Discussion in 'Supplier / Manufacturer Announcements' started by John Penry-Evans, Mar 27, 2019.
That's an ACE Redrive for a Briggs 993 Big V Twin.
The thing that stops me buying one of these CNC machined, anodised and well, pretty redrives is that nobody ever mentions checking for TV nasties or what the belt life is.
All you have to do is write: firstname.lastname@example.org and you will get all your answers. Ace has a Good Reputation. Belt Life really depends on the Person using it and Adjusting it. Old Style V-Belt/Cog Belt Drives were considered 200-250hrs, these new style Poly V Belts are a little better.
That is true. OTOH, these motors have pulleys attached to them and drive various bits machinery for thousands of hours. If the prop drive has similar attributes to a well proven application, it would seem the risk is pretty low.
No. How many bits of machinery usually driven by these engines have the inertia of a prop? You need to consider the complete system. A drive system that works perfectly for a low inertia load for 10,000 hours could have a lifetime of seconds swinging a prop.
"No" yourself. I bolded the "if" because it was apparently missed the first time. None of these small PSRU vendors have the resources to do a full TV analysis on every possible engine and prop that might be attached to their redrives, which is what your comment indicated you wanted. What I'm suggesting is that IF these engines are already driving equipment with characteristics similar to what you'll be doing (and that would include air boat propellers, which often have more inertia than what we'd choose to mount on a plane), then this field experience is applicable.
Yes, whether or not these have good reliability when swinging high inertia loads such as props is exacty what we need to know. TV problems will likely show as short belt life, though it is possible to break shafts if the belt is tough enough... Redrives usually have an easier time when load inertia is reduced. If you're selling $1000 redrives, it doesn't seem unreasonable to have tested them with a couple of the more popular engines and a typical range of inertias. Once you know the stiffness and torque capacity, you can mathematically predict a lot of potential TV issues. Resonance below idle can be accomodated with a little slip. Resonance anywhere between idle and full power is going to give problems at some point.
After doing extensive research engineering redrives for high rev, hi-power Yamahas over the years it turns out that cog belts for Yamaha 4-stroke 120-200HP sled engines are a no-no. Too much vibration at the speeds the PTO turns. But Micro-V belts don't have this problem cuz there're no "teeth".
But one thing too-often overlooked by experimental aircraft redrive designers take is the coupling of prop pulsation coupled to engine harmonics. When the waves combine you get a momentary perfect storm of bearing destruct energy, and folks who think belts absorb those vibes are sadly mistaken. No such luck.
One flaw immediately obvious on these PSRUs from this UK developer is the lack of an idler pulley. Belts change length over lifetime and even during use as they heat up, cool down, stiffen, and loosen. I can't recall seeing any automotive application of these "flat belts" w/o idler pulleys. Idlers damp belt "flap" and thus damp harmonics of the belt itself. More importantly, the idlers used are mounted on pre-loaded, spring arms to maintain the right tension at all times.
Imagine a belt shrinks in flight as it heats up (they tighten as they heat up). Snap goes the crankshaft. On the other hand, image a belt has become loose from stretch. If flight it slips, the cords break down, the belt comes apart and you are looking for a place to land. When it happens, there will little to no warning.
IMHO the use of the Micro-V on the 993 engine listed on the website mentioned above is pretty much bumping up against the upper limits of what may be considered acceptable for the power plant installation, but its getting pretty big, meaning length and weight are now no better than a gearbox or chain drive. But if you want a belt, it should be OK.
With lower HP engines you can get away with smaller width Micro-V belts desirable on engines up to perhaps 100HP tops as overall length and weight is still acceptable. After that, you either need Hy-Vo chain or gears to handle the revs and torque combo, since the belt width just gets silly and there's no point in using belts anymore.
Mohawk Aero is going with a Micro-V belt redrive for their new 80HP YG2 power plant kit for sale now, which is based on the Yamaha Phazer snowmobile engine, a 4-stroke, water-cooled, EFI engine that weighs 88 pounds bare, and about 130lbs with radiator, exhaust, etc. Until they get the new Micro-V belt drive tested they are selling the kit with an adapter that works with just about any gearbox, including Simonini, Rotax C or E, Hirth, AK7 (MAC)/ SPG4...
One last thought: How do you guys feel about belt drive in general? The resale value on an aircraft using belt PSRU may actually be lower than one using gears or HY-Vo chain. Hmmm...
The 993cc engines put out 33-40 stock HP, and going any higher than that on a continuous basis with any tricks (higher RPM, higher CR, better induction/exhaust, etc) is going to hit the limits of the aluminum air-cooled head to shed heat. The Valley Engineering setup (Generac engine) had some higher >takeoff< HP ratings, but couldn't stay above 40HP for long. So, using Micro-V belts for this engine would be well within the limits of 100HP limit you've described, right? If it is a problem and another approach would be better at 40-50 HP, then why are you using belts for your 80HP GY2 PSRU?
The 80 HP GY2 sounds like an interesting unit. How is it likely to price out?
Have your customers been happy with the SPG4 units? I've not heard anything bad about them, and they have a big following, esp in the trike world.
Those are all worthwhile observations and concerns. The Valley Engineering unit used an idler puller, as do most (all?) automotive installations. It seems appropriate, especially in an application where the belt is unlikely to get much proper attention. But if the Ace redrive relies only on the customer keeping things in adjustment and the inherent tension tolerance window of the belt itself, and if this has worked in actual flight for a lot of customers and maybe many thousands of hours (at these HP and torque pulse levels, driving a prop), then that's worth a lot--probably better than an in-depth engineering analysis, and testing like this would need to follow such analysis anyway.
I'd be fine with a >proven< belt drive. It's all about reliability, weight, and cost. Another factor is that a belt drive allows locating the prop hub higher than some other approaches, which is useful in a conventional airplane using a V or (especially) an inline engine (maybe not so important in a rotorcraft or trike). Resale value: Way down the list of importance. Gears and Hy-Vo chains make a lot of sense at higher HP levels, but the simplicity (no lube bath, etc), weight, and "inspectability" of belts offer some attractive benefits in the applications in which they are appropriate.
I'm fine with a properly engineered belt drive. But I have failed to find any test data on the available anodised CNC beauties, so I'll probably make my own. I looked into a toothed belt drive for 50hp. It needed a big belt to get TV out of the usable range. A yamaha would need a much bigger belt as it more powerful and higher revving. A properly designed soft system will pass through resonance somewhere between startup and idle. That means either a clutch, or some belt slip. I'm currently leaning towards a poly V belt as it is lightest, cheapest and fairly simple.
If you can find somebody with a small airboat who runs it a > lot <, (ideally, a commercial operation), that can be a good way to check it out. At the small fuel consumption rates of these small engines, at least it wouldn't cost a huge amount to build hours in a test cell. Make it realistic (throttle changes, gyro loading of the prop hub at rates typical of flight/spins, etc) and instrumented (belt and bearing temps, etc) and you could gain confidence in it pretty quickly.
Years and years ago I worked for Cascade Ultralights. They were using Honda 250cc 2 stroke engines and a belt redrive very similar to the Ace units. The tube carrying the prop pulley kept cracking. First we tried heat treatment, then ran a full length bolt essentially making the tube solid, finally went to round bar stock heat treated and stopped the cracking. And this was only 20 hp and a wood prop that weighed 3 lb.! If it were so easy to build a belt redrive, why would Rotax use a gear drive?
Not to say anything against Ace but units sold isn't units flying. Not quite so long ago I was going to put a Mazda rotary engine in an aircraft. The shop I had build the engine also had sold hundreds and had a great rep for their automotive work, too, but very few, if any, of their engines ever flew. Most went into shop queens that eventually went on to estate sales.
Both these comments are, like the kids say, just sayin'.
I know many of our redrives that have done well over 250 hours. One engine that has done over 400 hours here with the same belt. Only adjustments necessary
I know many of our redrives that have done well over 250 hours. One engine that has done over 400 hours with the same belt. Only adjustments necessary.
Don`t know why you`re fretting about belt drives. They`re proven before we started making reliable redrives.
Maybe I should hve given my contact details:
------- > No belt slap on ours as the pulleys are very close together, so idler pulley is a waste of time. 100`s of our redrives out there, no complaints !
John, I noticed the idle snubber pulley on some systems made by others. In some applications these pulleys are intended to improve the contact area on a smaller pulley, not so much to maintain a prescribed belt tension. Also, if they press the belt "in, " (which they must do to improve grip area on a small pilley), then they also flex the belt opposite to it's normal direction, which will serve to decrease belt life to some extent.
On the Ace units, how do you deal with the resonance issues that would be expected (typically at low RPMs)?
-------- > Our redrives have the correct grade steel shaft for the job and precision machined. Resistant to breaking, cracking etc.
In over 10 years, none of our shafts have had damage.
They also fit tractor and pusher.
I`d say they`re well designed redrives for high pulsing V-Twins.
-------- > We have had nobody telling us about vibration issues with our redrives.
I do know that most people tend to have a high tick over with the V-Twins, as they do vibrate a lot at low revs, even without any redrive on. The redrive does damp out some of the low rpm vibrations ans pulses. With the Poly V-belt the system allows the belts to slip slightly. That`s the beauty if Poly V-belts.
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