I have a ZDZ 40 and mounted it directly onto the fire wall and would like to reduce the vibration, maybe somebody has a trick for doing this

Lean the idle a little.
It should shake less

If you are looking for ome kind of soft-mount:

I made my own for an 58cc engine. The idear is simple. But It has to prove it's long term stability.

wvr what have you used for the rubber mounts this is the part i need to source

I have found rubber isolation mounts (and tons of other stuff) at McMaster Carr. www.mcmaster.com

They have everything a man could ever need and sell to the public.

WVR Nice looking installation. Particularly like the prop hub weight reduction... Did you fabricate or is it a supplier item?

And what prop is that? I've seen them before, but can't remember the maker.

The contrast of the white and black cf is just bonzer.

Hi there,

The prop adapter is as it came from the manufacterer..... (MVVS)

The prop itself is a Biela prop.....

The rubbers are 45-shore (hardness). seems soft, but because of the distance from the center of engine to the rubbers, it seems to be working fine.

Winfried

hi WVR

What are your ipressions of the engine ?

thanks
tim

Hi,

The engine so far seems to be handling fine. Start easily, picking up the revs very easy.

But my tries last saterday where not very succesfull. I made some flights OK, engine is not having any problems upsite down or with hard pulls/ short turns. (somebody else has got problems with a gas engine, picking up 1000rpm running upsite down so I tried that), so that part of the engine is OK. Power seems to be real good, engine is not run in, but it flies the PAF-trainer at 9Kg's as a F3A plane ....

But the whole day trough, the engine did run without a problem and then died suddenly, nomather which throttle position. It would run fine for a whole flight, land, tank, start again (without touching the needles) and then have these problems.

After searching back at home, I seems that I had a loose contact in de battery used for the ignition. But i only found one glitch, so not really sure. So new parts (battery/switch) are in place and i'm trying again shortly.

Also the support here in Holland is real good. If the new parts are not solving the problem I take the plane to importer (Pe Reivers) so he can help out.

So far I except these things as I am very new to gasoline engines, I know these things are really sensitive on the needles...

I will keep you posted,
Winfried

Keep going -
If you have perchance hooked to a seperate exhaust system - please let us know how the engine 's compliant mount works with the exhaust system

Hi Dick,

Sorry but it's not completly clear what you ask?

I guess that you are wondering how the exhaust is mounted flexible enough to handle the shaking of the engine due to the softmount?

The exhaust is mounted in such a way that it can swing around on two rubbers again. Will make a picture tommorow....

Winfried

The position of the rotating weight does change the overall engine balance. The results can usually be seen best at idle and by positioning the prop every 45 degrees and starting the engine and observing. Some positions can appear that they would shake the tail off.

Intresting!

I normally set to prop at a 2 o'clock (other blade at 8:00) for easy starting. What you say is that when I set the prop in a different position compared to the compression it can shake more (or less).... never knew this...


Will try this next time, just to see what happens.

Thx
Winfried

wvr
You might want to try the experiment with a prop that is abit out of balance. From postings here,
I would start with the heavy blade directly opposite the counterweight of crank and sample from the there.
If you try it, post the results here.

Theory and explanation supporting balancing can be found in the following engineering text.

Design of Machinery
Robert Norton
ISBN 0-07-909702-2

I stumbled on the concept while testing props in the driveway one Saturday many years ago. The tail of the airplane was secured to a tree with a rope used as a leash. Change a prop, crank the engine, tack the engine, then bring the engine back to idle and write the RPM down. Sometimes at idle the tail would dance vigorously. The serious shaking appeared to be associated with only a few props. When finished the props that danced were reinstalled and tacked again. Some didn’t dance at idle during the second test. Turns out that during testing the props were randomly installed relative to TDC.

A single prop was then installed at various locations relative to TDC and shaking at idle was observed. Shaking of the tail at idle is very different in different locations.

Much later overbalancing theory was discovered. Overbalancing is a technique that manufacturers use to distribute the forces more uniformly in the X and Y direction and reduce the maximum force vectors in a single direction. When we remove a magneto or install a prop we change the overbalance. Sometimes vigorous shaking is introduced by our changes.

Winfried,

Your flex mount looks excellent! I have been experimenting with this kind of stuff for years, and I can tell you that the "vibe" I get about your mount is good.
If anything, maybe you could make it a little softer by putting the rubbers closer inboard, or using less of them. Without the shocks I'd say your rubber setup looks about right, but with the shocks you can make it a lot softer than you think without running into problems.
By the way, where did you get them shocks? Are they from Toni Clark?


Bill,

Could you, or someone else, please explain to me how a pefectly balanced prop could do the things you say it did? I fail to see how a balanced prop could change the balance of an engine...

Here is one possibility for the prop position causing "unbalance".
Consider an engine with only one bearing forward the crankpin and one aft the crankpin. and a rather flexible crank design
Each time the engine fires--the crank bends-- center goes down - ends of shaft go up.
Now add heavy prop aligned with crank throw.
The propellor acts as a "gyro" and stabilizes the crank.
Now move the prop 90 degrees -
Prop no longer is in position to stabilize when firing occurs.
This is only theory I have considered which makes much sense- with properly balanced prop/hub/spinner assembly.
All of my own engines have two bearing forward the crankpin-and honestly I do not find that switching the prop position changes anything - BUT I do balance the prop/spinner assemplies in all possible axis.

Hi Rudeboy,

Thanks for the 'good vibe'

I already thought about playing with the position of the rubbers. They are already very soft (45-shore), but I know that Tony-Clark has got a G62 on only 4 rubbers, so it must be strong enough.

My first priority is to get the engine reliable , as you can read in a previous post, i have some unexplanable shut-off of the engine.

I also want to position the rubbers in such a way that the rotation will be more circular. With the current layout of the rubbers the engine is very 'hard' in horizontal way, but a lot softer in the vertical direction. Therefore the shock absorbers are not working in the optimum direction.

The shockabsorbers are of a 1/8 off road car. For the price of the tony-clark shock absorbers ($ 45 each) you can replace these shockabsorbers 2 times a year for 5 years in a row..... But the tony-clark ones are real good, so maybe, if I'm really happy with the way the softmount works I will upgrade to these 'install-andforget' shock absorbers.

The tony-clark ones are now in use for 3 years on a F3A plane, (see image) with a 'hydro-mount' on a OS-160. I siply copied this concept.

I will let you know when/if changes of rubbers positions made a difference.

Winfried

Interesting theory, Bills.
Makes alot of sense to me. With all the different masses moving and rotating inside the motor, balancing seams to be an impossible task. One thing I noticed with all my gassers I purchased. None of them were balanced properly at the factory. The magneto wheel is normally the culprit. Not only is it made from cast aluminum but it also has the magnetos built in which are heavier than alu. Even with counterweights on the opposite side it is likely off balance. Or the front face where the prop hub mounts onto has not been machined. I had one that was so much off that the attached prop hub was 0.7mm out of whack. Without a good lathe you out of luck.

Interesting theory, Bills.
Makes alot of sense to me. With all the different masses moving and rotating inside the motor, balancing seams to be an impossible task. One thing I noticed with all my gassers I purchased. None of them were balanced properly at the factory. The magneto wheel is normally the culprit. Not only is it made from cast aluminum but it also has the magnetos built in which are heavier than alu. Even with counterweights on the opposite side it is likely off balance. Or the front face where the prop hub mounts onto has not been machined. I had one that was so much off that the attached prop hub was 0.7mm out of whack. Without a good lathe you out of luck.

on my engines - there is very little unbalance - due to good design work by the manufacturer.
The gallopin iron on singles CAN cause problems but mostly in some rpm range which can be isolated - most of the ones I test have this occurring about 2700-3000 rpm.
The real vibration problem we see is actually reaction to the torque applied to the shaft .
There are designs for reaction isolaters which can help -a lot - BUT ultimately -all these can do is slightly soften th blow because primary impulse is simply RPM.

Winfred,

Would a photocopy of the theory be helpful? Overbalancing is a very complex subject, which I may not be capable of explaining in terms that would be understandable.

You can easily prove that the prop position makes a difference on most gas engines. Mount the prop at 0, 45 and 90 degrees relative to top dead center. Crank the engine with the prop in each position and observe the tail vibration. Some engines will be worse than others. The magnitude of the vibration in X and Y will depend upon the crankshaft balancing strategy of the manufacturer and the ratio of crankshaft weight to prop weight.

rubbered mounts,,, look here too,,,

https://sdp-si.com/index.asp


Jim

Later today it occurred that additional explanation concerning overbalancing might be necessary.

The author of ‘Design of Machinery’ Mr. Norton is a professor in the Mechanical Engineering department at MIT. The formulas and theory surrounding overbalancing are being taught to engineering students and future rocket scientists all over the country.

I simply observed the vibration results prior to discovering the scientific basis for the observation.