Finally putting my gear pants on, but wondering

[Daddyman58]

My -6A has been through phase 1 testing for a couple months. I've been dreading putting the wheel pants and gear fairings on.

I told myself I'd do it once the testing is complete, but that is bravo sierra.

The reason was I was procrastinating. Why? It is not like me at all, and there have been dozens of jobs during the build that I was inexperienced performing.
I read and thought about the procedure. My builder's book had an explanation, yet it did not match the drawings.
I read more, and researched, asked other builders, and wrote Van's.
What I really needed to do was just jump into the job and complete it like the the hundreds of other tasks on my plane.

Now that I'm mid job, I realize it wasn't that bad after all.
Maybe other builders also get hung up on jobs that they dread.
Just musings from my hanger.

Daddyman58

 

[Ironflight]

And now you get to do (much of) Phase 1 testing all over again because your performance numbers will be wildly different with pants and fairings!

 

[BoydBirchler]

Give us a report on the speed increase at the same fuel burn/ power percentage. If you have a fixed pitch prop it will need a few more RPM to make the same power, as you have less drag.

 

[graywoodworking]

And now you get to do (much of) Phase 1 testing all over again because your performance numbers will be wildly different with pants and fairings!

That's right. I had my gear leg and wheel pants off my RV-14A for a few weeks while I did some brake maintenance. I lost over 14 kts in cruise at the same altitude and power settings.

 

[Daddyman58]

And now you get to do (much of) Phase 1 testing all over again because your performance numbers will be wildly different with pants and fairings!

Ironflight,
Yep.
The leg fairings increased TAS by 8 kts.
Just flew with the wheel pants on the mains (only) added 4 more kts TAS in cruise.
Once all the upper + lowers are on and cleaned up and the nose pant, I remain hopeful for a few more "free" kts.

Daddyman

 

[71459]

Why do builders leave important aerodynamic parts like this off during phase 1 testing?

 

[mburch]

Why do builders leave important aerodynamic parts like this off during phase 1 testing?

There's a school of thought that says you should leave the gear/wheel fairings off for at least the initial flights, so you will know whether any out-of-trim issues are being caused by airframe or control surface rigging problems, versus misalignment of the gear/wheel fairings.

 

[Carl Froehlich]

There's a school of thought that says you should leave the gear/wheel fairings off for at least the initial flights, so you will know whether any out-of-trim issues are being caused by airframe or control surface rigging problems, versus misalignment of the gear/wheel fairings.

+1
This is a good point, as well as having the brakes easy to inspect. I fly with wheel pants off for the first few flights and would recommend other builders do the same.

On the second build rigging was straight as an arrow on the first few flights - then half a ball out when I put on the pants and fairings. I found my mistake - easy as I knew it could only be the pants/fairings.

Carl

 

[bonefishdave]

Why do builders leave important aerodynamic parts like this off during phase 1 testing?

I would think it’s the one thing you don’t have to complete that still lets the plane fly. Plus a lot of folks have fiberglass and resin reluctance maybe ??

 

[Roadjunkie1]

Those RVs with the Whittman tapered steel legs that have a stiffening system attached to the legs, some like to do several/multiple flights/landings to make sure whatever system they used to attach said stiffeners is solid rather than taking the fairings off and on............

 

[DanH]

Finish it all before you fly it. Everything. Even if it doesn't fly straight, diagnosis merely means removing the finished pants for one flight.

Fit the pants on the bench, early in the build, and you'll save a whole lot of crawling around.



First takeoff. Neat and complete.

 

[Daddyman58]

Why do builders leave important aerodynamic parts like this off during phase 1 testing?

71459,
Some folks (me included) think that as you define the envelope for the plane, it is possible to scuff/scratch or even leave pieces of them on the runway.
Or perhaps, that is just superstition.

A flying buddy of mine has a placard in his 182 "Caution Parts May Fly Off"

Dadyman58

 

[Daddyman58]

I would think it’s the one thing you don’t have to complete that still lets the plane fly. Plus a lot of folks have fiberglass and resin reluctance maybe ??

bonefishdave,
True. Aluminum sculptors can be wary of the fiberglass.
I think it is so simple to fix if I screw it up. Just blop some more on and sand, sand, sand and OK, a little more sanding.
Daddyman58

 

[Ironflight]

+1
This is a good point, as well as having the brakes easy to inspect. I fly with wheel pants off for the first few flights and would recommend other builders do the same.

On the second build rigging was straight as an arrow on the first few flights - then half a ball out when I put on the pants and fairings. I found my mistake - easy as I knew it could only be the pants/fairings.

Carl

The thing to remember Carl is that if you are breaking in a new engine, you want as much cooling air as possible - and you get that at higher speeds. Giving away fifteen to twenty knots at the top end (its not linear) is a bad idea when you are trying to keep cylinders cool at high power level.

This - to me - is the biggest reason to fly with pants on for the early flights (if you are breaking in an engine) - you can figure out trim problems very easily by taking the pants off when the engine has broken in.

Of course, if you’re flying with an “experienced” engine, it makes little to no difference - but I’d certainly have all fairings in place before trying to collect performance data.

 

[rockwoodrv9]

I think the biggest reason I found is I didnt want to take time from flying to do them later.

 

[mburch]

Fit the pants on the bench, early in the build, and you'll save a whole lot of crawling around.

Hey Dan, what's the secret for doing this on something other than an RV-8? I think that for any of the other models, including the RV-8A, the best you can do is to install the wheel pants on a wingless fuselage (leveled). The RV-8 gear seems to be a special case - unless there's a trick to duplicating the final alignment that I'm not seeing.

 

[PhatRV]

You should enjoy the jump in speed now the plane will have a lot less drag. During my first 20 hours of testing, I didn't have the wheel pants on because I wanted to do inspection of the landing gear after each flight. When I finally put on the wheel pants, the plane flew about 11 knots faster in cruise and I had to throttle back to keep the engine from overspeeding.

 

[hgerhardt]

Hey Dan, what's the secret for doing this on something other than an RV-8? I think that for any of the other models, including the RV-8A, the best you can do is to install the wheel pants on a wingless fuselage (leveled). The RV-8 gear seems to be a special case - unless there's a trick to duplicating the final alignment that I'm not seeing.

You could use this method: https://vansairforce.net/threads/installing-wheel-fairings—a-better-way.230221/
So much easier than doing it on your knees!

 

[DanH]

Hey Dan, what's the secret for doing this on something other than an RV-8? I think that for any of the other models, including the RV-8A, the best you can do is to install the wheel pants on a wingless fuselage (leveled). The RV-8 gear seems to be a special case - unless there's a trick to duplicating the final alignment that I'm not seeing.

Well, all of them attach the legs to something, like the triangular gear weldments which attach to the front of the spar, or to the motor mount. No trick to bolting a round leg into the weldment, and jigging that weldment above the bench. Same for a motor mount. Not hard to jig to a frame, or sheet of plywood. All of it is out of order per the manuals, but some of us don't follow instructions well anyway.

 

[Daddyman58]

Ironflight,
Yep.
The leg fairings increased TAS by 8 kts.
Just flew with the wheel pants on the mains (only) added 4 more kts TAS in cruise.
Once all the upper + lowers are on and cleaned up and the nose pant, I remain hopeful for a few more "free" kts.

Daddyman

Now with the intersection fairings on and a Full speed run: 167 KTS true 6500 ROP.
Daddyman58

 

[Mikeavny]

And now you get to do (much of) Phase 1 testing all over again because your performance numbers will be wildly different with pants and fairings!

Approaching end of build of my 14A and plan to leave wheel pants off for engine break in and then complete Phase 1 testing with wheel pants in place.

 

[71459]

Finish it all before you fly it. Everything. Even if it doesn't fly straight, diagnosis merely means removing the finished pants for one flight.

Fit the pants on the bench, early in the build, and you'll save a whole lot of crawling around.

View attachment 84484

First takeoff. Neat and complete.

View attachment 84486

This is good advice. Maybe leave off a few unnecessary options, sure, but is no benefit leaving the airplane aerodynamically incomplete.

 

[Ironflight]

Approaching end of build of my 14A and plan to leave wheel pants off for engine break in and then complete Phase 1 testing with wheel pants in place.

Here’s the thing - engine break-in require high power plus lots of cooling to prevent glazing the cylinders due to high CHT’s (due to the high power settings). If you leave the wheel pants off, you lower top speed significantly (15-20 knots), which deceases cooling by a HUGE amount (cooling is a square of velocity…or maybe a cubic? I forget). Giving away that many knots at the top end significantly increases your chance to glazing the new cylinders. You will not “increase the work the engine has to do” in an airplane by increasing drag - this is not a car or truck. Leaving the wheel pants off to increase the workload on the engine of an airplane is an old wives tale.

 

[BravoAlphaRomeo]

My 14A has 6 hours on it, currently flying with no wheel pants. Is there any downside to flying with just the nose wheel fairing and wheel pant ? I actually finished these a while ago. It’s the intersection fairings that I still have to do….

 

[Mikeavny]

Here’s the thing - engine break-in require high power plus lots of cooling to prevent glazing the cylinders due to high CHT’s (due to the high power settings). If you leave the wheel pants off, you lower top speed significantly (15-20 knots), which deceases cooling by a HUGE amount (cooling is a square of velocity…or maybe a cubic? I forget). Giving away that many knots at the top end significantly increases your chance to glazing the new cylinders. You will not “increase the work the engine has to do” in an airplane by increasing drag - this is not a are or truck. Leaving teh wheel pants off to increase the workload on teh engine of an airplane is an old wives tale.

 

[Mikeavny]

Thanks for the input Paul. Change of plan, wheel pants on!