What's new
Van's Air Force

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

Piano hinge height for vertical cowl line

Desert Rat

Well Known Member
Hey all.

Does anybody know where the upper end of the piano hinge should lie on the firewall flange for the lower cowl half?

Looking at drawing 28 the rivet callout leads me to believe it should be below the 5 rivet down from the skin lap. Am I correct in thinking that?

I’m asking because I’d like to go ahead and attach this piano hinge prior to installing the engine mount and asking here is easier than a logging the cowl out of the basement and trying to hold it up there by myself.

I could probably find this if I searched long enough, but I’m on my phone this morning so a detailed search is a hassle. hoping somebody knows off the top of their head;

Thanks!
 
Offering what I remember....

Those cowl sections will get cut by you in order to mate correctly. The placement of the hinge isn't super critical, but is benefitted by knowing where final mating edges will be.

I am sure there will be better answers coming from folks in the thick of that step, but I might hold off mounting the hinge half until those folks weigh in.
 
The cowl split will be based on where the engine hangs off the engine mount. The split needs to aligned with the prop and spinner centerline. You will not know exactly where that is until you mount the engine. You should wait on installing hinges until the engine is mounted and you position the cowl correctly.
 
Dimension is...

Here is a picture of that dimension on the -6 plans, 18 inches up from the firewall lower flange to the top of the hinge. ymmv etc.
 

Attachments

  • 16485638523851128237095738945288.jpg
    16485638523851128237095738945288.jpg
    223.4 KB · Views: 160
Careful with -6

So the RV-6 plans had a dimension, but the RV-7 (9) plans were drawn later, and no longer have the dimension listed. I would be very careful using the RV-6 dimension unless recommended by someone who has built both (or recommended by Vans)

The way I figured this out for my -9 (same firewall forward as -7) was to look at pictures of other -7 and -9s with same engine, and then count rivets.
 
So the RV-6 plans had a dimension, but the RV-7 (9) plans were drawn later, and no longer have the dimension listed. I would be very careful using the RV-6 dimension unless recommended by someone who has built both (or recommended by Vans)

The way I figured this out for my -9 (same firewall forward as -7) was to look at pictures of other -7 and -9s with same engine, and then count rivets.

Use the info at your own discretion. The RV-6 plans have many more dimensions than the -7 or -9, because the builder has to measure and fabricate a LOT more. Many of the parts, including the cowl, may be the same.
 
On my RV8, the upper end of the piano hinge is sized so that I can remove the hinge rod without it interfering with the upper engine mount. There was some trial fitting to ensure I can pull out the piano rod without it getting stuck between the upper engine mount and the inside surface of the cowl. I don't recall there are dimensions for the hinge location, only approximation based on the ISO view.
 
Terry,

I just completed this step over the past weekend. I had the same concerns as you and wanted to install the firewall side hinges before installing my engine mount.

What I did was clamp a piece of the hinge on the top edge of the lower cowl in the position I would want it. Then I positioned the lower cowl against the firewall to determine where the interference would be. Then I cut the side hinges to clear the top edge hinge.

Others may say that this is not 100% correct since the aft edge of the lower cowl will be trimmed when it is fitted, but I think there is still plenty of room. I can't guarantee that this method work yet, but it the approach that I took. Follow my method at your own risk.

One other note. I installed TI foil over the fiberfrax and this makes setting the rivets a little harder. I managed to put a few dents in my foil before I realized it was happening. After that I just used a thin strip of AL for protection and to help spread the load on the foil. That seemed to take care of the problem, but unfortunately I still have some dents in my foil.
 

Attachments

  • firewall_w_side_hinges.jpg
    firewall_w_side_hinges.jpg
    398.1 KB · Views: 252
Last edited:
Not critical if you make the hinge a bit taller, but might affect how easy it is to install/remove the pin during maintenance. What will be affected is how you mount the hinge onto the cowl. Either way is fine.

Pictured is a RV-6 (blue&white) & RV9 (red/white). Note the hinge installation on the cowling, one the vertical hinge goes right to the top, the other ends below the horizontal hinge line. Clean inner cowl is RV6, the dirty one is RV9.

Generally, the 6/7/9 firewalls are common, so the 6 hinge dimensions could be used. You later determine your cowling horizontal trim line to work with the material overlap & fit with your hinge.
 

Attachments

  • rv6.jpg
    rv6.jpg
    25.6 KB · Views: 175
  • rv6cowl.jpg
    rv6cowl.jpg
    20.9 KB · Views: 131
  • rv9.jpg
    rv9.jpg
    22 KB · Views: 150
  • rv9cowl.jpg
    rv9cowl.jpg
    23.1 KB · Views: 133
Last edited:
Thanks guys- What I ended up doing is measuring the height of the lower cowl half. It's exactly 17 1/2" tall as it comes from Vans.

Measuring the firewall, that puts the upper edge of the cowl between the 5th and 6th rivets down from the skin seam, which matches what I'm seeing via the rivet callouts on drawing 28.

Based on that, I went ahead and installed -4 piano hinge up to that point. I can always lop off an eye later if needed.

I get that there's an outside chance that may come back to bite me some how, but I think it will work out okay. We shall see...

Thanks everybody
 
Not quite to OP but a data point in the discussion

The upper cowl attach hinge in the -7 plans suggested an undersized pin.

I tried the full sized 1/8" pin and while snug, it works well for me.
 
Back
Top