Cowl Hinge Pins -- From the inside

[bullojm1]

A few weeks ago, Mike Reagan was nice enough to fly up to KDMW to show me how he inserts the cowl hinge pins from inside the fuselage. The advantage of inserting the cowl hinges from the inside is you don't need any cutouts on the front of the cowl where most people insert the hinge pins through.

This was one of the easier modifications/deviations I have done, not only in terms of time, but also money. It only took about $20 in parts and 4 hours in time.

So the idea is is to use 3/16" aluminum tube (ACS p/n 03-40300, $0.40/ft) to guide the pin from the F-902 bulkhead, around the NACA duct and to the firewall. There will be a hole in the firewall where the tubing goes through, aligning it up with the hinge eyelets.




Here is a 7/32" hole in the firewall. I started with a #40 hole for the first alignment, then enlarged it. The hole needed to be larger than 3/16" because at 3/16", the stainless firewall rubbed against the soft aluminum tubing very aggressively. I might make the hole larger if I can determine if a plastic snap bushing can be used here.



Next up was adding some holes to the F-902 bulkhead. I wanted to put the tubing on the inside of the F-902 to hide it a little. Mike Reagan had his on the outside, which is without a doubt easier to do. However, I am pretty (really) anal, so I always make things more difficult. The 3/8" hole on the forward side of the F-902 is where the 3/16" tubing goes through. Its center is 13/32" from the inboard edge of the F-902. This needed to be offset outboard somewhat to avoid conflicting with the vent tube. The other hole (#12)on the inboard edge of the F-902 is centered front-to-back on the F-902 and is set 1/2" down from the centerline of the 1/8" hole. This hole is for an adel clamp to sit inside of the F-902 bulkhead.




Since I am anal, I wanted a countersunk #10 screw (AN509-10R12 I believe) to be on the F-902 so the inboard surface is flush. I also needed to make a 3/16" spacer that would go between the F-902 and the adel clamp to offset the adel clamp outboard enough to center it with the hole I made (to clear the vent line). I countersunk this #12 hole to align with the dimple I put in the F-902.




I just slapped this together to demonstrate how it will all fit together when it is attached.




After assembling it all, here is how the inside looks.




And here is the forward side. One thing to note here is the eyelet on the bottom cowl needs to be closest to the firewall. Since the 3/16" tubing and the hinges don't align perfectly, you need to get the hinge pin started manually by helping the pin in that first eyelet. If you made the first eyelet on the top of the cowl, it would be much harder to get it aligned.




OK, now to make this a little more fancy. I bought some knobs from the hardware store to put on the end of the hinge pins. There were pre-tapped for some larger screws. However, they aren't tapped all the way through. There is about 1/8" worth of material at the end of the pre threaded hole that I drilled out and tapped to a 4-40 hole.




Next I threaded the end of the hinge pin to a 4-40 also.




So I have a tapped knob and a threaded pin. I wonder where this is going? Yup, I screwed the two of them together. It is really solid, but I will epoxy them together later on, as they do want to spin freely. Plus I think the knob is only threaded for about 1/8" or so since it is hollow on the end.




The end result looks freakin' awesome. I still have a little work to do to finish it up, but it's pretty much DONE!

[cjensen]

I read thru this on your site this morning Mike, and I have to say I LOVE this idea!

I like the cabinet knobs too!!

[Brantel]

I read this earlier on your site as well this morning. Looks great.

I might make this change to my cowl since I have not made any pin attach method yet.

[smithhb]

That looks sweet, Mike. Just wondering: How far back do you have to pull the pins before they exit the guide tubes?

[bullojm1]

That looks sweet, Mike. Just wondering: How far back do you have to pull the pins before they exit the guide tubes?

Thanks Bret! They are SWEET! I don't really recall how far they go back. I don't have my bulkhead in, so I can't say whether they go back that far. However, they pins are flexible enough so you can route them a number of ways. I didn't see that being a problem, and Mike Regen didn't say he had any issues with his.

[Bob Barrett]

Looks great Mike. I had planned to do that also but I failed trim the cowl overlap before attaching hinges. End result I had to remove the hinge pins because with the overlap made it impossible to insert and remove the cowl hinge pins. So I ended up spending over a $100 for Camloc fastners It is the way to go but do it RIGHT!!!

[jim_geo]

You mentioned being anal. Don't you know?...........You have to be anal to properly build aircraft.

[bullojm1]

How far back do you have to pull the pins before they exit the guide tubes?

Bret-

I trimmed my hinge pins today and took some ballpark measurements of how far back you have to pull the pin out. To pull the pin out enough so it is in the tube, but not in the hinge, the pin comes back approximately 2/3rds of the way between the F-704 and F-705 bulkheads. To remove the pin all the way, the pin comes back to 1/2 way between the F-705 and aft baggage bulkheads.

[smithhb]

That's going to work really nice.

I was trying to imagine how much you would need to pull the pins after the canopy and interior was installed and it seems you will have plenty of room.

[Spike]

I would say to others think hard before you do this. I spent yesterday helping a friend work on his 8A and he has done the same thing. Getting those pins back in to an assembled cowling (especially when cold) can be a real pain. Many times it is a 2 person job.

I like the handle idea, that looks nice.

[bullojm1]

True, the pins can be a real pain to get in or out no matter where they are inserted from (in the front of the cowl or from the cabin). However, there are a number of tricks to make the hinge pins go in with ease. The three things I needed to do were to sand the pins down a few mills to make their diameter a little smaller. Next I investigated on which eyelets they were gettign caught on. On those eyelet, I opened them up ever so slightly. Finally, and most importantly, if you put some wax (BoeLube) on them, it makes all of the difference in the world to make them go in quickly.

I think too many people give up on the hinges and go the camlock route. The camlocks are heavy, expen$ive and IMHO UGLY! Nothing beats the look of the clean cowl with hidden hinges.

[cjensen]

<snip>Nothing beats the look of the clean cowl with hidden hinges.

You got that right!! I'll be going hinges, and am thinking of copy-copying this too!

[Dan A]

I installed my hinge pins to insert thru the forward baggage compartment on my 8. It works good for me and they will wear in with time and get easier to insert. I like the bit of having no exterior hinge pin covers to marr the cowl.
Dan A

[aparchment]

Mike, this looks great. Thanks for the write up and photos.

Antony

[capflyer]

I would say to others think hard before you do this. I spent yesterday helping a friend work on his 8A and he has done the same thing. Getting those pins back in to an assembled cowling (especially when cold) can be a real pain. Many times it is a 2 person job.

When I first installed my pins this way it was difficult to get them in but after a little tweeking they go in very easily. First thing to do is be sure the hinge pin ends are tappered down to a point. Then, with each hinge, slide the pin in and be sure it goes from one eyelet to the next easily (alignment). One other thing I did was to use my deburring tool and give a slight inside taper to the inserting side of each eyelet.

The trick to putting on the cowling is to get the pin started into the first eyelet in the bottom cowl then put on the top cowl. After some experimenting with which pins to do first, I found in my case that doing the firewall pins first then the side pins made the process very easy. I can put my top and bottom cowling on (and mine is a 7A) in 5 minutes.

Mike R.

[Spike]

Sounds like some of you guys are having great success with this. Awesome.