I am considering a cowl retention system other than the hidden hinge design for attaching the upper cowl to the top of the fuselage. I see many builders choose to use SkyBolts at this location. Can someone explain the advantage of SkyBolts over just using #8 screws into nutplates with the big stainless washers under the screw heads? Is it strictly an appearance issue? I like the hidden hinge system, but getting the pins in and out on a -14 cowl is nearly impossible.
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Why SkyBolts?
- Thread starter Doug Rohrer
- Start date
Main reason for Skybolts is the speed of installation and removal of the cowl. The other reason is that the cups that the fastener sits in distributes the load to the cowl just a bit better than a screw.
Everyone complains about the under-cowl pins and yes, they can be a PITA. Normally it's the starboard side pin that goes in from the port side? The longer pin normally goes in pretty easy. I have larger arms, and it is tight. What I found works very easy is to lay the shorter pin in the first hinge before the top cowling goes on. Make sure the pins are clean and lubed with BoLube. Place the top cowl on very gently keeping the pin in the first hinge pin and carefully slide toward you. I'm in the middle of an oil change so the cowling is off and I will take a pic tomorrow. Easy pesee.
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I have the #8 screws into nutplates and they have worked fine for 26 years. My friend building a -10 has put in the SkyBolts - looks to me like their advantage is simpler removal with a half turn, they stay in place, and they look a bit fancier, but they aren't cheap. I use my drill drive in torque set mode and a phillips bit to deal with having to run the screws in or out.
If you do go with screws, while stainless screws seem tempting, plain steel ones will last much longer and won't gall up in the nut plate.
Builders have designed an access cover at the top hinge area so each pin is the same length and is installed form the outside of the cowl and then covered with a small plate.
Someone here has done this with a 7 and maybe post a picture....
See RV-10 plans made airframe......I much prefer the 14 design than my 10.
I have screws on that junction for my -6 and skybolts on the -10. Given the significant difference in cost and the minor difference in ease of removal, I'd go screws next time. For what it is worth, I have # 6 screws with tinnerman washers across the top cowl on the -6.
When I built my 7A the pins were accessible through the oil door. I bought my 10 (assume similar the the 14?), the builder did what gasman posted. A small plate on the aft center of the upper cowl over the hinges. As long as the hinges were installed correctly and the pins are clean and lubricated with BoLube it's a very easy process. I like the clean look of the hinge pins.
Same here as well as 1/4 turn on the bottom at the firewall as well as the top. Sktbolts on the 1st 4, the 7 and the 8. Pins all around on the 2nd 4 only because I built it to sell and didn't want the expense.
I like the clean look of the hinges but for me the ease of cowl re and re with Skybolts wins out. The upper and lower pins are a PIA and I dislike using screws all the way around the cowl. Although expensive, I find the Skybolts are the best compromise between looks and functionality.
Thanks for all the responses. I have built two other RV's with the hinge pins along the top and had a miserable experience with
both. I know all about pre-bending the pins, grinding an asymmetrical tip on the end, super polishing and lubing the pin, etc. but still grind up my arm reaching through the oil door. The -14A is taller and even higher and wider than the 6/7/9 models. I think I will go with hinges on the vertical sides and #8 screws with tinnermans on the horizontal split and the top joint. If I can find a deal on SkyBolts I may try them.
both. I know all about pre-bending the pins, grinding an asymmetrical tip on the end, super polishing and lubing the pin, etc. but still grind up my arm reaching through the oil door. The -14A is taller and even higher and wider than the 6/7/9 models. I think I will go with hinges on the vertical sides and #8 screws with tinnermans on the horizontal split and the top joint. If I can find a deal on SkyBolts I may try them.
My Cessna 150 has #8 sheet metal screws in sheet metal anchor nuts from the factory. There are about 2 dozen of them holding the cowls and I curse them every time I have to service the engine. Time consuming PITA and easy to damage the sheet metal anchor nuts if tightened a bit too much. Later Cessna 150s and 152s had 1/4 turn fasteners. I'll be using Skybolt type fasteners for all my RV-9A cowl fasteners.
I have worked on a few planes with the upper hinges and hate them. Big hands and arms and find it difficult, especially when the pins are tight. I used screws on my 6 in that area. Skybolts were wayyy to expensive. With a cordless drill, i bet i can get mine out within 30 seconds of skybolt users.
In the 10, they changed the design and the pins get installed from outside the cowl. A far superior design IMO and still hidden, minus the two pin ends sticking up. You could copy that on your 14. No special parts; all builder fabricated.
In the 10, they changed the design and the pins get installed from outside the cowl. A far superior design IMO and still hidden, minus the two pin ends sticking up. You could copy that on your 14. No special parts; all builder fabricated.
It seems to me a good solution is hinges for the horizontal split between top and bottom cowl. One can use extruded hinges here for greater strength. If you use screws or Skybolts you could fashion a fiberglass flange on the bottom cowl for the nutplates or Skybolts receptacles. The Skybolt aluminum flanges make a sawtooth that complicates top cowl installation, the cowl can work its way onto either side of adjacent flanges.
Skybolt grommet retainer rings:
- With Skybolts one can leave out the grommet retainer rings so the grommet/fastener assembly will fall out into your hand so the fasteners don’t protrude to the inside of the cowl and snag into the receptacles. Not necessary for top cowl to firewall intersection but very helpful for top to bottom cowl split.
- Also I suggest grinding the retainer ring gap larger so you can get a removal tool into the gap… I purchased the Skybolt tool for this and its fingers do not fit into the gap, will not work if I don’t grind the gap larger beforehand. I sharpened the fingers on a cheap retainer ring tool I had on hand and it was still difficult with the small as-supplied gap.
Note also post #16 recommending truss-head screws vs flat-head screws and a fiberglass flange added to the inside of the lower cowl for the horizontal split between upper and lower cowl.
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Looks like I'm the lone dissent here. I used the pins as per the plans all the way around on my -14 and would do it again. I like the clean look and it isn't too tough to get the pins in and out. Granted, the starboard upper pin is a bit more of a challenge to get in than the others, but it's not awful.
From my limited experience with some buddy's Skybolts, I don't particularly care for them from a looks or a convenience standpoint.
From my limited experience with some buddy's Skybolts, I don't particularly care for them from a looks or a convenience standpoint.
You'll find AN526 screws with a nylon washer under the head to be a far more durable choice. A Tinnerman requires a knife-edged hole, which in the long term doesn't work well in fiberglass.
If not screws, hinges work well down the sides. Skybolts everywhere else. I've lost way too much skin screwing around with firewall hinge pins, top and belly.
A glass flange added to the lower cowl (2" tape, 4 plies) makes a solid base for nutplates or Skybolt sockets. However, note an angle valve -8 or a Rocket probably doesn't have enough clearance for Skybolts over the valve covers....thus screws or hinges.
Yes, I know, tinnermans on the plenum lid. I failed to provide enough headroom for domed screws.
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One nice thing about hinge pins on the side is it's very easy when placing the bottom cowling on (especially with a 3 blade prop) is to bring it up half-way and "ladder" it up into place going up 2 and 3 hinges at a time. (I prefer not to have any help with the canopies, and this make it very easy for it to be a one person job)
Upper hinge pin pre-installed part way before top cowl goes on:
Went into this project thinking I would do Skybolts all around. I’m siding more with the piano hinges, I’ll use the Aerosport cover like I did on my 10. My only angst with the 10 is where to strategically push when getting the horizontal hinges to all sit correctly.
Between our three RV’s and now the Rocket, I have every attachment method you can think of, in many combinations. Standard all-Hinges, a mix of hinges and screws, a mix of hinges and Skybotls, and now I am doing all Skybolt on the F1 Rocket. Why? Well I like the Skybolts on the firewall (top and bottom) on our -3, and the way the F1 cowl was molded - with a nice overlapping flange/lip up front - using hinges there was goign to take some modifications (and I liked the front overlap). Our -6 has screws along the sides, and they work fine - but when you take the cowl off, you have to figure out where to put all those screws and Tinnerman washers, and on an open windy ramp, that is a pain. So the captured Skybolts are nice from that aspect.
Truth is, no matter what the fastener system, I can have any of our cowls off in five minutes, and back on in about the same time. Don’t overthink it too much!
Truth is, no matter what the fastener system, I can have any of our cowls off in five minutes, and back on in about the same time. Don’t overthink it too much!
Here are pics from my solution, mentioned already im post#5 by Warren (gasman).
It‘s not a -7 but it works like charme and they are really easy to install & take out.
I am sure i put them in&out at least as fast as skybolt/camlocs allow to take the cowl of.
You hardly even see it from 10 feet away if you’re not aware that they are there.
I chose hinge pins over skybolt/camlocs for the looks and the price.
It‘s not a -7 but it works like charme and they are really easy to install & take out.
I am sure i put them in&out at least as fast as skybolt/camlocs allow to take the cowl of.
You hardly even see it from 10 feet away if you’re not aware that they are there.
I chose hinge pins over skybolt/camlocs for the looks and the price.
For those using skybolts on the top/bottom side intersection... the only plane I've worked on that had those there was a real pain to get the top cowl off. Why? Because the dang skybolt pins keep sliding back into the holes enough to prevent getting the upper cowl off. All you have to do is simultaneously hold 8 or so of them 'out', and concurrently lift up on the top cowl. Am I missing a trick? Oh, and once those are held out a couple on the aft top edge will drop in and fight me.
With the piano hinge there, yank two pins, and the top cowl is free. [Ignoring the nose screws or whathaveyou, same problem on either setup.]
With the piano hinge there, yank two pins, and the top cowl is free. [Ignoring the nose screws or whathaveyou, same problem on either setup.]
Post #14 the paragraph labeled “Skybolt grommet retainer rings”.
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Why Skybolts?
You have to like the look. There are no advantages over properly installed hinge pins. Hinge pins are as easy to remove and install and have a “cleaner” look.
Now, If you have improperly installed hinge hinges they can be a real pain. I’m sure improperly installed sky bolts could be a pain also.
Hinge pins dominate the installed base of RV’s by a long shot. If they were such a problem, they wouldn’t be so common. They continue to be the standard.
If you like the Skybolt look go for it. I personally do not, but that’s the beauty of building your own machine.
You have to like the look. There are no advantages over properly installed hinge pins. Hinge pins are as easy to remove and install and have a “cleaner” look.
Now, If you have improperly installed hinge hinges they can be a real pain. I’m sure improperly installed sky bolts could be a pain also.
Hinge pins dominate the installed base of RV’s by a long shot. If they were such a problem, they wouldn’t be so common. They continue to be the standard.
If you like the Skybolt look go for it. I personally do not, but that’s the beauty of building your own machine.
So, everyone leaves off the retaining rings?
Certainly not but maybe they would if they knew about this hack... I leave the retaining rings out along the top to bottom cowl horizontal split and it works well.
I would have used extruded hinges there but the RV-14A I purchased has Skybolts for the top to bottom cowl horizontal split.
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A few pics of the RV10 hinge covers, super easy to remove and install. The plane has been flying for over 13 years.
I may have to rethink my plan. I will be getting a QB fuse kit. From what I can see in a few pics on the web, the QB fuse seems to have the top front skin riveted on, which includes the hinge sections across the top and down the sides. It also will make it very hard to install the rudder pedals and run wires and cables through the firewall. On my previous two builds, this skin was the last part installed so I could access everything behind the panel. Maybe try the pin system used on the -10...
Working on my 4th RV and it will have hinges all around after the last two had hinges all around. I can remove my cowl faster than if it had sky bolt all around and have had zero trouble putting them in. But I admit getting the fit right is more work and requires more attention.
Not sure what you mean. I recall needing to put a shim between the skybolt socket plate(s) and the firewall flange, and some strategic bending of those plates.
I had to add .032 shim between the Skybolt flanges and the inside of the firewall. I strengthened all edges on my cowl with a strip of CF and FG so mine is a little thicker.
I put the shim between the flange and the inside of the firewall just like you would if you put in the piano hinge. You know, now that I think about it, it may just be some transition material the cowl manufacturer put in to transition from the honeycomb material to the flat fiberglass. I do recalling reading something from Skybolt that it wouldn't hurt to add some kind of reinforcing material to prevent bulges in the fiberglass during flight. Thanks for the replies.
I’ve used a combination of hinges and skybolts on a number of Rv14s and have been very happy w the functionality and aesthetic (less screws or skybolts taking away from the paint scheme).
Hidden hinge pin along the split between the upper and lower cowl. Hinge pin is accessed through the cockpit - see photo below with the pins retracted and circled in blue. I like this verses the option of inserting the horizontal pin from the cooling air inlet area - it’s cleaner looking to me.
Here’s a photo (below) with the cowl removed:
Skybolts on top.
Vertical hinge between cowl and firewall.
Small opening where the horizontal pin comes in from cabin to join the upper and lower cowling (circled in blue as it’s hard to see the opening of the sleeve that the pin comes through)
Overall, I’d still like to find ways to improve ease of access (if only it was as easy as opening the hood on my car) but I find I can remove and replace the cowl solo.
Couple key notes:
* make sure the horizontal pin is lubed or it can be a pain to get it to slide into place.
* I find using skybolts across the top is so much easier than using screws. 1/4 turn and they’re open or closed. No screws to strip or keep track of when you remove them (how did I always lose one or a washer when I used them?).
*when installing the cowl, I put the lower on first. I position it on my harbor freight pneumatic stool (makes it easy to raise the cowl into place) under the engine and then get one of the vertical hinges lined up and drop the pin in just a couple rungs. Then I go and get the other side lined up and secured. Once I get the lower all full secured, I place the upper - adjust the inlets in place, and insert the horizontal pins by reaching in the cockpit (I’m standing in front of the wing making sure the upper and lower cowling hinge is interlocked) and feeding them in.
Sounds more complicated than it is.
Finally, I engage the skybolts.
