ww2birds

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Hi All,

A few days ago I posted to the braintrust for suggestions on replacing a bifurcated pipe on a Yellow F-18. Got some great advice from several of the resident experts. Problem is that once the plane is built it is virtually impossible to get the pipe in thru the main hatch. The advice was to cut off the tail just ahead of the mold line of the nozzles and insert the pipe from the rear. This is perfect advice for a new build ... a little harder to be enthusiastic about with a completed plane ... though of course it could work.

I thought about it a little and called Tam to see if he could make the first 5-6" back from the bellmouth pipe removable. It's part of the singlewall section of the pipe. It's tricky because the pipe is tapered in this section (in the "wrong" direction to make it easy to fabricate), but he was able to do it for me. The bellmouth part nests inside the main pipe.

The pipe is easily inserted thru the hatch with the removable section "telescoped" into the main pipe, then once in place pull the bellmouth section out and fix it with 4 SS screws.

Genius ... and mad fabrication skills! We are lucky to have someone like Tam to work with. Pictures below.

Dave McQ

roydefiant

Yes he does great work

yeahbaby

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Great info! I've often wondered if it would be viable solution. Let us know how it works at full power static test.

ww2birds

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I'll let you all know. Of course if something goes wrong, I'll have to replace my profile picture with one that looks like Elmer Fudd when his shotgun explodes :-)

The proof of course will be in the pudding, but it's a _really_ nice fit and felt totally solid even before the four screws went in.

SECRET AGENT

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If Tam made it I'd feel confident in it.

ww2birds

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Confidence is well placed! Did several full power static tests today, all worked perfectly.

thanks Tam!

I've attached the drawing I sent Tam in case it is of use to anyone .. it replicates the original Yellow Pipe. Your overall length might vary, and the tailpipe spacing is a little narrower than the center-to-center distance of the nozzles in the fuselage itself .. but I had already set up all the pipe mounting that way.

Once you have the removable single-wall section inserted, you just push it inside the main tube so it only sticks out about 1/2" for the mounting flanges. In this configuration it slips nicely thru the main hatch, and once inside, you just pull the bellmouth section forward, attach to the main pipe with 4 SS screws, then attach the bellmouth. Cool.

Dave

yeahbaby

My Feedback: (21)

Nice work amigo. Did you put a bead of high temp silicone around the telescoping piece? Great to hear.

ww2birds

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No, I did not. The bellmouth part is inside the main tube with about 3/4" overlap and a really tight fit .. so any exhaust leakage would have to go "backwards" and out. Wish you had suggested that before I mounted it .. I probably would have added some just for "belt and suspenders" though :-)

Dave

yeahbaby

My Feedback: (21)

LoL well I am glad you have 3/4" overlap should be plenty but yea you never know and it would atleast give you an indication of loose bolts...metal to metal rubbing etc.

Vincent

My Feedback: (61)

I doubt whether any hi temp silicone will handle the heat in that section of pipe, at least not for very long. I would consider installing screws with some meat on the heads so you can drill a hole thru them and run some ss safety wire thru all the screw heads to keep them from backing out. That would be your worst nightmare. I am surprised tam didn't think of attaching a couple of straps to the rear section so that after you coupled it there was a way to attach the straps to a former independent of the front section. That would hold everything nice and snug. Just my 2 cents

ww2birds

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It's hard to describe here .. but since the section of the pipe where the parts couple is tapered (really, reverse tapered .. it gets bigger as it goes away from the bellmouth), when you pull it out to its operational position, it is impressively tight .. with no screws at all. The screws are of course tightened securely. The fit is a testament to Tam's fabrication skills. I am sure it will work well.

Dave

SECRET AGENT

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There are high temp silicones that can withstand up to 2500 degrees F. No way our turbines or pipes get that hot.

I like your bulkhead idea, probably over engineered but definitely solid.

Doug Cronkhite

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Tam is a mad scientist..

ww2birds

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Several years ago, Tam also made me a two-piece pipe for a Skymaster T-38 that had an even more restrictive install via its main hatch. This pipe mated in the double wall section, and had a second set of mounting tabs for support at the joint which was just ahead of the LE of the stabs, right before the bifurcation. There were no screws around the periemeter (no way to do on a double wall section)... just a slip fit ... of course much further back from the turbine, so much cooler. But it works perfectly too... a Mad Scientist indeed :-)

Dave

ww2birds

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Flight update: flew the F-18 at First in Flight .. all went well. Two-piece pipe highly recommended as a retrofit for this F-18!

Dave