My knowledge of what would differentiate aerospace from automotive is minimal.. but based on a high reliability requirement, I'd probably shy away from elastic elements. Drastic temperature changes, high cycle rates, etc on aircraft are not going to be elastic-friendly.

Solutions exist for belts without tensioners. Toothed belts can be run without tensioners if the systems are designed correctly. And then there's always gears and chains.

Hi SwinnyGG,
Thanks for the reply.
I agree that it would seem more logical to use a chain than a belt especially given environmental factors.

As for the difference, having worked in both Aero / Auto industries for many decades, I would say is significant, in short much higher standards & costs (on the Aero side).
Aero parts typically have to be selected from a QPL (Qualified Product List) which means they have gone through quite a lot of rigorous tests, hence expensive.
Of course it goes without saying it does not mean that an Automotive part is so inferior it's simply does not need to meet the same level of requirements.
Nor would folk be happy paying aerospace prices for automotive parts.

Unfortunately I've already been provided pre-selected hardware of which is a compressor that is an OTS product including a 6x40° pulley, no teeth of course.
I must admit I am only just getting into the project so I am trying to get to grip with all criteria and requirements.
I'm not sure why a toothed belt or chain drive was not selected.

I have the understanding that I've not a lot of leeway to change the system, I think a lot of that is governed by commercial agreements / negotiated contract by Purchasing dept etc.
I am essentially tasked to make a mounting solution so I plan to design the best I can with what I have.
I will also highlight the reservations / concerns that could introduce Failure Modes into the system.

Still hoping someone can give me a definite yes / no as to a self-tensioning

Thanks for your input and thought, very much appreciated.

Best Regards

Tetragrammaton :)

I guess what I was getting at is that 'self tensioning' i.e. elastic v-drive belts exist.. but I doubt they are certified for FAA requirements.

If you're stuck with the hardware you have and don't want a separate tensioning mechanism in the drivetrain, your only option that I can see would be to design the mount for the compressor such that it provides for tensioning the belt.

Ok yes, I see your point regarding certification, there probably are some but I need to expand my search to see what I find.
That is generally the direction I have been working on.
I am essentially designing tensioning system into the compressor mounting bracket.
Utilising a tie rod for adjustment.
I need to utilise integrated tension system so as to reduce the system weight and drag on the belt from using an separate tensioning system.

Thanks.

Best Regards

Tetragrammaton :)

What you propose has already been considered, a very VERY long time ago. Granted, materials science has come a long way in 100 years, but the basic physics of the problem have not changed and you'll have a serious problem with your concept.

Tension in the belt is proportional to the torque that can be applied at any given wheel. That torque is only applied by friction, and friction is directly proportional to the net forces on the belt wrapping around the pulley wheel. When driving a belt (at least one of the wheels always does this) then there is a differential in tension from one side of the pulley to the other. That differential in tension represents an elastic displacement otherwise known as "stretch". A belt with a low stiffness will stretch to relieve the tension applied by the driving wheel, rather than apply the torque to the other driven wheels. So the belt loosens instead of applying more torque. It will just slap around.

You always need stiff belts, or they just don't work. The SAE standard probably specifies a limited range of stiffness values (though I haven't checked, but I recommend you do so).

Also, are You thinking 'drive-belts' with or without teeth? Operating for short duration, intermittently or continuous [no power... up-to variable/full-time power]?

'Smooth/semi-smooth' belts have had great operational success, long-term in automotive applications [light duty]… but tensioning devices are clearly needed.

Teeth would imply need for mating gears and 'timing'... which is a high wear environment.

NOTE. The ONLY high-power belt-drive system I'm aware of that is not tensioned... are 'chain belts' immersed in lubricants.

Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
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Stretchy V belts are a real thing on automotive engines. I've never seen one in reality, but they do exist.

Cheers

Greg Locock


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Any guess on whether they're used without idlers, Greg?

The ONLY technical details I can find on them is that the microV can be used for 2 to 4 point drive, and internal gluing of the cords is used in some of them. So I'd guess that's one reverse idler and 2 outputs and one input. I can find no design guides, they are not retrofit items, so I guess you'd need to talk to an applications engineers at Gates or Conti or Dayco or AC Delco.

Cheers

Greg Locock


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