Wheel pant intersection fairing - interesting design

[walter]

Was browsing the net and found a photo of the WAT (Whelen Aerospace Technologies) wheel pants for the Cirrus SR series aircraft. The wheel pant intersection fairing looks interesting. I wonder if it's more aerodynamic than our standard wheel pant fairings. Thoughts from the aerodynamically minded?

Wheel pant/Fairing: https://cdn.shopify.com/s/files/1/00...g?v=1549513614

Website Link: https://flywat.com/products/main-pants-cirrus-iceskates

[scsmith]

The trade-off here between the two concepts (the one pictured vs a typical RV fairing) is between intersection interference drag and wetted area and form drag.

It is generally not too good to have an airfoil-shaped strut intersect a body at an acute angle. The boundary layers from the two bodies merge and aggravate each other, and it is possible to get some separation. This is less of a problem if the strut is not lifting, and if the strut is pretty thin (in percentage of thickness to chord). Both of these factors make the normal RV intersection fairing work pretty well.

The pictured fairing has gone to great lengths to ease the intersection angles so that the boundary layers on the two surfaces have much less interference. But in exchange for that, the designer has created a very thick cross section with a lot of wetted area and frontal area.

I would be very surprised if the pictured fairing has less total drag than a typical RV type fairing, well executed.

[pjc]

Originally Posted by scsmith

The trade-off here between the two concepts (the one pictured vs a typical RV fairing) is between intersection interference drag and wetted area and form drag.

It is generally not too good to have an airfoil-shaped strut intersect a body at an acute angle. The boundary layers from the two bodies merge and aggravate each other, and it is possible to get some separation. This is less of a problem if the strut is not lifting, and if the strut is pretty thin (in percentage of thickness to chord). Both of these factors make the normal RV intersection fairing work pretty well.

The pictured fairing has gone to great lengths to ease the intersection angles so that the boundary layers on the two surfaces have much less interference. But in exchange for that, the designer has created a very thick cross section with a lot of wetted area and frontal area.

I would be very surprised if the pictured fairing has less total drag than a typical RV type fairing, well executed.

Steve,
Agreed on the Interference, wetted, and form drag comments, but the WAT pants will produce far less induced drag as your pocketbook will be $6,000 lighter. What a luxury experimental aviation is!

Peter

[Sky Designs]

The timing of this thread coincides nicely with development of an integrated gear leg & lower intersection fairing for the RV-6 and RV-7.

The design approach I chose is a fun counterpoint to the approach WAT chose for their Cirrus fairings. You can see that the intersection fillet is much smaller resulting in less wetted area and less frontal area.

Another factor in sizing of the intersection fillet was my desire to not have so many "extra" screws just for attachment of the intersection fairing to the wheel fairing. Only one of the five screws attaching the intersection fairing is not already part of either holding the front and rear wheel fairing halves together or a bracket attach location.

Gotta admit that the little door in the WAT fairing for airing up the tires is pretty nifty...just not $5,995 nifty

[AeroDog]

Nice looking fairings. Are you planning to offer these for other RV models?

Jerre

[Sky Designs]

Are you planning to offer these for other RV models?

Yes, the wheel fairings you see in the photos are designed to allow those wanting the greater rolling diameter and width of 6.00-6 tires to have an easy-to-install and lightweight wheel fairing option. We have wheel fairing kits for RV-6 & 7, RV-8, and RV-12.

Matco offers a nice 6 inch wheel & brake that is perfect for RV-12 - it fits on the standard axle, is lightweight, and the tires can be used "tubeless". http://www.matcomfg.com/MHE6BESERIES...v-2336-30.html

[scsmith]

Ken,
Don't most people glass their intersection fairings onto the wheel fairing and split it along the same parting line as the front and rear half of the wheel fairing?

So no screws at all to attach it. The intersection fairing becomes integral to the wheel fairing. That's what I did.

Originally Posted by Sky Designs

The timing of this thread coincides nicely with development of an integrated gear leg & lower intersection fairing for the RV-6 and RV-7.

The design approach I chose is a fun counterpoint to the approach WAT chose for their Cirrus fairings. You can see that the intersection fillet is much smaller resulting in less wetted area and less frontal area.

Another factor in sizing of the intersection fillet was my desire to not have so many "extra" screws just for attachment of the intersection fairing to the wheel fairing. Only one of the five screws attaching the intersection fairing is not already part of either holding the front and rear wheel fairing halves together or a bracket attach location.

Gotta admit that the little door in the WAT fairing for airing up the tires is pretty nifty...just not $5,995 nifty

[RV-4]

Hi Ken

''Are you planning to offer these for other RV models? ''
--------------------
If you ever have a kit for the RV-4, I will be very interested.

Thanks

Bruno
rv4@videotron.ca

[gmcjetpilot]

I guess if you own and fly a $175K to $500K (not kidding) Cirrus single engine plane you can afford $5995 for wheel pant intersection fairing...

As was said above, just eyeball engineering the fat gear leg to wheel pant intersection fairing does not appear to be better than sliced bread (greater wetted area, frontal area). Intersection/interference drag is life when ever anything intersects, like wing to side of body. Van's wing to body sheet metal and rubber seal is easy to install, but my RV4 had fiberglass fillet fairings... Did it help? Don't know. However my 150HP C/S Hartzell, SL top speed of about 206 mph, 75%@8000ft cruise 194 mph, which is about the same or a few MPH than 160HP RV-4.

However you will get slightly lower drag with good DETAILS. As was said having smooth gap free, edge free fairing, as in glassing in integral to wheel pant to gear leg fairing verses screws is likely give you a tiny advantage.

Another way to lower drag is used the smaller LAMB tire and smaller fairing. I went with smaller tires/fairing initially. However before installing it I went back to the 5.00X5 and Sam James wheel pants... (I just don't like the looks of Van's wheel pants, but drag rise they are fine.) I chickened out on the smaller LAMB tires. The 5.00x5 is pretty small for mains on an airplane that can weigh 1800 lbs, on soft fields. Just me... Speed is fine, but if you flip on landing the fun stops...

I also went with wider fiberglass gear leg fairings (RV-7). My RV-4 had very short chord aluminum ones.... The later fiberglass ones from Van are wider. The fiberglass ones from Team Rocket are wider still.... Keep in mind Van has cast some shade on wider gear leg fairings due to possible changes in stability and/or spin characteristics. Nothing has ever been determined, but just be aware.
.

[plehrke]

Expensive, ugly, and really not a discernible drag reduction. Any one of the three separately would keep me from buying.