Boomerang1

I'm just about to make some struts for my jet & came to thinkin', why not make a weak link in the strut? Why not make a sacrificial piano wire link at the top of the strut, say 3/16 dia, which would be strong enough for good landings but would bend in really bad landings? After a 'not so perfect landing' if the link was bent just replace the link from the spares in your flight box instead of being out for the day. Less bent struts, less stress on the aircraft.

Has anyone tried this or any reason why it would not work? - John.

JMCJET

Yes. And then, invent the electricity. [8D][8D][8D]

Your post surprised me. The devise you describe has been used in models for centuries.
Is it a new kind of fusible? When you finished put some pictures.

Regards from the other side of the world.

Boomerang1

JMCJET, in more than 30 years of modelling Ive yet to see one, perhaps Portugal is a nation of 'leg benders'! [sm=lol.gif]
Or perhaps we are still waiting for them from the house of Bob? [sm=lol.gif]
Or perhaps there's more money to be made from selling new struts? [sm=wink_smile.gif]

The only thing close I've seen is on the nosegear of a friend's Eurosport, a mild steel 1/4 inch pin supports the strut but it's main function is the steering pivot. Nothing like it is used on the main gear (Robart 630), the strut end goes straight into the aluminium block. - John.

grbaker

My Feedback: (29)

Using 3/16 music wire to mount a strut to a retract trunion, used to be the normal method. It worked OK for the lighter DF models. As Airframes got heavier, most retract manufacturers got away from this method, due to the music wire bending even when landings were "greased in".

digitech

My Feedback: (10)

here you go:

Boomerang1

Thanks Gary, I got keen last night & made a start on my lathe. I did include 3/16 pins & my jet is on the small side at 21 pounds so I'll have to see if they are TFU or work o.k. If no good I'll just make new top halves & mount straight in the retracts.

Thanks Sandor, those legs look great & may fit into the cutouts in my wings which were designed for straight struts, not trailing link, as the axle line looks in line with the leg under no load. Any more details, where, when, how much, weight of plane? If not available I'll put my Chinese hat on & copy them! - John.

roo

Boomerang, your idea is sound and has been around a long time as others have said. Even Dave W has recommended it in print, using a clamp to hold the trunnion while bending the "strut" back in shape. My friend had a special tool made up to hold the trunnion for this purpose and was good enough to get one made for me also. What I dislike about using these bendable pins to connect the strut to the trunnion is the fact that you need to file or grind flats on the pins to stop them rotating even with a greaser and then brakes. Some pins come with flats already done but these are invariably in the wrong place and it is a devil of a job to grind these flats in EXACTLY the right places, unless you have access to a lathe etc and know how to use it !. Regards, Paul.

Woketman

My Feedback: (6)

The sacrificial plates (not the strut, but still in the load path) that many manufacturers (like BVM) mount their gear on is a good example of this. Good idea, but not new.

JMCJET

John: Please never forget that here, if needed, we broke don't bend.[sm=punching.gif]

So, about what really matters: if you have space try something like this. Very easy and bullet proof.

Regards again [8D][8D][8D][8D]

Woketman

My Feedback: (6)

WOW!!! That's way better than sacrificial plates, but takes more room and more weight. Really cool set-up!!! Great design!

Boomerang1

Thanks JMCJET, that's a different way of thinking about it! I probably cannot fit this idea in the wing now it's finished but it goes in the memory bank for sure especially for noselegs like the one shown.

Woketman, are the plates sacrificial or just designed to be big & therefore flexible? I based my model on another wood jet, the DV8R, so the mounts are strong but rigid so I'll have to work on the 'bolt on' bits - John.

Woketman

My Feedback: (6)

Well, I've never had a BVM jet but from what I've seen the plates are both, flexible (to a degree) and sacrificial.

Boomerang1

One leg done, one to go. Roo mentioned problems aligning the flats on the pins but I think I've got that beat. The alignment is not critical due to the 1/2 inch hole in the trunions. I'll adjust the tracking in the trunion clamp once all is together. I hope to get to a jet fly in this weekend to try it. - John.

Boomerang1

Just an update on the struts, they work great, just as intended! On the 3 good landings they did not bend. On the 4th I landed in a dip on the runway (grass strip) the model bounced about 5 feet back into the air, I gave it full power again to ease the bounce & settled a little heavier than normal very slightly bending the 3/16 pins. I put the legs in the vice & pulled them straight again.

The only problem found was the pins rotating slightly in the top aluminium block causing the wheels to splay out slightly. I'm going to fit short 1/16 piano wire pins to hold everything in alignment instead of relying on the grubscrews. - John.