I am in the process of tweaking and fine tuning the setup on a BVM Maverick that I have converted to Turbine power. Along with the conversion I added about 6 to 7" of wing span on to each wing panel to help carry the added weight and to make it a one of a kind unique airplane. This is the second Maverick that I have converted and added wing span to and the first one flew like a dream in all respects with a fairly mild drop of the right wing when stalled. This stall occurred at a quite low airspeed and was not a factor during normal flights.

The new airplane also flies on rails and quite well but likes to try to drop the left wing at speeds when I don't think it should be. This new airplane is on the heavy side (why Im not completely sure) but it is still within a reasonable flying weight for an airplane with this much wing and and having a thicker airfoil than other airplanes of this size and style.

My goal with this airplane is to get it to stall straight ahead and at a reasonable airspeed. I made three flights last Sunday and did some stall tests at high altitude and regardless of flaps up, down part way or fully down it always falls off pretty hard to the left. Where this becomes an issue as you might guess is on landings. When breaking the sink and transitioning to a nose high attitude for landing if I get a little aggressive or rapid with with up elevator inputs that left wing will try to drop at a speed where it just shouldn't be and makes for some exciting and ugly landings.

After last weekends flights I added three separate chunks of nose weight each weighing about 2.5 to 3 ounces for a total of about 8 ounces. I did not actually measure the effect of how far this moved the CG forward but having a fairly long nose it moved it a fair amount no doubt. I also programmed the ailerons for crow operation.

I made the first flight with the full 8 ounces of lead and some up high stall tests and it still fell off on the left wing but at what seemed to be a more reasonable speed. Landing was much more solid but had some trouble getting the nose up very much for landing. I just remembered I also increased the flap deflection at full flaps a bit from the previous week. After the first flight I increased the upward crow defection a bit and took out 3 ounces of lead. Stall was still the same left wing drop at the same reasonable speed. Landing was still kind of flat and did not get the nose much above level for touchdown. All in all Im on the right track it seems.

For tomorrows flight I am going to take out one more 2.5 ounce chunk of lead.

The only other thing that I am contemplating doing is adding a small stall strip to the right wing only to see if I can get it to stall at the same time as the left wing and therefore fall more or less straight ahead. I have never done this or heard of it being done and Im wondering what the everybody thinks about this idea. Obviously a better idea would be to get the left wing to delay stall until the right wing stalls but I don't quite know how to do that ? And whatever I do I don't want to disrupt the way it flies otherwise in clean high speed flight. For an initial stall strip I cut a 4" length of brass tubing about 3/32 diameter and taped to the leading edge of the right wing about 5 or so inches outside of the wing root.

The good news is im flying off of a vertically unlimited length of asphalt so if the stall tests at altitude don't go well I can always land fast and just let it roll.

One thing that I have not done is check the airplane for lateral balance but my guess is its not to far out of balance. I will try to check it later tonight and so what I find.

Im open to other ideas thoughts and suggestions.

Brian,

Lateral balance would be a good check to make. I would think added nose weight would aggravate the stall needing more elevator to lift the nose, I might be wrong there.. Your flight testing and theories seem sound and I think you are on the right track. I would only make one change at a time so you know what helped. What is your reason for the brass tube on the right wing?... To induce a stall sooner on the right side ?? If so, that will do it !! I know it will work. You can tape a broom stick across the leading edge of a C-172 and it will not fly.


Danno

Sounds like you are doing all the right things. A heavy loaded plane will stall that way. You could try a Aliron gyro. I have been using them for years on all my planes. If now that you are moving the CG and the plane lands nice then you might have to live with it. One thing to ck is your elevator travel. I set mine so during flair the stick is almost at the stop. If you have to much travel the plane is snapping. Good Luck Dan Avilla

Good comments on checking lateral balance and such. That's the first place to check. But the wing still stalls akwardly, correct? Before trying to induce more stalls in different parts of the wings with stall strips, I would suggest trying to tame a stall overall by another wing mod (since you've already modded it once, what's another mod?? ). You mentioned that you added crow, and that's one way to try to force the wing center section to stall first but you still have some sporty behavior it seems. Lateral balance, longitudinal balance, control deflections checked.. it's time to try something else.

The first thing that popped out at me was that you extended the wing length. One thing to consider is that when designing aircraft, there are many competing and complicating factors in aerodynamics that steer engineers to do what they do. Some of the more basic choices are wing planform (swept, straight, tapered, delta) and along with planform basics we also have airfoils, blended airfoils, washout, leading edge radius modifications, flex patterns, etc. Then we have weight and wing loading. And it goes on and on but those are basics. Each of these choices can have drastic effect on lift and drag in different phases of flight, stall behavior, etc.

So you were entered into the game when you added wing span. I know you wanted more wing area, but by adding wing length you also changed the wing planform by increasing aspect ratio and reduced the wing tip chord. A swept and tapered wing with a high aspect ratio and a narrow wing tip chord by definition stalls at the tip first. This is an elemental behavior of this type of planform. BV probably designed the Maverick with the smallest tip chord he could get away with while retaining good handling. He probably was taking advantage of the efficiencies that higher aspect ratio wings enjoy (reduced drag) and was also able to squeeze in a little bit of sweep without hurting the stall behavior too much (wing sweep in model airplanes is mostly a stylistic or CG placement treatment only, it usually takes away from sub sonic control / performance).

One idea is to add some wing fences - a-la Mig 17. This will help tame spanwise flow around the wing tips and probably delay the stall out there by a few miles an hour.

The main feeling I get however for a more permanent fix to this dilemma is this: You could add a drooped leading edge cuff from 1/2 span outward. It's essentially something like a small dog tooth. The leading edge will increase in chord at the dog tooth and also provide camber so that the stall in the outer wing area will occur at a much higher angle of attack from half span outward as compared to the wing root. As a benefit, with a swept wing, if your root stalls first you will get a natural nose pitch down moment to aid in recognition and rapid recovery before the model is in a deep stall. Though at a greater cost in time/effort/high speed drag than a quick lateral balance/CG balance/Elevator deflection mod fix, a drooped outboard leading edge mod is probably the most SURE FIRE fix. Since you have turbine power, I generally don't think you have to worry about top speed being too badly effected by a leading edge droop mod and the extra wing area and stall protection it will bring will get you want you originally wanted with more wing area.

Dogtooth:
http://en.wikipedia.org/wiki/Leading-edge_extension
http://en.wikipedia.org/wiki/Dog-tooth

Leading edge cuff
http://en.wikipedia.org/wiki/Leading_edge_cuff
http://arc.aiaa.org/doi/abs/10.2514/...journalCode=ja

For $25 this is the best deal in the business if you are messing around with modifying or designing model airplanes (don't spend $100 at Amazon...) This book will show you how to do these things on model airplanes and how to stay away from a bad mod or fix one. Not construction advice, more of what to build to make a model fly well. How to build - you already have that figured out.
http://www.airagestore.com/books/pla...ft-design.html

The only way to eliminate tip stall is in the wing geometery and airfoil design. A good flat bottom at the wing tips and 2-3 degrees of washout will do it.

Eddie P,

Very informative !!! I am having some of the same issues (I think, haven't flown the model yet, but hearing the stories associated with this model. ) Skymaster Hawk 1/5.5 scale. One of the earlier versions. Funny you bring up wing fences.. Some of the hawks have them and some don't. I am really thinking about putting some on there because of this exact issue. Also ventral fins.. Some hawks have them, this one does not. I would sure like to hear your thoughts on my problem. I too am thinking along the lines of reflex and crow in the ailerons. I will PM you and give you my e-mail and phone #. Please call me if you can.. internet is hard sometimes.. Looking forward to the visit !!!


Regards,

Danno

Just a couple observations about your efforts with this modified Maverick as I have an unmodified EDF Maverick that is roughly 15 1/2 lbs RTF and  has lasted me for quite a few years:<div>1) Leading edge droop - this actually was a BVM available mod for the Viper and Maverick during the nitro days with these models. More forgiving low speed handling with some sacrifice of top speed. I don't find it to be necessary.</div><div>2) Crow or aileron reflex - remember that unless you did a bigger mod than just extending the wingspan, the ailerons are really "mid-wing" (more so with extended tips) and don't extend to the tips. Thus the crow or reflex aileron still does not alter the effective AOA at the wingtip no matter what.</div><div>
</div><div>Mine has flown for years with good behavior when the CG is at the BVM recommended point, not forward and not aft. When I tried a more aft CG the stall behavior tended towards a pronounced wing tip drop.</div><div>-Mike</div><div>
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Was the original wing built straight and symmetric. And the same questions for the extensions? Sounds basic but a lot of building surfaces aren't straight and people had no idea. Marble slabs and pool tables provide the best foundations for a good true wing build.

Plus one, sums it up well.
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I'd suggest contacting BVM to see if any of the Leading Edge Droops are still available. These were made from molded stryene and were designed to be mounted with double sticky tape. Also verify the CG and throws provided on BV's website: www.bvmjets.com. Note that the Maverick was quite critical on the CG and elevator throws especially when fully fueled. I build and flew one of the early production models for about a dozen years- a great flying jet, even if a glo/nitro DF.

Art ARRO

Or other thing to check is rudder trim. Airplanes will drop to the deflected rudder at stall (assuming everything else is straight). Even a very minor deflection (undetectable to the naked eye) will cause a roll off to that side. Just for grins put in a touch of left rudder trim and see which way she breaks. A lot easier than cutting up your wing etc

Dave

Excellent point !!! The rudder... The most forgotten and least used control surface in R/C..


Danno

I have used stall strips of sharp triangles next to the wing root with good luck.
Tape on to see first.