ameyam

I just maidened a Phoenix Extra with a DLE20 and my mentor remarked that it tends to stall at landing. Its supposed to be 3.2 to 3.6kg but mine is overweight at 3.85kg. Measures to lose weight (foam wheels, CF LG, LiFe for ignition, flying without cowl or spinner etc) did not work or could not be implemented. Note that the stall is not so much a tip stall as a flat nose down stall, atleast as I observed

To reduce the stall tendancy, I am considering adding winglets to the wing tips to make the wings more effective. Essentially SFGs but much smaller, may be 75mm or so tall alltogether. Considering tracing out the wing tip profile on a 2mm thick balsa ply sheet and then installing the same on the wingtip with blind nuts on the inside. Then make the winglet out of sheeted balsa frame with airfoil profile and screw it in place with 4mm screws through the bling nuts. Will build of a shape that has max area towards the trailing end. This airplane has large ailerons, so the winglet will go only as far as the hinge line

How good an idea is this?

Ameyam

weazel1

sound good did the same thing on a seagull extra 300 but used plexyglass instead and yes it did help

speedracerntrixie

My Feedback: (29)

It sounds to me like you are just going to add more weight to an already heavy airplane. There is no fix for heavy other then weight loss. On an airplane like this 1 pound can easily be lost just through careful selection of equipment. BTW do not fly without a cowl, the poor aerodynamics resulting is not worth the weight loss there. Post detailed pictures and I will come up with at least a dozen suggestions for losing weight.

pimmnz

Here's the go, winglets are a drag reduction 'fix' and will show a slight improvement in fuel consumption over a long range, high altitude flight, say 4 hr at 35,000 ft. So for your purposes, prolly not what you expect. A tip 'fence' might help a model prone to tip stall, but you say yours does not, so, prolly not much to be gained there, either. You say your model is a bit over the advertised weight, this translates to a slightly higher airspeed at the point the angle of the wing to the airflow will start to break down. This angle cannot be changed, regardless of the weight the wing will always stall at this angle, but lighter means that it will do it at a slower speed, which is what you want. If you want to make the wings 'more effective' then you could make them bigger...or the model less heavier...maybe a bit of washout might help, but given your description of the stall, unlikely...besides, adding more bits to the model will increase the weight a bit, making the stall happen at a slightly higher speed, not what you are looking for...I am afraid that the only way to lower your stall speed is to make the model lighter, or rather, reduce the wing loading.
Evan, WB #12.

karolh

How about posting a picture or sketch of what you propose to use.

Karol

Desertlakesflying

My Feedback: (28)

I put hoerner wing tips on my P-51 to help with lift since it is missing about 3 1/2 on each side of the wing.

ameyam

Actually, the stall fence, the winglet, hoerner wing tips etc all do the same thing. All wings lift because of the higher pressure below. At the wing tip the air leaks over from lower to upper side. This forms a wake vortex which adds drag. Further, as the wing goes through the air, it displaces air. Air wanting to take the path of least resistance, flows along the tapered leading edge instead of over the wing (this is called washoff I believe, havent read up on aerodynamics in several years). All of these make the wing less effective at the tips.

All those who fly passenger aieplanes have seen the winglets at the tips. In Boeing these are curved upward whereas Airbus prefers T-tips. If you see eagles or ducks in flight, you will see the outermost feathers curved upward. They all have the same function. These winglets prevent the air from leaking over and force the air to go over the wing. This has two effects- it makes the wing more effective in contributing to lift by zoning the air pressures and it reduces wing rock- wing rock is caused by one wing tip stalling then the other. Yes, the wing tips also add drag- I believe its called lift induced drag or it is a component of lift induced drag. But it makes flight more stable. The same principle is employed in F1 wings- you see all the nose and tail wings have end plates that serve this purpose. In addition to reducing wash-off, they make flight more efficient by reducing energy loss in eddys at the wing tips

In our hobby, SFGs serve the same purpose. Large ones add more rudder authority by making the rudder contribute more towards steering rather than stabilizing the airplane.

Winglets wont add too much height- I dont intend to make them too large, just an inch above and below the wing and restricted to the fixed part of the wing only. I feel its a good idea

With respect to losing weight, I already have 3.25" foam wheels installed. I retained the stock LG instead of the CF LG (80g addition) and used 4 cell NiMH insted of LiFe (40g) addition. There is not much else I can lose to save weight. I didnt install the cowl (though I test fitted it) as the engine is still in break-in and I didnt install the spinner as it will just make it more nose heavy (its already 15mm front of the recommended CG). Both save weight, not a bad idea to keep them off

Ameyam

karolh

I recently modded my Big Stick's wing in an effort to increase it's roll rate by removing the stock tapered wing tips and adding end plates instead. The plates were cut from 1/8" lite ply and follow the airfoil shape of the wing from L/ edge to the ailerons extending 1/2" above and below the wing. With a small percentage of aileron differential added they do make a quite difference, and many thanks to Ed Moorman for his assistance in getting it right.

Karol

ameyam

In airplanes like the Big Stik, UCD etc that dont have the winglet, the triangular wingtips do the same thing- they prevent the air leakage from bottom to top. They also serve another purpose if I am not mistaken- the triangular tip generates a vortex that gives a huge amount of lift for a very short time at a high angle of attack. They also create a very stable flying airplane. Thats the reason why many classic airplane designs- UCD, Stik etc have them. If you break or remove them, the minimum landing speed will increase. At a minimum, they will cause a roll effect if there is a differential. Dont ask me how I know

Ameyam

ec121

My Feedback: (2)

Ed Moorman did an article in RC Report about the tip fences several years ago. They lower the stall speed to a degree. He tried several configurations. Maybe someone out there has the article in a file. As I remember, a fence about 1/4in all the way around the tip worked fine. Also if you are stalling straight ahead on landing, you can learn to reduce the elevator and land parallel to the ground instead of holding the flare nose high until it drops to the ground. A side benefit of that type of parallel landing is that you will look like you know what you are doing instead of crashing to the ground and spreading the gear.

karolh

I read Ed article on the subject of adding end plates and had several talks with him about possible configurations etc. for my particular model. As I recall tapered or elliptical shaped wing tips are the least effective in promoting lift while square tips or end plates are the most effective, plus have an added benefit as they also help to reduced the stall speed of the model.

Karol

opjose

Land faster and/or move the C.G. forward.

It is not unusual for an Extra to drop the nose on a stall, it is not a "trainer" after all.

speedracerntrixie

My Feedback: (29)

How is moving the CG even farther forward going to help? He already said he was further forward then the instructions called for ( Manufacturers are usually forward to befing with ). That will make his situation even worse!

Like I stated before, flying without the cowl messes things up, put it back on. Post some pictures and I will find at least a dozen things to do to reduce weight.

karolh

The model in question here is a GP Big Stick 60.

Karol

karolh

The model in question here is a GP Big Stick 60.

Karol

red head

Throttle management !!!!! And reduce weight. ENJOY !!! RED

ameyam

Will post pics in the evening. Need to go to work now

Ameyam

jkr_1100

My Feedback: (15)

Throttle management, flairing, and changing the CG will get you what you want. Other things are more "drastic."

ameyam

The issue is I want to 3D the airplane. Its very much capable and seeing I can fly comfortably at 20-30% power, it will easily 3d as long as there is power. Adding the winglets will also improve harrier handling- thats what I want to achieve as well

Ameyam

ameyam

Here you go. Lets have those suggestions. One thing I cant do- move the rudder servo back. There is no way or ply to install it there. Also, I am not going for mini size servos either

Ameyam

Jetdesign

My Feedback: (8)

The Winglets will work in theory. As stated above, they serve the purpose of keeping the low pressure above the wing and prevent some of the high pressure air from spilling up over the side of the wing. The spilling high pressure air reduces overall lift. As such, adding winglets and thus increasing lift should help prevent stalls of a plane with an increased wing loading.

ameyam

I would like to attack the issue from both sides. Is there ANY way to reduce weight safely?

Ameyam

opjose

Eh no, you jumped into a thread started by someone else....

"I just maidened a Phoenix Extra with a DLE20 and my mentor remarked that it tends to stall at landing"

opjose

Recommended C.G. settings are exactly that, recommendations.

He is complaining about "stall" or wing drop on a plane that does exactly that even when properly set up. It is an acrobatic plane after all.

That in itself indicates that he is not used to the characteristics of a typical Extra and as others have indicated, not properly managing throttle.

Given that, moving the C.G. forward will FORCE him to bring the plane in faster preventing stall/drop.... he can experiment with that as necessary.


The .2kg difference in weight he states will BARELY affect the performance of that plane, and unfortunately he is zeroed in on the wrong thing. The OP has a rather long history of doing this given his many prior posts and threads where he's done the same thing.

So instead of concentrating on fixing the plane, the "pilot" needs a bit of work.

BTW: .1 - .2kg over specs, I would consider "light", I'll freqently and purposely throw larger packs onto my 1.20-1.40 sized planes and end up a full 1/2 lb heavier or more than specs... I've never noticed any problems what-so-ever.

pimmnz

amayam, you cannot, in this case 'attack the issue from both sides'. If your model is not tip stalling, then anything on the wing tip won't help, other than adding drag and weight. So far as the weight control is concerned, then it is probably too late, this needs to be addressed at the design stage. However, if you wish to do something about it, and have the time to start stripping the covering and rebuilding, then start at the tail. Anything lost here will perhaps triple the weight loss as you remove weight from the front as well, to maintain balance. Rebuild the tailplane and fin in light strip and laminated outlines and ribs, then brace to the hinge spars with 40lb fishing trace or similar. Start rebalancing by first removing any ballast, then start moving batteries around first. If you want to '3D' (I always thought all my models were '3D') and snaps are part of your flight, then anything on the wing tips that reduces the ability of the wing tip to stall will also reduce the ability of the model to snap, as snaps are stalled manouvers. So remove them, if you have them. On models like this having a big heavy steerable tailwheel is nonsense, a simple wire skid will work just as well and save maybe half a pound at the front. You could also remove any foam turtledecks, if you have them, and replace them with a few stringers and recover, foam has no structural strength. Other than that there isn't much you can do, other than redesigning and starting again. I note that you have servos at the tail, removing them to the cabin area and using cables will certainly help.
Evan, WB #12.