lot of info , applicable to larger craft

Another example of a commercial kit that is engineered to,"crash well". Overly built and under engineered, any fool can make 5 pounds of wood do 5 pounds worth of work, the trick is to make 4 pounds of wood do 5 pounds worth of work.

It would be interesting to build a redesigned wing, without as much "triple taper", as well as look for places in the fuselage where dead, fun robbing weight lurks, then see what we have. If you get the mix right, ailerons rigged to act as flaps that are coupled to the elevator can improve low speed stability, but if you're over weight, they can exascerbate the situation too.

Dick Hanson wrote.... You might want to go to Kirby Chandless'web site and look at the comments made by the team on wing design.
The info there is very applicable to models ....

Dick, you might want to enlighten us with this website... or is this just name dropping?
Allan

Name dropping?
why in the name of ----would Ido that?

What is so hard to swallow about DICKs' advice? If this plane was built light enough, [inspite of it's inherent design flaws that don't scale down well], the low speed handling problems go away. All the other "fixes" are gimmicks that only postpone the inevitable. On this .40 sized model, the outer 15% of each wing panel is just going along for the ride at landing approach speed, and at the weight it is being asked to carry.

For those who actually give a rat's ass about aerobatics - go to Kirby Chandliss' site - Red Bull Co pilot page - watch and listen to the info and demos of why the plane is like it is .
I really can't understand why those who profess to have an extensive formal background in why things fly - can't understand that the "fixes" on many full scale planes --simply do not apply to these small slow models .
The business of the leading edge shape - sharp for snap -rounded for smooth flying -is simply not applicable - look at the best full scale aerobatic airfoils -if you still doubt this
One more time -for good flying models of this size --it is ALL wingloading and power --everything else is compromise .
Some wag once said---
Don't let education get in the way of garnering knowledge.
Don't get upset - just go take a look
If the info provided on Chandless'web page is of no help in your understanding aerobatics - I will be surprised

Is this the site? www.redbullcopilot.com [&o] Oh, I can't get into it. Uncle's computers are slightly outdated.

Yes - wait a few seconds till the display comes up in centre of page which says the PLANE- open that .
Then open the commentary and video on wings/control surfaces etc..
Note the wing leading edge profile .( for the doubters out there).
Let me know what you think of the information .
worthwhile?

http://www.redbullairrace.com/
That's the link to the Red Bull website, for anyone who might want to peruse it. Forget doing a search on Google for "Kirby Chandliss" because you won't find it that way.
No thanks to Mr. Hanson, who seemed unable to ACTUALLY include a useful LINK to it.
On the site:
I didn't exhaustively explore everything on the site but did not find anything of use to a model airplane designer (certainly not like those sites dedicated to model aeronautics). Maybe I missed the good parts - and now Dick will be so kind as to provide the specific links and instruction to all this golden information?
As for the advice to eliminate weight, sure it will help but only in proportion to how much one can actually lighten the plane. Afterall, this model (GP Extra300 .40 size) is a KIT so what can you do, buy your own balsa and start over? You might as well get some plans and build from scratch. If you can get a few ounces out, yeah, it will be better - but only marginally and that's all you would expect from any of the other "fixes" suggested.
I think people should not get their shorts all in a knot just because someone questions their favorite "truths".
regards,
Allan

okay,
After I posted my last message, I found Dick's latest
>Yes - wait a few seconds till the display comes up in centre of page which says the PLANE- open that .
Then open the commentary and video on wings/control surfaces etc..
Note the wing leading edge profile .( for the doubters out there).
Let me know what you think of the information .
worthwhile?<
So I went there, and did that. Talk about a useless site... gee did you all know that the rudder makes the plane TURN, and the elevator makes it ROLL.
wow.
Newly informed,
Allan

correction for my mistyping, the ailerons makes it ROLL
A.

My my -
I thought you might like it -
How was I to know (based on your comments about turbulators ) that you already were deeply versed on aerobatic craft.
Sorry I mentioned it.
So - to the original query- forget the weight comments -- I was wrong -