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  #1  
Old 07-18-2017, 07:03 PM
Chattin35 Chattin35 is offline
 
Join Date: Jul 2014
Location: Boise, ID
Posts: 185
Default Speed increase from wheel pants and gear leg fairings

So, I just finished installing my wheel pants and fairings. Thought I would share the results (spoiler: she fast).

Before...



Install...

I jacked the plane up by wrapping a tow strap around the base of the engine mount. Once the plane was off the ground I leveled the longerons and lowered the a/c until the wheels were just off the ground (1/8'' or so). This gave me the "in flight" orientation of the wheels. Then I lined up the pants using a couple of points on the aircraft center-line (as close as I could get) and the tread on the tires and the rear of the wheel pant. Alignment was to the plans except for adding a 1/4'' spacing b/w the top of the tire and the wheel. The idea behind adding some clearance is because I fly off grass fairly often and plan to add bigger tires at some point. The pants are still very close to the ground, however. If I was doing it again, I'd add even more clearance.

I heard a couple of local builders talk about going crazy trying to gnat's a$$ the fairings and ending up with a yaw anyway. So, I didn't spend much time lining everything up. Just measured a center-line point at the tail and firewall and dropped some plum bobs and marked equal distance points on the fairings at an inner and outer location. Then, I used Van's string method to get them close. You can see I didn't jack the plane up for this as another builder told me not to bother with that either.



Results...

Just the pants on this morning. Flew the speed runs in a square box, at 8000' DA, wide open at 2700 RPM. Overall, the pants added 4 knots to the speeds I was previously seeing at this altitude/power setting. No noted yaw so I'm happy there. Surprisingly, I noticed a 3-4 knot decrease in stall speed. Although, that might just be because I was light on fuel. It stalled around 46 knots with full flaps - which was the slowest I've seen so far.



Later this afternoon I flew another speed box with the fairings installed. It gave me another +8 knots! I was truing out at 175 plus or minus a couple knots at 8000' DA. Awesome! It was a little bit bumpy. So, not the best conditions to get a precise reading. But, I'm stoked. The pants and fairings work as advertised.

And best of all, no yaw! I guess I got lucky there. I was expecting to have to experiment with the alignment to get it flying straight. But, I think we're gtg.

After...



TL/DR: Wheel pants and fairings gave me +12 knots at 8000' DA, wide open 2700 RPM. Trued out at 175 kts. They work as advertised.

To be continued after intersection fairing install...
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  #2  
Old 07-18-2017, 09:48 PM
CubedRoot's Avatar
CubedRoot CubedRoot is offline
 
Join Date: Sep 2013
Location: Ooltewah, TN.
Posts: 428
Default

NICE! 175 Knots at 8000 and you still have the wing fairings to do? It'll be interesting to see what those add.

Would you mind sharing your engine, prop and weight specs?
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RV-7 Slider -
Tail kit Completed - March 2017
Wing Kit Started - June 2017
My Build Log: http://www.theskunkwerx.com

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  #3  
Old 07-18-2017, 10:30 PM
Chattin35 Chattin35 is offline
 
Join Date: Jul 2014
Location: Boise, ID
Posts: 185
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Quote:
Originally Posted by CubedRoot View Post
NICE! 175 Knots at 8000 and you still have the wing fairings to do? It'll be interesting to see what those add.

Would you mind sharing your engine, prop and weight specs?
You bet. I kept it simple - built it light and to the plans.

1043 lbs empty.
Stock IO-360-M1B and Hartzell BA CS prop from Van's.
Vetterman 4-pipe exhaust.

Oh and the intersection fairings join the gear fairing and the fuselage and the fairing to the wheel pant. Not related to the wing .

Last edited by Chattin35 : 07-18-2017 at 10:44 PM.
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  #4  
Old 07-18-2017, 10:40 PM
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CubedRoot CubedRoot is offline
 
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Quote:
Originally Posted by Chattin35 View Post
You bet. I kept it simple - built it light and to the plans.

1043 lbs empty.
Stock IO-360-M1B and Hartzell BA CS prop from Van's.
Vetterman 4-pipe exhaust.

Oh and the intersection fairings join the gear fairing and the fuselage and the fairing and wheel pant. Not related to the wing .
Ah.. I was thinking you were referring to the little gap where the wings meet the fuselage. It's hard to tell in those photos that you may have already done that.

I'm always impressed by how the least little bit of fairing work can give such great improvements in speed and efficiency.
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RV-7 Slider -
Tail kit Completed - March 2017
Wing Kit Started - June 2017
My Build Log: http://www.theskunkwerx.com

VAF Donation paid for 2017
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  #5  
Old 07-19-2017, 10:22 AM
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Raymo Raymo is offline
 
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Location: Richmond Hill, GA (KLHW)
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Excellent. I picked up ~20 Kts after installing the gear/wheel/intersection fairings on my -7A. The mains previously had the inboard fairing mounts installed and I suspect they were causing a lot of drag as well.

I'm cruising at 155 TAS, 7.5 GPH at 8500. Catto 3 blade NLE is smooth!
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RV-7A - Slider - N495KL - First flt 27 Jan 17
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  #6  
Old 07-19-2017, 01:47 PM
Chattin35 Chattin35 is offline
 
Join Date: Jul 2014
Location: Boise, ID
Posts: 185
Default Another speed run...

Did another speed box this morning in smoother air. Confirmed 175 KTAS (plus or minus a couple) at 8000' DA.

Can't wait to see what the intersection fairings add.

EFIS pic...



My #2 CHT gauge is acting up again. I'll have to troubleshoot and fix that.
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  #7  
Old 07-22-2017, 10:40 AM
Chattin35 Chattin35 is offline
 
Join Date: Jul 2014
Location: Boise, ID
Posts: 185
Default Upper intersection fairings

Test flew the upper intersection fairings today. Surprisingly, no noticeable speed increase. I'm still 175 KTAS at 8000' DA, wide open, 2700 rpm.

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  #8  
Old 07-22-2017, 12:03 PM
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grubbat grubbat is offline
 
Join Date: May 2012
Location: Ga
Posts: 457
Default Wheel Pants less

Curious to know how much you will loose if you ditch the huge wheel pants but leave the gear leg fairings and intersection fairings but add hub caps on the wheels. Of course you would also have to ditch the long Van's axle nut and get a standard castle nut to fit under the hub caps.
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  #9  
Old 07-22-2017, 08:01 PM
sblack sblack is offline
 
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Location: Montreal
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Quote:
Originally Posted by Chattin35 View Post
Test flew the upper intersection fairings today. Surprisingly, no noticeable speed increase. I'm still 175 KTAS at 8000' DA, wide open, 2700 rpm.

Many people mention a decrease in stall speed with these fairings. You might want to check that. Nice installation job.
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RV 4, with an engine...and other stuff
VAF dues 2016

Last edited by sblack : 07-24-2017 at 06:11 PM.
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  #10  
Old 07-22-2017, 08:03 PM
sblack sblack is offline
 
Join Date: Dec 2009
Location: Montreal
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Quote:
Originally Posted by grubbat View Post
Curious to know how much you will loose if you ditch the huge wheel pants but leave the gear leg fairings and intersection fairings but add hub caps on the wheels. Of course you would also have to ditch the long Van's axle nut and get a standard castle nut to fit under the hub caps.
There is a large wake behind bare wheels. The pants make a big difference. Hub caps do nothing to address that wake. This has been well established.
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