whats "pressure recovery wheel pants"

[flybynight55]

Can someone explain to me what are pressure recovery wheel pants. I've looked on Vans Aircraft, but can't find them. Thanks, Tom

[gmcjetpilot]

Originally Posted by flybynight55

Can someone explain to me what are pressure recovery wheel pants. I've looked on Vans Aircraft, but can't find them. Thanks, Tom

It's just a name, Van calls his last wheel pants as "Pressure Recovery". Others also sell wheel pants and call them pressure recovery designs.

It defines a aerodynamic principle of, well guess what, of recovery of pressure. The idea is to sharpen the pencil and use airfoil shapes to make a lower drag wheel pant. The shape promotes better air flow around the wheel pants. What is the pressue recovery part? Apparently the the aft part of the fairing recovers the pressure built up in the forward half, in a word producing either less drag or some thrust, thus the pressure recovery. It also I guess means laminar flow. You see it in the old Myers airplanes which Mr. Lancair used as a model for his early designs, had a fuselage that necked down quickly aft of the cockpit.

Most of this theory and word pressure recovery came out of Reno formula air race guys from their research and experimenting. They have very long and highly tailored aft sections to their typical wheel pants. They also seem to have max width further aft and use curved surfaces. Again its just a name, but there is some PFM behind it (pure freaking magic).

Its a theory and it has merit and no doubt may or may not work in practice fully, but Van over his 30 year history has had 3 major wheel pant changes, one piece, two piece and the last and latest greatest "pressure recovery" wheel pants (*also a two piece design). Each wheel fairing design was faster than previous one, so there must be something to it. The latest and last PR faring has been around now for at least 8 years. You can see the PR has a much more bulbous front and skinny aft end than the other designs. Now Van's PR wheel pants do look different than the ones at Reno.

There are other pressure recovery designs for the RV from Lightspeed engineering and James Aircraft. (*The two piece allows tighter wheel to faring fit and gap around where the tire protrudes; a one piece must slip over the whole tire, making a large gap and drag. This has nothing to do with PR.)

Keep in mind watch little details like the joint where the two fwd/aft halves come together and the intersection faring. Poor details will trip air flow and affect drag. The, "if it looks good it is good" rule applies. Also wheel pant alignment is key and critical, as it is for the gear leg faring.

Here is a cool web site that explains this and shows how to design and make your own PR wheel pants (was working not its not?):

http://www.geocities.com/mgd3/flying/wheelpants.htm

or Google: pressure recovery wheel pants

[DeltaRomeo]

I've often heard them referered to as 'Dolly Partons'. You'll get it when you see them.

b,
d

[RV7Factory]

Originally Posted by gmcjetpilot

Here is a cool web site that explains this and shows how to design and make your own PR wheel pants (was working not its not?):

http://www.geocities.com/mgd3/flying/wheelpants.htm

Small world. I occupied the hangar next to Mike. He is ALWAYS tweaking something in the hunt for more speed.

[hevansrv7a]

Originally Posted by DeltaRomeo

I've often heard them referered to as 'Dolly Partons'. You'll get it when you see them.

b,
d

That's Sam James's term for Van's version because Sam's are narrower, side to side. Sam acheives this by making the center of the wheel fairing inboard of the center of the tire, thus covering the brakes, as does Van's, but with no offset outboard from the big axle nut. He also recommends (but not in the written instructions) forming the rear bulkhead inside the fairing to conform to the shape of the tire, like a bicycle fender.