What's new
Van's Air Force

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

Skybolt flanges and Cowl Stiffening

mfleming

Well Known Member
Patron
Im getting ready to order the Skybolt firewall kit for my -7.

Couple of questions for those that have gone before me:

  1. Should I order the flanges or is it easier to drill the holes in the cowling by making your own flanges?
  2. I've read Dan Horton says add some carbon fiber strips for stiffness, is this just on the inside?
  3. Hinge or Skybolt for the horizontal section of the cowl?

Any other tip appreciated
icon14.gif
 
[*]I've read Dan Horton says add some carbon fiber strips for stiffness, is this just on the inside?

I don't know what you read, but I run with high cowl pressure, and adding a few glass plies didn't stiffen my cowl edge as much as I would like. So, for the next one...

Carbon is higher modulus, i.e. less stretchy than glass fiber. In this application, apply a ply or two of unidirection carbon tape on both the inside and the outside of the cowl edge. The tapes become tension and compression members separated by a core. One side only won't do anything useful.

A glass tape over the carbon tape on the inside will serve as a wear buffer, minimizing carbon contact with the aluminum parts. You'll need some micro on the outside to blend the tape. Shim as needed to match surface height with the boot cowl.
 
1. Order the flanges. Its a huge time saver.
2. I didn't, but I also didn't use the maximum suggested spacing. I ordered a few extra fasteners and kept the spacing closer together. I'm also using a plenum which should keep some of the pressure off the upper cowl, so I'm prepared to go back and add carbon reinforcement but I'm hoping it isn't needed.
3. User preference. I went skybolt for everything.
 
My Skybolt kit will be for sale soon

Hi Michael,

I just went through this same decision and actually purchased the "Upper Firewall" kit for my RV-7 ~$200, including the two tools needed for installation. However, being a newb I found it a bit difficult and a bit too complicated to understand the installation work required (I know I'm just running out of patience). At the suggestion of a multi-builder friend, I abandoned the Skybolt idea and decided to install a flange with nutplates and simply use screw fasteners along the upper firewall. I extended the flange down each side just far enough so that the upper portion on each side of the lower cowl could receive a screw fastener; below that, the vertical/straight portion of each cowl side has the hinge installed.

Sure, the screws don't look nearly as neat and professional as the Skybolts (screws are the domed cadmium plated (I think) #8 screws with a nylon washer underneath). But, the final fit is excellent, very secure and the procedure was something I was familiar with. I'm super happy with the results. This was one area that I didn't want to go with the hinge. I used the .02 shim with the flange and it helps to reinforce and make a flush finish between cowl and skin.

Hinge for the horizontal portion and very happy with the result there too.

I don't mean to dissuade you at all! I found that my "keep-it-simple" mindset was being a bit challenged here with the Skybolts. I haven't had time to post my kit for sale, but I figured that when I do get around to it, it would likely sell quickly since the Skybolts are a very popular thing, and for good reason.

Ryan
 
Found a photo Mike. This one has multiple plies of glass tape on the inside edge. It's not bad, certainly not like some I've seen. Still, it does bulge and I gotta look at it. Oil door too, and got about 8 plies of 9oz. This was a job for carbon/core/carbon.
-
 

Attachments

  • cowl bulge.jpg
    cowl bulge.jpg
    59.7 KB · Views: 504
  • Cowl Shim.jpg
    Cowl Shim.jpg
    220.8 KB · Views: 478
Carbon

Excellent timing!
I am right in the middle of the process and ordered a 20 piece kit to do the cowl split.
My notes are on my blog. They are edited as I go so be careful.
Dan's carbon suggestion will be done.
Sorry. Never figured out how to post a vertical image
 

Attachments

  • 20211026_150100.jpg
    20211026_150100.jpg
    213.3 KB · Views: 483
Use plain strips down the sides of the fuselage. The scallops can catch the corner of the cowl when you slide it upward into place...paint chips!
 
Use plain strips down the sides of the fuselage. The scallops can catch the corner of the cowl when you slide it upward into place...paint chips!

This is very true. It is like a chainsaw hitting your cowl.
For me, I would either use a hinge at the split or make the strips myself. I didnt like having to cut down the pieces to match the spacing I wanted. It would have been much easier to fit the cowl, mark and drill pilot holes, then expand the holes to fit the fasteners.

Maybe on my next one I will do a left and right split so I can take off 1/2 at a time!
 
I just made the flanges myself, but this was before they sold them with the kit or I probably would have bought theirs.

Looking back, it's probably better to make your own so you can be sure all the holes are perfect.

Not much narration, but a few photos here:

http://www.rv8.ch/installed-camloc-fasteners/

As you can see, I used the skybolts around the firewall, and hinges along the horizontal interface between the top and bottom cowl. I'd do it this way again.

I also get the bulging but I'm too busy looking out for bogies and mountains and my magenta line to really let it bother me. :D

IMG_5093.jpg
 
Another cowl stiffener option

I took Dan’s comments seriously regarding cowl bulge. On my recent build, I fabricated a U shape channel of glass and bonded in just forward of the Skybolt fasteners on the inside of the cowl. Minimum weight, maximum stiffness !
If you would like pics, email [email protected].
 
Sorry. Never figured out how to post a vertical image

Larry,

If you're using a mac, click on the image (opens Preview), click the Rotate Left tool 4 times ( rotate the image 360°), save it then upload -- I don't know why this works...

A windows PC might do the same thing, don't know..

B
 
Like DanH's suggestion, I pitched the individual mounting plates for continuous strips running across the top and sides (and bottom) of the cowl/fuse interface (I did 100% Skybolts) and decreased spacing a bit to 3" to minimize potential puckering.

Undrilled strips:
DSC_5901-M.jpg


With Skybolt sockets installed:
IMG_0412-M.jpg


I did find that I had some static puckers in the cowl (not due to internal air pressure in flight, just slightly imperfect mounting) in the high-curve region of the top cowl. I cut some slots and relief holes, scarfed the top slot edges, protected the mounting surfaces, and epoxied the gaps closed with glass/epoxy and wood block and a tight strap around the cowl to close the gaps.

I don't see any air-pressure induced puckers with this setup; no additional stiffening was added to the mount surface; just a tighter Skybolt spacing.

IMG_0629_HEIC-M.jpg
 
Found a photo Mike. This one has multiple plies of glass tape on the inside edge. It's not bad, certainly not like some I've seen. Still, it does bulge and I gotta look at it. Oil door too, and got about 8 plies of 9oz. This was a job for carbon/core/carbon.
-

Thanks Dan, very much appreciated.

Excellent timing!
I am right in the middle of the process and ordered a 20 piece kit to do the cowl split.
My notes are on my blog. They are edited as I go so be careful.
Dan's carbon suggestion will be done.
Sorry. Never figured out how to post a vertical image

Thanks Larry, I'll visit your log

I took Dan’s comments seriously regarding cowl bulge. On my recent build, I fabricated a U shape channel of glass and bonded in just forward of the Skybolt fasteners on the inside of the cowl. Minimum weight, maximum stiffness !
If you would like pics, email [email protected].

Thanks Larry, I'll email you

Like DanH's suggestion, I pitched the individual mounting plates for continuous strips running across the top and sides (and bottom) of the cowl/fuse interface (I did 100% Skybolts) and decreased spacing a bit to 3" to minimize potential puckering.

Undrilled strips:
DSC_5901-M.jpg


With Skybolt sockets installed:
IMG_0412-M.jpg


I did find that I had some static puckers in the cowl (not due to internal air pressure in flight, just slightly imperfect mounting) in the high-curve region of the top cowl. I cut some slots and relief holes, scarfed the top slot edges, protected the mounting surfaces, and epoxied the gaps closed with glass/epoxy and wood block and a tight strap around the cowl to close the gaps.

I don't see any air-pressure induced puckers with this setup; no additional stiffening was added to the mount surface; just a tighter Skybolt spacing.

IMG_0629_HEIC-M.jpg

Nice Photos.


My takeaways:

  1. Home made tabs might be nice since the spacing and drilling will be exactly what the builder decides. It seems that getting the holes drilled precisely with the factory tabs might be a difficult task.
  2. Decreasing the distance between the fasteners also seems to be a good idea to minimize buckling.
  3. Increasing the stiffness of the cowl lip with carbon fiber inside & out has benefits.
 
I just made the flanges myself, but this was before they sold them with the kit or I probably would have bought theirs.

Looking back, it's probably better to make your own so you can be sure all the holes are perfect.

Not much narration, but a few photos here:

http://www.rv8.ch/installed-camloc-fasteners/

As you can see, I used the skybolts around the firewall, and hinges along the horizontal interface between the top and bottom cowl. I'd do it this way again.

I also get the bulging but I'm too busy looking out for bogies and mountains and my magenta line to really let it bother me. :D

View attachment 17556

Nice write-up
icon14.gif
 
Do you remember how many extra fasteners you needed due to the decreased spacing?

I think I used an extra 5. I also dimpled my flanges instead of countersinking them at first, so when I re-ordered all my flanges to fix that mistake I just tacked on an extra 10 sets of fasteners to make sure I had enough. I still have a few left over, so it was definitely less than 10. I think I was aiming for 2.25 or 2.5" spacing instead of the maximum of 3". I can't recall the actual numbers right now, but I shot for about 0.5" less than the recommended max.
 
Skybolts

I'm installing mine. Skybolt flanges are designed for 3-1/2" spacing. They could be cut on the end without the joggle to get 3" spacing. I've got 8 from the cowl split up to the center plus one in the center. That's 17. Figure one more each side at 3".
That's 19
I plan 8 each side along the split. 16 total. Figure 9 each side at 3".
That's 18
Bottom depends on gear. So far it looks like 7 each side and bottom for 14. Add one each side at 3".
That's 16
Total 53.
They sell a kit with 52. You may want a few extra for the oil door or spares.
I don't recommend piece meal any more than absolutely necessary. I recently ordered a 20 unit kit. Piece meal was over $100 more.
Hopefully with Dan's carbon sandwich, 3-1/2" will suffice. I also have a plenum.
 
Do you remember how many extra fasteners you needed due to the decreased spacing?

I did the following:

19 across the back top cowl to fuse
5 vertical each side for the lower cowl to fuse (10 total)
3 each side, bottom between the exhaust stack bump and gear leg (6 total)
9 horizontal each side to attach the top and bottom cowls

That's 53, plus two more for the oil door. Wirejock nailed it, above.

I did not use any of the floating receptacles ... everything fit nicely without.
 
Floating receptacles

I did the following:

19 across the back top cowl to fuse
5 vertical each side for the lower cowl to fuse (10 total)
3 each side, bottom between the exhaust stack bump and gear leg (6 total)
9 horizontal each side to attach the top and bottom cowls

That's 53, plus two more for the oil door. Wirejock nailed it, above.

I did not use any of the floating receptacles ... everything fit nicely without.

When I was browsing, all of the kits are floating receptacles now. They do sell the rigid but it will be by piece.
 
When I was browsing, all of the kits are floating receptacles now. They do sell the rigid but it will be by piece.


Are the floating ones undesirable? Also I couldn't find the page related to Skybolt installation on your blog.
 
Are the floating ones undesirable? Also I couldn't find the page related to Skybolt installation on your blog.

I have all floating. Works well for me. I was worried that the cowl would move around, but once they are all fastened, no movement.
 
Skybolts

Are the floating ones undesirable? Also I couldn't find the page related to Skybolt installation on your blog.

The floating are easier to use. I would order the standard kit.
52 unit if you plan cowl split as well as firewall. That's at the standard 3-1/2" spacing. Figure another six or more at 3".
The draft for the article is front page posting. It's a comprehensive cowl install article. Skybolts are about 1/2 way down.
 
Last edited:
OK, My head is spinning after looking at all the Skybolt information on VAF, blogs & the Skybolt website.

Questions:
  1. If I make my own smooth firewall tabs (no scallops) what thickness aluminum do I use?
  2. If I use 3" spacing on the firewall, do I still need stiffeners?
  3. What about the tools sold on the Skybolt website...do I need them?

Whew ;)
 
OK, My head is spinning after looking at all the Skybolt information on VAF, blogs & the Skybolt website.

Questions:
  1. If I make my own smooth firewall tabs (no scallops) what thickness aluminum do I use?
  2. If I use 3" spacing on the firewall, do I still need stiffeners?
  3. What about the tools sold on the Skybolt website...do I need them?

Whew ;)

Its been a long time, but I think I used 0.040" for the strips. (might be 0.032").

I got everything fit with straight strips, then came back and added scallops afterward. One advantage along the top was being able to bend them down slightly to avoid the puckers that Bill Benze talked about.

I used 3" spacing, added some glass uni tapes on the inside, and still have minor puckering. May bet worse when I start closing down my cowl exit, upping the pressure inside. "next time" some carbon uni inside and out.
 
Skybolts

OK, My head is spinning after looking at all the Skybolt information on VAF, blogs & the Skybolt website.

Questions:
  1. If I make my own smooth firewall tabs (no scallops) what thickness aluminum do I use?
  2. If I use 3" spacing on the firewall, do I still need stiffeners?
  3. What about the tools sold on the Skybolt website...do I need them?

Whew ;)

1. I measured the Skybolt flanges @ .050".
2. I added a .025" shim between the flanges and firewall flange to add some space for additional glass and carbon fiber I added. I glassed in a 1" strip to stiffen the edge of the cowl.
3. Tools. Yes. Get the kit with the plier and keeper install tool.
 
I don't know what you read, but I run with high cowl pressure, and adding a few glass plies didn't stiffen my cowl edge as much as I would like. So, for the next one...

Carbon is higher modulus, i.e. less stretchy than glass fiber. In this application, apply a ply or two of unidirection carbon tape on both the inside and the outside of the cowl edge. The tapes become tension and compression members separated by a core. One side only won't do anything useful.

A glass tape over the carbon tape on the inside will serve as a wear buffer, minimizing carbon contact with the aluminum parts. You'll need some micro on the outside to blend the tape. Shim as needed to match surface height with the boot cowl.

Is there a particular carbon fiber cloth tape to use on the cowl? I don't see carbon fiber cloth tape at ACS...where's a good source? I assume 2" tape would be about right.
 
1. I measured the Skybolt flanges @ .050".
2. I added a .025" shim between the flanges and firewall flange to add some space for additional glass and carbon fiber I added. I glassed in a 1" strip to stiffen the edge of the cowl.
3. Tools. Yes. Get the kit with the plier and keeper install tool.

And a couple more things - get 200 Viton o-rings to secure the sockets into the cowl, I have not used the retainers, only o-rings. And put screws in place of the Skybolts on either side of the exit chute. The Skybolts only use spring pressure to hold the cowl on and it will move enough to mark the contact points.

All but 8 of mine are fixed. Not a problem if the holes are accurately positioned when drilling the cowl. The curved sections require floaters for installation and removal ease.

Screen Shot 2021-11-17 at 8.06.28 AM.png
 
Last edited:
O-rings

And a couple more things - get 200 Viton o-rings to secure the sockets into the cowl, I have not used the retainers, only o-rings. And put screws in place of the Skybolts on either side of the exit chute. The Skybolts only use spring pressure to hold the cowl on and it will move enough to mark the contact points.

All but 8 of mine are fixed. Not a problem if the holes are accurately positioned when drilling the cowl. The curved sections require floaters for installation and removal ease.

View attachment 18357

The new kits come with o-rings. They are intended as temporary keepers. Kit also comes with several sets of screws, nutllates and tinnerman washers for other areas.
 
Is there a particular carbon fiber cloth tape to use on the cowl? I don't see carbon fiber cloth tape at ACS...where's a good source? I assume 2" tape would be about right.

Dude, you want me to Google for you?

There are lots of online sources for composite materials. Anyway, this is about education and recreation. Find some examples, do the reading, pick some candidates, and link them here to get opinions regarding your choices.
 
Dude, you want me to Google for you?

There are lots of online sources for composite materials. Anyway, this is about education and recreation. Find some examples, do the reading, pick some candidates, and link them here to get opinions regarding your choices.

Ummmm, that’s what I’m doing and I’ve seen plenty of posts where you shared your expertise… so I asked.

Sometimes to much information is very overwhelming. I’ve spent countless hours reading about installing Skybolts… you’re even listed in the Skybolt instructions as a resource. I get this is an educational project and WOW has it been. Just spent a year wiring the a/c and avionics.

So yeah, I found a source for carbon fiber tape, and have a good idea how to do this from things I’ve read…. Just thought I’d check in with the most knowledgeable guy around before I proceeded.
 
May bet worse when I start closing down my cowl exit, upping the pressure inside.

Steve, a heads up. When I pushed cowl pressure up to current levels, inspection showed signs of stress in the firewall/skin flange on each side of the cowl outlet. The Skybolt tabs, being cantilevered, were multiplying the stress due to pressure. I went back and added braces to the tabs. The photo, clipped from another illustration, isn't great, but you can see the fingers on the Y-shaped braces inserted under the Skybolt flanges. Long time now, no further issues.
-
 

Attachments

  • Tab Braces.jpg
    Tab Braces.jpg
    122.6 KB · Views: 289
Tape

...

So yeah, I found a source for carbon fiber tape, and have a good idea how to do this from things I’ve read…. Just thought I’d check in with the most knowledgeable guy around before I proceeded.

I have fiberglass tape. It has a ridge on either side to keep the tape from fraying. Makes it tricky to use . I usually trim it off before placing the layup.
You may want to consider it if the carbon tape is similar. I just bought a yard of 60" and slice off whatever width is needed. So far one strip inside covered by a layer of regular glass has really stiffened the split. I will be adding a similar around the inside firewall edge. Vans plans call for some sort of parts around the nose gear and exit as well. I'll get there someday!
 
The option to use as permanent . . .

The new kits come with o-rings. They are intended as temporary keepers. Kit also comes with several sets of screws, nutllates and tinnerman washers for other areas.

I guess Ned was listening and added these to the kits when I first posted about them. I said Viton as the first ones I used were some other material and broke in service. I have 200 hrs and consider the Viton as permanent. This size does not interfere with the assembly.
 
Excellent. So what did you pick, and why, and what is your plan?

Man, you sound just like my 11th grade physics teacher :rolleyes:

So I'm going to experiment. I found some plain weave 3K carbon fiber tape with a 0.012 thickness (couldn't find twill tape). I also purchased some carbon fiber uni-web 2.9oz tape. Both from ACP Composites.

After trimming my cowl, hopefully I'll have enough material to lay up two test articles. I'll play around with layers and different combinations.

I'm using the west system and already have some different weight fiberglass cloths and tapes, as well as different fillers.
 
Steve, a heads up. When I pushed cowl pressure up to current levels, inspection showed signs of stress in the firewall/skin flange on each side of the cowl outlet. The Skybolt tabs, being cantilevered, were multiplying the stress due to pressure. I went back and added braces to the tabs. The photo, clipped from another illustration, isn't great, but you can see the fingers on the Y-shaped braces inserted under the Skybolt flanges. Long time now, no further issues.
-

Ah good to know, thanks.
 
I have fiberglass tape. It has a ridge on either side to keep the tape from fraying. Makes it tricky to use . I usually trim it off before placing the layup.
You may want to consider it if the carbon tape is similar. I just bought a yard of 60" and slice off whatever width is needed. So far one strip inside covered by a layer of regular glass has really stiffened the split. I will be adding a similar around the inside firewall edge. Vans plans call for some sort of parts around the nose gear and exit as well. I'll get there someday!

There are varying qualities of carbon uni-tape, but none have the ridge that woven glass tapes have. They use a cross stitch of polyester thread to hold the unidirectional fiber bundles together. The quality difference is how the edge is finished. Some are somewhat shaggy, and some are held by the cross stitching well enough that they have a smooth edge.

Uni tape will lay down flatter (thinner) than bi-directional woven tape for the same fiber size (e.g. 3K). Also it puts all the fibers in the direction you want for stiffening, rather than waste half the fibers running perpendicular that contribute nothing.
 
There are varying qualities of carbon uni-tape, but none have the ridge that woven glass tapes have. They use a cross stitch of polyester thread to hold the unidirectional fiber bundles together. The quality difference is how the edge is finished. Some are somewhat shaggy, and some are held by the cross stitching well enough that they have a smooth edge.

Uni tape will lay down flatter (thinner) than bi-directional woven tape for the same fiber size (e.g. 3K). Also it puts all the fibers in the direction you want for stiffening, rather than waste half the fibers running perpendicular that contribute nothing.

The seller, ACP Composites, advertises "absolutely no fraying when cut"...we'll see.
 
Instead of glass or carbon fiber, why not epoxy and rivet an aluminum strip on the cowl and add a spacer under the tabs?
 
Based on this thread I’m feeling like Sky Bolts aren’t worth the hassle!

Having done both ways, I would not buy the pre cut scallops. They act like a saw when you are installing the bottom portion. Also, I reduced the spacing so I had to cut each scallop to make them fit and getting them all cut the same was not as easy as I thought it would be.

I would use the skybolts on the firewall and hinge to hold the upper-lower parts together. On an A model it is not easy to get the bottom cowl on and off especially with a 3 blade prop. The scallops on the cowl can scratch the prop if you are not very careful and dont use something to protect it.

They look nice but are tricky to adjust and the phillips heads can be stripped if you are not careful. I have had a few lose the small bar at the bottom of the screw requiring replacement.
 
Plain or Unidirectional Carbon Fiber?

Starting to fit my cowling for Skybolts and realized the SB flanges are hitting the honeycomb as I see happens with many builders. Ground off the honeycomb and want to stiffen the edge with CF on the inside and outside.

I've read extensively here and web on CF and still have a question on what type of CF - Unidirectional or a plain weave? I read the UNI lays down flatter and will provide stiffening in the desired direction for cowl bulging. My concern is the aft edge of the cowl seems kind of flimsy (can bend if picked up the wrong way) - any risk of the uni CF cracking etc. in the non-longitudinal direction if picked up wrong or will it provide enough to strengthen up the flimsiness? Or is a plain weave preferred?

Thanks,
Rob
 
Last edited:
CF

Anybody? Any input on uni or bidirectional carbon fiber?

DanH?

I won't even pretend to know as much as Dan, but I am an "anybody" and I did reinforce the edges with CF.
I just bought a yard from Spruce. Uni I assume. I cut strips a little wider than 1". Every edge has a strip inside covered by a strip of fiberglass. Also Spruce stuff. Sorry, I don't get into the Uni or Bi thing. :D.
I also added a .032" shim under the Skybolt flanges to adjust for the thicker edges.
 
Cracking me up. Thanks Larry. I have flanges and cowling fitted, etc. It's 50/50 on uni or bi so I guess I'll flip a coin.
 
This thread has been most helpful. No scallops for me. Used 0.032 spacer for the carbon fiber stiffeners.
Will be using ~3” spacing. Am I missing anything?
.
IMG_1394.jpeg
 
This thread has been most helpful. No scallops for me. Used 0.032 spacer for the carbon fiber stiffeners.
Will be using ~3” spacing. Am I missing anything?
. View attachment 53866

That looks great Webb, I would hold off on riveting, or even deciding what thickness of shim to put between the Skybolt mounting strip and the inner face of the cowl flange, until after you have done the actual cowl stiffening so you know just how thick it comes out, and adjust the shim strip accordingly. You may have done that, sorry if I missed that. But adding that thought may help others.

To the question of what type of carbon to use, I would use some of both uni and bi-directional. The uni is the most effective at stiffening between the fasteners, minimizing the bulges. Then, I would finish with a ply of bi-directional over the top of that and lapping up onto the existing cowl glass, maybe 2" or 2.5" wide. This will help with stiffening the edge in the direction of edge-flexing when you handle it.

As a rough ballpark, you can count on uni tapes being 0.005"--0.008" thick, and 0.010"--0.012" for the bi-directional cloth, depending on weight of fibers. I'm assuming 3K fibers, which is probably the most common. A fanatic would say to put a ply of fiberglass over the top of all those so that you don't have carbon contact against aluminum, but the aluminum will presumably be primed, the carbon is all epoxy-coated, and this isn't like a structural bond where a little bit of corrosion can destroy the bond. But I do keep a roll of very light weight, fine weave fiberglass tape, 2", for exactly this purpose.

Also when you lay those tapes in, put a strip of peel-ply over them and smooth that out with some pressure. This will work some of the excess resin out, help distribute the resin in case you have any air bubbles or lean spots, and give you a nice smooth surface when it cures and you peel that off.

BTW, I used 3.0" spacing and kind of wished I had used 2.5". Before I reduced my cowl exit area, the cowl layed pretty flat between fasteners in flight. But now, with the higher internal cowl pressure, I see more bulging. Next time, I'll use carbon instead of glass, as I've described here, and may opt for the closer spacing too.
 
Steve, a heads up. When I pushed cowl pressure up to current levels, inspection showed signs of stress in the firewall/skin flange on each side of the cowl outlet. The Skybolt tabs, being cantilevered, were multiplying the stress due to pressure. I went back and added braces to the tabs. The photo, clipped from another illustration, isn't great, but you can see the fingers on the Y-shaped braces inserted under the Skybolt flanges. Long time now, no further issues.
-
I just saw this note from DanH. I am just now doing my first Condition Inspection after the cowl exit mod last winter, so I will give this area a close look.
 
I used 0.032 for the shim. Planning on 2 carbon and 1 glass layer.
Also thought a one piece flange would potentially reduce puckering since there the flange doesn’t narrow between the fasteners.

I’m wondering if I should add strengthening strips to the cowl sides while I’m at it.
 
Not the sides. Down on the bottom, on each side of the outlet, area B in the sketch.

If we think about it, it's real common to see broken hinge halves in the same location, on RVs with standard cowl attachments. It get worse when we pump up cowl pressure. The firewall is more or less rectangular, and the cowl tries to inflate to a round shape. We can see the rear edge of the cowl pushing out at A, but you can bet there is plenty more at B and C.

Cowl Pressure Shape.jpg
 
Back
Top