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Wheel pants and landing gear fairings

rongawer

Well Known Member
I've read many different posts on the value, or non-value, of wheel pants and gear fairings. So, I've been experimenting and collecting some data and finally have a full report now that I finally have my wheel pants on, and the also made and installed main gear fairings with RV Bits intersection fairings. Noting that Van's says about 4KT for the pants; I can confirm that.

What I've found is that without any fairings on, I cruised at about 111 KTAS at 7500 feet at economy cruise power, averaged over about 100 hours of flying.

Then I installed the wheel pants and flew to KOSH and back this summer. I found I cruised about 115 KTAS for the same power averaged over the whole trip between 7500 and 9500 MSL.

And then I installed the main gear fairings and just returned from a trip to Nashville, down to Pensacola and then back home (C83). Over that trip I found I cruised at about 118 for the same power settings.

And at FT, well, she really gets after it.

And for the pundits, no, that's not calibrated data, it's just averaged flight time over about 250 hours. But a real set of data points no less.

I'm also finally figuring out this "posting photos on VAF work-around" thing.

Left gear
pn6sbGbl.jpg


Right gear
1ElcZiEl.jpg


All done (ok, done with installing the gear :rolleyes:)
VZdFcFEl.jpg
 
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Good info, Ron

I intend to add main gear fairings sometime after certification and a thorough test series. Until I saw your main gear fairings, I thought that I had two options - get a set of RV-8 fairings or make up a set myself. I'm very interested in where you purchased your main gear fairings or did you make them? Please advise at you convenience. Thanks, Ed
 
Useful numbers, so thanks for posting. I have the same setup and thought that they probably added no more than a couple of knots, so three knots is good.
 
What was the total price, all in, to add those 7 kts? A cost value proposal. If you put a lot of hours on your RV, kind of wondering the payback period in efficiency?
 
Pants and legs

My buddy with an 8 reported 3 knots improvement with the wheel pants, but 6 or so from the leg fairings! The gear legs were significantly more important on his plane. Together they were only like 8 knots improvement..they didn?t quite add together.
 
As another data point, on my new 7A I recently added the pants and legs and intersection fairings and gained 9 knots. On my 12 I gained 3-4 knots for just the wheel pants with only the nose leg fairing.
 
Fairings

I used Texas Aeroplastics for the top and bottom of my gear. They are made out of plastic but they are made for the RV 12 and fit nicely on wheel pant and fuselage. Havent determined how much they add to top speed. These cuffs fit the standard gear legs with openings at rear for brake lines
 
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Regarding the speed gains, understanding that speed is proportional to drag squared, the faster normal cruise speed, the greater improvement in speed drag reductions make. For example, an RV10 that cruises at 175KT will likely see 10-15 knots reduction (160-165KT) without gear fairings. But an RV12 that cruises at about 2/3 the speed should see less speed change for the same drag change; so 6-7 knots total is in line with that.

For costs and setup, I bought my intersection fairings from RVbits.com, although I noted that are now sold through Cleaveland Tools as well, which will save on shipping from S. Africa. I believe the price was about $180 with shipping.

I bought the GEAR LEG FAIRING ROD from Van's for the 'A' models. You don't want the FLAT leg ones as they're too wide for the 12's legs and RV Bit fairings are formed to fit the ROD ones. I don't recall the cost, but they too were about $200.

So all in, about $400 plus some misc hardware.

For installation, RV Bits includes instructions for the intersection fairings, but it's pretty simple. You will need to cut the gear leg fairings down substantially; I recommend starting at the narrow end and measuring up about 19". Then fit them up, mark to match the fuselage and cut again. My fairings are 17.5 short side to 18" long side...YMMV...measure twice...

I used 8-32 Rivnuts on the fuselage (4 per fairing) and 8-32 nut plates on the wheel pants (also 4 per fairing). You could use sheet metal screws if so inclined or go with #6 screws as it's fairly small load.

I did not run piano hinge the whole length, but rather just the middle 10", which is very adequate; this allows for inserting or removing the pin out without having to remove the wheel, yet holds the entire trailing edge firmly shut, especially once the IS fairings are in place, which clamp the ends.

I used 1/2" foam weather stripping at two points wrapped around the gear to support the fairings. You will find the fairings fit fairly snug and no additional measures, such as wood or epoxy, are really needed, but you may decide differently. I found that installed the way I did, there is no alignment needed as the fairings are snugly aligned to the 12's flat gear legs.

As for payback from efficiency? Well, at 118 knots I'm cruising about 6% faster for the same fuel burn than I was at 111 knots. A rough ROI based on 250 hours a year, which is about my average, and use a 5% improvement with $5 for 100LL and 5 gph as a consumption (my flight planning numbers), that's about $300 a year in savings, so it pays me back in about 18 months or a couple years burning MOGAS at $3.50/gal. But frankly, I've generally stopped doing economics and ROI's on airplanes, especially after the Baron... my wife wanted me to sell the thing and fly SouthWest - missing the whole point; which is that I just did it because I wanted to and I could. And they give the little bird a nicer looking set of gams.

BTW, my wife actually flew with me the whole way to Pensacola last month and even commented that she enjoyed it. I consider that "paid in full".
 
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Real lesson learned...

That last comment about your wife and ROI says it all.

Don't want your last words on earth to be something like "wish I had ..."!

Cheers
 
Wheel pants .. check. Easy access to valve stem .. fail.

I too have seen speed increases after recently installing wheel pants and gear leg /intersection fairings on my RV-12. My airspeed increases appear to be in line with those previously mentioned.

But gee! What a hassle it is now to check tire pressures. I'm sure those of us that have wheel pants on our RV-12's would gladly pay for a well machined, chrome plated, heavily spring loaded trap door system that would allow easy access to the tire's valve stem. A good looking, well thought out, form fitting assembly that can be installed without trashing an existing paint job.

Perhaps a worthy project for Aircraft Specialty to add to their wonderful line of support products for the RV-12.
 
John... I just drilled 1" or so holes in the wheel pants to be able to get an extension in there. It didn't look too bad when the wheel pants were bright yellow, and now that they're black you can't even really see them. Well worth it to be able to check tire pressure in 10 minutes instead of an hour.
 
Excellent write up and discussion especially considering our wheel pant parts just arrived. :)
 
+1 for the hassle of checking tyre pressures. Maybe Vans could give some thought to designing a flush-fitting inspection door for wheel pants? I installed 1" diameter clip-in plastic disks only to find the valve stem is not perpendicular to the rim and it's too hard to get a filler extension on. If you put a plastic disk in, make sure it's big one. Taking the rear pant section off to check pressures is a nuisance, however you do get to inspect the tyres and brakes, so it's not all bad. For the record, I used RV8 flat gear leg fairings without any problems. They're plenty wide enough and fit snugly.
 
Tire pressure

What I did is install these on each pant:
Tube Access doors

If you note, the wheel pant brackets have 1" holes in the forward and aft sections that the tire stem lines up with. I chose the aft holes and used a laser level to mark the stem, mount the pants and then cut the hole for the access door, which use 4 #40 rivets to mount. Easy enough.

And then I simply bought 6" air chuck extensions from Amazon and tire pressure checks are a breeze.
 
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tire press

is it possible to put those tire pressure monitor devices inside the rims like on cars and motorcycles these days?
Full disclosure, i dunno how they work. It's all magic...
 
Dennis,

Spotting a low tire is pretty easy, so my issue was access to add air. Access ports work, but you end up jockeying the aircraft back and forth to get the stem aligned with the port, and you are pretty much doing it blindly.

My Cherokee wheel pants allow stem access for about a 60 degree arc at the bottom. Maybe not as aerodynamic as Vans design, but much more convenient to add air.

A 12 owner I know got a flat, and the wheel pant was supporting the weight, so it as necessary to jack up the plane to get the wheel pants off and add air so it could be towed to spot for maintenance.

Rich
 
Dennis,

Spotting a low tire is pretty easy, so my issue was access to add air. Access ports work, but you end up jockeying the aircraft back and forth to get the stem aligned with the port, and you are pretty much doing it blindly.

My Cherokee wheel pants allow stem access for about a 60 degree arc at the bottom. Maybe not as aerodynamic as Vans design, but much more convenient to add air.
Rich

My low tech solution for this is to put a bright paint dot at the bottom of the tire sidewall to mark when the stem is lined up. Yes, you do need to move the plane a little bit, but this works fine for me.
 
Tire pressure

is it possible to put those tire pressure monitor devices inside the rims like on cars and motorcycles these days?
Full disclosure, i dunno how they work. It's all magic...

Look up tire pressure monitoring systems..they sell them on amazon, and they screw onto the valve cap..
 
Dennis,
Spotting a low tire is pretty easy, so my issue was access to add air. Access ports work, but you end up jockeying the aircraft back and forth to get the stem aligned with the port, and you are pretty much doing it blindly.

Some time ago I had a nose wheel tire with very low pressure but it wasn't visible until I got into the aircraft and added my weight to the nose tire. I didn't see anything unusual in the preflight but, fortunately, I had a friend (who is also a RV-12 owner) notice it when I boarded. After I got out we both looked at the tire but, even with foreknowledge, the low pressure wasn't evident.

I have wheel fairings, leg fairings (cut down RV8 if I remember correctly) and intersection fairings. My experience is about a 5-6 kt gain with the wheel fairings and no perceptible gain with the leg and intersection fairings.

Finally, I do not use the fairings with my local flying which is the vast majority of my time in the air. In addition to just checking the air pressure, they cover up my brake lines, brake fittings, brake pads, etc., all of which I check during the preflight and can't do with the fairings on. To tell the truth, when I'm flying locally I don't care how fast I'm going. When I plan a trip, I take the 30 - 45 minutes to mount the fairings.
 
Actually, drag is proportional to speed squared.

Regarding the speed gains, understanding that speed is proportional to drag squared, the faster normal cruise speed, the greater improvement in speed drag reductions make. For example, an RV10 that cruises at 175KT will likely see 10-15 knots reduction (160-165KT) without gear fairings. But an RV12 that cruises at about 2/3 the speed should see less speed change for the same drag change; so 6-7 knots total is in line with that.

For costs and setup, I bought my intersection fairings from RVbits.com, although I noted that are now sold through Cleaveland Tools as well, which will save on shipping from S. Africa. I believe the price was about $180 with shipping.

I bought the GEAR LEG FAIRING ROD from Van's for the 'A' models. You don't want the FLAT leg ones as they're too wide for the 12's legs and RV Bit fairings are formed to fit the ROD ones. I don't recall the cost, but they too were about $200.

So all in, about $400 plus some misc hardware.

For installation, RV Bits includes instructions for the intersection fairings, but it's pretty simple. You will need to cut the gear leg fairings down substantially; I recommend starting at the narrow end and measuring up about 19". Then fit them up, mark to match the fuselage and cut again. My fairings are 17.5 short side to 18" long side...YMMV...measure twice...

I used 8-32 Rivnuts on the fuselage (4 per fairing) and 8-32 nut plates on the wheel pants (also 4 per fairing). You could use sheet metal screws if so inclined or go with #6 screws as it's fairly small load.

I did not run piano hinge the whole length, but rather just the middle 10", which is very adequate; this allows for inserting or removing the pin out without having to remove the wheel, yet holds the entire trailing edge firmly shut, especially once the IS fairings are in place, which clamp the ends.

I used 1/2" foam weather stripping at two points wrapped around the gear to support the fairings. You will find the fairings fit fairly snug and no additional measures, such as wood or epoxy, are really needed, but you may decide differently. I found that installed the way I did, there is no alignment needed as the fairings are snugly aligned to the 12's flat gear legs.

As for payback from efficiency? Well, at 118 knots I'm cruising about 6% faster for the same fuel burn than I was at 111 knots. A rough ROI based on 250 hours a year, which is about my average, and use a 5% improvement with $5 for 100LL and 5 gph as a consumption (my flight planning numbers), that's about $300 a year in savings, so it pays me back in about 18 months or a couple years burning MOGAS at $3.50/gal. But frankly, I've generally stopped doing economics and ROI's on airplanes, especially after the Baron... my wife wanted me to sell the thing and fly SouthWest - missing the whole point; which is that I just did it because I wanted to and I could. And they give the little bird a nicer looking set of gams.

BTW, my wife actually flew with me the whole way to Pensacola last month and even commented that she enjoyed it. I consider that "paid in full".
 
Having wheel pants without a way to access the valve stem would be a non-starter for me, especially when it's so easy to build in a solution when you're installing them. I didn't invent this but I've used it on two RVs now and plan to use it for my -12 as well...
http://romeolima.com/rv3/rv3works/ideasproducts/ideasproducts.html#AccessDoors

I'm also planning on not only wheel pants but intersection fairings both top and bottom, which it seems contribute just as much drag reduction as the pants. I also plan on gear leg fairings as the OP of this thread installed - good info Ron, thanks!
 
Actually, drag is proportional to speed squared.

The affinity laws, a.k.a pump laws are generally known, where N= speed, V= velocity, H=headloss (drag) and P=power. Noting that N⍺V, N⍺H^2 and N⍺P^3. So, if you want to go faster 3 knots will take 27 horspower, but the same 3 knots can be gained by only reducing drag by 9 pounds force. This is all proportional and using the transitive properties of multiplication, can be applied in either direction.
 
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My low tech solution for this is to put a bright paint dot at the bottom of the tire sidewall to mark when the stem is lined up. Yes, you do need to move the plane a little bit, but this works fine for me.

My new Air Specialty 500-5 4 groove tires from Aircraft Spruce, came with that red dot already on the tire, to be aligned with the valve stem on assembly. Indexes the valve stem, nicely. The RV-12 I bought, the previous owner graciously had installed these leg pants. My ferryman made great time flying back from South Carolina to KWHP, averaged 4.9 gallons per hour burn rate on 50/50 mogas, when easily available, (some for sale cheap at $2.29 /gal near Midland TX) and 100LL. Always maintained at least a 92 octane, blended.
 
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My new Air Specialty 500-5 4 groove tires from Aircraft Spruce, came with that red dot already on the tire, to be aligned with the valve stem on assembly. Indexes the valve stem, nicely. The RV-12 I bought, the previous owner graciously had installed these leg pants. My ferryman made great time flying back from South Carolina to KWHP, averaged 4.9 gallons per hour burn rate on 50/50 mogas, when easily available, (some for sale cheap at $2.29 /gal near Midland TX) and 100LL. Always maintained at least a 92 octane, blended.

The dot on the tire is not the same dot being talked about in the post you quoted.
The dot added to the tire to indicate when the stem is aligned with the access hole (if one has been made) will be in a different location.
 
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