I finally got my edge into my shop this last weekend for some touch up work to solve a few issues I had been dealing with for a while. My edge, formerly a little tail heavy (pre slimline muffler) became nose heavy (post slimline muffler) and I was having some trouble with it tip stalling and rocking badly in harrier and elevator. This was after a crash so I was rather confused as to what I had screwed up...

I laterally balanced with 9 grams of lead on one wingtip to offset the repairs to the other wing. I also added 36 grams of lead to the tail attached to my tail wheel to see if it would help...

ROCK SOLID! I hit it perfectly this time! I did a harrier today, walling it in and getting the throttle right. With my elev full back and no ail use at all I let go of the throttle stick entirely and held the transmitter doing nothing except full back elevator and let it cruise for a good 3-5 seconds. It finally needed some steering and I had to stop playing arround... but it was still impressive as hell.

In adition to the better harriers its less tip stall happy. I can now transition from a upright waterfall loop into an elevator without scaring the **** out of myself. My father almost lost it when it tip stalled during a IMAC routine the other day and that was what decided to make me search for a cure!

I'll be moving things soon to get rid of that lead in the tail but it sure doesn't see it now.

Hope this helps some of you guys setting up for planes now! I'll get a CG measuerment next time I have the wings on in my shop.

-Ian

I think you are using the wrong terminology, it's unlikely the plane is tip stalling during any IMAC routine. If it was reall "tip stalling" changing the lateral balance would probably not help.

I think you are referring to "snapping out", a phenomena where the wing stalls during a maneuver because of excessive control input. This can happen on almost any plane if you use too much elevator.

It is fairly unlikely that everything will be exactly equal from one side to the other. There will almost always be some difference that will make one wing stall slightly ahead of the other. Or, in this case, even though they stalled at the same time the plane would fall to the heavy side. If it's during a loop, say, and the wing stalls the plane will appear to snap out of the loop by "falling" towards the side that stalled or to the heavy side.

By laterally balancing it you got the two sides very close to the same and now both sides stall at the same time. You still may be using too much control input and it can bite you later.

TF

Actually I think you missed the second part of my post. My aircraft IS snapping out aka tip stalling. A forward break in stall is a general wing stall but when an aircraft drops a wing its usually one wing tip stalling.

Now as for the part you missed. I dont think that the lateral balance did much of anything, I was just being a perfectionist and eliminating everything. What did the most was the CG change. On the edge, a nose heavy CG seems to result not only in horrible 3D characteristics, but also in an awful tip stall configuration, probobly having to do with the CG being signifigantly off of the center of lift.

As for my father snapping out of a split S, yes he was a little low and pulled too hard, but it was not even CLOSE to as hard as he should have been able to pull without any trouble.

I'll report back to tell if forward CG is universally (for edges at least) responsible for snappy behaivour. I have re-balanced chixwithtrix aeroworks 29% edge which has always had similar characteristics more tail heavy and we will see how it does.

I too have been battling similar characteristics with my Extra Special.
(I am running a Brison 3.2, and B&B smoke system, and I think I am ~17 lbs, rudder servo in tail)

I have noticed improved 3D flight characteristics, specifically with harrier/elevators when moving CG back too. The trade off I have found with aft CG, is that on a calm day, the thing does not want to land. (Running a MSC 22X8). I'm still dialing in that CG sweet spot.

An example: I have my RX battery in the forward area of the rudder servos tray. It wing rocks hard, and if you are not ginger enough on the elevator, going into a wall can cause a wing to snap (forward CG). I moved my battery back 3�, and we noticed an improvement the following flight. I then moved it back another ~3� and elevators were rock solid. The trade off of course was landing required a few go-around before it would descend. It just wouldn’t come down. I moved it forward since then. I plan to take the smoke out again to see how is the CG combo works with the CF landing gear W/O pants. Absolute take-off weight will also impact these performance characteristics.

We need a ballast on a track, controlled by auxiliary channel to change CG fore/aft in flight then we could have best of both worlds.

If your CG is excessively far forward, the elevator has to be trimmed to provide more down force. The wing feels this down force as extra weight, thus increasing the wing loading of the plane. The plane also has to fly at a higher angle of attack to compensate for the increased down force, thereby giving you less margin before you reach critical angle of attack (i.e. stall).

An airliner or cargo plane can actually get better gas milage loaded with an aft CG because the wing is carrying less weight.

There are other factors involved, but I thought this was an interesting note.

Man am I confused now.[sm=confused.gif]

ibange, I think you're talking about two different problems. The way I understand it (someone correct me if I'm wrong) is;

A "tip stall" is a slow speed problem caused when one wing stalls before the other. But it is the wing that stalls.

"Snapping" is altogether different. When a plane "snaps out" of a loop or other maneuver it's caused by the elevator stalling. It's a combination of too much speed and to much elevator throw. When the elevator stalls you loose both pitch and roll stability (because one elevator stalls before the other). The result is the same as performing an intentional snap roll (except for the surprise factor[X(]).

Two different problems, two different cures.

Sillyness....

Maybe Canadian planes got better fuel consumption at aft CGs. Depends on what you mean by Aft. 40% 50% ??

I was an Aircraft Loadmaster in the USAF for 25 years. For 24 of those years, I was responsible for the proper loading
of all the Planes I flew on. C-124s, C-123s, C-135Bs and C-141As. On all of those planes, the CG limits remained the same.
18 % to 34 %. Desired take-off percent was 30 %.
I have seen U S Airways ND 80s take off at less than 10 %. I have seen the British BME 146s take off at 46 %.

Even with all my experience, I do not claim to be an expert, but it seems to me, that if an airplane is tailheavy, you would
need additional power and some down elevator trim. Nose heavy would require more power and up elevator trim. Accessive
trim equals more drag, requiring more power to maintain planned airspeed, thus, poor fuel consumption. Some of our loads
did not allow for desired takeoff CG. (Missles, tanks, etc.) That's why T-tail Stabalizer/elevators that rotated came about. They
provided the trim necessary when desired CGs could not be met by non-normal loads.

I believe our RC models follow these principles to a certain degree, but I must admit that, beyond what I have noted, I am not
well versed on stalling. I know a noseheavy model will not do a good spin. I understand that too little airspeed will cause stalls.
I'll need to further my knowlege more, to understand tip stalls and snap outs.

Gerald

Hmmm... I am a USAF C-130 pilot on loan to Canada. It is in our USAF regs to load the aircraft toward the aft end of the CG envelope (which is variable between 15 and 30 percent based on gross weight and which fuel tanks are used) as part of our fuel conservation policy. We don't have a T-tail (thank God) and I'm sure our window is a little slimmer. The plane just flies better and gets up on step better and cruises a little faster with an aft CG. It's kind of a pig with a forward CG.

Big picture... with any normal airplane following the rules of longitudinal stability (as taught general aerodynamics courses) the tail always pushes down because the CG HAS to be in front of the aerodynamic center or the airplane will be uncontrollable (without a computer). The more nose heavy the plane, the more it has to push.

I'm still trying to figure out how a plane with zero incidence on the wing and stab can fly at a positive angle of attack... I believe it has to do with a shifted aerodynamic center. When I get more time I'll research that.

Oh... it's my understanding that a "Tip Stall" and a "Snap Out" are the same thing... one wing stalling before the other. Stalling is defined as exceeding critical AOA for a wing.

You can do this by slowing the airplane down until the AOA increases past its critical limit. You are increasing AOA as you slow to keep generating the same amount of lift. Lift = 1/2 * Coefficient of Lift * Air Density * Wing Area * Velocity squared. The coefficient of lift is dependant on airfoil characteristics and AOA. So, if you slow down, AOA must increase to keep lift the same.

Another way to stall is heavy elevator inputs at high airspeed (below cornering speed... you can look that one up in an aero text... I would need pictures). The elevator increases AOA, increasing Lift beyond required (thus inducing G forces). If you keep applying more and more elevator eventually you will reach a point (critical AOA) where you get enough flow seperation on the wing that it cannot produce any more lift. This is an accelerated stall. If one wing reaches its critical AOA before the other (because it is heavy, is mounted at a different incidence, has a different shape, etc etc) you will "snap out".

As far as I know, elevator stalling is not possible before wing stalling. In the Herc we can actually stall (or rudder lock) the vertical fin with excessive side-slip, and in T-tails you can enter a "deep stall" when your already stalled airplane gets to approx 20-30 degrees AOA and the wing blanks the air from hitting the T-Tail (yes I once flew a T-tail... ug). I've never heard of an elevator stall in an aerobatic bird.

The term "Tip Stall" originated with the glider groups of the 70's and is a misnomer. There are several type of stalls, but a "Tip Stall" is not any of them. A forward stall with a straight ahead break can be an approach or a departure stall. When one wing stalls, it is usually called an accellerated stall. Generally due to the increased AoA of one of the two wings. All of them are caused by increasing the wings angle of attack until airflow separation occurs. This can happen at any attitude and airspeed, which is one of the reasons the admonishment of "keep your nose down in the turns" came into being.

A heavy wing on one side of the plane will create the need for additional aileron trim to counteract the force of gravity for that wing, increasing drag. At the correct airspeeds and attitudes, this aditional trim induced drag will induce a stall for the one wing.

A sudden breaking out of a maneuver is called a snap, or cross control stall, and is caused by excessive or incorrect use of the controls. It's actually an accellerated stall, with an over the top break.

Hmm, no such thing as a tip stall. Have you ever seen stall strips on a full sized plane? What would these be for? What purpose would washout serve? I'm sure you can give me very convincing answers on these questions.

Jim

Different airfoils stall differently. Some from the inside out, some from the outside in. Washout lets the wing stall from the inside out (the tip is effectively at a lower AOA) so that the ailerons on the ends of the wings remain effective.

Any imbalance between lift on the wings will cause a roll. If one wing stalls before the other, or PART of the wings stalls before PART of the other wing, with or without washout, you get an abrupt roll... aka a "snap".

Also.. aileron trim. Te wing with down aileron trim effectively has flaps deployed (however small). One effect that flap have is that they LOWER the critical AOA (though they produce more lift for a given flyable AOA). Thus, if your left aileron is lower than your right, the left wing will reach stall sooner than the right (at a lower fuselage AOA), cause a snap to left when you reach stall.

Aww darn, you beat me to it. But you detailed it better anyway.

Stall strips are used for several purposes. One is to delay the stall. On some planes testing during the certification process noted that the aircraft stalls at too high of an air speed to meet the classification qualifications.

Other aircraft were noted to have a stall that was too violent, and stall strips at specific locations were added to "buffer' the stall. Other aircraft had stall charicteristics that were not active enough in pre-stall warning, so strips were added to enhance the stall buffet.

BTW, there are also devices called "Vortex Generators" that are placed at many different places on the fuselage of some full scale aircraft to lower stall speeds and assist in preventing "Dutch Roll".

As a few others here, I have a lot of time in full scale medium and light aircraft.

thats what you use with the paint right

Sounds good to me

build yerself a good aerobatic foamie with wing loading of say 5 oz ft.
Now demonstrate all of these theories.
Or hell - try em anyway.
Some surprises may occur.

Wow, this thread went far out there...

Honestly It may be one entire wing stalling in my case whether it starts at the tip or not... I dont know. I have always refered the wing dropping as tip stalling. In any case I just gave my symptoms and my fixes in hopes that someone else would be able to use 'em.

Dick, I absolutely agree with the theory. The practicality can be a little difficult with the 150, tho.

Ibange, Some of really are having fun with this thread. The answers can get super interesting.

My theory is that tapered wings are more prone to tip stalling because the tips have a shorter chord than the root and stall at a slower speed.. If the wings are matched in wieght and in design however they should stall together. I also know that a heavy wing/wing tip WILL stall before a lighter one just as a plane with heavier wings will stall before an identical plane with lighter wings.. I also know that trim and engine thrust may play a role when you get down to the nitty gritty.. Only we as R/C pilots take these planes to the edge at such low altitudes on a daily basis.. I could be wrong on some of this though.. One thing I have realized from the first time I logged onto R/C universe is the wealth of Brains and intelligence.. I am glad that I enjoy a hobby that is so technical and I guess that's part of the reason we get so much out of it..

Just a comment, the wings on our 28% planes have a 12% airfoil at the root and 14% at the tips specifically to keep the tips flying at low speeds.

TF

is this true with the wings on my 28% special with the sharper leading edge

Yes this is true on all Extras and Edges built up to this date.

TF