Volfy

My Feedback: (23)

I read in Ed Moorman's RC University http://members.home.net/rcuniversity/WingTips.htm about his experiments with wing tip plates and am very impressed. However, even though it makes very good sense, it conflicts somewhat with some of the older NACA studies I've read, which indicated that a rounded thin wing tip has less induced drag than a thicker or blunt wing tip. Or does it? Perhaps a blunt wing tip generates more wake vortices, and thus induced drag, than a "squared off" wing tip with a thin tip plate attached. Then again, perhaps the scale factor is at play here, since the NACA studies are on full scale aircrafts.

I'm trying to decide what to do for the wingtips of a couple of ARF wings after I ditch those cheapo plastic shells. Any suggestions? References or articles I can go read?

bobparks

The basic answer is to do whatever you feel like.

I have been an aeronautical engineer for 20+ years, and have finally come to the conclusion that if some wing tip design really was better, it would be obvious and people would not still be arguing about it all the time.

Besides on an ARF, you are not talking about having outstanding aerodynamics to start with, and even the best of tips wont make a noticeable difference.

bob

Mike James

I have to agree with Bob. There may be differences that could be measured with some scientific instrument, or shown in a wind tunnel, but what can you SEE or "feel" when flying the model?

I've done a kabillion experiments over the years with models, and I think that at the Reynolds numbers we usually fly at, these details are negligible. However, you could make a plywood plate on the wingtip, and try attaching different configurations yourself, and see if you agree. (Wingtips aren't too time consuming to make.)

Ed_Moorman

My Feedback: (1)

All of my conclusions were based on actual model tests.

In some cases it is difficult to apply full scale aerodynamics. As one reply already stated, we are operating in such a low Reynolds number area we are essentially off the chart. This is the reason the large models fly better, and also the reason the TOC type competitors fly as large a model as allowed. They just fly better.

As for the wing tips, try several of the different types and note the results for landing speed, stalls, spins, roll rate and others you can think of. I think you'll find the end plates give a higher roll rate and a lower landing speed.

I published this same data in my R/C Report magazine column, "Fun Aerobatics," and two modelers tried experiments with plates and sent me the results. Both agreed on a higher roll rate and a slower landing speed.

Volfy

My Feedback: (23)

Ed, I didn't know you frequent this joint. Then again, I haven't been here long enough to know much.

I'd agree that for the 1.20 size and under, just about any wing tip design will work fine. Heck, I remember reading in an article that some guy built a fun-fly with an airfoil shaped from his wife's stiletto. So many of the smaller models are overpowered and flying on the motor more than on the wing anyway.

I'm a little rusty since my undergrad Fluid Dynamics classes 15yrs ago, but for the bigger models (1/4 scale and up), the Reynolds number do begin to approach those of full scale aircrafts. Of course I don't mean 747s, but the RVs and Cessnas aren't all that much bigger than some of these newer 1/3 and 40% ARFs.

As I have not progressed too far beyond the basic RC flying skills stage, my main interest is to improve low speed and stall characteristics. In another words, keep the plane flying good and me out of trouble. That is why Ed's article grabbed my attention. I guess I'll just have to keep the wingtips squared off and try a few simple bolt-on tip designs to see what happens. Thanks all for the comments.

majortom-RCU

My Feedback: (40)

If it's worth your while to search on that other forum (the slow one) you can probably find the post within the last year or so concerning an end-plate experiment in which a modeler fitted removable end-plates, trimmed the plane with both end-plates on, then removed one and flew again. To get the model re-trimmed in the roll axis he reported two clicks of aileron correction were necessary. Two clicks is not a whole lot, but it is a more tangible result than many other popularly debated design mods.

bobparks

Ed wrote

>All of my conclusions were based on actual model tests.

Sure, but you didnt actually measure the drag on any of them. On virtually any full scale airplane (i.e. where performance is worth money) drag is important, and tip plates are actually very draggy. Yes, you will get some aileron effectiveness, and you can cut the stall speed, but you can get the same results with less drag by other methods.

Winglets can be thought of as tip plates "done right", but even then, its usually better to just increase the wing span a bit. The problem with winglets is that they work well at only one flight condition. Fine for retrofitting airliners, but marginal on sailplanes.

As for the Reynolds Number comments, yes we have sort of low RN, but for most RC power planes, its not THAT low and the basic principles still apply. (FWIW, I do a lot of engineering work on Mars airplanes, and there the RN is pretty low.. 1/5 to 1/10 of your typical RC .40 sport plane, but transonic Mach and things are pretty different there).

bob

Ed_Moorman

My Feedback: (1)

You are still thinking like a full scale flier. Except for racers, sailplane fliers and maybe a few experimenters, nobody gives drag a second's thought. Certainly not the vast majority of RC fliers who fly sport and fun fly planes. Drag! We hover planes. that's power. Drag-bigger engine. Besides, if we were really concerned about drag, we wouldn't ever fly a biplane!

As for winglets, I have seen them on sailplanes, a couple. But other than that, let's get serious here. We fly upside down. You need, at least, I need something that works both ways, upright and inverted. In addition, I would kill winglets on my planes with hangar rash. They just aren't practical on sport RC planes.

End plates, on the other hand, work on RC models. I'm an engineer so I know what's in books, but I am also a long time modeler (I flew my first powered plane in 1950), so I also know what works. You need to slap on some big plates and see what happens. Do the experiment.

I published information on end plates in my R/C Report column several onths ago. Recently I had 2 fliers send me data and photos on their experiments. These will be published in the April issue. One plane was a mini-Wonder, a scaled down version of a Sig Wonder for a 400 electric. It was a tip stalling fiend. The plates stopped the tip stall and increased the roll rate. The second plane was an RCS 1.4 powered, Goldberg Ultimate. The owner reported a much slower and nicer landing.

Try end plates. Naturally, they don't solve everything, but they do help in certain areas. Send me the results of your tests and photos and I'll publish them.

Mike James

Right, Ed!

A rather well-known example of the effectiveness of end plates is on the original (.40 size) "Hots". That model had unexpectedly good slow speed characteristics, and VERY fast roll rates. Mine looked like a cartoon when you rolled or snapped it at high speed.

Ed,

Can you be of assisstance with my "wing and stabilizer arrangement for aerobatics" post, also in this "Aerodynamics" list?

bobparks

Ed wrote:
You are still thinking like a full scale flier. Except for racers, sailplane fliers and maybe a few experimenters, nobody gives drag a second's thought.

If you go back to the first post in this thread, the topic of induced drag came up.. I was responding to that. Also, your web page makes a lot of claims about low drag. My point is that all the real measurements don't back up your claims. I agree, if you don't care about the drag, tip plates can have some advantages.

Ed said:
Besides, if we were really concerned about drag, we wouldn't ever fly a biplane!

You can do efficient biplanes. For some cases they can have performance advantages over monoplanes.

Ed said:
I'm an engineer so I know what's in books, but I am also a long time modeler (I flew my first powered plane in 1950), so I also know what works.

Ok you have be a few years on me. (I was born in 51 and didnt get around to power free flight until 1959). But I also have designed planes that got a few world records and a Harmon trophy, so yes, I have some clue about what works too.

bob

LDaba

My Feedback: (2)

I have read Ed Moorman's article on end plates. Does anyone else have firsthand experience with these? I am planning to use them on a sport plane. They will attach with 4 screws,so I can add or delete them at the field. I am new to these, and I am looking for input.
I have average flying skills and would not want to get in over my head. By average skills, I mean I can do the basic school maneuvers in a left or right hand pattern and can do a reasonable performance of advanced maneuvers.
Thanks in advance. Happy landings Tony

bobparks

Tony,

The tip plates can increase aileron effectiveness, but as long as you are comfortable flying normal maneuvers reasonable size tip plates wont do anything to make the plane hard to fly. (If you put on tip plates that are a couple feet high on a .40 size trainer, it may get a bit wierd ;-) )

So, go try it, have fun, and post the results here.

Bob

Scorpionjack

The most effective aileron's are sealed Aileron's! Tip plates can control lateral movement of the wing as does a rudder. Tip plates are not creating dirty air across a control surface so they have no viable use other than a stabilizer ie. Rudder.

A 100% totally clean wing will have lousy control capabilities at various speeds. Thats why Aircraft have what is called a Vortex Generator. What this?(It's a bunch of little piece's of metal sticking up in different directions to dirty the air prior to it getting to the control surface.) Dirty Air.

Say you purchase an ARF or build any of the funfly style aircraft, of any performance nature with Flat wing tips. You take it to the field and it just won't stay put on knife edge. Always wants to fall out, your always fiddling with the ailerons trying to maintain a crisp knife edge. You now put some winglets on it and it holds steady. Why? Because you've created two more rudder surfaces.
Now you take that same aircraft and buy some clear Ultra-coat if you have an Arf. And you seal the Whole length of the Aileron's and the Elevator. Your Airflow across these surfaces no longer have the gapppppppping Hole/slots and I'll gaurntee(Texas Draw LOL) you that your aircraft will have a new personality. More responsive as well as CA Hinges are now double protected. Chances of High speed flutter has reduced 50 %. Hope this makes a little sense. If not I'll be a little more eliquent/literary on the next response.

Anti-Stall Wingtips: They work better with low speed aircraft and Clark Y Airfoils. Reason behind them is a Clark Y is a Flat Bottom wing it's always creating lift as long as the Aircraft is in motion. The 45 deg under cut Tips(Typically called Anti-Stall tips in the hobby) have a self righting tendancy. In other words if you let go of you controls on a bank cut the throttle back and the plane will try to right it self.

slam

Tip plates reduce the flow from bottom to top at the wing tip and reduce vortex size and therefore drag and therefore improvr performance.

Scorpionjack

Ok dennis;
How? Your talking about a 1/16" or 3/32" thick slab of wood on the end of a wing. The Only area it affects is with regards to a vortex is 1/16" or 3/32" at the trailing edge of the Winglet!

Inverter

I wonder if vortex generators would work on models.

Rotaryphile

I have experimented a fair bit with breakaway tip plates on a competition fun-fly model, and found that they improved performance considerably - quicker loops, better handling near stall, and slightly faster roll. Large tip plates will reduce induced drag only at high lift coefficients - the saw-off point is around 0.5 Cl. You need to have roughly equal plate area above and below the wing. If you place more area above the wing, you get a dihedral effect which may be undesirable. It is far more efficient aerodynamically to simply increase the wingspan rather than using plates. Plates are useful for reducing induced drag within a given span.

Hal deBolt

Hi Volfy.

Hal deBolt

Hi Volfy,
Your post range a bell with me and I have some positive data
on the use of pure winglets on model aircraft.
Several years ago I conducted some aerodynamic comparative
testing of several factors. One was to comparatively evaluate
with using them and not.
I had detailed winglet parameters from NASA.
Vehicles used were electric powered gliders (600 sq. in.), one a
canard. So that powered flight and glide could be observed.
Nasa had indicated a 3% increase in efficency with winglets. My
flight observations would suggest more than that, they diffinitely
improved performance. Rate of climb was greater with more stability, Glide was faster and flatter. No bad effects were noted.
The observations suggest a reduction in drag over normal tips just as NASA saw. The increase in stability was an unexpected asset.
Bottom line is they do improve performance at small cost.
However, first winglets are NOT tip plates. They must be properly
designed and installed with the proper alignment.
Possible shortcoming: improperly installed they can increase drag.
Ever wonder why Burt Rutan uses winglets on ALL his designs?
Good luck!

Hal deBolt

Ollie

There is a circulation, or vortex which exists along a wing producing lift. At the wing tips, the axis of this vortex gradually turns 90 degrees and forms the tip vortices which trail behind the wing tips. Along the span of the wing, the vortex produces an up-wash ahead of the wing and a down-wash behind the wing. The acceleration of the down-wash times the mass of the down wash is equal to the lift force. For a given amount of lift the down-wash is short and intense for low aspect ratio wings but longer and less intense for high aspect ratio wings. It is the lower intensity of the vortex at the tips that produces lower induced drag. If the wing tips are are equipped with infinite tip plates, the vortex is cut at the tips and there is no vortex flow beyond the tips. The two dimensional flow at such tips is more efficient. For finite tip plates the vortex is reduced but not eliminated. Various practical tip shapes can affect the flow around the tip by moving the tip vortex in or out a small fraction of the wing chord at the tip. This small change in effective aspect ratio has only a small affect on the induced drag. Unless the mission of the aircraft involves fuel economy, range or glide ratio the small differences in drag are quite inconsequential. In the case of aerobatic aircraft, drag which limits acceleration can even give a competitive edge.

Cactus.

My Feedback: (1)

why arnt we seeing props with tiny little endplates to lower drag and spin faster?
and would putting on endplates work well on fast planes like Dusts? or would the drag from the face of the tip plate be greater than the advantage given

Ollie

The shroud of a ducted fan acts as an endplate without putting any extra mass at the ends of the blades. That's why the clearance between the blade tips and shroud needs to be so small. The mass at the ends of the prop blades has to be minimized to control the centifugal forces. If too much mass were added at the tips the blade would not be able to stand the stresses and fly apart. Many props are already on the verge of doing that without the mass of end plates.

Planes like the Dust produce the required lift by a combination of high speed and low coefficients of lift. At low coefficients of lift the induced drag is already low so the opportunity to lower it is limited. It would take a very large end plate to lower the induced drag appreciably and that would make much more parasitic drag than the induced drag reduction. If end plates resulted in net drag reduction you would see them on airliners for fuel efficiency and range advantages and on sailplanes for L/D advantages.

Cactus.

My Feedback: (1)

so thats why they have the fins and not endplates.
i did make some upturned wingtips for my small glider as the block gave pleanty to do this with. when i knocked one off i noticed no tip stalling, while it sounds like they dont work, remember the other tip is on the heavy wing now covered in solartex, so it at least canceled out that weight

Hal deBolt

Hi Phillybaby,
Prop tip plates:
20 years or so ago a propeller manufacturer reported experience
with so called tip plates. Not just a flat plate attached to tip but
more like if you took a section of the blade near the tip and bent
it around a radius upward. You want a 12" diamiter, take a 14" prop and bend 1" of each tip upwards.
Report suggested improvements but time erases details for me.
Anyhow at the time I felt the idea worth a try. I had a Quadra powered 1/3 scale RV-4 which flew well with a 20 x 6 prop.
I cut a 20" prop to 18" and installed 1/2" duplicates of what the
full scale used, now diameter was 19".
Comparative test: Was aware of normal take off distance. Rv
would complete 1 vertical roll , then stall out. This was with stock
propeller.
Tipped prop: RPM increased 700. Take off was some shorter
level flight speed was about the same but seemed brisker.
RV would now do two vertical rolls and continue a bit before
stalling out
T believe I performed a comparative thrust test and saw more
thrust with tipped prop, don't recall details.
Bottom line: tipped prop diffinitely was improvement, thinking now winglets could do even more.
Short coming: prop was wooden as was tip. Taxing in tall grass
prop clipped a tough weed, exit one tip plate!
Current thought: with the plastic props the strength problem
probably could be easily solved.
OK? Good luck!

Hal debolt

can773

My Feedback: (1)

Hey

I think you guys need to spend more time flying and less time thinking

I have used flat tips, rounded tips, tip plates, angled ones, blue ones, red ones (ok thats enough) and guess what, they dont make a difference. When the sun is out and it is turbulent, the wind is 90 degrees cross @ 20mph, your tips dont matter!!!! The likelihood of you ever noticing a difference is slim to none, if you do notice a difference it is likely because you are looking for it and seeing something that is not truly there. Stick on what you think looks the coolest and burn that fuel.