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Wheel pant aerodynamic improvement?

brad walton

Well Known Member
It would be relatively easy to minimize the gap between the tire and the wheel pant fairing by the use of baffle air seal material riveted inside the wheel pant and cut so it just touches the tire. I assume this would help to reduce the turbulence that results from air flow in and around the gap. I'm interested in thoughts on whether this may produce a useful reduction in drag. I believe DanH has done something similar with siliconized fiberglass. Maybe others have tried this too. Is it worth the effort?
 
Others have done similar mods for racing, check this archives.

However, you gain around 10 knots from the gear leg fairings and five from the wheel pants. How much speed do you think you will gain?

With this in mind, I set my wheel pants high so I wouldn't damage them on a rough grass strip.

If I was into racing, I would look for every quarter knot but I'm not a racer, so I am happy to give up a little speed and future maintenance issues.
 
Lopresti had an option that fully enclosed the wheel in flight and would open for landing. I never heard from anyone that had tested them.
 
What would that do to the cooling air when braking? For the very slight gain in speed you may be trading overheating of the brakes and a possible fire.
 
yes - it's worth it

2-3kt gain. I used 1/8" baffle material, cut to just rub on the tire. I think 1/16" material would work a bit better, but it's not so easy to find (silicone, with the re-inforcing threads in it).

DanH's idea of molding the seal materaail to shape is another of his good ones.

The heat issue is genuine - I left the aft pcs off, as the taxi at Reno is quite long, and sometimes downhill...so some cooling is needed. I would not use this mod on a nose-wheel ship unless something was done to assure cooling, or heavier brakes are installed.

The Lopresti device looked promising, but after a couple of 'gear up landings', it might get expensive.... a cooling flapper door would be ideal, if such could be rigged.

Carry on!
Mark
 
I would caution builders trimming the wheel pants too close to the wheels. In the real world of cross wind landings the tires flex a lot. I have had to open up the gaps to prevent tires from rubbing.

Maybe I should work on my landings? :cool: ;)
 
I would caution builders trimming the wheel pants too close to the wheels. In the real world of cross wind landings the tires flex a lot. I have had to open up the gaps to prevent tires from rubbing.

Maybe I should work on my landings? :cool: ;)

X-winds or not, momentary spin-up increase in tire diameter is astounding and will tear up the fore and aft clearances if too close. Hard landings cause the tire to momentarily increase in width. Give yourself "a fingers clearance" all around and you should be fine.
 
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Lopresti had an option that fully enclosed the wheel in flight and would open for landing. I never heard from anyone that had tested them.

This was actually a Jim Bede design from many years ago.
 
Thank you for the responses, just what I was looking for. I had not considered brake cooling which would certainly have to be accounted for. The Lopresti/Bede idea is a good one but probably beyond my ability to engineer. I now have a little over 260 hours and no problems with tire/fairing clearance. I have the larger 180 x 350 tires and keep the pressure up above 40 psi.
A one or two knot increase in efficiency would be worth the effort. Equal to about 4 or5 HP without an increase in fuel burn. Got to love free energy.
 
Brake overheating with fully shrouded openings has not been a problem in 400 hours, and I use 'em pretty hard.

The disks are an energy storage mass. They acquire energy at a very rapid rate, just seconds really...consider your total braking time. In comparison, they lose that energy to the atmosphere very slowly. Overheating is a function of how they are used, not how they cool.

Many RV drivers don't grasp how close they are to brake overheat even without wheel pants. The Clevelands supplied with a 2 place kit are only rated at 117,500 ft-lbs. Here's the math, per Cleveland and the FARs:

Kinetic energy per wheel (ft-lbs) W =
(0.0443 x landing weight x velocity^2) / number of wheels

Using plausible numbers for gross:

.0443 x 1850 x 65 x 65 / 2 = 173,130 ft-lbs (Uh oh!)

Let's land solo with 10 gallons and roll to 60 before braking:

.0443 x 1360 x 55 x 55 / 2 = 108,446 ft-lbs

Point is this...you have capacity for one full stop landing before you need to fly around a while and let the disks get back to ambient. Shrouded wheel openings may slow that process, but that's about all.
 
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For those like me that had never noticed the signature line previously, it is worth the visit to actually see a radial on an RV8 ! What a project!

Is there a reason they didn't stay on the market long? Maybe the speed claims were a little to good to be true.....
 
This was actually a Jim Bede design from many years ago.

The retractable wheel pant was developed by Mr. Bede, and not so long ago (2009) the product won the LoPresti Award for Innovation. The AvWeb article below states that at the time they were planning a price of $1,995 per pair and expecting to have them available for the RV-7 or RV-10 later in the year?

http://www.avweb.com/news/snf/SunNFun2009_LoPrestiAwardGoesToRetractableWheelPants_200235-1.html

BedeCorp?s website is still active?it would be interesting to contact them and ask about availability?

http://www.bedecorp.com/
 
Seems to me I remember a wheel pant suggestion from Vans in a very old RVator or maybe even the plans where it suggested using brush fibers, mounted to the inside of the pant, so they would brush up against the wheel and close the gap.
I don't think I have seen any wheel pant that was actually made like this, though.
 
The retractable wheel pant was developed by Mr. Bede, and not so long ago (2009) the product won the LoPresti Award for Innovation. The AvWeb article below states that at the time they were planning a price of $1,995 per pair...

$50 or so in materials:



One goal was to mount the pants very low for maximum tire coverage. To make it practical, the entire bottom of the pant was cut away after the rubber was formed over it. You can see the cut line extending back to the tail. It means the bottom is flexible, and shrugs off bumps. Good thing too, as there is only about 1" of ground clearance behind the tire, and I run 50 psi. As you can see, I added a few wear layers there.

8oz plain weave impregnated with room temperature cure urethane rubber between 4 mil plastic sheets, just as you would use epoxy. Even use the same PVA release film:



Very few folks notice the galoshes:

 
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$50 or so in materials:

http://i1368.photobucket.com/albums/ag200/Dan51/RV-8%20Build%20Log/Wheelpant%20Galoshes/250hourswear300W_zpsd3628316.jpg

One goal was to mount the pants very low for maximum tire coverage. To make it practical, the entire bottom of the pant was cut away after the rubber was formed over it. You can see the cut line extending back to the tail. It means the bottom is flexible, and shrugs off bumps. Good thing too, as there is only about 1" of ground clearance behind the tire, and I run 50 psi. As you can see, I added a few wear layers there.

8oz plain weave impregnated with room temperature cure urethane rubber between 4 mil plastic sheets, just as you would use epoxy. Even use the same PVA release film:



Very few folks notice the galoshes:

http://i1368.photobucket.com/albums/ag200/Dan51/RV-8%20Build%20Log/Wheelpant%20Galoshes/Clearance_zps922cb53d.jpg

So the red is where the "hard" wheel pant stops, and the white is where the rubber stops? I like it!
 
So the red is where the "hard" wheel pant stops, and the white is where the rubber stops? I like it!

Yep.

Rubber is PMC-780 Dry:

http://www.smooth-on.com/Urethane-Rubber-an/c6_1117_1148/index.html

3lb trial size is enough for two wheel pants:

http://www.smooth-on.com/Urethane-Rubber-an/c6_1117_1148/index.html?catdepth=1

Also need an adhesive to glue them on when you’re done:

http://www.smooth-on.com/Urethane-Rubber-an/c6_1118_1269/index.html

and some black pigment:

http://www.smooth-on.com/Urethane-Rubber-an/c6_1118_1202/index.html

Usual disclaimer: Do what I do and you may die.
 
Matco Manufacturing

Dan,

The MatcoMFG brakes for the 10 would appear to have sufficient (heat) residual for multiple landings based on your calculations. True?
 
Dan,
The MatcoMFG brakes for the 10 would appear to have sufficient (heat) residual for multiple landings based on your calculations. True?

I dunno. What is the KE rating, how fast do you land, and how heavy?
 
Dan

Does your rubber skirt overlap the tire, just rub against it or is there still a small but smaller gap.

Thanks for your idea. Now I just need the time.

Paul
 
The Matco wheel/brake set for the RV-10 is rated at 225,000 ft-lbs. Looking at Dan's calcs and extrapolating (roughly) this can be exceeded at high gross weights...still more of a margin than the stock set.

.0443 x 1850 x 65 x 65 / 2 = 173,130 ft-lbs (Uh oh!)

RV-10 grosses at 2700# so half again as many ft-lbs, around 253K (assuming you get on the brakes at 65) Doing the calc backwards says at full gross you'll exceed this if braking above 62; at 2000# it'd take braking above 71, and so on and so forth.

==dave==
 
The retractable wheel pant was developed by Mr. Bede, and not so long ago (2009) the product won the LoPresti Award for Innovation. The AvWeb article below states that at the time they were planning a price of $1,995 per pair and expecting to have them available for the RV-7 or RV-10 later in the year?

http://www.avweb.com/news/snf/SunNFun2009_LoPrestiAwardGoesToRetractableWheelPants_200235-1.html

BedeCorp?s website is still active?it would be interesting to contact them and ask about availability?

http://www.bedecorp.com/

For those who are relatively new to homebuilding:
Before handing Bede Corp money, it might be wise to educate yourself in homebuilding legal history.

Charlie
 
...any before and after numbers?

No, the galoshes were installed before first flight.

Does your rubber skirt overlap the tire, just rub against it or is there still a small but smaller gap.

Started out with very little gap. Don't really know what I have now. It will self-adjust (wear) without harm.

The Matco wheel/brake set for the RV-10 is rated at 225,000 ft-lbs....RV-10 grosses at 2700#...get on the brakes at 65..

(0.0443 x 2700 x (65 x 65))/2 = 252,676

....so as Dave points out, there is not two full-stops worth of rated heat storage in those Groves, assuming no cooling time between applications. Obviously there is some cooling time while going around a pattern. Point is, be aware of a cooling time requirement, which will be longer with gap-sealed wheelpants.
 
Does anybody remember hearing about a wheel fairing mod that was an opening in the trailing end of the pant - a slot - to reduce the drag of the air that entered through the opening around the tire? The baffle in the aft wheel fairing had an opening near the top of the baffle plumbed via a tube to the aft slot that would vent air that entered around the tire, thereby reducing drag, theoretically. I believe it was tried on the fixed gear Radial Rocket TD, and they claimed about a 5K improvement in cruise airspeed. If that worked, it would also allow brake cooling because of this improved airflow - seems like anyway.
 
Ray Cote had wheel pant doors on Shoestring one year to get around the "fixed gear" rule for Formula 1 racers. Sometime in the 1970s...don't remember the exact year.
 
Does anybody remember hearing about a wheel fairing mod that was an opening in the trailing end of the pant - a slot - to reduce the drag of the air that entered through the opening around the tire? The baffle in the aft wheel fairing had an opening near the top of the baffle plumbed via a tube to the aft slot that would vent air that entered around the tire, thereby reducing drag, theoretically. I believe it was tried on the fixed gear Radial Rocket TD, and they claimed about a 5K improvement in cruise airspeed. If that worked, it would also allow brake cooling because of this improved airflow - seems like anyway.

Scott, my memory ain't what it used to be but I recall a few posts concerning drilling a hole in the main gear wheel pant bulkheads behind the tire using a hole saw then another in behind the wheel opening towards the tail end of the pant. I don't recall the tube you mention but that would keep mud, ice, etc from accumulating where it would be difficult to clean out. I searched for the thread but came up empty. I don't think you are miss remembering.
 
Does anybody remember hearing about a wheel fairing mod that was an opening in the trailing end of the pant - a slot - to reduce the drag of the air that entered through the opening around the tire? The baffle in the aft wheel fairing had an opening near the top of the baffle plumbed via a tube to the aft slot that would vent air that entered around the tire, thereby reducing drag, theoretically.

Pretty sure that one is BS. Flowing air through a wheel pant would be just like flowing air through the cooling system, mass x loss of velocity = drag. Reducing drag would require a reduction of mass flow, or increased exit velocity. With no requirement for flow (like cooling), the most effective way to cut drag would be to reduce mass to zero.

Drag due to the tire opening is well documented in automotive design. It's mostly circulation within the opening. Note that very low drag cars enclose the wheel openings as much as possible.
 
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