Scott Hersha

Scott Hersha

Well Known Member
Come on guys. Where's the discussion on the aerodynamic affects of the hole in the back of David Cook's wheel pants??? I'm doing the finishing work on my RV-8 wheelpants now and need that extra knot that will propel my past Jon Thocker and let me claim the title of 'the fastest RV-8 on the airport' (HAO)... oh yah, did I mention, I don't have my wheel pants and intersection fairings on yet? That might help too. What do you aerodynamicists have to say? Is there pressure build up inside the pant that slows you down? If so, then I think the hole will help. If it's just to drain water, maybe the hole should be a little smaller. If this subject has been addressed somewhere else here, please help this poor fiberglass dust-fazed rvator find it.

Scott Hersha
Phase I test 31 hours
RV-8 Fastback
 
Not so fast Scott

Just so no one's confused, all Scott was missing were the intersection fairings! I think you should be methodical about this Scott, do the intersections first. Then cut the hole.

For those that may be interested Scott and I have recently completed RV8's with nearly identical setups.

Brand new ECI Titan engines built by Jimmy Brod of JB Aircraft Engines
Tapered Barrel cyl.'s
9 to 1 pistons
Carb.'s....... Scott's is a 4164 mine is a 3878
Van's latest baffle kits, I would say our baffling is identical.
Oil coolers on the aft baffle, Scott's is Van's oil cooler II, mine is a SW 8604?
Our basic Avionics package is the same except for Scott's Icom A210 and my Garmin SL40
Dynon D180/AP 74/ Dynon non heated pitot tube
Garmin 496
Garmin 327
Safe Air... non flush static vents and pitot/static/AOA tubing kit

When we fly side by side our airspeed,altitude, OAT, and TAS are identical. My airspeed in the cruise regime has been found to be accurate via numerous calibration runs while breaking the engine in, to be dead on + or - 1 knot.

The key differences in our planes are: Scott's is a fastback and he's running 1 Lightspeed electronic ignition.
Scott has a Whirlwind 2 blade prop, I have a Hartzell BA 7497 prop.

I hope to do a formation start up, taxi, and takeoff, then full throttle climb to 8000 to 10,000 ft. Recording or downloading #'s from the Dynons.

Maybe we can put to rest the debates on Carb. nozzles, and oil coolers.

If Scott should turn out ultimately faster than me, be assured that it will be at the expense of his health, due to massive fiberglass/micro/ flox dust ingestion in the pursuit of maniacal fit and finish!!!:D
 
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Must be a lot of studying out there.....

I keep coming back and checking on this post......I can't think of this Mod being that important. I guess even if it is a little, it is worth the increase because its a small/easy Mod. Can anyone explain how this works? I really am curious.
 
OK, there is no way in H3!! that is a speed mod

I do think all the RV Blue Class racers should implement the mod though. Well, all but Race #71

Bob Axsom
 
I brought this mod up to a friend that races at Reno(formula 1, biplanes) today and his response was, if you provide for outflow you effectively increase the wetted area. Meaning you not only have the exterior of the wheel pant wetted area you now have the inside wetted area also. So there might not be a net benefit.
 
Faster Faster!!!

(I brought this mod up to a friend that races at Reno(formula 1, biplanes) today and his response was, if you provide for outflow you effectively increase the wetted area. Meaning you not only have the exterior of the wheel pant wetted area you now have the inside wetted area also. So there might not be a net benefit.)




Did ya think about the fact that the pants are lighter?

F=L/d wt x hambuger x L2 + ###= OU812
 
Unless you are...

SportAvServ said:
(I brought this mod up to a friend that races at Reno(formula 1, biplanes) today and his response was, if you provide for outflow you effectively increase the wetted area. Meaning you not only have the exterior of the wheel pant wetted area you now have the inside wetted area also. So there might not be a net benefit.)

.....
Click to expand...

...sucking air up from around the wheel opening and expelling it at the new rear hole....

Perhaps the reduction in turbulence around the wheel (assuming there is a reduction...:)...) can outweigh the increase in wetted area?

The hole is in a low pressure area and will tend to suck air out of the wheel pant.
 
Disagree

az_gila said:
...sucking air up from around the wheel opening and expelling it at the new rear hole....

Perhaps the reduction in turbulence around the wheel (assuming there is a reduction...:)...) can outweigh the increase in wetted area?

The hole is in a low pressure area and will tend to suck air out of the wheel pant.
Click to expand...

Gil - I have to disagree with you. There is a support wall (call it a rib if you will) on the inside of a main wheel pant. In other words, even with the hole, it is not possible to have a continuous air flow unless there has been a hole cut in the support wall.
 
Other Idea

Perhaps he intends to fit a couple of those small jet engines now used for model aircraft, one in each wheel pant. It may be possible to get an extra 30lbs of thrust! Would also help at high altitude.:)
 
OK I'll bite. I'm not an aerodynamic engineer and did not stay at a holiday inn express recently but....


Seems the hole is of a size and location to drain water/ debris from the wheelpant assuming there is an opening in the bulkhead.

I think if you wanted a speed increase it would be better to open the internal bulkhead with a small exit hole and cut a slot in the exact tail of the wheel pant. I am "assuming" this would generate a slight negative pressure at the aft end of the wheel pant to help recover airflow while leaving the inside of the wheelpant pressurised.
 
JET ENGINES,,, come on guys

What I,m planning are two corn cob radials with pusher props cut off for ground clearance.... Laugh on guys, this airplane is the fastest of the rv,s that I,ve built (4&6) trueing out at 220 even with the woosywheel in the front..
There is a 1 inch tube going from the top of the bulkhead to the bottom of the pant,,, It,s sole purpose is to vent any pressure buildup.
 
OK... that...

Webb said:
Gil - I have to disagree with you. There is a support wall (call it a rib if you will) on the inside of a main wheel pant. In other words, even with the hole, it is not possible to have a continuous air flow unless there has been a hole cut in the support wall.
Click to expand...

..shoots down my theory.

But, if there is a "sealed compartment" back there, then the hole appears to be useless.... air cannot flow into or out of it, and aerodynamically it essentially does not exist....:)

Might as well just use black paint....:D
 
David, can you offer some theory please?

Here's a guess. As I understand wheelwells in cars and wheelpants on airplanes, air circulates around the tire as in the first sketch. Your vent would stop or reduce that circulation if sized correctly. It might cause more drag if it were too big.

Disclaimer; I ain't no aero whiz <g>

 
Possible explanations:
1. Them mice gotta have somewhere to live!
2. Brake cooling, or in the event that fails and fire results - tailpipe for jet exhaust.
3. Create endless speculation on VAF.
:)
 
fl-mike said:
Possible explanations:
1. Them mice gotta have somewhere to live!
2. Brake cooling, or in the event that fails and fire results - tailpipe for jet exhaust.
3. Create endless speculation on VAF.
:)
Click to expand...
I'm an AE, and I go for #3...:rolleyes:
 
DANH
Good drawing,,,, you hit it on the head. A tube goes from the bulkhead in the wheelpant and ends with the hole shown in the photo.. No rime nor reason, just a hunch that it might help a little......

Dave cook Mtnflyer
 
Question: Do the wheels spin in flight after you've braked them to a standstill? I guess it'll be difficult to see this from the cockpit though.

My hunch DanH is that the airflow is opposite to what you have shown in your first diagram. The high pressure will be in front of the tyre and the low pressure behind, making the flow move anti-clockwise as shown in your drawing.

My aerodynamic theory is that flow around the outside of the wheel pant is much more efficient than any internal flow, therefore all efforts should be put into minimizing or eliminating internal flow, not adding features to allow it to happen.

A
 
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