What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Cowl Fastener/method choice

What cowl fastening method

  • Hinge

    Votes: 47 40.5%
  • 1/4 turn (Skybolt, Camloc, etc)

    Votes: 32 27.6%
  • Screw/nut plate

    Votes: 2 1.7%
  • Combo

    Votes: 32 27.6%
  • Other

    Votes: 0 0.0%
  • Dumb question.

    Votes: 3 2.6%

  • Total voters
    116
  • Poll closed .

Freemasm

Well Known Member
Bit of a nube question but I'm serious. What cowl fastening method did you use choose ? Why you settled on your choice (besides it was in the instructions)? Would you have done it differently? Would really like to hear from someone who's installed different options/maintained multiple.
 
Last edited:
On the 6, I used screws top and bottom and hinges elsewhere. I didn't like what I read about hinges wearing out on the bottom and for the top I didn't like what I read about difficulty getting the pins out.

On the 10, I went full hinges, except used SS hinges on the bottom due to stress killing the stock hinges. I hear that the forged hinges also hold up, but the SS was cheap and readily available at McMaster in town.

The quick lock stuff looks nice, but cannot bring myself to spend $500 for it. Both builds were on a budget.

Larry
 
I used hinges everywhere but I sure wish I had cams on the bottom at least. Them sons of Bs are sure expensive though. :)
 
Several years before I started my RV-3B project, I had a hangar neighbor with an RV-8. He had a very great deal of trouble with his cowl hinges. Made an impression.

And I've got a C180 with the cowling screws, which dissuaded me from that.

The only thing readily available and thought-out are the 1/4 turn fasteners, so I'm using them. However I bought a brand which has since gone out of business, sigh. Nothing wrong with them, as far as I know, but still - orphans.

Dave
 
Skybolt vs screws vs hinge

My 3 had hinge on sides and skybolt on firewall.
Hinges are a PITA and Rivets pop the filler over them. You could drill holes in the hinge flange and epoxy a glass tape over it to create an epoxy riveted stress relief. The wire needs to be undersized and ends secured with ugly clamps or complicated medallions.
Skybolts are nice, but you cannot get the cowl off if they remain secured in the part. You just remove and put in a cup and individually replace for assembly. Their main appeal for me is the ability to adjust for cowl surface alignment IF you leave a gap between the cowl and underlying structure ( ask me how I know..duh)

So, my new RV4 is all Skybolt. In hind sight, i would consider other quarter turn options or screws with SS washers The only negative to screws is vibration security. Blue loctite is a PITA and nutplates without tapping are also. My $.02
 
Would use more hinge if I was building today

I did Skybolt 1/4 turn fasteners on the firewall upper & lower cowl - except the bottom where I used screws. I used hinges to join the upper & lower cowl halves.

If I were building today, I would definitely use hinges on the vertical portion of lower cowl-to-firewall and would strongly consider ditching the Skybolts on the top cowl-to-firewall. I think the hinges give a better fit and look better.

The Skybolt fasteners do make it easier to remove the top cowl but if I had just stayed with the plans from Vans, I would have saved time and money.
 
The guy that built my airplane used Skybolt fasteners on the entire upper and lower cowling. I have found them to be excellent. They are very secure and very convenient.
 
Skybolts

I used Skybolts for several reasons.
The adjustment is number one. If you use them, add a shim between the flange and the firewall or fiberglass. Without it, the cowl may sit shy of even.
They do require more work. Read some tips. I have a document on my blog.
 
I never liked the look of SkyBolt type fasteners so have stayed with hinges - but modified.

I use 1/8” SS pins on the top cowl to fuselage hinge instead of the smaller diameter pins in the plans. The smaller diameter pins are needed to make the bend, but if you take the 1/8” pins and carefully reduce the diameter of the last 10” or so they make the bend. What this does is reduce the slop in the top cowl hinge.

For the bottom cowl to fuselage hinge I use the much stronger MS20001P extruded hinge. The per plans hinge tends to break off eyes from vibration as they are fairly short. I’ve never had a problem using these extruded hinges.

Note - if not using extruded hinge on the bottom I recommend three #6 screws and associated plate plus nut plates on each side as substitute.

Carl
 
Opposite of Rick...I'd again use Skybolts on the entire firewall perimeter. I've dinged my hands too many times R&Ring upper cowl hinge pins. Skybolts are also used to drop the airbox shell.

The horizontal seam is a toss up. Current cowl is #8 screws, and a glass flange with nutplates on the lower cowl. The goal was to be pretty much air tight to limit excrescence drag. Really locks the cowl halves together too, no shake, no fretting. In and out is fast enough with a power screwdriver.

A #10 behind the prop on each side enters a nutplate in a 0.060 aluminum tab

Offset hinge will also close the air gap, i.e. hinge pin eyelets not on the split line. Use one hinge half with a wide flange.
.
 

Attachments

  • Cowl Flange.jpg
    Cowl Flange.jpg
    220.9 KB · Views: 248
  • IMG_3696.JPG
    IMG_3696.JPG
    86.8 KB · Views: 267
  • Plenum Soft Spot left.jpg
    Plenum Soft Spot left.jpg
    106.3 KB · Views: 269
I used 1/4 turn Skybolt or equiv. on the upper firewall. Pleased with that. Later retrofitted them in on the bottom at the firewall. Should have done that originally as the hinges didn't last long there.

I'm working on a 7 that has Skybolt or equiv everywhere. What a pain to get the top cowl off and on! Since they float in/out they keep hooking themselves everywhere. Ditto with the sides of the lower cowl! FAR better to use hinges there!
 
Skybolts

I used 1/4 turn Skybolt or equiv. on the upper firewall. Pleased with that. Later retrofitted them in on the bottom at the firewall. Should have done that originally as the hinges didn't last long there.

I'm working on a 7 that has Skybolt or equiv everywhere. What a pain to get the top cowl off and on! Since they float in/out they keep hooking themselves everywhere. Ditto with the sides of the lower cowl! FAR better to use hinges there!

There's a trick to it. When you release one, use a pick, tiny screwdriver or mini plier to lift the stud as far as it will come out. Cowls will pop right off.
 
There's a trick to it. When you release one, use a pick, tiny screwdriver or mini plier to lift the stud as far as it will come out. Cowls will pop right off.

Yeah, but they won't stay there. I pull out the front 4 on the cowl and stretch a couple of rubber bands to keep them out. Then they will stay that way.

Skybolt Tip 01.jpg
 
Offset hinges on the upper/lower cowl spit. Skybolts all along the firewall. #8 screws/plate nuts on the forward cowl spilt behind the spinner. #6 screws/plate nuts on the inlet. No retainers on the Skybolts. They come completely free when released. This makes removal/install much easier.
 
Last edited:
8 was all piano hinge and the Rocket is a mix of piano hinge and 1/4 turn. New cowl on the Rocket (and any future airplane where it makes sense) will be all piano hinge. Easy to install, best looking, gap sealing, easy to service, light and inexpensive. Whats not to like?
 
8 was all piano hinge and the Rocket is a mix of piano hinge and 1/4 turn. New cowl on the Rocket (and any future airplane where it makes sense) will be all piano hinge. Easy to install, best looking, gap sealing, easy to service, light and inexpensive. Whats not to like?

Tend to agree other than the top cowl/firewall junction. I'd go with screws and nutplates there and hinges elsewhere. My -6 is set-up as I describe, the -10 has Milspec fasteners securing the upper cowl to the firewall. I think the Milspecs cost more in time, money, and operational hassle than they are worth.
 
Skybolts

I have a three piece split cowl on my ten…all skybolts. Putting the cowl on or taking it off takes less than 5 minutes by myself, less with help. The split cowl allows removal or installation with no prop interference, too.
 
Tend to agree other than the top cowl/firewall junction. I'd go with screws and nutplates there and hinges elsewhere. My -6 is set-up as I describe, the -10 has Milspec fasteners securing the upper cowl to the firewall. I think the Milspecs cost more in time, money, and operational hassle than they are worth.

Funny. I ESPECIALLY like the piano hinge at the upper cowl to firewall junction. It takes a fraction of the time to get the pins in or out compared to camlocks.

I guess this is why they make so many flavors of ice cream.
 
8 was all piano hinge and the Rocket is a mix of piano hinge and 1/4 turn. New cowl on the Rocket (and any future airplane where it makes sense) will be all piano hinge. Easy to install, best looking, gap sealing, easy to service, light and inexpensive. Whats not to like?

But how? Making assumptions but isn’t the oil door is way forward? How do you reach the upper hinge pins? I’m installing a four banger so the mount is looong. Plenty of room between FW and engine so imagining how I would reach it is not forming in my mind.

Another issue. My cowl is super tight. Don’t know if I’ll have room for anything other than a hinge for the split lines.
 
In my "future case", there will be ample access on the top of the cowl at BL 0 due to a design feature to install a RH/LH pin. But a small, inconspicuous access panel would be easy enough to add to the standard 10 or Rocket cowl.
 
But how? Making assumptions but isn’t the oil door is way forward? How do you reach the upper hinge pins? I’m installing a four banger so the mount is looong. Plenty of room between FW and engine so imagining how I would reach it is not forming in my mind.

Another issue. My cowl is super tight. Don’t know if I’ll have room for anything other than a hinge for the split lines.

You will definitely have to research, plan, and execute with care. Although I installed all SkyBolt, My next venture will certainly be with hinges, save the lower firewall issues.

I had the idea of maintenance issues and trouble with removal/installation. My 10 Friend used stock hinges and he can have it off or on as fast as me, maybe faster for removal. The gaps are tight, the loading is spread more evenly down the interface lines, and the lines are clean in paint.

One thing, keep in mind the 1/4 turns are not axially fixed, and are held in place only by the compression of an internal spring and friction. It does a allow a little movement that frets and dusts at contact points. You can make some experimental pieces to try this out for yourself. A little applied research.

Hinges are a more rigid connection with less movement opportunity.
 
You will definitely have to research, plan, and execute with care. Although I installed all SkyBolt, My next venture will certainly be with hinges, save the lower firewall issues.

I had the idea of maintenance issues and trouble with removal/installation. My 10 Friend used stock hinges and he can have it off or on as fast as me, maybe faster for removal. The gaps are tight, the loading is spread more evenly down the interface lines, and the lines are clean in paint.

One thing, keep in mind the 1/4 turns are not axially fixed, and are held in place only by the compression of an internal spring and friction. It does a allow a little movement that frets and dusts at contact points. You can make some experimental pieces to try this out for yourself. A little applied research.

Hinges are a more rigid connection with less movement opportunity.

Amen to this. After having the top cowl on and off a few times during construction I decided to dedicate an afternoon to fine tuning all the hinges. I adjusted the pin shapes, sharpened the ends, and found some eyelets out of alignment. Been super easy to install for 2 years since then, and I've learned to take care of the cowl hinges when off the plane. A slightly bent eyelet can cause problems, but just a little care and awareness will avoid this.

It saddens me that so many people just don't even give the hinges a chance. look at how many have commented that they would go back to hinges next time, that says it all and should have been a poll question.
 
The guy that started my RV9A build used the piano hinges and they do work, look great etc but, they are a pain to insert, especially the short upper one. Refitting cowls becomes a two man job unless you have the arms of a gibbon and get very lucky.

If i was building another RV from the start I would almost certainly go with Cam Locks which whilst not as aesthetically appealing are easier to use single headedly
 
Why?

"...It saddens me that so many people just don't even give the hinges a chance..."

Why? Just because one person likes the hinges doesn't mean it is the "right" way to do it. Everyone has their own view of what is "right" and works best for them, you shouldn't be sad.

In my case, I started with the hinges, and after many frustrating attempts to push a wire through 30" of eyelets, removed them and installed the sky bolts. I will never go back to the hinges...
 
Skybolts!!

Skybolts all the way. Fantastic product with incredible customer support. Makes cowl removal quick and easy. Used them on both 7's that I built.

On my new 7 I even used them on the wheel pants. 10 minutest per side to check tire pressure, and they look great.
 
My purchased 4 had Camlocks on the firewall for the top cowl and hinges everywhere else. I liked how it worked out so I did the combo on my 7. Skybolts across the top and bottom and hinges on the sides. Quick and easy on and off for both top and bottom cowls. I did my next 4 with all hinges. A bit of a PIA for the top cowl. I prefer the Skybolts for the upper and lower firewall and hinges on the vertical and horizontal sides. That is what I will do on my 8. I like the clean look of the hinges on the sides but prefer the ease of the Skybolts on the top and bottom. Each to their own.
 
There's no right answer. I have found Skybolts difficult to retrofit but hinges around the fuselage join made the cowling very difficult/time consuming to remove. I have kept hinge to join the top and bottom halves and vertically down the firewall. As builders about time to remove/fit their cowlings before deciding. Dreading having to remove your cowling is no way to be.
 
Simple, cheap, good looking...

...Is how my wife describes me -- not necessarily in that order or in a complimentary fashion...

For my cowl-to-fuse-attachment I chose MS24693-C50 (f.k.a. AN507C8R8) - #8-32x1/2" stainless screws, with reduced flange Tinnerman washers (#6 - 39006F), into MS21047-L08 (K1000-08) plate nuts.

From a distance it looks like 2700 series CAMLOC's, but doesn't have the little spring clip washers falling out on the ramp or in flight.

The cowl halves are mated using MS20007-P4 and P5 hinge material.

YMMV

B
 
8 finished 18y ago. Hinges all around EXCEPT the pin runs from the CABIN forward for an extra 'clean' look.

WORST decision/deviation I ever made in the project. Fitting on aft face of gear tower accepts the pin, which runs through aluminum tubing to small hole in the firewall. The pin/aluminum tubing needs to be perfectly lined up in order to engage the first eyelet of the lower cowl. Often takes between 30-90min to recowl the airplane and for what..? Don't do it even if Richard VanG tells you to.
 
Mine is hinges all around, per plans. The only thing I would do differently is add a couple screws at the inboard side of the hinges on the bottom cowl to firewall. I have lost 1 eyelet on each side, but hasn't progressed past that. I like the clean look of the hinges. My wingtips are attached with piano hinge as well.

Well fitted hinges work great. I can remove or install all the pins with no trouble at all. I do condition inspections and maintenance on various RVs and other aircraft. I can get my cowl on and off faster and easier than most of the 1/4 turn cowls I have come across. Nothing wrong with going that direction, but if you take your time to get it right, the hinges work great. My least favorite spot for the 1/4 turns is at the top cowl to firewall, they like to catch on the sides.

That said, I have encountered many very difficult-to-remove hinge pins. I think it is pretty common, but in my opinion is a builder error.
 
Agreed that there are some tough hinges out there, and also agree that is a result of builder error or lack of attention to detail in most cases. Even my plenum lid is held on with piano hinges. Takes seconds to get on or off.
 
No Hinges on the bottom

My 9A kit came with 1/16” thick plates that are to be riveted along the bottom of the firewall. The bottom of the cowl is attached with screws through three nutplates in each plate. No hinges along the bottom. Van’s must have changed the plans.
 
Hinges

My purchased RV-3B has 1/4 turn along top of firewall, screws on sides of lower cowl and hinges where upper and lower cowl joins. Has ugly bumps along top cowl between 1/4-turns.

So I used all hinges on my RV-4 (except front behind spinner). Cut a small slit in top cowling for pins so I don't have to access them thru oil door. Plan is to make a cover for the pins with one or two screws.

Would definitely do the same again: lightweight, simple, inexpensive and nice joints. Also much faster to remove/insert.

Finn
 
Back
Top