Speed improvement from fairings/wheelpants

Ron Lee · #1 10-18-2007, 09:54 PM

At data performed at 11,500' DA WOT. RV-6A, O-360, 9.5 pistons, carb.
Four course speed runs using IAS. As long as all the IAS were close I considered it a valid test.

1) No fairings or wheelpants on. Gear leg stiffener on back of nose gear.
Baseline for speed changes (IAS speeds: 156, 156, 155, 155 mph)

2) Added main gear leg fairings, intersection fairings and wheelpants. Wheelpants primed and basically smooth but not painted. All other parts painted. (IAS speeds: 173, 171, 172, 172 mph)

Speed increase over baseline 16 mph. RPM increased by about 80 as well.

3) Added painted nose gear leg fairing, intersection fairing (to bottom of cowl) and unfinished (not even primer) nose wheel pant. (IAS Speeds: 175, 174, 175, 173 mph)

Speed increase about 3 mph.

Total about 19 mph. It may have been higher if the baseline did not have the nose gear leg stiffener which may have acted a bit like a fairing.

n2prise · #2 10-18-2007, 11:21 PM

I got 15 MPH increase on my RV-9A. The first flight was the only one I flew with the gear legs bare and no wheel fairings. I was flying at 2,300 RPM and 23" manifold pressure both times.

gmcjetpilot · #3 10-19-2007, 12:12 AM

Quote:

Originally Posted by Ron Lee

At data performed at 11,500' DA WOT. RV-6A, O-360, 9.5 pistons, carb.
Four course speed runs using IAS.

1) No fairings or wheelpants on. Gear leg stiffener on back of nose gear.
Baseline for speed changes

2) Added main gear leg fairings, intersection fairings and wheelpants. Wheelpants primed and basically smooth but not painted. All other parts painted.

Speed increase over baseline 16 mph

3) Added painted nose gear leg fairing, intersection fairing (to bottom of cowl) and unfinished (not even primer) nose wheel pant.

Speed increase about 3 mph.

Total about 19 mph. It may have been higher if the baseline did not have the nose gear leg stiffener which may have acted a bit like a fairing.

Nice Nice Nice data, thanks for taking the time to measure this before after.

hevansrv7a · #4 10-19-2007, 03:42 AM

RV-7A, Superior IO-360 180 hp, James cowl, plenum & wheel fairings. At least 19 kts.

pierre smith · #5 10-19-2007, 06:01 AM

We made 186 MPH with the nosegear leg fairing and upper intersection fairing on at 7500 DA. It shot up to 202 MPH or better with everything on, plus around 200 FPM more climb...we were very pleasantly surprised. A whole different airplane and even harder to slow down.

Craigs prop also gained a bunch of RPM, redlining at 2700, just as he said it would at WOT.

Regards,

Janekom · #6 01-16-2008, 07:15 AM

Hi Pierre,
I agree - there was a huge increase when we added all the goodies!
Slightly off topic but:
Can you or someone else tell me why the RV6 has got a nose leg stiffener?
I assume it is the same as on the 7A main gear?

The reason for asking is that I am considering adding a stiffener to NOSE gear of the 7A we are currently building.
Thanks.

L.Adamson · #7 01-16-2008, 07:31 AM

Quote:

Originally Posted by Janekom

Hi Pierre,
I agree - there was a huge increase when we added all the goodies!
Slightly off topic but:
Can you or someone else tell me why the RV6 has got a nose leg stiffener?
I assume it is the same as on the 7A main gear?

The reason for asking is that I am considering adding a stiffener to NOSE gear of the 7A we are currently building.
Thanks.

The stiffener is an option now. In the "old days", RV6A kits came with two piece aluminum fairings for the mains, and you had to make a smooth fiberglass wrap around wood stiffeners for the nose gear. No pre-made fiberglass fairings existed.

As to preferences in regards to being better or worse (except for ease of building), I don't have the answer.

L.Adamson

elippse · #8 01-17-2008, 09:46 AM

Hi, Ron! 'Sorry to rain on your parade, but the rpm increase is not consistent with the speed increase. Typically you should experience 100 rpm increase for each 6 mph to 10 mph speed increase, the latter with a higher pitch prop. Your TAS from IAS would be 184.7, 205.0, and 207.4; that would be a 20.3 mph TAS increase from the first to the second! That should have given you a 280 rpm increase for a 76" EFFECTIVE pitch prop. Consider this: if your prop has an EFFECTIVE pitch of 76", that means you will travel 76" forward for each revolution. 100 rpm would give 100X60X76/(12X5280)=7.2 mph. It is possible that the fairings changed the air flow at the static ports to give an IAS error. This shows the fallacy of using IAS even for relative testing! The only true check of performance increase is to measure two-way GPS groundspeed.

Kevin Horton · #9 01-17-2008, 10:09 AM

Other builders have reported around a 20 mph TAS increase when adding wheel pants and gear leg fairings, so the speed increase reported here appears credible.

Perhaps the tach errors are different at the two different rpms. If so, perhaps the real rpm increase was more than 80 rpm.

Ron Lee · #10 01-17-2008, 10:58 AM

It was what I recorded. If my speed improvement is consistent with what others got then using IAS was "close enough." I have done GPS runs and it is too time consuming for my needs.

My philosophy is to try to get the best data possible knowing that there may be errors. To the extent that others inputs and suggestions can improve what I do...thanks.