My take on hinges, when done right a thing of beauty
The hinges I recommend you definitely upgrade or super size are the Aft (vertical) lower hinges on along the firewall.
Think about it. You are cruising 200 mph and that big split shell, called the cowl, is taking the brunt of the dynamic aero loads, both inside and out.
First outside areo loads. The lower front half of the cowl is this big slope from the spinner down to the bottom where its horizontal. It's like skies on an olympic ski jumper, a barn door, but a barn going 200 MPH. Now ALL the load of the cowl comes out at the firewall. The cowl is cantilevered off the firewall. Since most of the load is pushing up, the cowl is being pried off. Top firewall hinges are in compression and sides lower hinges are in tension. Since the lower cowl scoop does not allow fastening, most of the load is taken by the aft side hinges. These are the ones I RECOMMEND LARGER EXTRUDED HINGES HERE.
Now look at internal air load. Assume for a discussion you have the standard baffle and soft seal. The upper cowl is used as the lid to a pressure plenum. Needless to say the top wants to leave the bottom. So the halves have forces that makes them want to not be one and it also adds to that UP load on the aft lower firewall hinges. HOWEVER the James cowl works with a dedicated pressure plenum or "dog house" that does not rely on the cowl.
This is an advantage of the James style cowl over stock, less cowl load. Not using the cowl top as a pressure plenum is a large relief in loads to all the hinges, especially the long side hinges and aft lower firewall hinges. The outside air-loads are still there.
Hinges: (Tips and Hints)
Front spinner: Screws and nut plates for sure on the inboard edge of the spinner (vans stock cowl). I even add extra plys and a metal backing plate riveted on. This is a critical area. May be a larger extruded hinge may work, however the "James Style" is different of course.
Side (horizontal) halves: Vans size is OK in size but the real problem is people install them with preloads. There are lots of info on how to install them with out too much stress. I won't go into too much detail (because its written in RVator and other places). However here are a few ideas:
-During assembly you bonding the hinge on with clecos, with the cowl halves and pin installed. Once the epoxy is set, you take it apart and rivet the hinges on.
-Also you don't align the pin center-line along the split, you move it up, taking load off the eyelets.
-A similar technique to the above is having the hinge line angled slightly up going from fwd to aft, relative to split line. Start the hinge center-line low (below split slightly) and go up, as you go aft. This has a similar affect as the above pin center-line offset to split line. It actually makes getting the pin in and out easier. The cowl side is curved. Angling the pin "straightens" it out a little, making in & out easier. I think Van's hinge size is adequate. If you keep up-sizing everything you add weight. Side hinges look better (if skillfully built) than camlocs IMHO. (No offense nucleus, RVbySDI and all camloc fans). I never had a problem with a side hinge breaking; the aft firewall side hinges is another issue.
Aft Top (firewall): I like screws. It takes time but its solid and cheaper than camlocs but elect screwdriver drill makes quick work of them. Threading pins in through the oil door is a pain. I did use hinge/pins but had access top center of the cowl. You could see the end of pin (little bent angle), but it made access so easy.
Aft Lower Side (firewall): see above, make heck for stout
Aft Bottom (next to scoop): Hinges or screws. The bottom hinge does take load but they are so very short. On the RV-4 there is no bottom hinge I recall. Consider tying to add a screw or two on each side of the cowl.
I love hinges and think camlocs are expensive & overkill but fine in limited use. I have seen it overdone and I don't like the looks (
No offense nucleus, RVbySDI and all camloc fans). Camlocs do add cost and may be weight. I do like nut plates & countersink screws as a low cost option to hinges or camlocs. Also screws are darn secure. They have more "clamping force" than camlocs. When I put screws in BTW I did not make them heck for tight, just snug. It is cheap and light weight. Yes there is a little more turning of a screw driver, but I have an electric screw driver, so its no big thing. I also use screws sparingly in a few locations.
Hope that helps. Usually follow the plans will be best. Often the cowl has problems due to installation issues, namely pre-loading the pin.
When hinges are done well, they are a thing of beauty (and durable).
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PS: Rolled hinges have LOTS of sharp edges and burrs. I know it takes some time but it is well worth it to go over the thing with a dremel and sand paper and what ever you can to blend sharp corners and burrs. You would never build you RV the way hinges are. This is why some hinges crack, they just have stress concentration / crack starter's all-over. Add pre-load plus air loads and they will fail.
PSS: Internal cowl bumper hint - I mentioned a lot of the aero load is on the sloping lower front of the cowl. One idea that was floating around which I did was put a bumper inside the cowl from the engine to the cowl. You put a bracket on the lower front of the engine. You have a threaded industrial "foot" with a swivel rubber bumper or foot, typical at the base of office or industrial furniture. The threaded nature gives you adjustment. The idea is the foot is just almost touching the cowl, so when you go fast and the cowl moves (and it does) the deflection bumps up against the stopper. It works very well. You will see some minor rubbing between the cowl and bumper. You could bond a rub plate or surface where the bumper contacts the cowl. This will relieve a lot of prying load and make your cowl move less in high speed flight. Yes the engine moves, so you have to make the bent angle bracket which is slightly flexable. Also with a small gap between the soft rubber foot and cowl, engine movement will not be an issue. Trust me the cowl is deflecting a lot, especially the older cowls with out core. The new cowls may not need this as much. Also make sure your baffles are not hitting the cowl. That engine load will load the cowl. Because the engine shakes around the crank, the outboard edge of the baffle is critical. The above bumper is NOT affected by start and stop engine shacking movement as much. However if doing aggressive acro the engine will sag. Again just experiment and leave a gap. Put some "tell tale" indicator on the bumper to see if and how much it contacts the cowl. If you think about it having that one bumper to take air loads helps.
