Adding winglets to ARF wingtips
 

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

RE: Adding winglets to ARF wingtips
 

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

RE: Adding winglets to ARF wingtips
 

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.

RE: Adding winglets to ARF wingtips
 

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.

RE: Adding winglets to ARF wingtips
 

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

Karol

RE: Adding winglets to ARF wingtips
 

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.

RE: Adding winglets to ARF wingtips
 

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

RE: Adding winglets to ARF wingtips
 

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

RE: Adding winglets to ARF wingtips
 

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

RE: Adding winglets to ARF wingtips
 

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. :D

RE: Adding winglets to ARF wingtips
 

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

RE: Adding winglets to ARF wingtips
 

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.

RE: Adding winglets to ARF wingtips
 

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.

RE: Adding winglets to ARF wingtips
 

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

Karol

RE: Adding winglets to ARF wingtips
 

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

Karol

RE: Adding winglets to ARF wingtips
 

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

RE: Adding winglets to ARF wingtips
 

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

Ameyam

RE: Adding winglets to ARF wingtips
 

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

RE: Adding winglets to ARF wingtips
 

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

RE: Adding winglets to ARF wingtips
 

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

RE: Adding winglets to ARF wingtips
 

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.

RE: Adding winglets to ARF wingtips
 

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

Ameyam

RE: Adding winglets to ARF wingtips
 

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"

RE: Adding winglets to ARF wingtips
 

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.

RE: Adding winglets to ARF wingtips
 

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.

RE: Adding winglets to ARF wingtips
 

I agree, the pilot needs work Opjose. In fact I havent flown in close to six months because our field was out of operation with tall uncut grass. I also agree with nose weight and throttle management comments you make, just I dont want to lose the airplane in gaining those skills back.

If 0.1 to .2kgs is not much of a weight gain (actually its 0.4 to 0.5kg gain as the stock should be 3.4kg) I am not too concerned. I am practicing on the sim already with scale models to get the throttle management and glide slope correct

No, I cant rebuild the tail etc. Remember, I have no counter weight anywhere in the airplane. Making the tail lighter will only make it more nose heavy.

The measures I had identified to lose weight were CF LG, foam wheels, LiFe for ignition (I am using NiMH now). I didnt use the CF gear because they told me CF is brittle (though Hobbyking was saying this gear is unbreakable). I already have foam wheels on it. I dont have a additional LiFe battery. If a capacity of around 2000mAh is recommended, its weight will be close to that of a NiMh.

I was thinking of 1300mAh with diodes in series, will that be sufficient for ignition for max 5 flights of 10mins?

Where else can the model lose weight?

Ameyam

RE: Adding winglets to ARF wingtips
 

To lose additional weight, use a wood prop and CF spinner. If you fly 2.4 then you might want to consider using one battery for both ignition and Rx power.

Karol

RE: Adding winglets to ARF wingtips
 

Yes, I did consider one battery. I am using the TH-8 module. But they told me it not advisable both on the RCU forum and on my field. Thats why I asked what are the safe ways to reduce lose weight

Ameyam

RE: Adding winglets to ARF wingtips
 

You're over thinking it.

The weight is FINE as is, don't screw with that any more.

Instead learn to land with a bit more throttle.

I teach students to fly the plane high and keep bringing the throttle back SLOWLY as they fly until they find the point that the plane will begin to no longer fly level no matter what you do with the elevator, and rather decends in a controlled manner.

That's the throttle setting you want to use until the plane is just inches over the runway. Once it's less than a foot above the runway, you chop the throttle completely while holding it as level as you can, and it will decend and land by itself.

It is so low at this point that tip stalls or regular stalls are merely "landings".

RE: Adding winglets to ARF wingtips
 

Excellent advice.

Karol

RE: Adding winglets to ARF wingtips
 

There is only one more 'safe' way to loose weight with this ARF...remove the engine, ignition module and battery, and replace it with the comparable glow motor. Then you move the tail mounted servos to the cabin area, and maybe rebuild the tail surfaces, to rebalance. There really isn't any other thing you can reasonably do to remove enough weight to make a difference.
Evan, WB #12.

RE: Adding winglets to ARF wingtips
 

Obviously you either havent flown aerobatics much or you have never taken the time to set them up correctly. A properly set up Extra is one of the easiest airplanes to fly. If you doubt that then I suggest you download the current IMAC unlimited sequence and imagine trying to fly it with an airplane that is difficult to fly. The only difference between a trainer and this sort of airplane is that an Extra has no self righting tendencies, it will go where pointed but is very predictable and forgiving. The fact that an airplane will fly 3D at all is proof positive that it is no harder to fly then your average aileron trainer as long as it is correctly set up. As far as you wanting to make an airplane heavier, that is just plain rediculous except in the case of a sailplane where ballast is used for windy days for better penetration ( Higher potential energy equalls more kinetic energy ) but this is onlt because it dosent have an engine in front.


Ok weight REDUCTION............... From the nose back. Tade the MA prop for a Vess prop. Not only lighter but better thrust to boot. The engine mounting screws are excessive. Not only too long but can be reduced to 3mm. The mount to firewall screws are most likely the same. The end of the mount could be trimmed 6-8 mm. Sand the inside of the cowl with 150 grit paper, a good 15 grams could be taken out. If you want to use a spinner, us a Dubro unit with the lightened backplate. You cut a hole in the firewall between the mounting holes. It offers no strength and is dead weight. The engine will have better air available to it and will run better anyways. Replace the trottle linkage with a smaller tube and a 1.5mm CF rod. A mini servo for throttle would cut a good 20 grams too. Move the rudder servo as far back as you can get it. It can be mounted on a couple 6mm rails. Replace the steel pull pull cables with nylon coated kevlar. Move the fuel tank to where your rudder servo is now. This will give you the CG shift you need. Get rid of the foam around the tank, it's dead weight. Gas engines run at a lower frequency and you will not have a fuel foaming issue. Use a peice of 3mm ply and make lots of cut outs for a tank mount. A single peice of velcro slightly smaller then the tank and a couple velcro straps with secure the tank. If the tank is bigger then 500ml then replace it to a smaller one. That 20 dosen't need alot of fuel. Moving the fuel tank will require you to cut out the canopy floor, more weight savings. Replacing the landing gear and wing tube with CF units will be a big drop but also the most expensive. The stock gear can be lightened. Drill 18mm holes between the mounting screws and yes the mounting screws are too big, replace them with 3mm hardware. The end of the gear where the axles are can be rounded off. If you have 2 wheel collars on each axle replace the inside one with a nylon spacer and the outter one with an aluminum collar. World models have the aluminum collars in 4mm. A few of the screws in the tail look a bit long, replace them with shorter ones. The rudder horn is heavy, get a pair of nylon control horns and replace. Forget the LIFE batteries, get lipo. A 1300 mah for RX and 900mah for ignition. That should be plenty for your 5 flights. You don't have digital servos so power draw is down. No need for big servos. Team Losi makes a great little 6V regulator the weighs next to nothing and is rated at 10 amps. You could easily drop 20-30 grams out of the fuse by sanding excess material. The inside edge of formers for example. If any of the servo or power wires are longer then they need to be, shorten them. I'm sure there is more but this is what I get out of the pics. Hopefully some of these suggestions will help you find even more.

RE: Adding winglets to ARF wingtips
 

RE: Adding winglets to ARF wingtips
 

Didn't see they were digitals but even though not very power hungry. I wouldn't call CF gear brittle. On a landing that would bend your aluminum gear will most likely delaminate a CF gear. The cood news is you can flow some thin CA into the delam, clamp it for a couple hors and it's as good as new.

I realize you may not want to go through all that effort but remember that with this hobby, you will only get out of it what you put into it. I intended this to not only be of benifit for you but others too so I went into a fair amount of detail. I do think that once you fly a really light airplane you will have more appriciation for how much better they fly. I expect alot out of my airplanes and put alot of effort into them, I realize that is not for everyone and as long as you have fun it's all good.

RE: Adding winglets to ARF wingtips
 

I love carbon gear, it's the only way to go for me. I find it much more resilient than aluminum. Get good gear from Graphtechrc.com, not the junk from the Chinese hobby stores. You should be able to get a set for $40 and save probably 80-100 grams.

RE: Adding winglets to ARF wingtips
 

grams beget ounces, ounces beget pounds.

Building a light airplane is an all encompassing exercise that starts with a critical design review before any wood is even cut (this includes covering selection). A traditional doped silk/silkspan or glassed coverings add considerable strength and rigidity to a structure, which CAN be fed back into structural material selections/sizings allowing for structural weight savings. Plastic coverings add nothing structurally and require stronger internal structure.

I've reworked a few ARF's and put them on diet plans for other people. An ARF diet plan is much harder than a scratch build diet plan because you'll wind up being forced to keep significant chunks of substandard structure and/or poorly selected wood.

In your case, with the gasser brick you've chosen to bolt on up front for an engine, the first place to look is at the engine itself. There's probably several ounces that could be shaved off that gas engine by a machinist (or with a Dremel if you have the patience). Every ounce off the engine is a few ounces less tail weight you need. Putting the engine on a diet plan is a win-win all the way around. Cast cylinder cooling fins and head fins are always good targets for shaving some thickness off. External case webbing can have lightening holes drilled in the corners. Casting flash can be ground off. If it has a steel prop nut/washer, substitute a lighter aluminum hub. Look at any spinner critically. Some of the TruTurns have extremely heavy (like about 4oz) solidish aluminum backplates. They can be riddled with lightening holes and rebalanced to save a couple of ounces.

RE: Adding winglets to ARF wingtips
 

I agree with the issue of putting good landing gears on the airplane but there is no way to get graphtech. It will cost twice the basic price to get it to India. I know the HK CF gears are quite good and cheap and thats why I got it. It was reputed to be unbreakable but the guys on my field told me not to use it. I will add it in once I get more used to the airplane and start doing 3D with it. Till then I would persiste with a bendable aluminium gear rather than a shatterable CF one. I think we should leave this for later

I am not desperate enough to try and mod my engine. Phoenix models are sturdily built which is why I picked this model. Remember, its a test rig before I open up my Funtana which is much more expensive

I am thinking of putting in a GP nylon spinner with lightened metal backplate (which I was using on my glow airplanes) simply to be able to use a starter. For the time being the cowl is off till I can get the engine broken in.

Ameyam

RE: Adding winglets to ARF wingtips
 

Oh Gawd...

You're dealing with a relative novice that has little experience, not an IMAC flyer.

His plane is over specs by a very small margin, he's never had to deal with 3D aerobatic planes, nor those that have inherent instabilities designed in for tumbling, snap, etc. purposes.

You CAN obtain very light Extras that loose many of the idiosyncracies of a normally loaded Extra, but that is beyond his scope. That is why he wants to STRENGTHEN things, as his landing skills are not up to it yet.

I've followed the OP through many such threads as he has progressed, answering his questions all along, and there have historically MANY MANY times such as this where he is focused on something too advanced for him to think about.

Your advice is like answering an overweight rider who asks about making his bike lighter to make things easier, by telling them about Carbon Fiber bike frames... it's a specious response in this case even though technically correct.... the bike rider needs to loose the weight not the bike.

Ameyan needs to fly more and stop fretting about a .2kg weight difference.

The context of these posts is important, something you've overlooked.

RE: Adding winglets to ARF wingtips
 

I agree, I need to fly more and think less right now. Alos, my landing skills are not yet upto the Extra's requirements, but they are getting there.

I think, I did conclude my thoughts with my yesterday's post. Today is a working Saturday and its been a hectic week, again I have not yer touched my sim. May not be flying tomorrow, need the rest. I will takeup the landing issue next week when Saturday is a holiday and then take it from there

Ameyam