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Speed increase from wheel pants and gear leg fairings

Chattin35

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

Before...

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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.

rj5Vg7Bl.jpg


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.

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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...

hYaj2EDl.jpg


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...
 
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?
 
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 ;).
 
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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.
 
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!
 
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...

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My #2 CHT gauge is acting up again. I'll have to troubleshoot and fix that.
 
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.

wNnMbdQl.jpg
 
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.
 
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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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.
 
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.

They are called "pressure recovery" pants for a reason. :)
 
Hub caps vs huge wheel pants

To answer my own question, the hub caps cost me 1.5kts over the "pressure recovery" wheel pants. For me, the ease to check air pressure and also use the tire as a step to clean the windscreen is well worth that whopping 1.5kts.
 
To answer my own question, the hub caps cost me 1.5kts over the "pressure recovery" wheel pants. For me, the ease to check air pressure and also use the tire as a step to clean the windscreen is well worth that whopping 1.5kts.

I think you haven't done enough testing to actually know........

I agree the leg fairings are worth the biggest speed increase, but the wheel pants are good for more than 1.5 Kts
 
Agree

That's probably true Scott. Maybe my wheel pants were not constructed tight to the wheels to begin with or maybe some other variation somewhere else in the process. The hub caps are painfully simple. Over the next several months I'll keep a watch on the data and see if I can detect a change.

I think you haven't done enough testing to actually know........

I agree the leg fairings are worth the biggest speed increase, but the wheel pants are good for more than 1.5 Kts
 
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