v6goose

Hi guys...

I'm sure there is a good reason I shouldnt ask this question, but as a new DL owner I have read contradicting opinions on this topic.

Do I hard or soft mount my DL in my TF GS P51?

Cheers

Goose

Truckracer

My Feedback: (19)

Read the Revolution 50 Vibration thread regarding vibration problems. This owner had other problems but a weak firewall seemed to contribute to the problem. Soft mounting can be the same as a weak firewall. Soft mounts can be made to work but most people have found that hard mounting on a very firm firewall works best.

Rfabbre

My Feedback: (6)

It depends on what soft mount you use. The only one that I know of that really works is by Merle Hyde. He does not advertise but sells many by word of mouth. Lot's of the top competitors use them exclusively. He is Chip's father.

altavillan

My Feedback: (1)

It depends on how you use the mounts. If you are looking at concistent engine rpms at or near full throttle then soft mounts work well. If you are using them on a plane that has to change throttle settings a lot (like 3D) then soft mounts are not good. At some point in the throttle curve harmonic vibrations will probably be worse than normal hard mounting vibrations. But you can make mounts with hard rubber that will absorb some of the high rpm vibration and reduce lots of airframe fatigue. 1/2" to 3/4" conveyor belting is very hard stuff and makes excelent shock absorbing mounts with no noticable Harmonic vibe tendencies. Blended rubber/fiber truck mud flaps make good thinner cushions.

The way I do it is to drill engine mounting holes large enough to insert copper tubes that the bolts slide through as guides that protrude past the firewall about 1/16" both ways. Then use a square of one of the above isolators on each side of the firewall. See pics in EF 88" Yak thread about page 203. I think my 3W56 could run full throttle and not shake a glass of water.

Gravel quarries have tons of used belting to get rid of. Buy a mud flap from Napa or simalar store.

rcdude7

My Feedback: (264)

I have seen cheap soft mounts that result in engines shearing muffler bolts. This may not happen with a very well designed system that restricts and dampens engine movement correctly though. These types of mounts can be pretty expensive.

What kind of mount were you thinking of buying?

BaldEagel

These MVVS mounts are superb, no harmonic vibration, just smooths the whole thing out, less vibration through the airframe and therefore less noise, throttling up down or blipping does not move them around, I used the rubber bits when installing a engine in my Yak as the firewall was not wide enough to take the mount itself, the bits are available seperatly from some sourses in the UK, I don't know about the US though, there is a lot of uninformed information flying about concerning Isolation mounts, but untill you have used a hard mount and then gone to a correctly set up Isolation mount in the same airframe and experienced the difference its hard to make a subjective comparison.

Mike

Dr1Driver

I've run a Zenoah G-62 in a giant Stinger, and a G-38 and G-23 in Fokker Dr.1s. All on hard mounts.
The Stinger firewall was 1/2" ply. The G-38 firewall was 3/8" ply, and the G-23 was on 1/4" ply. All used blind nuts with socket head cap screws through the engine mounts from the front. I believe the G-62 had 1/4" or 5/16" and the G-38 and G-23 both had #10. All props were very carefully balanced. I never had any problems with vibration to the airframes. I've watched soft mounts almost shake the engine off and the resulting reaction on the airframe was worse than with hard mounts. I'm currently building another Dr.1 with a G-26 and it will also be hard mounted.

Hard mounts all the way for me!

Dr.1

BaldEagel

I'v run MVVS 45's and 58 Pro's on isolation mounts without any breaking up of either the firewall or airframe, thats why I said in my last post "correctly set up Isolation Mounts" not soft mounts, there is a massive difference between just putting a soft mount between the engine and firewall and a purpose designed Isolation mount, I will never hard mount an engine again, I even mount my electric conversions isolated from the firewall in some manner, Hacker even recommend it with their gearbox motors to lessen the noise.

It may seem a good idea to use the type of mount shown below as an easy way to do it, but they are the soft mounts that Dr1Driver has probably seen and will shake an airframe to bits.

Mike

dirtybird

My Feedback: (5)

The trouble is a correctly set up soft mount has to be engineered for each situation. It would be best if the manufacturer supplied one that could be adjusted for you installation. How much do you think that would cost?

v6goose

Hi guys...

Thanks for all the information, great response!

The TF GS P-51 suggests a 'soft mount' system and is the rubber grommets sandwiched between the firewall and a plywood plate followed by the standoffs.

I dont have much experience with gassers and have seen one nearly rip the nose off a plane that had very hard rubber blocks between the standoffs and the firewall - something I now know is a bad idea.

I simpy want to have a smooth running engine and airframe and given that there is a lot of scale stuff on my Mustang, I dont want it shaken off or broken.

I like altavillan's idea [link=http://www.rcuniverse.com/forum/m_5452111/mpage_201/key_/tm.htm#]Mount[/link] as well as shelling out the $ for a Hyde or similar mount. The poll is 50-50!

Keen to hear some more...

Cheers


Goose

540horses

i agree with hard mounting.it allows the air frame to dampen the vibration. i believe it is dr1driver who just sold me his g-23 on ebay. when it arrives, it will get new cylinder,piston, rings and bearings. i have spares from my raco jackrabbit days. im gonna put it in a 1/4 scale cub i failed to sell. and motor will be mounted solid. if you want the motor to fall apart, you soft mount it. the instructions with my gt-74 said soft mounting voids the warranty on muffler breakage. voids bisson warranty as well.

Dr1Driver

540horses,

If you're hopping it up, then you can install all those parts. As is, though, it doesn't need them. Runs great, but might be a little small for a 1/4 Cub. What's the weight?

Dr.1

540horses

well ive seen many cubs with the g23 as a matter of fact hanger 9 has the latest cub version which is 106 span. mine is 100 anywho they offer this in a combo with the g20, also a great motor. i will definetly run it before the overhaul to replenish the memorys of how wonderful a beatup looking zenoah can run. then ill make it brand new in about a half hr. at no cost. cant wait to get my hands on it.

BaldEagel

Every car and full size aircraft engine in the know world is soft mounted. Ali mufflers will not take any vibration if cantilevered off the engine without support, they will eventually fatigue and fall apart.

Mike

Truckracer

My Feedback: (19)

Just about every high performance and racing application uses solid mounting. Many automotive soft mount applications are for creature comfort more than structural necessity.

BaldEagel

Neither my race prepared Porsche 930 or my full race M3 have solid mounts, at that point I will rest my case.

Mike

rmh

OK - but those setups are tuned soft mounts and that is far different from simply adding a soft platform
what no one has mentioned is that a soft mount is worthless if it amplifies the bad frequencies -and some do --some don't
I made my own soft mounts for years --the best being a cradle which allowed only rotary motion -then had an adjustable damper -to match the engine.
For almost all single cyl set ups -- a wide solid mounting base -which transfers loads directly to the primary longerons (or side sections) is best
this is mass damping in it's most simple effective form
On cars -racing/non racing types there are many methods - most now use a fluid filled mount -but again these are tuned to the engine/chassis - not the same thing .

onewasp

Permit me to "unrest" your case. You have cited some decent machinery but hardly the epitome in racing (unless you are paying for it ;-) )-------stressed engines (courtesy of Colin Chapman) are 'soft mounted' in name only.

pe reivers

Soft mounting an engine in grommets, or the MVVS iso mounts, or the Dubro iso mounts for that matter works very well. I have had firewalls fail in hard mounted engines, but not when soft mounted. this goes to show, that the peak forces that are transmitted to the airframe are far less with soft mounting.
The "rubber stud mounting" that many use, are bad in three aspects
1) they show a severe engine shake at low rpm. Hydraulic dampers to the resque
2) They have a very pronounced resonant frequency that can shake the plane worse than without the dampers. Resque see 1)
3) When they fail, the engine back plate is not restrained. IOW, the engine then is only kept by the cowl

When carefully adjusted to the airframe these rubber studs work very well.

Grommet mounts, or similar, work most of the time without any added effort. Resonant swing is not in one single frequency, and when it does occur, the amplitude is very small.

540horses

mike a porsche is a factory preped vehicle for the road. ever been in a drag car. your motor would jump clean out with rubber mounts not to mention what the engine movment would do to the frame and setup. soft mounting is for human comfort only. there is no need whatsoever to soft mount a model airplane engine unless you like punishment. they can produce bad frequencys, poor throttle control, magnify vibrations and break things off the engine. so go ahead and soft mount em. ill come out and help you find it crashed in the woods from the multitide of problems soft mounting can cause. this is my experienced opinion and dont understand why people go out of their way and spend money to do harmful things to their airplanes. not meaning to be nasty in any way and wish you the best of luck. 540

v6goose

Hmmmm... I had a feeling this topic would be like discussing religion.... lets face it... Rc IS a religion

12 to 9 say hard mount, I'm still listening to the voices of experience.

Cheers guys

Goose

Tired Old Man

My Feedback: (1)

The professional stuff I fly is soft mounted, but the only reason for that is to isolate high frequency vibrations and keep them away from the camera. To do it right will only cost you several thousands of dollars in R&D and later manufacturing costs, but it can be done. The MVVS method works reasonably well but it's a very long term benefit for the cost and effort. An engine that is hard mounted to a reasonably strong firewall using a balanced prop and spinner will work out just fine for the life of the airframe. The noted lifespan is dictated by the length of time it takes the operator to use dumb thumbs and hit the ground. Now if you really think you're going to be flying that plane 20 or so years from now it just might be worth the effort. As Dick noted, the best mounting methods still tie into the fuselage longerons. Those old hardwood beam mounts that extended forward from the sides of the fuselage worked extremely well and for the low cost and complexity were well worth their weight.

The one exclusion to the above might be with a composite airframe which is prone to resonance. Using a grommet mount might quiet the airframe down some, but so would installing a few stiffeners in the right places.

rmh

When the YS 1.2 engines came out -I had to do a fix on my kits for those engines - the long period between pulses really created some killing thumps .
One of th first things I did was the old time proven trick of simply feeling around the model and finding what kinds of vibrations were occurring On some glas models -adding a balsa crutch did the trick -on others a stif intgrated mount and crutch etc..
The problem is typically best resolved by treating the engine and airframe as a unit. The old "there is only one soft mount worth having " answer - is not really true - there are many ways to fix th e problem
-years back -on big machinery -we used test equipment - which was placed on the frames and panels and the frequency and intensity was measured -and then - we cut n tried -various fixes (measure with a micrometer and cut with an axe)

I had to help quiet down a F3A pattern plane with a 40 gasser - it had a "soft mount " (really a very tight rubber mounting -which may have helped -but the real problems were from the hard flat surfaces which would ring like a banjo - and linkages and wheels - a -pita
PPS-I never had a full race M3 BMW (what the heck is a BMW full race kit?) but a friend had the first Alpina here big Webers etc- ZF box -Recaros etc..-and I had one of the first BMW 1800 sedans -and a Austin Healey that would suck up Porsches like they were standing still (with the help of a small block Chev).
I now have a old 1/10 race Subaru Loyale and a 926 (old ) Mazda -for my hot rods -but my Volvo wagon w/305 HO Ford did have e soft (well sorta ) mounts, but who cared

Dr1Driver

I'm still listening to the voices of experience.

Over 25 years in R/C and over 10 years in giant scale say hard mount.

Dr.1

yakman

Hard mounts are easy, cheap and they work.