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Tip: Vertical cowl split - A models

RKellogg

Well Known Member
Getting the lower cowl on my -7A was four-hands work during the cowl fitting process. Then I saw a famous airshow plane at AirVenture with the RIGHT half of the cowl removed... light bulb! After more study and a bit of glass work, this is what it looks like.

>> No fasteners in the cowl inlets.
>> Nose gear fairing is integral with cowl halves, no separate pieces.
>> Top and bottom seams are piano hinge. Firewall seams are quarter turns.
>> Top pin is accessed through a flush 'badge' behind the spinner.
>> The bottom pin is removed from the rear of the air exit duct, and is self retaining, by the spring hook formed in the handle end, see pix.

Bottom hinge is offset one inch to the right to clear the nose gear. Top hinge is offset one inch to the right to have some semblance of asymmetry.

- Roger







 
That is just plain gorgeous! My only question is where would I put all those nice quarter turn fasteners I have been fighting with? ;)
 
cowl

That was a great idea. I think that will be wonderful, instead of fighting the nose gear leg and back of spinner.
 
It's this kind of innovation that humbles me. The workmanship is excellent and I can see how it will lead to further innovation. Well done.
 
Thanks

I am like Vern, humbled by this. Roger - what a great idea. It makes sense in so many ways. Nice work and thanks for the pictures.

My wife has a friend who made some pretty good chocolate sauce and she asked her for the recipe - she said no! Im glad most people here are so willing to share their ideas. Thanks
 
quarter turns...

That is just plain gorgeous! My only question is where would I put all those nice quarter turn fasteners I have been fighting with? ;)

Sometimes wrestling with quarter turns is like juggling cockleburrs while wearing woolen mittens... but they are great when they work!

Roger
 
Very nice!
Wondering if it will be OK on a cowl with the snout.

The snout cowl obviously complicates the vertical split. It would be desirable to have the entire snout on one half or the other. That might drive a curved seam, which would be a challenge for the piano hinges. Might make it easier to connect the air intake to the filter box... ?? Haven't yet studied that one yet. Good question, Jan.
 
Hmm... This makes me wonder if it could be combined with the mod that puts the cowl hinge pin into the fuselage... Run the top cowl pin through the firewall and back to the top of the instrument panel, and you could eliminate the little cover by the spinner as well...

Something to keep in mind if I ever replace my cowling, for sure...
 
A really elegant solution. Have you discovered any downside so far? Looks great, but most of all it looks easy to remove.

Any mod that makes it easy to remove the cowl is a safety mod in my view.
My cowl is a pain to take off, and I have to discipline myself to check under the hood on a regular basis.
 
Agreed.

It's always a tossup between pulling the cowl on the 6A or having a root canal.

I'll be interested to see the work-arounds for the air intake snout. And more details on the gear leg fairing split.

-Stormy
 
I'm not expert enough to know how feasible; but what about 3 pieces for the snout version? One narrow piece containing the snout and air exhaust, possibly semi-permanently mounted, not removed often, slotted to handle nose spar. Then 2 upper halves, easily removed?

GH
 
Looks very nice and interesting.

I wonder how tight the joint on top is and if any cooling air is exists thru the joint?
 
"Abilene Paradox?"

It's interesting to note that there have been thousands of RV's completed and no one, or perhaps very few, has attempted this modification before. Any one who has wrestled a -6A, -7A, -8A, or 9A knows how much trouble they are. I'm wondering what the factory design team thinks of this.

Is, or was, there a reason NOT to split it vertically?

Anyone heard of the "Abilene Paradox?"
 
Very nice!
Wondering if it will be OK on a cowl with the snout.

Sure, just make the entire snout removable.

CIMG2881.JPG


P3300019.jpg
 
The vertical split is how it is done with "Brand S", and they have quite a few flying. We'll be doing it that way on our new build, and it looks quite straightforward.
 
It's interesting to note that there have been thousands of RV's completed and no one, or perhaps very few, has attempted this modification before. Any one who has wrestled a -6A, -7A, -8A, or 9A knows how much trouble they are. I'm wondering what the factory design team thinks of this.

Is, or was, there a reason NOT to split it vertically?

Anyone heard of the "Abilene Paradox?"
It wouldn't even have occurred to me to try it, since A.) the factory supplies the cowl in two horizontal pieces; it "seems" correct since that's the way it was designed and manufactured, and B.) as it's my first RV build, I wouldn't really know how much (or little) of a PITA it is to get the cowl off and on until way after the time for making decisions like that. I think I'm in the majority on that.

It's a pretty cool modification; I'm building a taildragger so I don't know that there would be enough benefit for me to justify the extra work. Probably not. Still... pretty cool, and even if I don't do a vertical split it has given me a couple of interesting ideas to explore when it comes time to do my cowl. If I live that long.
 
It's always a compromise...

A really elegant solution. Have you discovered any downside so far? Looks great, but most of all it looks easy to remove.

Any mod that makes it easy to remove the cowl is a safety mod in my view.
My cowl is a pain to take off, and I have to discipline myself to check under the hood on a regular basis.

Jim, I was initially concerned about the top seam deflecting and/or leaking cooling air. Ground testing with a leaf blower to pressurize the cooling air volume indicated that neither was a problem. Will keep an eye on it as the hours build. The top seam was microed on release wax to get a tight fit, partly for cosmetic reasons. The inner surface of the split is shaped to provide a smooth surface for the silicone engine baffle that crosses the seam.

There was a fair bit of thought that went into structuring the baffling so that it would lay into the pressurized volume with the cowl approaching from the side. Mostly works pretty well, one place I must hold the baffle up with a thumb in the air inlet to prevent it from folding the wrong way. I suppose this is not much different than other solutions.

Pulling the lower pin out rearward is a bit less than ideal, as one must kneel on the wet, soggy apron to reach the pin. Considered pulling the bottom pin from the front and hiding it with another badge, but took the easy way out.

The right side comes off first and goes on last, since the oil door provides a grab location.

- Roger
 
Is, or was, there a reason NOT to split it vertically?

Only reason I can think of is that it will require quarter-turn fasteners, since the standard piano hinge attachment won't work around the corners of the cowl if split vertically. Not a significant reason IMO. Nicely done!

Greg
 
Only reason I can think of is that it will require quarter-turn fasteners, since the standard piano hinge attachment won't work around the corners of the cowl if split vertically. Not a significant reason IMO. Nicely done!

Greg

Rumblings from prior builders convinced me that quarter turns were an improvement over piano hinges at the firewall. I had the quarter turns mounted before considering the vertical split concept, and ... that is why the top seam is offset from centerline! A centered seam would have bisected a quarter turn.
- Roger
 
Rumblings from prior builders convinced me that quarter turns were an improvement over piano hinges at the firewall. I had the quarter turns mounted before considering the vertical split concept, and ... that is why the top seam is offset from centerline! A centered seam would have bisected a quarter turn.
- Roger

Agreed. I have quarter-turns on my upper cowl and prefer them to the piano hinges. Was just noting that the vertical split would eliminate the possibility of the standard piano hinges.

Cheers,
Greg
 
One more benefit to this would be ease of inspecting the baffle seal while the cowl is on. At least half at a time..........

For those having cooling issues, would be nice to actually see where/how the seal is contacting the cowling.
 
New build...??

The vertical split is how it is done with "Brand S", and they have quite a few flying. We'll be doing it that way on our new build, and it looks quite straightforward.

Apologies if I should know this, but what is your new build?
 
One more benefit to this would be ease of inspecting the baffle seal while the cowl is on. At least half at a time..........
For those having cooling issues, would be nice to actually see where/how the seal is contacting the cowling.

Now there's an interesting thought!

Roger, my compliments on the beautiful glass work.
 
Great idea and execution!
I see no reason why you couldn't leave the top one piece and still split the bottom.
 
Because it eliminates a seam, smooths the intakes and reduces cowl leakage?

Yes and no. Cowl leakage on the side isn't a big issue because it is outside of the high pressure area (baffles). Besides, you might have leakage issues along the center part line. It would make removing the cowling that much easier because you pull the top and then just have two small bottom sections (three, if you make one for the air intake).

This is just me, I would rather have part lines along the sides where I don't see them than one right up the middle.

Don't get me wrong, what I think the OP did was outstanding!
 
Excellent idea! Wonderful execution! Might have to be a copy cat!

One thought tho - monitor the back lower hinge area for wear & potential eyelets breaking off. Based on damage Ive seen on many RVs going thru my shop, this area is subject to oscillation from the turbulent airflow down there & I envision the hinge line a perfect spot for the exit ramp to flex up & down. You could add a vertical brace if it does show signs of wear.

Good Job!
 
Roger, I also see an altered exhaust...... Will that be explained in another post?

Very perceptive, Gasman. Maybe. There are also two mechanically-actuated cowl flaps, more later. First order of business is 22 more hours of Phase One, so that my financial backer can get a ride in her new plane!
- Roger
 
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Hinge eyelet fatigue?

Excellent idea! Wonderful execution! Might have to be a copy cat!

One thought tho - monitor the back lower hinge area for wear & potential eyelets breaking off. Based on damage Ive seen on many RVs going thru my shop, this area is subject to oscillation from the turbulent airflow down there & I envision the hinge line a perfect spot for the exit ramp to flex up & down. You could add a vertical brace if it does show signs of wear.

Good Job!

Valid point, Ralph. The bottom part of the exit scoop is quite flexible. But I am guessing that the turbulence-induced flexing will create rotation around the hinge pin rather than flexing of the eyelets. In the conventional embodiment, one half of the hinge is attached to a rigid structure and the flexing is entirely focused on the very edge of the first eyelet until it fails, and then the second, and before long the entire seam is unzipped. Ping me again in 12 months.
- Roger
 
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I'm not clear

on why this would preclude the standard piano hinge along the top of the firewall. Just split in a different place (now the top centerline instead of nearer the oil door) for pin insertion, right? What am I not visualizing here??

Stormy
-6A
 
on why this would preclude the standard piano hinge along the top of the firewall. Just split in a different place (now the top centerline instead of nearer the oil door) for pin insertion, right? What am I not visualizing here??

Stormy
-6A

Yes, but the vertical firewall seams, especially the left, become difficult to access. Aren't these usually accessed after removing the top cowl? The bottom pins could be accessed from the exit scoop.
- Roger
 
The vertical split is how it is done with "Brand S", and they have quite a few flying. We'll be doing it that way on our new build, and it looks quite straightforward.

It's kind of funny that there are a couple of builder mods for a horizontal (RV-style) split cowl on those airplanes :)

Each has its advantages, I guess.
 
Great idea and execution!
I see no reason why you couldn't leave the top one piece and still split the bottom.

On my Tiger the floppy lower cowl has a spot welded seam that frequently fails. If a repair is done with screws and nutplates you get a two piece, vertically split, cowl in the process.

http://www.bondline.org/wiki/Lower_Cowling_Split

This proves very useful for simple things like oil changes which may involve removing only one side of the lower cowl, while still allowing a good inspection of the lower end of your Lycoming.
 
I had the opportunity to see this aircraft in person at Morris. The cowl work, amongst other things, is fantastic! The whole plane looks great.

Roger, i was one of the guys who pulled up next to you in the maroon 150 a few weekends back. Hope the phase 1 testing is going well.
 
I had the opportunity to see this aircraft in person at Morris. The cowl work, amongst other things, is fantastic! The whole plane looks great.

Roger, i was one of the guys who pulled up next to you in the maroon 150 a few weekends back. Hope the phase 1 testing is going well.


Had a great time chatting on the ramp! Tx for the kind words. Hope your project speeds right along. Building was fun, ...but flying is funner!

-Roger
 
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