Author Topic: Soft mounting engines  (Read 308 times)

Offline Yoda

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Soft mounting engines
« on: 05, December 2017, 11:45:51 PM »
Hi,


Well it seems the Hyde mounts are no longer available and I've so far failed to find a suitable second hand mount. I'm now considering mounting the engine on large lord mounts. I've only ever used Hyde mounts but I know a lot of you have used lord mounts for soft mounting two strokes back in "the day". Just looking for advice re mount diameter versus engine weight etc. Common sense would say to go for the shortest mounts with largish diameter. Correct?


The engine is a Desert Aircraft 200cc flat four which weighs 5kg, produces ~20hp and about 45kg of static thrust. I know this is a bit bigger than F3A but the same principles would apply, just on a bigger scale. Being a flat four the engine is already very smooth but I want the whole set up as vibration free as possible. I'm currently looking at lord mounts (four of) 20mm in diameter and around 20mm length. The shore choice is pretty limited so I was going to play it safe and go for the harder mounts initially, even though I think I could probably easily get away with the softer mounts, especially with it already being a smooth engine.


Any info/advice would be much appreciated.


Angus

Offline Alan Wild

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Re: Soft mounting engines
« Reply #1 on: 06, December 2017, 07:47:27 AM »
I used lord type mounts as you describe back in the days of two strokes,but only really doing as others did, so not much help there.
But just wondering if you'd considered DIY Hyde-type mounts?
Never tried it myself---inertia rules OK---but you may know that the late Matt Kebabjian (sp?), MTK on RCU wrote lots of stuff about it, apparently making many for his own use.

Offline Kevin Caton

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Re: Soft mounting engines
« Reply #2 on: 06, December 2017, 12:16:54 PM »
What size engine do you need a mount for Angus? I have a used pre-drilled Hyde mount, but it may be for a 140. I can measure it this evening and let you know.

Offline Yoda

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Re: Soft mounting engines
« Reply #3 on: 06, December 2017, 11:04:40 PM »
Quote
What size engine do you need a mount for Angus?


200cc


Quote
But just wondering if you'd considered DIY Hyde-type mounts?


Unfortunately I don't have the time to even attempt making my own Hyde mount Alan. Combined with a recent house move and getting everything set up, realistically making my own Hyde mount just isn't going to happen at the moment. Besides, I'm not even sure I'd want my first effort trialed on such a large engine. Also on a bit of a time line so its either getting hard mounted as was done with my Swiss 330 or I'll be experimenting with commercial lord mounts.

Offline Keith Jackson

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Re: Soft mounting engines
« Reply #4 on: 07, December 2017, 08:05:19 AM »
Hi Gus,

If I were you I'd look at what other guys use with that engine, or contact the manufacturers and see what they suggest. Did Merle offer to help?
BTW remember that Lord mounts are not necessarily made to work in extension, mostly they are used in compression, with things sitting on top of them. Steve Plummer is having a go with Lord mounts with his YS185; it may be worth contacting him to see what spec he's using?

Keith
« Last Edit: 07, December 2017, 08:10:14 AM by Keith Jackson »

Offline peter brett

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Re: Soft mounting engines
« Reply #5 on: 07, December 2017, 09:28:41 AM »
Hi Angus
I soft mounted a 40cc 4 stroke twin in an F3a plane in the past using the 12mm mounts. I used 6 of them between an aluminium plate bolted to the back of the engine and the firewall it worked ok but I often wondered if it was worth the extra trouble. The problems of exhaust mounting is another issue.
I would say that reducing the vibration with an undeveloped system is a lottery and could make the whole thing worse rather than better. Inevitable increased engine movement could give rise to more forces being transmitted to the airframe and the resultant variable thrust line during manoeuvres could cause its own problems.
From what I have seen these are pretty impressive engines and taking the safe option so that you can concentrate on the aerodynamic set up and flying is the best way forward for me.


Peter


Offline Yoda

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Re: Soft mounting engines
« Reply #6 on: 07, December 2017, 10:54:05 AM »
Hi Keith, unfortunately Merle didn't offer to help. Chip did say there were some "issues" to get sorted but he didn't go into any details. Will try him again in ten days or so. Most people just hard mount their large petrol two strokes, as I have so far. DA recommend hard mounting their engines but I think this is more from an exhaust warranty point of view i.e. they won't warranty one of their exhausts that has been bolted to a soft mounted engine. Hard mounting the big twins and flat fours is ok but you do get a lot of vibration transmitted to the airframe with the big singles. To be honest, I really don't need to soft mount the DA 200. It is very smooth as is, I just wanted it as perfect or as good as I could get it. Perhaps if I can't get a Hyde mount I just need to accept that I'll be hard mounting it. Yes, a lot of those lord mount are just intended for use in compression. I had intended to experiment with lord mounts on my DA 150/CARF 260 but I never got around to it for various reasons so I'm literally at step one of the learning curve.


Hi Peter, yes I agree, potential for many issues and as most guys flying large petrol planes don't soft mount I am heading into the unknown. As you say, reducing vibration in an undeveloped system may well be a lottery, it might even make it a lot worse. I'm now thinking Hyde mount or hard mount.


Angus

Offline Stuart Mellor

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Re: Soft mounting engines
« Reply #7 on: 07, December 2017, 09:27:01 PM »


Angus -that's a big engine for Lord mounts! If you go the 'lords' route - you need big diameter -small thickness, due to the engines weight, overhang &  probable  'bounce' on the rubbers which you don't need. But I think you need industrial stuff.

There are plenty of lord style suppliers - have a look at 123 bearing for example.

Best I ever had were called 'Apache' mounts - with big snubbing washers either side of the rubbers (similar to the smaller Dubro/Gator rubbers.) Completely captured & therefore safe. Not sure if they are still available though....

« Last Edit: 07, December 2017, 09:30:43 PM by Stuart Mellor »

Offline Yoda

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Re: Soft mounting engines
« Reply #8 on: 07, December 2017, 10:12:15 PM »
Hi Stuart,


Yes I was doing some measuring there and came to the conclusion that 20mm diameter would be too small. Now looking at 25mm X 15mm nitrile bobbins from Polymax - an increase of 56% in the area of the rubber.


Will have a look at those mounts, thanks.

Offline Mike Wood

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Re: Soft mounting engines
« Reply #9 on: 08, December 2017, 02:59:28 PM »
"Completely captured" like the Du-Bro ones, sounds like a good idea on something that size!

m