View Full Version : Soft mount of engine possible?
SeaHawk
10-30-2006, 06:41 PM
I guess this is aimed at the Bergens. Is it possible or would there be any advantage to 'soft' mounting gas engines on some sort of dampening mounting system opposed to the hardmounting system that everyone uses? I'm sure there is a good reason it hasn't been done yet.
MarkWebber
10-30-2006, 06:48 PM
Quick is doing it on their gasser. How well it works, I don't know. Bergen heli's are known to be made from G10 for it's vibration attenuation capacity.
I wondered how well the quick unit could maintain pinion allignment being that the heli isn't rigidly fixed in position. Their engine mount doesn't appear to have enough play that it would move a lot. Then, we don't want much movement in our pinion setups either.
PaulH
10-30-2006, 07:16 PM
Actually that wouldn't be a problem on the Intrepid. The entire clutch assembly, including pinion, is firmly held in place by the triple bearing block in the upper frame. The fan/hub assembly turns the the clutch through a pair of delrin pins. This is what makes the clutch self-aligning.
In theory, soft-mounting the engine wouldn't affect anything because of the self-aligning clutch. The standoffs that separate the upper and lower frames would need to be 1mm or 2mm longer to provide enough space for rubber isolation mounts. Something similar ot the rubber grommets on the canopy could be used as a starting point.
Really, this isn't as crazy of an idea as people think. Even the engine in your car is iso-mounted.
MarkWebber
10-31-2006, 05:17 AM
IMO the benifits of isolating the engine w/o including the clutch would significantly reduce the effectiveness of the isolation mounts. Yes, our automotive drivetrains are isolated from the chassis. The difference being that that system is fully isolated. Yet, have a single mount fail to isolate and you'll quickly discover how poorly the system functions with that one failure.
I think your looking for trouble. I feel engine vibes need to be dealt with not isolated. Any isolation mount will only remove some of the vibes not all. I would think that the vibrations could be dampened but could create a resonation as well. In this dampening you may not get the indications you need say for a rich running needle setting vibe in the tail.
PaulH
10-31-2006, 09:19 AM
Mark,
The engine of your car may be isolated, but the system is certainly not "fully isolated". At some point you have to turn the drive shaft, which is hard mounted. To further make the point: If you have four-wheel drive or all-wheel drive, the transfer case or center differential are not isolated with the engine. At some point, parts of the drive train are fastened to the frame of the car without vibration isolation. The universal joints are what connect the parts. The self-aligning clutch on the Intrepid works almost like a universal joint, which is why it may actually work.
Gyan,
We're running single cylinder engines. You will never eliminate vibrations. But, if we can find a way to reduce them, then the mechanics of the helicopter will have a longer MTBF and the electronics, like the gyro and tail servo, won't have to work as hard. As for engine tuning -- much of it can be done by ear.
MarkWebber
10-31-2006, 12:23 PM
I don't know if we're getting of topic or not. But, as a former ASE mechanic, I can attest that I can think of no modern auto (2 or 4wd) that has a drive train not isolated from the chassis. While the drive shafts or CV shafts are firmly attatched, the driven element (axle or hub) are also isolated at the srping shackles/control arms.
But what does come to mind are the belt driven helis. Which models, I can't think of now. However, if you were to isolate the engine from the frame and belt drive the main shaft, you would be on track for what Seahawk is looking to acheive, no?
I do agree completely that our heli's are helped alot by doing what we can to reduce vibes. It's amazing how hard your gyro works when the carb tuning is just a bit out. :shock:
OK Paul, if the main man thinks it's possible, I have the perfect mounts to try it out. (I love being on the edge!! :lol: ) There is the matter of the landing gear strut attachments, something will have to be fabricated for that but no big deal. I'm more concerned about the clutch, & the self alignment aspects of it. If the engine is vibrating within the isolators and the clutch is not, those delrin sleeves will take a pounding. What do you think Chris? :D
PaulH
10-31-2006, 02:11 PM
Mark: I stand corrected! :) I never thought of the fact that the driven element is also "soft mounted" in some way or another.
I like the idea of a belt drive. Other helicopters have done that. If nothing else, a belt will lower the transmission noise and reduce gear mesh issues.
Gyan: Would it be worth soft-mounting the entire lower frame? Instead of using longer spacers, use the same rubber grommets between the lower frame and the spacer as you use between the engine mount plate and the frame.
Of course. bottom plate, head mounting bar, engine side mounts all have to be rubber mounted. Rubber grommets won't do it. I have just the hardware for it if Chris thinks the delrin bushings will take the beating. Let me know Chris.
MarkWebber
10-31-2006, 06:21 PM
Paul
That might be the ticket there. Isolating the whole lower frame assembly and engine while belt driving the main. Hmmm.
PaulH
10-31-2006, 07:11 PM
The issues I see with doing this are:
1. Finding sprockets to replace the pinion and spur gears.
2. Moving the engine and triple bearing block forward to separate the sprockets enough for the belt drive to work.
3. Isolation mounting the engine.
4. Isolation mounting the triple bearing block.
In my mind, #4 is the hardest because it sits between the upper frames. The only way I can think to accomplish this is to mill out the corners to make room for the dampers.
tigger28
10-31-2006, 11:41 PM
Belt drive sounds like a great idea.
This would require more extensive machining: build a modular engine mount from aluminum that holds the engine and triple block assembly as a single monolithic unit. This eliminates engine-clutch misalignment issues (once assembled properly) and could add rigidity to the engine output shaft area.
Engine Mount/clutch assembly bolts into existing frame holes using isolation mounts.
The only connection points between the power plant and the airframe then become the rubber iso mounts and belt.
Bottom frames would probably need to be widened. Could be achieved simply with turned spacers, longer bolts and wider L/G, battery tray bars.
More iso-mounts could be added to the upper part of the lower frames for more support.
If you are really enterprising, design the modular mount so it can be adapted to a variety of power plants, i.e. RC series, electric.
Cons:
- cost of materials
- machining skill/equipment required
- matching belt/pinions etc. to airframe may require a fair amount of trial and error
to determine best parts choice.
- belt tensioning, life and friction effects also need to be considered.
However it would be really depressing to do all this work and find that vibration was not significantly reduced, or a new set at a different frequency was introduced.
Are there are existing examples of belt-drive mains for RC helis?
MarkWebber
11-01-2006, 05:30 AM
However it would be really depressing to do all this work and find that vibration was not significantly reduced, or a new set at a different frequency was introduced.
That would be the rub!