Has anyone ever seen a study of wheelpants. I.e., anything that says they are anything but just aesthetics. Do they serve any aerodynamic purpose at all on an RC plane. thanks.

Full-scales, pants make a difference, or they wouldn't be used!
On models, it's more asthetics than performance improvement, although for competitions where a fixed gear is required, fairing the wheels is probably worth the slight amount of improvement, when legal.
Otherwise thin wheels serve the purpose.
Williams Bros make a dandy selection of skinny wheels for the speed enthusiast, which also look good on the plane.

yeh -on models - it is simply a looks thing-
even on the full scale stuff going back to the 1930-/40 etc., airshow daredevils- the wheelpants were among the first things to go -They simply were extra weight .
The Bucker designs - the best in the world for aerobatics for many years - used only tiny mud catcher fenders.
for max cruise -best speed/ least fuel consumed - streamlined covers do help --on some full scale stuff .
The best trade off design is probably the one used on the Sukhoi 31-- a tiny wheel fairing, behind each main wheel.

As was alluded to above it depends of the flight regime you are interested in. If you are going for speed or endurance it is well worth it especially if you have fat tires. Lower drag means going faster. There has been a lot of work documenting the results, notablely the in Horner drag and performance book. Look at the full scale designs that have them, they have usually been thought out by careful designers and work as desired.

Usually in RC work the pilot makes enough mistakes that cause drag that the pants don't matter, but, if both pilots and airframes are equal then the difference pants bring might help. Do note as they also said that a knife edge wheel (which is mostly impractical on full scale) whe used on a model is a very low drag affair.

In a competition aerobatic machine it becomes difficult to make a case to add wheelpants. Great static thrust and light weight are needed. Lowest drag isn't necessarily a good thing when designing a constant velocity airplane.

Properly done they do look good though on anything.

I agree with the others that it depends on the flight regime. Personally, I wouldn't think of building a serious pylon racer WITHOUT wheel pants when allowed in the rules.

Something I've noticed about our model wheel pants is that, compared to full scale, they seem to be much bulkier. We need comparitively more clearance to prevent binding, and we leave a lot more wheel sticking out because of drag from grass runways. I wonder if all that cancels out any potential drag reduction?

I flew without wheel pants for the longest time on my radiocraft extra. For vertical down lines, power off, a 4% mix of down elev to throttle was required to hold a down vertical line. I then added wheel pants to the plane and without changing the mix the plane was tucking more and more as it gained speed. I reduced the mix to 1% and now it holds a perfect vertical down line. So for me there was a noticable difference, and wheel pants made my plane fly closer to neutral.
talk to you soon,
Jon

yeh -added drag changed the picture.
Also -the wheel pants add area - so no matter how streamlined - you have more surface area.
which equals more drag.
But as mentioned - you do look better with your pants on.
on a pylon racer - I would bet you couldn't tell any difference in lap time -pants on or off.
I still have a set of pylon pants and wheels - about 3/8" wide pants - over 1" in thick wheels.

On a model, they're 99% aesthetic, but imagine how unattractive this SST.40 was as designed, with trike gear.

This depends. The drag coming off objects such as wheels or struts is usually pressure drag (the drag associated with bluff-bodies or seperated flow). The drag coming off a well-streamlined shape such as a properly designed wheel pant is usually skin friction drag. Depending on the type of flow, Reynolds number, etc., the skin friction drag can often be much smaller (sometimes an order of magnitude or more) than the pressure drag without the fairing. Assuming again that the pant/fairing is designed properly with little to no flow seperation, the savings in drag can be very significant despite a doubling or more of surface area.

About the added surface area, take a look at wing struts on just about any plane that uses them--Cub, Taylorcraft, Aronca, golden age racers etc. The struts are airfoil shaped. There certainly would be less surface area if they just used round struts but airfoiled struts are used because they offer less drag.

On a pylon racer you probably would win your bet about the difference in lap times not because wheel pants don't offer any advantage but because most pilots (including myself) aren't consistent enough to be able to tell a difference. But it is the little things that add up and the sum of all can make a difference.

Wheel pants will generally reduce the drag produced by the landing gear. But then, so what? If you are racing, it may just help. If you are flying aerobatics drag is not necesarilly a bad thing.

I believe the cruise speed of a FS Cessna 172 is improved 2.5 kts by wheel pants, or less than 2%.

I fly mostly sport / aerobatics at the field, and wheel pants add tons of headaches as far as maintenance and care needed. So, I defeninitly support flying without pants![sm=RAINFRO.gif]

Agreed. I fly without pants too.

Dude, I'm in Orlando. That's entirely different in Alaska![X(]

Please tell me where you are flying without pants and I will come and photo the sight ............ On second thought........ maybe not ........ don't want to break the camera.

Here's Cessna's logic for not changing the design if their crappy wheel pants:

Mid 1970s: We are selling lots of airplanes. Why mess with sucess?

Now: We are not selling many airplanes. Can not justify spending any money on R&D.

Well designed wheel pants can make a big diference in speed for a full scale plane. The wheel pants on the Lancair Columbia are good for something like 17 knots. That's about as good as retracting the gear but without the weight, mechanical complexity, cost, etc.

cirrus

On the models, the aerodynamic effect can be significant.

I built a 4*40, and after a while decided to home-make some wheel pants for appearance. installing the wheel pants changed my elevator trim 3 clicks. (had to give it down trim because of reduced drag below the wing. These were SIMPLE teardrop profile, flat ply wrapped wheelpants too... (the draggiest design there is in wheelpants)

Later, I clipped a rock landing and had to take off one wheelpant that was rubbing the wheel. (was too lazy to take off the other) suddenly I needed 4 clicks rudder trim and 2 clicks up trim. There were no other changes to the aircraft... just lost one wheelpant.

If it can make that much difference on the slow flying 4*40... think what better wheelpants wll do on faster models.


You will also note that Pylon racers with fixed gear ALL use wheelpants. These things add weight. Weight is an enemy of a racer. if there was no aerodynamic reason to use the wheelpants you can bet they wouldn't be there.

*********

When SPEED is not a consideration, then the weight will be, as in the aerobatics example. For low speed aerobatics the weight is a bigger factor than the drag reduction. But for anythig except low speed aerobatics, the wheel pants are highly desired.