Steve Ashby

Steve Ashby

Well Known Member
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I have been pondering the manner in which I will affix my cowling to my firewall. What are the pros and cons of the piano hinge vs the 1/4 turn fasteners? What say you flyers?
 
Piano hinge works great for the vertical between the lower cowl and firewall, and the horizontal between the upper and lower cowl. Across the upper cowl to firewall, they work OK but are often difficult to install and remove. Hinges don't work well at the lower cowl to firewall. The pressure and vibration tend to break off the hinge eyes over time. The same between the upper and lower cowl at the spinner. Most people use screws or quarter turns here.
 
My -4 has been flying with hinges for about 6 years. To date, I have broken 3-4 eyelets and will soon ground the plane to switch from hinges to 1/4-turn fasteners.

The broken eyelets are along the horizontal hinge sections between the upper and lower cowl halves and between the firewall and upper cowl. So far I have not seen any damage to the vertical sections attaching the lower cowl to the firewall. I hope to have better luck with the 1/4-turn fasteners.

Regards,
Dean Pichon
Bolton, MA
RV-4
375 hrs
 
1/4s on the upper cowl-firewall for sure. Besides broken hinge eyes, it's often a two-man job to get the mess aligned to drive in the pin, perhaps over a hot engine to boot.

JOhn Siebold
Boise, ID
 
I'm using the piano hinges all around, and have not had any significant problems yet....515 hours, about 1.7 years of flying. I think I have one hinge eye on each side on the lower (short horizontal) fasteners that might be thinking about giving up. One nice thing is that with age, the hinges are easier and easier to install - obviously some wear occurs between the pins and the hinge eyes.

The hinges across the top/rear of the upper cowl take some fiddling to get right, and yes, if you have to remove the cowl with the engine hot, it is a good idea to have a long sleeve shirt - there are warm pieces of metal in there!

I think that the 1/4 turn fasteners are a good solution, and considered them briefly, but decided to go with Van's solution to start (there are an awful lot of RV's flying with the hinges!), and knew that I could change later if I needed to. Haven't had a reason to change yet, and the "fastener-less" appearing cowl does get compliments!

Either way works - just make sure that if you go with hinges that you try minimize residual forces in the system - in other words, the hinge pins shouldn't force or pull things into alignment (too much) - the hinges pretty much align naturally, or you're just asking for wear and breakage.

Paul
 
I have hinges all the way around on my RV-8

When it was new they were a bear to get in and out. As I learned the technique and the airplane "loosened up" they became much easier to work with. I still always thought about converting to 1/4 turn fasteners until I asked a guy with them on his RV-8 and he said he hated them. He says he may even convert over to the hinges.

I have an eyelet on each side across the bottom that are broken.

So I guess that is one vote for hinges.



Bruce
N297NW
RV-8 (458 TT)
 
No hinges for me

I started with hinges everywhere except at the top and by the spinner. The bottom hinges broke in something like 10 hours. The side hinges probably lasted around 30 or 40 hours. The hinges that join the top cowl to the bottom cowl didn't start breaking until around 850 hours when they started breaking one by one on one side only, starting at the front. Except for the top to bottom cowl hinges, I replaced them all with screws into nutplates as they broke. I used too many screws and they are a pain to remove and replace, but nothing has broken on them.

By the spinner I started with screws into aluminum plates and switched to steel plates when the aluminum ones broke at 150 hours or so.

I know most people have way better luck with hinges than me, and they are also probably way better builders but that is one of the few things I would do differently if I knew then what I know now, there wouldn't be any cowling hinges on my airplane.
 
I have the hinges all around per the plans on my 7A. No problems and very easy to remove and replace.

Roberta
 
Hinges here too..

I have hinges all around except on the bottom. Easy to install and look better IMO. 2.5 yrs, 550+hrs no problems at all.
 
Rolled vs. Extruded

The piano hinge Vans supplies is the inexpensive 'rolled' aluminum hinge. If you are worried about longevity, go to Wicks or ACS and order the appropriate amount of 'Extruded' piano hinge. The cost is about 2.5-3 times more expensive than the rolled stuff. Probably last 5-10 times longer.
 
The Interesting Question.....

Now my engineering curiosity is piqued.....we have good builders that I have a lot of respect for on both sides of the issue - and I do mean GOOD builders - those that have had problems with hinges, and those that haven't. I wonder if there is a way that we can figure out what makes the hinges work, and what makes them break? My pet theory is pre-tensioning (loads applied due to slight misalignments), but maybe it's vibration? Could it be folks with dynamic balancing have better luck? I don't know, and unfortunately, I'm not sure how we'd figure it out....but it is an interesting question!
 
Hinges 2,006.6 hours later

September will be 10-years since first flight. 2,006.6 hobbs hours since first flight, hinges are still intact with only one (1) eye having broken. They are the CHEAP ones that Van supplied with the kit.

I do have an aluminum cover at the front of the cowl that has nutplates that fasten it to the top and bottom of the cowl. IMHO, this helps off load some of the air loads on the hinge pin and keeps the hinge pin from coming forward into the back of the prop.

See Mel's post about not using hinges on the bottom of the cowl and behind the spinner. Sounds like he and I are set up the same way. I have #10 screws and nutplates.

rv6flyerhotmailco.jpg
 
My 7A plans show to use the nut plates to attach the upper and lower cowls together behind the spinner and that's what I did. The rest is the rolled hinges. The side and bottom hinges along the firewall are a heavier gage steel hinge with 1/8" pins. The horizontal (longitudinal) hinges and the top firewall are the AL hinges (1/8") and use the 0.090 pins. All parts supplied in kit.

I chamfered the edges of the AL hinges (so the edges did not bind when bent) and prebent everything with the pins installed. I drilled holes in between the rivet holes for epoxy to soak into (hinge only). After the hinges were riveted on, I ran epoxy resin over the hinge edges and into the holes I drilled. So far I have no breakage or cracking of the hinges or fiberglass or loose rivets. This was all done almost 4 years ago with over three years of flying (150+ hrs).

I think the fitup of the cowl and the carb mounted airbox and the baffles is critical to prevent the engine from rocking and beating up the cowl. Also, minimizing vibration will help (as Paul said).

Time will tell if I did everything right. I haven't done the prop balancing, yet, but my engine and prop are very smooth running (Lyc 0-360 A1A and Hartzell BA). The pins insert and withdraw fairly easily and everything goes together without any binding or contorting. The cowl halves pretty much pop into place and line up to each other without any hassle.

Roberta
 
Cowl hinges

One reason for hinge pins that are difficult to insert/remove and hinge eye failures may be due to distortion of the hinges when riveted to the cowl.

The technique I used, with complete success so far, is to mount the hinges using the fiberglass cloth between the hinge and cowl and holes in the hinges for the resin attachment to the hinge. But, I did not rivet the hinge to the cowl until the epoxy resin had cured for a day. I dipped the cleco end in used motor oil for release from the resin and only clecoed the hinges in place while the resin was curing. This prevented any distortion of the hinges by setting the rivets while the resin was still flowable.
 
After talking to some RVers with many flying hours I used hinges on the horizontal run between upper and lower cowl and on the vertical run lower cowl to firewall. All other places I used #8 SS Phillips screws with drilled out #6 SS dimpled (tinnerman?) washers and platenuts--looks like the camlocs on my old Mooney but cost much less. I also used proseal to bond the hinges to the cowl the night before I riveted the hinges using soft rivets designed for fg -- this was done to avoid the rippling mentioned in another post. Screws/nutplates also on the front of the cowl between the spinner and air inlet !!

Cheers,

db
 
I am intrigued with the idea of replacing my rolled hinges (with several broken eyelets) with extruded hinges as was recommended by one poster. Is anyone flying with extruded hinges who can comment on the performance?
 
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