Slight repair required

[old martParticipant @oldmart]

The team restoring the Piasecki H21 have given me a piece of the mechanism connected to the front rotor head. It looks like a casting, judging from the granular surface of the break. It will probably have to have a section grafted in as the parts bent before breaking. The width of the H section is about 3".

[old martParticipant @oldmart]

[John ReeseParticipant @johnreese12848]

I would use oxy-acy using cast iron rod and ferro flux. Normalize after weldinf.

[Paul KempParticipant @paulkemp46892]

Is that ferrous or non ferrous? Thought weight was prime concern in aviation so assumed everything would be alu or variants of?

Paul.

[Brian OldfordParticipant @brianoldford70365]

Posted by John Reese on 19/12/2019 21:30:55:

I would use oxy-acy using cast iron rod and ferro flux. Normalize after weldinf.

If iron, without a specialist muffle to do a pre-weld preheat and (more importantly) post-weld normalise I wouldn't even think about welding. Brazing would be far safer thus minimising the likelihood of producing brittle carbides each side of the weld.

Ali is a completely different ball o' wax.

 

Edited By Brian Oldford on 19/12/2019 21:44:10

[Robert Atkinson 2Participant @robertatkinson2]

Hi,
Is this for a static restoration? The original parts are almost certainly forgings. Weight and strength are critical on aircraft especially helicoptors. If this is even a ground running restoration you need to be very careful how they are repaired.

Robert G8RPI.

[Michael GilliganParticipant @michaelgilligan61133]

Not my specialist area at all … but … that looks like it might be a magnesium component which had aged badly.

The crystalline structure changes with age, and stress-corrosion cracks are commonplace.

May I suggest that you check the density of the material before proceeding.

MichaelG.

.

In case you had forgotten: Archimedes is you friend

http://hyperphysics.phy-astr.gsu.edu/hbase/pbuoy2.html#arc

 

 

Edited By Michael Gilligan on 19/12/2019 22:38:01

[old martParticipant @oldmart]

Sorry, I had to re write the whole lot when the photo's wouldn't work. The original mentioned aluminium, and I missed it out afterwards. I'm pretty sure it is a casting, so the manufacturers must have overengineered it for whatever function it performed. The cables attached are at least 3/8" diameter. Some of the related parts are indeed steel forgings. The entire aircraft is a wreck, there is no danger of any part ever being in working condition.

[Michael GilliganParticipant @michaelgilligan61133]

Thanks for that assurance … we can all sleep peacefully now

MichaelG.

[Jon LawesParticipant @jonlawes51698]

Piasecki were not always the very pinnacle of aircraft engineers…

If you haven't already look up the PA-97 Helistat.

 

Edited By Jon Lawes on 20/12/2019 10:04:41

[Nicholas FarrParticipant @nicholasfarr14254]

Hi old mart, if it was mine, I would get as much paint off the surrounding areas to be welded, preferably by bead blasting. Then I would heat the bent section up a bit and straighten it out the best I could (you may need to cut a little of the metal away each side of the break, to allow it to close up) and then bevel each side of the mid section. Then clamp a piece of thickish flat steel bar along the mid section each side and using a TIG welder, tack it together on the outside sections, then remove the clamps and steel sections and proceed to weld the mid section. I would then cut a "V" bevel almost all the way through the outside sections including the partially broken bit and then weld them up. Once welded and cooled, dress it down with a flap disc.

It would of course be best to try and identify the actual composition of the material for the best filler rods to use, but any good welding outlet supplier should be able to advise you on the most suitable filler rods, other wise.

Regards Nick.

[Mick B1Participant @mickb1]

Maybe I don't know nuffin', but I really can't imagine how any repair of a critical component in that condition could ever pass any sort of airworthiness inspection if there were actual live people gonna be depending on it to carry on living.

I'd say the only way forward would be to make or obtain drawings of the part to its correct dimensions and make new out of properly warranted and released material.

[OldironParticipant @oldiron]

Posted by Mick B1 on 20/12/2019 11:43:54

Maybe I don't know nuffin', but I really can't imagine how any repair of a critical component in that condition could ever pass any sort of airworthiness inspection if there were actual live people gonna be depending on it to carry on living.

I'd say the only way forward would be to make or obtain drawings of the part to its correct dimensions and make new out of properly warranted and released material.

Posted by old mart on 19/12/2019 22:39:39:

Sorry, I had to re write the whole lot when the photo's wouldn't work. The original mentioned aluminium, and I missed it out afterwards. I'm pretty sure it is a casting, so the manufacturers must have overengineered it for whatever function it performed. The cables attached are at least 3/8" diameter. Some of the related parts are indeed steel forgings. The entire aircraft is a wreck, there is no danger of any part ever being in working condition.

Mick B1. Maybe you missed this part of the thread

regards

[old martParticipant @oldmart]

I don't think it is magnesium, but a small sample will get tested just in case. Any repairs are limited as we do not have any welding facilities and the budget is, as normal, zero.

[Mick B1Participant @mickb1]

Posted by Oldiron on 20/12/2019 12:04:03:

Mick B1. Maybe you missed this part of the thread

regards

Yeah, I must've been so traumatised with horror at the idea of any aircraft depending on the pictured component that I missed the tiny comment halfway down the thread…

[OldironParticipant @oldiron]

Posted by old mart on 20/12/2019 12:39:51:

I don't think it is magnesium, but a small sample will get tested just in case. Any repairs are limited as we do not have any welding facilities and the budget is, as normal, zero.

Why bother to weld or braze it at all. Just knock as straight as possible and cut a couple of shaped plates to fit each side and bolt it together. Use countersunk bolts on the visible side. A bit of filler and paint and it will do the job of sitting there & looking useful. If the dimensions are not perfect but within 1/8" or so it will get the job done for next to nothing.

regards

[Brian HParticipant @brianh50089]

Oldirons suggestion is a good one. It will be quick and cheap and will let anyone know in the future that the part is unserviceable.

Brian (ex aerospace quality manager)

[noel shelleyParticipant @noelshelley55608]

If it's alli then the low temp "welding" alloys will work well on a job like this. READ the instructions VERY carefully and if you can weld FORGET all you know. BUT take a small shaving and test by burning that it's NOT magnesium first. Good luck. Noel

[HopperParticipant @hopper]

Posted by old mart on 20/12/2019 12:39:51:

…. Any repairs are limited as we do not have any welding facilities and the budget is, as normal, zero.

That does limit things a bit then.

Old Iron's suggestion of a couple of reinforcing plates with screws through to cobble it together for display purposes is about your only option. Sounds like it should work for your purposes.

Bit of epoxy between the plates and the part might stop any slopping around if the screws work loose during display manoeuvres etc.

Edited By Hopper on 21/12/2019 02:30:18

[Cornish JackParticipant @cornishjack]

With over 3000 hours helo time on a wide variety of such, I would have found some excuse to avoid the Piasecki 'Flying Banana' even in pristine condition – that particular piece of (possibly) mag alloy would best be left 'as is' as a warning!!

rgds

Bill

[Neil WyattModerator @neilwyatt]

Posted by Jon Lawes on 20/12/2019 10:04:24:

If you haven't already look up the PA-97 Helistat.

Oh dear.

In brief, four (old) helicopters attached to a blimp by a poorly designed framework.

During the first take off, a gust of wind induced a wobble that made one of the helicopters broke off, which in turn made the other three fall off.

Unfortunately one of the four crew was killed.

Neil

[SamsarandaParticipant @samsaranda]

I would like to be present, but at a suitable distance, if it is welded and found to be magnesium !
Dave W

[SillyOldDufferModerator @sillyoldduffer]

Posted by Neil Wyatt on 21/12/2019 09:58:42:

Posted by Jon Lawes on 20/12/2019 10:04:24:

If you haven't already look up the PA-97 Helistat.

Oh dear.

In brief, four (old) helicopters attached to a blimp by a poorly designed framework.

During the first take off, a gust of wind induced a wobble that made one of the helicopters broke off, which in turn made the other three fall off.

Unfortunately one of the four crew was killed.

Neil

Old Mart has a fascinating machine for display in his museum (Weston-super-Mud?), but not perhaps the safest flying machine ever made. The Aviation History description includes:

… the engine had to be running smoothly at 800 rpm before the rotors could be engaged. With no load on it, the engine could easily over speed. If this happened even once, the engine would have to be re-built.

When it was time to engage the rotors, engine RPM had to be slowly increased from 800 to 1300 rpm. While opening the throttle, the pilot had to flip a switch which activated the friction clutch. The friction clutch gradually connected the rotors to the drive train. With this done, the pilot would engage the jaw clutch mechanism, which fully connected the rotor system. Sometimes, the system bypassed the friction clutch and went directly to the jaw position by itself. When this happened, the rotors (which were hollow and covered by a thin veneer of mahogany) would shatter from the sudden acceleration to high RPM. The danger to anyone standing near the helicopter is obvious. This is why the crew chief had to crouch under the cockpit until the rotors were fully engaged.

What fun!

Dave

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