Torsional Vibration on a long shaft?

[RSD]

Oh so there is a limit...

Yep apparently. There are some 12 rotor engines out there in a weird V formation with four rotors on each of three shafts.

On two rotor engines the eccentrics are at 180 degree from each other and they just alternate. On more than two, is there any logic to the firing order, and what is customarily used in each of three, four, five, and six rotors?

I don't know the answer to this one, but I don't believe that anyone has built a five rotor - seems to be one, two, three, four, six, twelve.

Next, I am curious what the max continuous hp (cooling limited) are for aluminum housing engines. And is it different between side ported and peripheral ported systems?

Billski

I have heard a figure of 94 SHP for that which came from Tracy Crook I think, but I don't know whether that was for an all aluminium engine and what the porting was.

 

[BBerson]

Looking for animation, all that I saw was of the rotor running. There is a fixed gear and a gear in the rotor, and that keeps the rotor in time. The eccentric shaft runs down the middle with a big journal for each rotor. The rotor transmits power to the eccentric... Is that what you were talking about?

looks pretty good. The flywheel attachment to the eccentric shaft is rigid. The key is to align a counterweight to the correct position, that huge nut with 360 ft-lb of torque on it locks flywheel and hub to the eccentric shaft.

For three and four rotors, folks have talked about how they are more than one piece. I am unfamiliar...

Billski

The animation is on the left side of my wiki link.
In your video they have a one piece eccentric shaft (with two eccentrics).
So for a six rotor, I assume a custom one piece eccentric shaft (with six eccentrics) would be made?
Or some sort of press fit, as Charlie said.
Fitting three separate complete engines together with couplings would obviously be extra heavy.

 

[wsimpso1]

I have heard a figure of 94 SHP for that which came from Tracy Crook I think, but I don't know whether that was for an all aluminium engine and what the porting was.

Tracy Crook's info is 13B production with cast iron end plates and intermediate plates and side ports, intended to meet emisdions rules and give wide torque bands.

 

[RSD]

The animation is on the left side of my wiki link.
In your video they have a one piece eccentric shaft (with two eccentrics).
So for a six rotor, I assume a custom one piece eccentric shaft (with six eccentrics) would be made?
Or some sort of press fit, as Charlie said.
Fitting three separate complete engines together with couplings would obviously be extra heavy.

One piece. I'm fortunate that I have plenty of room for a long straight engine, a six rotor in all alluminium is a similar weight and length to the Allison turbine that it is replacing.

 

[RSD]

Tracy Crook's info is 13B production with cast iron end plates and intermediate plates and side ports, intended to meet emisdions rules and give wide torque bands.

Ah OK - a 13B with the aftermarket alluminium end and intermediate plates is considered to cool considerably better but I don't know precisely how much by.

 

[rv7charlie]

Tracy Crook's info is 13B production with cast iron end plates and intermediate plates and side ports, intended to meet emisdions rules and give wide torque bands.

I don't recall Tracy being being quite that specific (94HP), but his ~90-100 HP number (using 'stock' Mazda housings) came purely from worries about keeping the engine cool enough to avoid either short or long term damage. Nothing related to road use/emissions/torque bands. Racers groove the rotor housings to help turbulate water flow & sweep nucleate boiling off the water passage surfaces, and these are 50-60% duty cycle.

RSD, do you have hard info on aluminum cooling better, or is this interweb lore? I wouldn't bet on an all-aluminum engine cooling any better without data. The 'stock' engines have been known to have issues at higher outputs in road racing with the aluminum rotor housings getting 'soft' and shrinking under the through-bolt loads, causing the housing stack to get loose. Other than Mazda themselves (using proprietary housings), I haven't heard of anyone using all-aluminum versions in anything other than drag racing. The current time-to-climb record holder RV-Rocket engine was all-aluminum, but it was really just a drag racer, running methyl alcohol and <deleted; invalid info was here>.

Charlie

 

[rv7charlie]

I'm on the road for a few days. I'll post some pics when I get home showing the original coupler, and if I can find them, the updated rigid coupler.
The original uses 4 ea 'rubber'~2" dia discs (donuts) on ~6" radius. They seem to start getting tired at around 500 hrs on the 13B/Renesis.

The rigid switched from an auto trans flex plate to an aluminum racing flywheel (+~8 lbs), with roughly the same size input shaft.

Same 6 pinion drive on 20B, but the P-port 20B guy had to beef up a lot of the hardware 'around' the planetary gearset. Never had any issues with the gearset itself, though.

My layman's understanding is that (on the 13B rigid) lash handles keeping resonance below idle; iirc, it will start to 'rattle' below ~1200 engine rpm. Of course, there's minimal impulse strength at that rpm/prop load. Remember, torque never goes negative with 2 or more rotors, so the gears never see reversed torque at normal operating rpms.
Edit: RE, quill shaft action: IIRC, at one point during discussion on the Flyrotary list, Tracy ok'd modifying the original box to using the original input shaft direct coupled to our choice of an aluminum or lightweight steel racing flywheel. So quill shaft style decoupling seems unlikely.

Quoting myself...
I'll try to attach an image of the original RWS coupler/damper plate, and the page from the install manual showing detail of one damper 'donuts'. The mounting radius is closer to 4" than 6".

RE: quill shaft operation, There's at least one turbo'd 13B (well over 200 HP) flying in an RV-6 that is using a lightweight steel racing flywheel (in place of the auto-trans flex plate), and I *think* the spline coupler shown in the pic is attached directly to the steel flywheel. I'll update if I discover that I'm in error. Same input shaft to the gearbox. The input shaft is around 1" dia and no more than 3" from the damper plate splines to the sun gear.

 

[mm4440]

I don't recall Tracy being being quite that specific (94HP), but his ~90-100 HP number (using 'stock' Mazda housings) came purely from worries about keeping the engine cool enough to avoid either short or long term damage. Nothing related to road use/emissions/torque bands. Racers groove the rotor housings to help turbulate water flow & sweep nucleate boiling off the water passage surfaces, and these are 50-60% duty cycle.

RSD, do you have hard info on aluminum cooling better, or is this interweb lore? I wouldn't bet on an all-aluminum engine cooling any better without data. The 'stock' engines have been known to have issues at higher outputs in road racing with the aluminum rotor housings getting 'soft' and shrinking under the through-bolt loads, causing the housing stack to get loose. Other than Mazda themselves (using proprietary housings), I haven't heard of anyone using all-aluminum versions in anything other than drag racing. The current time-to-climb record holder RV-Rocket engine was all-aluminum, but it was really just a drag racer, running methyl alcohol and had a 'total loss' cooling system.

Charlie

Hi, Two truck radiators in series under engine, not total loss cooling.

 

[rv7charlie]

Hi, Two truck radiators in series under engine, not total loss cooling.

OOPS; you're right. I'll edit my post. Don't know what I was thinking about, but it was obviously the wrong plane.
Thanks for the correction!

Charlie