Aviator 25

I have a Great Planes Extra 300S .60 and have recently put a DLE 20 engine on it. the plane's weight is around 8.5 lb without fuel (I was hoping for less weight). The plane takes off in a very short time and flies great, the engine has a lot of power, But the problem is when I come in to land. As I approach on final the wing tips start to drop hard left and right (stalling I'm guessing), but when I speed up the plane to stop the stalling it will not set down on the runway, it just keeps flying. I was thinking of using flaperon mixing to try and solve the problem. Will this work or just make it worst? How much flaperon should be used?

speedracerntrixie

My Feedback: (29)

It will make it worse. Where is your CG? My guess based on limited info is that you are nose heavy and are actually stalling the tail not the wing. How much back stick are you holding during approach? That airplane has 744 sq in of wing so 8.5 lbs is not too bad.

Aviator 25

Interesting, your right the plane is nose heavy. I was thinking of moving the rudder servo from inside the fuselage to the tail and mounting it on the outside like other planes do. This way I can use the batteries to set the CG right. Would it be worth still using flaperon mixing after I get the CG right to help with landings?

JimCasey

My Feedback: (1)

I am not a fan of flaperons.  They are deployed at low-speed, High AOA.  They cause huge adverse yaw ( mix in 50% or more rudder if using flaperons) .  I have found that they help stall the slow wing, when you are already too low and slow for comfort. 

FLAPS on the other hand, are wonderful.  They add lift and drag, let you fly with the tips at lower AOA, thus reducing adverse yaw.  If you pop flaps ON final, the plane will balloon higher than the intended glide slope.  If you pop flaps as you turn final, they will scrub off your speed in the turn and the landing will be slow and flat...with altitude controlled by the throttle trim. 

BMatthews

Using flaperons in the downward direction will make things worse. Instead use Spoilerons which angle the ailerons upward. They aid in killing the wing's lift but do so in a manner that ensures that the ailerons will not work to produce the stalling you're trying to avoid.

rctech2k7

My Feedback: (1)

Based on your plane you don't need that flaps to land. You plane doesn't have too much wing loading to use high lift devices. Although flaps are very helpful on low airspeed but as you've said increasing airspeed makes your plane difficult to descent, it's also the same thing when adding wing camber or flaps. Therefore I agree with BMatthews advice on the otherhand to reduce lift and increase rate of descent.

speedracerntrixie

My Feedback: (29)

Guys, your missing this key bit of information. Once the CG has been corrected the airplane will have much better landing manners. It will also fly inverted without having to hold a bunch of forwand stick.

rctech2k7

My Feedback: (1)

That's also a good info for pitching characteristic but it will only affect lift very slightly. When CG is move aft the aircraft loses its own stability which require to land in lower angle that might result in increase of speed or balloon effect. I believe the aircraft being nose heavy is the one that helping the pilot to be above situation and also to inform him that she's about to stall, without that most likely the plane would snap.

larrysogla

I agree with BMatthews....you want to kill the lift NOT increase the stall characteristic...........the spoilerons will kill the lift and not make the stall characteristic worse that what it is now. Larry.

cfircav8r

My Feedback: (1)

Only fix one problem at a time. The most obvious is the CG issue. After you fix that fly it and see how it fly's. You will have other adjustments to make after that, such as elevator throw and trim. If you change more than one thing at a time you will be chasing problems until you eventually get it all balled up.

speedracerntrixie

My Feedback: (29)

Wrong wrong wrong.................I have been here so many times it's starting to get rediculous. IDIDNOTSAYTOMAKETHECGANAFTPOSITION. I said the CG is too far forward and needs to be moved back to where it is supposed to be. Please read things correctly before shooting down good advise!

cfircav8r

My Feedback: (1)

CG will not effect the stall other than increase (nose heavy) or decrease (less nose heavy) the speed at which it stalls. How it stalls is controlled by wing design and pilot inputs.

Edit: this was not directed at you Speed I forgot to hit the reply button.

rctech2k7

My Feedback: (1)

Sorry I didn't mean to hurt you, just one word is enough for me to understand. I didn't said a bad advice in fact a good one with regards to the pitch... Moving CG is not a bad advice but depends on plane's setup and preference as we can see from OP "The plane takes off in a very short time and flies great". The only problem is on landing. It's not actually relevant but just to give info to the OP that changing CG will not affect lift. You've told me that I'm wrong then prove it technically... I will prove also to you that our advice is correct as far as the OP is concern. I will give you a chance to start in favor to you to express lift in the function of CG.

speedracerntrixie

My Feedback: (29)

OK a nose heavy airplane requires up elevator to stay level, even more at slow speeds. The slower the airplane goes, the more up elevator has to be applied. During landing at some point the elevator just loooses most of it's ability to hold the nose up. The pilot can feel this as control softness and obviously increases airspeed. Thus the airplane lands fast.

More questions for the OP. He already said the airplane is nose heavy. Another guess is that he has more then 20 degrees of elevator throw and if he tries a relitivly tight loop, the airplane will snap out of the loop. I'm sure inverted flight takes quite a bit of forward stick. All of these are signs of the CG being forward of the center of lift. I am going to post a video of one of my airplanes during landing. Not the best quality video but if you pause it just as it passes the camera you will see literally no elevator deflection. This is an airplane that is set up very close to neutral stability. Also notice that although the flare is quite short as I didn't have much room, the landing speed is quite slow.


http://www.youtube.com/watch?v=bpm4cwaFrAg

rctech2k7

My Feedback: (1)

OK, very good... That's comply technical way that down force on elevator adds load to the wings which require higher airspeed at constant AOA. However Lift and CP are not constant with respect to AOA.

Forgive me if I'm getting farther from the subject but just wanna clear that there are two alternative solution on this topic at this time. By taking differential lift from moving CG or by increasing downward force using our solution to find out which is more effective.

This is why we need to raise the nose up on landing to slows down. When AOA increases center of pressure (CP) moves forward up to higher coefficient. CG must not go after the CP otherwise the plane will be able to land. This is why a non-nose heavy aircraft require to nose down to compensate for CP change. Maintaining CP after CG will make the plane able to descend smoother. At higher AOA the plane will benefits from lower speed, at nose heavy a plane will benefit from higher stability. Most likely the plane lands above stall level but lower in speed.

The force and moment torque generated at the tail which contributed to airspeed and wing loading is almost negligible at higher AOA.

On the other side using spoilerons, spoilers, crow has plenty of effect to the lift reduction due to wing camber and CL and this is proven effective for light aircraft or even to high performance aircraft which require smooth descend. However flaps, flaperons are proven effective to high wing loading aircraft to slows down and shorten the landings.

cfircav8r

My Feedback: (1)

Again he already said the CG is off. He needs to fix that and then fly it and see how it does. Set it up as it was designed before having him make changes counter to that design. Besides you can't change more than one thing at a time and have a properly set up aircraft. Fix the CG, fly it, and then get back to us and tell us the results. Only then can we give useful advise.

rctech2k7

My Feedback: (1)

Both of you with speed are right for correcting CG. However it will only influence lift for a small amount compare using the other solution given by BMatthews. The aircraft will still be light.

This kind of aircraft can be able to land at almost zero speed if I'm not mistaken. The prop wash to the tail actually help the aircraft to be in control at lower speed. Considering w/o prop wash as for analysis but with the present of thrust, forward CG will help the plane to descend at landing configuration, it will also recover itself if the plane stall or engine quits with enough altitude. Reality there's prop wash that helps to be ahead of stalling the tail. So far I don't see any behavior from OP that the tail stall first prior to the wings which is the limitation.

If it's really needed I'll show you here later on how CG helps and by using BMatthews advice will have the best result as far as landing problem is concern. For the mean time check this diagram, it will explain why both of you are correct.


It was my approximation for determining differences between a neutral CG and nose heavy I used on takeoff analysis. The neutral CG has the shortest distance while nose heavy has longer one and faster takeoff speed. I check their differences with regards to lift factor and found out that since we don't have airspeed indicator to determine actual speed, by using elevator input and preset will give assurance that once aircraft airborne she's already above safe speed. For landing, increasing AOA provided with power will slows down...
This is also a sample showing how AOA affect it. This is hornet with proposed additional HLD and not applicable to standard F-18 model.


BMatthews advice is proven technically and in flight that will help light wing loading aircraft to process descend rate. Gliders and other model jets are also using this feature on their landing. However for heavy high wing loading uses flaperon as their features to slow down, I’ve tested it on my scale F-18 and it works but due to lower energy instead of using spoiler I prefer to leave aileron as it is.

cfircav8r

My Feedback: (1)

I never said his way wont work, what I said was fix the known CG issue and fly it before you change anything else. He has stated the CG is wrong, and any changes made before fixing that could very well be unnecessary, and may only make things worse. Set up the A/C per the design specifications, fly it, then adjust one thing at a time, flying after each adjustment. Continue this procedure to get the desired performance to suit your flying style.

Bundubasher

Flaperons may have some applications -but it is a handsomehigh tech method of crashing a plane
I very embarressingly crashed a Cessna Centurion of all planes this way - testing flaperons.

You are bound to stall one half of the wing if you have to use the ailerons.

I do cheat sometimes when landing my 3rd scale Super Cub by feeding in a tiny bit of spoilerons on final approach to wash off height and speed, but that is a different story - Cubs are almost immune to gravity..

Cheers


Bundu

rctech2k7

My Feedback: (1)

Thanks for explaining one more time. On what I undertand from OP is that the aircraft gains extra weight and power. So I'm expecting some increase on idle thrust and torque also. The author is free to correct me if I'm wrong. If he stated that CG is wrong then it must be corrected first. Our concern are both not to endanger the plane on the flight so following correct procedure are required.

rctech2k7

My Feedback: (1)

Please correct my info from post 15 that "CG must not go after the CP otherwise the plane will be able to land". It's a typo error. It must be:

CG must not go after the CP otherwise the plane will not be able to land.

Aviator 25

All great info guys.
I agree with cfircav8r that I should try one thing at a time. I have moved the rudder servo to the tail and adjusted the CG at 4.125" from the LE at the fuselage as the manual for this plane recommends.
I flew this plane in the past with a YS 110 and it was great flying and landing, but with the cost of fuel I decided to change over to the DLE 20 gas engine. I have to admit that I just did a quick finger tip level test of the CG after installing the DLE. The plane did seem a bit nose heavy at the time but I have flown planes in the past that were noes heavy with no problems so I thought this would be ok (but it seems that maybe this plane does not like it). After doing a proper CG test I can see that it was out enough that I had to move a servo to the tail.
I will try the plane with the new CG adjustment as soon as the wind gives me a break (soon I hope). I'll let you know what happens.

Thanks guys.

speedracerntrixie

My Feedback: (29)

Aviator, good to see you are on the right track. With the CG in the correct position the airplane will fly much better overall. I know you were happy with the flight performance before but expect an improvement. I have " ruined " many of sport pilots by showing them how to set up their airplanes to fly better then they would have thought possible. Afrer that they always take more time getting the settings correct. As an IMAC unlimited pilot to be competitive I need my airplanes to be as easy to fly as possible and that can only be accomplished by going through a process of getting the airplane trimmed to do so. Typically it takes me a good 50 flights to get an airplane flying really well. Even then, when the new season starts with a new sequence, I have to tweak my settings some to suit the new sequence. After you get the CGset if you would like more info to really get that Extra flying well, let me know. I think it would be great to do something like this here so guys can see the trimming process in action and the benifits as we go through it.

rctech2k7

My Feedback: (1)

Thanks for update. This is just for information only, without having too much nose heavy an aircraft with more powerful engine with extra torque and weight is not considerable a big issue, the aircraft can escape anytime from stall. However since it’s too nose heavy due to difficulty in changing the pitch, higher trim and faster cruising speed so therefore it must be corrected for the kind of aircraft.

For using spoilerons, this setup has capability of increasing stall angle, shifting center of lift forward which counter act nose heavy while reducing lift at positive angle. Following the law of aerodynamics this is applicable in reducing lift for aircraft with plenty of lift...

rctech2k7

My Feedback: (1)

It's not necessary for me to show some diagram on how forward CG helps, I agree with the latest update on this thread in which the aircraft can be improved with the proper CG location. However on my previous diagram, it just the same thing except it's not horizontal but with AOA where an aircraft can generate more lift and drag at higher coefficient. As we can see from the horizontal drawing that the tail down force (T) is getting higher when CG moves forward.

T = W * dw/dt (not derivatives but the ratio of distance to weight center and tail from landing gear)
where dw = dLG - dCG
and dCG is the distance from CG to LE

T is a force generated by dynamic pressure acted on the surface of the tail with respect to angle and air velocity. In other words the trim varies with respect to airspeed of an aircraft at constant CG location...

Well, I agree, it’s all depends on the flying style, design, application of an aircraft as well as the structure that varies with respect to speed and stability...

Thank you for all of you guys for sharing your valued input...