dhillfolk

My Feedback: (195)

Steve, if nothing else, you are creative

hsukaria

I don't know, it seems to me that the beam mount method is stiffer. The rear offset mounting seems more prone to vibration since it is less stiff.

aussiesteve

I don't know where you are coming from but feel free to prove me wrong.

I quite extensively researched the subject or mounting system when designing some engines last year. That research included some market research that showed about a 50:50 wish for beam vs Standoffs for Engines in the 20 - 30cc size range and a preference for standoffs in the larger size ranges.

MLD 35 - Happy customers, DLE 30 - both have happy customers but I doubt that those customers base their experience on whether or not the engines are beam or standoff mounted. Each to their own I say - my personal preference in that power range are 3W and MVVS products but they are neither Chinese nor low initial purchase cost.

But then again, having an IQ of above 70, I also am able to accurately mark out and drill 3 or 4 mounting in a firewall.

I'm outta here

Whistling Death

I love it when aussiesteve gets on a roll.

apalsson

My Feedback: (1)

Said who?

aussiesteve

My Grandma says I'm cool

Hey Blake
It's been WAY too boring around here lately - time to wind things up a bit

Woody218

My Feedback: (24)

If you guys don't think mounting an engine on standoffs is secure, then I suggest you go look at the way a full-scale radial engine is mounted.

Whistling Death

Speaking of that, I almost tee tee'd in my britches when I saw how the Pratt and Whitney in a Corsair was mounted to the airframe. It's hard to see how that little frame can hold on to that monster of an engine.

dhillfolk

My Feedback: (195)

I helped a friend install a new 7 cyl Jacobs radial in his Cessna 195 awhile back & there were no singular unwelded standoffs in that mount. By singular I mean, loose or unassociated/welded to adjacent members such as we're addressing here w/o thru bolts.
If there are full scale unwelded spacers (4) such as in the small gassers being addressed here supporting a full scale motor outwards the same relative distance w/o thru bolts, I'd sure like to see or know of same.
I don't believe difficulty in drilling a (4) hole pattern is a problem w/ these spacers, but maintaining equal parallelness & torque between the motor & a pliable wood surface so as to not pre stress flimsy crankcase mtg tabs is.
I've read of these tabs breaking & to me it's perfectly understandable from an engineering standpoint.
This design would be rejected from the get go in a reputable US engineering facility. Of course an adequate thickness metal plt against the wood helps but is not a guarentee for parallelness.
The other problem easy enough to calculate is, as the spacer len increases w/o thru bolts, the torsional or twisting moment increases proportionately.
W/ beam mounts, less imbalance is transmitted to the motor mounts which are of a robust cross section that can handle same w/o fracture.
That's my 3 cents from expirence & 45 yrs of mech engineering.
I tried to resist stirring the pot here but it was like back raising our 3 kids, sometimes you have to jump in & draw the line regardless of thier knowing everything.

aussiesteve

Who said anything about the pros and cons of through bolts?

In fact the pliability of the wood actually works in the favor of the standoff mounts (provided each node is of proper dimension) much the same a any other form of resilient mount.

The picture is of a typical standoff mounted engine that is in an airframe which I will be taking flying tomorrow. It is a very common 55cc engine of good quality. Note the small dimensions of the cast mounting lugs yet they do not have a history of breakage. most of the engines in our hobby have mounts that are excessively strong for the common loads other than "earth created negative acceleration".

aussiesteve

And here is a picture of a mount for a Full sized Extra (I know this item very well indeed, It is welded and it is not finish machined as there are also resilient mounts on the end of this, )
around 360 BHP compared to our 5 BHP.

Antique

My Feedback: (4)

A 3/16" aluminum plate bolted to the standoffs and then bolted to the firewall takes care of any misalignment...

Truckracer

My Feedback: (19)

I laugh a bit every time I see a beam mounted engine firmly bolted to a pair of wimpy, reinforced plastic mounts. Now that is a secure system for sure!

There seems to be a common, molded mount that comes out of China that many companies are using. Engines bolted to these mounts can easily be deflected with little hand pressure. Yet people feel these are secure. It seems that few, high quality aluminum beam mounts exist these days.

I come from a pylon racing past where engines could not be mounted too firmly. We paid high $$$ for very high quality motor mounts. A beam mounting system means something if you have a quality mount to bolt the motor too. Wimpy plastic mounts just don't get it.

hsukaria

My concern is the torsional load from the model engine standoffs. There are no diagonal cross-members as shown in your picture in a typical model gas engine mount.

hsukaria

Your mount looks very solid since the standoffs are so short. How about when standoffs are at least an inch long? How to they dampen vibration and torsional loads from the engine?

Truckracer

My Feedback: (19)

My first standoff mounted engine was a DA-50. Before that, all my gassers were radial mounted, usually by a plate or other mount that was either part of the engine or a separate bolt on piece. When I first looked at the standoff mount system, I couldn't imagine it being strong enough to handle that mass of engine suspended out there on the end of those posts. But in practice, it seems to work very well, extremely well actually. The standoff system seems to work simply because of the mass of the system. Most of the better engines use heavy lugs on the engine coupled to fairly massive standoffs. Couple this to a fairly stout firewall and you have a troublefree system that is more than up to the task of supporting the engine. Standoffs have the added advantage of leaving rear carbs fairly out in the open for easy linkage and fuel line installations.

I've really grown to dislike beam mounts on any engine. Like many things when you go to gassers, beam mounts can stay with the glo engines and I won't miss them. If companies will start providing quality machined or cast aluminum beam mounts, I will reconsider them. But for now, beam mounts will remain a PITA system for me.

hsukaria

Ok, so maybe either mounting approach will work well if done in a proper, quality manner. But how about absorbing the higher vibrations of a gas engine? Is either mounting setup better? I have seen guys at the field with good gas engines that were shaking their planes apart. They kept having to check and replace loose or missing screws. One guy lost a biplane upper wing to vibrations from a good gas engine (trashy cheap ARF he bought from a lower quality source).

Sorry about asking so many questions, I have not tried a gas engine yet and am trying to gain enough info to make a good decision in the future.

w8ye

My Feedback: (16)

Beam mounting works nice for profile models

hsukaria

Can't argue with that one.

Truckracer

My Feedback: (19)

First off, I'm not a mechanical engineer so I can't make statements based on theory and training. I do have considerable experience with modeling in general (well over 45 years) and have an extensive general mechanical background. I would have to believe that a good standoff mounting system would allow more torsional and other engine movement than good beam mount system. But in practice it doesn't always work out this way. I would think the beam mount system would be superior but in practice beam mount engines seem to get bolted to less than ideal mounts! Mounts that many times allow more engine movement than an average standoff system. Point here being that either system can work well if it is executed well.

As far as gassers causing problems with airframes, yes it happens. Sometimes it is the airframes fault as some are just built too light for the expected application. Overall a quality engine mounted to a decent airframe will have a very long life regardless of the mount system used. Just like engines and airframes in general, most will meet their end in the dirt somewhere long before they wear out.

In short, buy quality engines and bolt them to quality airframes ..... execute the various installations with care and skill and you will have great success with gassers. Just like glo powered planes, some guys will always have problems where others never seem to have any problems. Does that tell you anything??

aussiesteve

Truckracer, you have hit the salient points and "It don't take a rocket scientist to work it out"

Fact is that whatever mount system is used, it needs to be designed and applied correctly.
A poor design of a beam mount bracket is going to give accuracy issues.
Long Standoffs without decent diagonals also give torsional deflections higher than what would be ideal.

The point of the post of my engine mount was to show one proper method of mounting. Attached are a couple of pictures I "borrowed" from another RCU thread that shows how one of the most experienced Gas engine users mounts his. They are of the same mounting the second one is the finished product.

Huskaria - for the guy who you saw lose a wing due to engine vibrations, Maybe it was a good engine but the fact it was vibrating to that extent shows it wasn't a good implementation. It was most likely a very badly tuned engine if it was vibrating to that extent.

This thread started out as a list of Brand names for Chinese manfuactured Engines. The sheer number of those brands shows that people are happy to buy cheap. The use of long standoffs shows the general want of the flyers to wish to get airborne as quick as possible with their (also cheap) ARF's.

Well, it is pretty difficult to have Cheap, Good and "Ready to fly in a short time with little effort" - you can pretty much only ever have 2 of those 3 choices. A little work is usually required if long term reliability is wanted.

I fly a number of profiles and will agree that beam mount crankcases sure make those easier. My current build is an 80cc one but haven't seen a beam mount in that size (well, not one I would want to use anyway).

What would make a much greater difference would be if side mounted carbs were used properly (These can be crankase inducted similar to the 3W US series of engines or the MVVS ISS series but they are not in the scope of this thread - TMM are another with this design and they are in the scope of this thread). Then the "ready to fly in a short time" without the need to do additional work would be supplied.

Again - it is not the Engine mounting design that is the issue with the rear standoff design - it is the incorrect implementation of that that causes the problem. The only crankcase lugs I have ever seen broken were either as a result of a crash or similar such load (I have seen lugs broken from shipping damage) or as a result of a Low cost engine supply requirement.

Use whatever mount you like and whatever works for you but if you want a long term, low maintenance and low running cost relationship with the airframe - make sure good materials are used with a good design, do a bit of work up front (no matter which mounting system is used) and tune the engine properly - assuming a good running engine is installed in the first place.

Now back to the scheduled program but a couple of questions
Which oil do you use on your engine mount (Sinopec or Petrochem?), Should I use the HobbyKing 2.4 Receivers for my throttle and is "%&^" brand any good? (they have run out of letters so are now using symbols - but I saw them available very cheap)

yak-54

SO WHAT?
SOME OF THEM, ARE EXCELLENT ENGINES I HAVE THE DM AND DLA BOTH ARE BETTER THE MY DA ENGINE.
ILAN

Experten109/40

My Feedback: (-1)

so I may have missed it, but DLE20 is a copy of what engine? I think I read Desert Aircraft ?

hsukaria

Does DA even have a 20cc? It couldn't possibly be a copy of anybody elses with the smaller size and mounting design.

Experten109/40

My Feedback: (-1)

they do not. thats why I asked. somebody mentioned it in one of the many many pages
and nobody seemed to question it.(?)