airega1

My Feedback: (204)

I have a Brison 6.4 and I'm wondering if anyone out there is using soft mounts for twin cylinder engines? At this point I can go either way

JeffH

My Feedback: (43)

I have always heard that is bad idea. Something about resonance and such from the twin cylinders. I think the giant scale racers found this out the hard way when their motors kept breaking off.

tande

My Feedback: (48)

I don't know---I have a "Hyde Softmount" on a small twin, (YW48) & love it!---to start with, onboard battery drain life is about double---also no more fasteners coming loose or vibration fatigue problems in general, cowling cracks etc.---from now on I won't setup anything without one!---JMO

dirtybird

My Feedback: (5)

I think you have to decide what you want to protect - the airplane or the engine. An engine that large,even a twin, is going to shake the aircraft. If you use soft mount then you can overstress the engine. Your choice.

airega1

My Feedback: (204)

How do you overstress an engine using soft mounts?

Gremlin Castle

My Feedback: (14)

I have had a Brison 6.4 on a Extra 300Xs for the last 6 years and see no evidence of vibration related problems. A friend also has one mounted on a Lanier Extra for at least that amount of time and has not experienced any problems. His must have at least a hundred more flights on it than mine has.
I also have a DA 150 mounted in a large Bearcat and have seen nothing that would indicate vibration is a major problem.
A well designed vibration mount would probably show a difference after the 350 to 500 flight mark but the operative word is "well".
Most model mounts straddle the area between voodoo science and compromise. Having been involved in the past with vibration and shock mounting large diesel powerplants and their radiators and exhaust systems I can say that all mounting systems only work within a range.

dirtybird

My Feedback: (5)

Soft mounts allow the engine to move. Thats why less G's are transmitted to the airframe.
If the engine moves bending moments are created in the engine.
I once soft mounted a Veco 45. The result was a broken crankshaft.
There are some manufacturers of engines and mufflers that void the warranty if a soft mount is used.

airega1

My Feedback: (204)

Hey Gremlin, I don't think the Brison 6.4 was on the market 6 yrs ago, but anyway you didn't specify if you're using a soft mount or not.
Thanks for the reply
Frank

tande

My Feedback: (48)

I simply can't comprehend a valid argument against REDUCING airframe vibration---if soft mounting an engine is a bad idea, is the automotive industry aware of this concept!?---

Diablo-RCU

My Feedback: (1)

Automotive engine mounts aren't the same as model airplane engine mounts. The typical model soft mount allows the engine to jump around a whole lot. Ever drive a car with a broken engine mount? When you floor it, the engine bangs around from the torque reaction. Same thing happens when you soft mount a model engine.

Gremlin Castle

My Feedback: (14)

The 6.4 has been around for a while. This particular one is what became the Millenium series with the blue cases. Mine has a polished aluminum case. You are right it has been five not six years. No I am not using shock mounts and neither is the other referenced aircraft.
As a further note I have installed what may well be the last of the Brison 4.8 twins on a Aerotech KI-84 Frank. Gary and company built it from the remaining parts inventory. This replaces a 4.2 Sachs with shock mounts. The new installation runs smoother than the original.

airega1

My Feedback: (204)

Thanks a lot Gremlin, I appreciate the info

extragiles

Hey Guys

Here is an issue nobdy talked about. With soft mounts your engine RPM will surge 150-250 RMP at idle. I can tell you I have not seen any of the better IMAC pilots using them. I have hundres of flights on three different A/C and never had vibration issues.

Allen

JB Rekit

My Feedback: (3)

The only mount I have ever used or buddies of mine is the Hyde mount. All were on a DA 150, 3W 150, 3W 200, and 3W 212. None had idle/ surging problems (that could be why it wasn't talked about...but there are other mounts out there that might cause this, I don't know)

The reason I like it is b/c the servo gears don't need to be replaced as often and the batteries last a little longer per charge due to the servo not pulling as much amperage to hold center. Not to mention less stress on the airframe.

And as far as none of the better IMAC pilots using them I know of at least one that I think is pretty decent by the name of Chip Hyde that uses them.

But to each there own and having flown a lot with and without them, I guess if I was real nose heavy, I would fly without one, but all things being equal, I am pleased with the results and will continue using them.

Stall Speed

I would not drive a car with a broken engine mount. And a airplane engine mount is alot different than a vehicle engine mount. Use the soft mount!

rmh

there are soft mounts and then there are soft mounts . some "soft mounts are that, in name only.
most are POS
the best setup for our engines IF you use a remote exhaust setup, restrict axial movement to a minimum.
Most let engine seek it's own position -On many engines -this is a baaad idea.
For most setups - really good mass balancing - thu proper motor mount design- is best.

Done correctly, there is no wind up in a "motor box " .
many motor boxes act like a big rubber band and amplify torque reaction.
Ideally the fuselage is as stiff as a poker. from stem to stern.

transmission_dr

My Feedback: (1)

Ah, the eternal to soft mount or not debate!

Here's the reality.

All full scale automobiles soft mount their engines.

All full scale aircraft in current production (and most all out of production aircraft) soft mount their engines.

All off road equipment soft mount their engines.

The engineers who design this equipment must know something! After all 100% of the full scale equipment designers use soft mounts.

What do folks in RC think, that the laws of physics and vibration do not apply to RC?

If the engine when soft mounted moves around too much then guess what, YOU HAVE THE WRONG MOUNT, it is not up to the task at hand. A properly mounted engine will not move around too much. Just look at our full scale counterparts! Yes the engines will move around, THEY ARE SUPPOSED TO, that's what the mounts are there for, to protect the airframe and its contents from vibration.

Unfortunately a good selection of soft mounts at reasonable prices are not readily available to us RC'ers. Lack of a suitable mount is the only really valid reason to not soft mount. All the other arguments are just plain BS.

Pick a good soft mount and your air frame and electronics will love you and give you a long service life in return.

My $1.50

rmh

well Jerry - I understand your argument
Did you know?
Race engines-have- NO soft mounts
Also what we need -which works better is called MASS balancing-which requires that the engine and the airframe become unitized.
If we had multiple impulses per revolution - -a soft mount would work nicely
we don't
typically we have ONE pulse per revolution
twin or single same deal.
I have designed very succesful soft mounts and sold em - -I started with the POS YS 1.40 which will beat the ball off a pool table.
On th gassers tho - all in all mass balance works best for most applications
Get a soft mount calibrated incorrectly and the damage is worse than no mount at all.

dirtybird

My Feedback: (5)

At Toledo one year I asked all manufacturers of soft mounts that I could find how many G's their soft mount would reduce vibrations, and over what frequency range. Not one had any test data. It leads me to believe they don't know what they are doing.

JB Rekit

My Feedback: (3)

The race engines are kind of a bad example because they will sacrifice everything for a few more rpm (midrange, airframe longevity, equipment longevity, etc.). If your goal is to make the most possible power at all other costs then a soft mount would not be reccomended.

I don't believe a soft mount is for everyone because:
1. They are a bit pricey
2. Some people probably don't fly enough for it to make a difference long term on the airframe
3. Service on gear replacement in servos has been very good and people may think it is easier to replace them more often than to bother with a soft mount.
4. They may be out to get every last RPM they can (Even with my 40 # extra with cans etc, I still use a soft mount and feel I still have enough power to use a 3 blade prop and not lose anything, so thats not an issue. It would be an issue if I was racing though and I would have gone in a completely different direction setup wise but for giant scale "I" definately like the results I have had with using a softmount vs. not.) Just depends on what everyones goals are for their plane and how they plan to maintain it and how long they plan on it lasting.

tande

My Feedback: (48)

DITTO!

rmh

Don't know what they are doing?
Awful strong opinion.
Soft mount= Bull Sh-- in most cases
Why ?
Simple - we tested em.
Unless the engine will self align along the crank axis, the resultant "whip" induced can wreck exhaust systems and may break mounts/fuselage etc.
An EFFECTIVE soft mount , will reduce idle pounding and if really lucky, will also stop high speed frequency pounding.
I use a very simple test for the engine mounting.
You run the engine thru the entire rpm range and feel along the ailerons and elevators
BOTH should have minimal movement .
In most cases , we find that a modern engine , single or twin can be tuned for very little bottom end shake
High end problems are typically prop/spinner related.
Get this stuff right and the solid mount adds to the mass damping of the engine.
Final result - very smooth operation.
BUT adding a "super duper " soft mount to a setup which is not correct in both of these areas ,simply lets the engine really get into motion
Most vibes are interactive between the airframe and the engine.
Simply hoping a soft mount will be a fix to either problems is wistful dreaming.

dirtybird

My Feedback: (5)

Yes I know its a strong opinion.
Let me add that it sounds to me that you know what you are doing. I would also add that if you used an accelerometer instead of just feeling the airplane I would be even more impressed.

rmh

Back about --40 years -- we had an industrial machine problem - -resonance
We did use instumentation to get numbers to show the troops .
But -the fixes were based on simply feeling and listening to the damn thing.
When I was running the gone but not lamented YS 4 stroke pattern stuff, I found that tuning the fuselage was an extremely large part of killing the vibes before they killed the airframe.
the fuselages we had, would have a strong , localized point of vibration-just prior to the wing-- we added a simple stringer along this point and smoothed up the entire airframe.

As coincidence would have it - I am doing another "vibe" fix today.
this time the culprit it is the carburetor being used .
It has really good top and center speed metering but so far the very bottom is wrong- so now to drill teensy holes in the throttle plate to get a leaner low idle - which stubbornly remains shaky.
A European mount that is always held up as a "fix" is a simple plate- pivoting on the crank axis - a hydraulic damper "hopefully" snubs the spikes of each firing , to smooth vibration.
The result is cumbersome.
Again I faught a really poor design I was asked to fix, on a 100 lb load washer extractor , which used almost exactly the same fix.
The problem was that our "engineer" tried to use automove shock absorbers to control the loads.
these would get smokin hot in short order.

A classic case of too much book time and too little practical experience.

dirtybird

My Feedback: (5)

I understand your point. Experience is a great teacher.
However use of a measurement instrument can sometimes lead to some surprises.
For example many years ago when I was into pylon racers I borrowed an accelerometer from the Boeing cal. lab and made some measurements. I found about 100 G's existed in the then ultimate engine the K&B RR 40 when installed in an airplane. That was peak to peak as I used an oscilloscope as the readout instrument. For RMS you would devide by 2 times the sq rt of 2.
What was surprising to me was that when I placed the accelerometer in an empty servo case (it was about the same size as a servo motor) and mounted the servo with the rubber bushings as we normally do there was no reduction in the reading. Since then I don't use the bushings unless I want to. In wings I just lay the servo down and put a brass strap over it. It helps avoid flutter. In thirty years I have never had a servo failure that can be traced to vibration. But then I don't fly as much as some people.
My theory is the vibration is so high frequency and of such amplitude that the rubber bushing becomes solid and the vibration passes right throuh them. The rubber just does not have time to react.
This is the main reason why I was asking for test data. Maybe they have but have found the same thing I did. That it really don't do anything for you.