Re-drives Belt or Chain ?

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rv7charlie

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Both the ancient Ross drives and the more recent Real World Solutions drives were/are planetaries. The gear assemblies themselves are typically near bulletproof, but you still have to couple them to the engine (with appropriate torsional resonance protection) and to the prop. Lots of off the shelf ratios; some will reverse rotation and some turn the same as input. But...the gearsets typically come from automotive or (more commonly) heavy duty diesel truck automatic transmissions. They're going to be too heavy for an ultralite. The Ross & RWS drives weigh around 45 lbs. You might find something out of a Euro or Asian micro car, but you'd be on your own designing a case. Alignment is pretty critical.

The Ross drives had issues on some engines (no thrust bearing for the input shaft, causing damage to the engine). The RWS drives are pretty solid when operated within torque/HP limits. RWS no longer produces them because the designer/owner finally retired. However, at least one group is trying to bring them back with some (unnecessary, possibly detrimental) mods. And the plans/parts list is now open source, if you want to go into production.
 

PMD

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What "disqualifies" planetaries is the LACK of any. Years back, (IIRC) there was a unit offered. I guess lack of demand caused it to go out of business (like so many other aviation ventures). Again, IIRC, some, or most GA engines with reduction used planetary units.
I mean if you have to reduce RPMs, it seems there are 3 "more simple" options: belt redrive (cog or Vee), chain redrive (what REALLY started this thread), and ADAPTED existing gear box redrive (Rotax, etc.)
There are bazillions of planetary gearsets, found in every slushbox driving down the road into the junkyard. Here is one company with a long history of same: Alternative Power For Experimental Aircraft
One of the POTENTIAL advantages of a planetary gear drive would be putting the pinion (sun) gear directly onto the crank, but that precludes any sort of vibration damper (quite important), so you need a coupling of some sort (see Ross using cluched center - as do others).
 

rv7charlie

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The drive on the rotary in that article is a RWS; not a Ross. The exploded view and the one on the Sube look to be Ross.
 

Lendo

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The only real problem with Planetery PSRUs is the Planets need some clearance to self center which results in unnecessary Lash (free-play) of the prop. No so with the Internal Spur gear in ring gear arrangement of Powersports. A Mechanical Engineer told me chain gears are OK on lower HP engines, but must be lubricated well. Which looks to be the case with the Kohler PSRU, which looks to have a quite hefty Chain as well.
George
 

Lendo

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Some interesting articles.
kitplanes.com/engine-theory-8/
kitplanes.com/wind-tunnel-55/
George
 

rv7charlie

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The only real problem with Planetery PSRUs is the Planets need some clearance to self center which results in unnecessary Lash (free-play) of the prop.
This is a difference, but not necessarily a problem. It can, in fact, be an advantage. The last version of the RWS drive before the designer's retirement was designed to be run on a 2 rotor with an 8 lb flywheel, and no separate harmonic resonance damping device at all, as long as relatively a light weight (wood or composite) prop is on the plane. The designer's RV4 has been running this system for several hundred hours.

The Powersport design forces resonance above typical max operating frequency by being very stiff (translation: heavy) with custom gears (translation: expensive), while the planetary based systems are set up for resonance below minimum operating frequency.
 

Hawk81A

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Very interesting. Again, I had seen the Kohler thing some time back. I'm not a fan of the unsupported engine shaft. I'll throw another one out there for "thinking outside the box" : Possibly using a 1:2 lower unit gearbox from a larger outboard motor. Thoughts?
Yes, the engine would have to be mounted "sideways". Possibly using a V-twin VERTICAL shaft from a riding mower?
 

EzyBuildWing

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If I remember correctly Ed Schram's Rotorway Exec helicopter had multiple V-belts and then a final duplex chain-drive reduction.....?
Maybe it still does.....
 

ToddK

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Greg at Mohawk Aero has built at least one, maybe more Yamaha PSRUs with a HyVo chain.
 

b7gwap

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We’ve kind of bounced around it a bit, but for me chain drive is out due it its failure mode of becoming a steel scourge/whip in an aluminum china shop. Motorcycles protect the rider’s leg and the transmission output with heavy guard plates.

cog belt failing could be similarly destructive.

PSRUs are tricky business. Getting one to transmit power efficiently, at a usable weight, and be strong enough to withstand all forces (there are more than meets the eye) with acceptable factor of safety requires some technical chops I don’t have.

While we’re spitballing though, does a hybrid internal combustion/electric prop drive count as a PSRU? Works for locomotives, but that’s a slightly heavier duty application… :)
 

challenger_II

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Generally, when a cog belt fails, the teeth shear off: the belt doesn't part.
All of the notions thus far proposed have their own set of mousetraps. A considerable amount of
what One uses depends on the amount of power to be transmitted. My personal favorite, for 20-60 input HP, is the Gates HTD cogbelt. It has a good operational history, as long as you keep up with the belt inspection, and replacement.
 

Swampyankee

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Planetary is the way to go.
The ALF502 I was test engineer on used a planetary gear set with 17,500 rpm input and 7600 rpm output, carrying about 8,000 hp. P&WA uses them on their slightly larger geared turbofan (one wonders how many ex-AVCO people worked on that...)

On the other hand, I would be surprised if anyone without a very well-equipped machine shop would have a chance of making one. Making high-power gear sets is as specialty operation.
 

Aviacs

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Seems like Lycoming tended to use planetary gearsets in their geared engines; Continental used simple straight tooth spur gear pair.
What did the gearset in the little Lycoming GO-145's look like?
Nose cone suggests planetary. Was there a quill shaft between the crank and the gear input?
 

Vigilant1

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Is there a practical way to adjust gear lash on a planetary drive? If we are designing a "stiff" system (for TV purposes), is there a way to keep it "stiff" as the gears wear?
 
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