How many people are interested in a GOOD safe psru for the rotary?

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Bobby Hughes

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While it is true that rubber spring elements waste a fraction of the spring energy stored and released on each cycle, they can be designed to last thousands of hours with decent airflow over them. Evidence is engine mounts on things like, cars, trucks, and airplanes and giubos used as universal joints in many automotive powertrains. These gadgets are doing the same thing - deflecting to new equilibrium position under mean torque and then vibrating while isolating the engine vibration.

Rubber springs are poor thermal conductors, which can make the task vexing. One approach that greatly extends part life is simply to use elastomers compounded to stand higher temperatures while maintaining modest temperatures with decent airflow over them.

Billski
I found that better heat shielding between the PSRU and exhaust pipe improved damper life. The last set I changed had developed only minimal flat spots. Prior to having the batch manufactured I would rotate the dampers 180 degrees opposite the flat spots at annual. This seems to allow the existing flat spots to return back to a more normal condition but likely had some permanent compression.

Bobby
 

Pale Bear

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OK, .. using rubber, or springs in a damper design. Fluid, or viscous dampers?, instead .. surely someone has also looked into that, as well, right? I suppose that the life cycle of this kind of thing would be marginal?
 

dwalker

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Billsrv4 is there any movement forward on your PSRU? I am pretty interested in it after watching the video and seeing how it is packaged.
 

Billrsv4

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dWalker, Due to the covid situation I lost my 9-5 job. I am still working on the reduction gear. 1 portion remains in design. I will continue but very slowly.
Wish I could say more, but there is only a small chance to make money on it. I was hoping to provide for my own aircraft and defray my costs with sales. had to stop everything to keep the lights on.
Bill
 

dwalker

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dWalker, Due to the covid situation I lost my 9-5 job. I am still working on the reduction gear. 1 portion remains in design. I will continue but very slowly.
Wish I could say more, but there is only a small chance to make money on it. I was hoping to provide for my own aircraft and defray my costs with sales. had to stop everything to keep the lights on.
Bill
Completely understand, looking forward to seeing more as things hopefully improve.
 

Lendo

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dwalker, I understand the PSRU design is very good, but what Bill has also done is develop a fail safe, Peripheral Port (PP). Don't know the exact design, but what I do know is it's his IP and I can't discuss the little I do know. Most PP's are prone to leaking water (coolant) into the Combustion Chamber - not a good thing as well you might imagine. I had some ideas but his is much better.
George
 

dwalker

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dwalker, I understand the PSRU design is very good, but what Bill has also done is develop a fail safe, Peripheral Port (PP). Don't know the exact design, but what I do know is it's his IP and I can't discuss the little I do know. Most PP's are prone to leaking water (coolant) into the Combustion Chamber - not a good thing as well you might imagine. I had some ideas but his is much better.
George
I am pretty set against peripheral ports for my application. I do have, and plan on using, a set of semi-peripheral port housings. These are done in such a way that they are unlikely to leak into the rotor housing, and the method of attaching to the intake manifold itself is o-ringed to prevent coolant from being sucked into the intake or worse, the coolant becoming pressurized under boost.
 

rv7charlie

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No need to bother him; it's a Real World Solutions drive, designed/mfgrd by Tracy Crook.

BTW, two things immediately jump out at me in that image. First is, wondering how much pitch-up range is there with the backseat stick in place and that big box in the back seat. The other is the pilot's shoulder belt attach point. Safety wonks say the over-the-shoulder, to the floor mounting point will result in compressed vertebrae in an accident.
 
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Lendo

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dwalker. I guess your concern with the PP is low rpm rough idle. I believe Powersport solved that with Butterfly in Port housing, close to the combustion chamber.
I'm unsure as to the exact nature of Bill's design, but he feels he has that sorted, also port sizing is important for our low RPM power requirements, 6,000 to 6,500 approx. The correct PP size is excellent of Volumetric Efficiency and a smaller port does that with higher velocity and I'm guessing a butterfly in the port controls the lower end flow and keeps things running smoothly at the lowest of RPM.
Just my take on it all
George
 

dwalker

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dwalker. I guess your concern with the PP is low rpm rough idle. I believe Powersport solved that with Butterfly in Port housing, close to the combustion chamber.
I'm unsure as to the exact nature of Bill's design, but he feels he has that sorted, also port sizing is important for our low RPM power requirements, 6,000 to 6,500 approx. The correct PP size is excellent of Volumetric Efficiency and a smaller port does that with higher velocity and I'm guessing a butterfly in the port controls the lower end flow and keeps things running smoothly at the lowest of RPM.
Just my take on it all
George
My concern with any type of P-Port is they tend to leak. Even if they are steel and welded in place to the steel liner, over time the weld can crack. The aluminum press fit, stepped, and sealed full P-port setups have gotten very reliable these days. Even so, I am strongly considering not using the semi-p port housings I have and instead using standard Series 6-8 rotor housings.
If I were going NA, I would strongly consider going P-Port, but since I am going to use boost I feel like the semi-P will be just about right to give good power in the 6000rpm range with good economy and the ability to throttle back and cruise with good power as well. I could be wrong, almost all of my P-Port experience is in engines turning 8-9K rpm continuous, so my frame of reference may be skewed.
 

Lendo

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dwalker, I would suggest you speak to Billrsv4, I'm sure he would agree with you on PP leaks, however as an Engineer, I'm sure he has that all sorted, maybe a private discussion seeing your degree of knowledge and experience. My thought are why put in a Turbo considering weight and additional complexity. If the Turbo was for attitude compensation power- well that's another thing.
Just being the Devils advocate here.
I wish we had a lot more builders heading in the same direction.
George
 

Billrsv4

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Knowing the origin of this scheme, I am definitely interested. I am curious as to the bearings in the prop shaft.

Billski
Billski, The bearings I selected for the new Psru are Timken Tapered roller bearings 85mm, quite stout. don't know if I will attempt to sell anymore. Vans Airforce became quite hostile to alternate engines. I don't need the hassle. I am sorry that those folks expecting this won't get the chance.
Bill Jepson
 

Martin W

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.

Building a PSRU is not all that difficult
The main difficulty is isolating the power impulses from the engine
These impulses are a vibration and are destructive to gears.

That is why turbo-props are so successful ... turbines run super smooth and their planetary gear-sets are trouble free.

Now I make my point .... is an automatic transmission available for the Mazda rotary ?? ... if so use the torque converter between the engine and gearset which will produce a very smooth power transfer . Heavy of course , but other damper-couplers add weight too.

General motors did it that way in their 1970's era Cadillac Eldorado and Olds Tornado .... not only that ... the GM motorhome used that drive system with great results ... hundreds of thousands of trouble free miles.

Not a very good picture but red circle indicates where torque converter sits between engine and gear-set.

gm chain drive.JPG
 

wsimpso1

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OK, .. using rubber, or springs in a damper design. Fluid, or viscous dampers?, instead .. surely someone has also looked into that, as well, right? I suppose that the life cycle of this kind of thing would be marginal?
The really big deal is architectural. Get the the first torsional mode at least half an octave below firing frequency at your minimum engine speed and it will isolate well with small vibration everywhere else. A prop speed of 1000 rpm is around 1800 engine rpm. A four-banger at 1800 rpm idle works out to a vibrational swing of about 0.5 degrees each way around mean deflection. Not much... Take it up to big torque and 4500 rpm in flight, and the swing is more like 0.2 degrees. Lots of rubber elements last a long time time at those levels. So do springs, etc.

Viscous dampers? Bad idea. They only really work well at large deflections. You get large deflections at or near resonance. If you are operating near resonance, you already have BIG vibration problems, and then converts power to heat instead of propulsion, adding to your cooling drag.

In vibe control you have two main options:
  • Get stiffnesses high enough to put operation safely above max firing frequency - 2-1/4 octaves above is generally considered enough - and build to stand the power pulses through the system. This is called a "stiff system", and was used by Ev Hatch in PowerSport;
  • Get a soft element between the engine and rest of the powerteam to put operation safely below min firing frequency - 1-1/4 octaves below is generally considered enough - make the system lash free until after the isolator, and peak torques are only moderately higher than mean torque. This is called a "soft system" and is WIDELY used in powerteams of all sorts from chain saws to power generation turbines to container ships.
Everything else is much harder to make work, heavier, and adds to your cooling load. Ugh.

Billski
 

rv7charlie

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Perhaps it would also be helpful for us non-engineers to put example frequency numbers to the principles.

For instance, with a 'soft' system, if we idle a 4 cyl 4 stroke engine at 1500 rpm, would lowest fundamental be 3000/minute / 60 = 50 Hz? Does that mean resonance should be somewhere below ~20 Hz (>1 octave below)?

For a 'stiff' system on the same engine, if it runs at 5000+ to 8000+ with the Yamaha sled engines, would the fundamental be somewhere above:
16000/minute / 60 = 266 Hz? Do we also need to consider 3rd order, 4th order, etc frequencies? If only the fundamental is of concern does the math show that resonance should be 266 * 2 * 2 = somewhere above 1100 Hz(>2 octaves above)?

Now, which method is harder/heavier/more expensive to achieve?

If one or more cylinders' output fails while in flight, does either method offer any better protection, or would it even matter?
 
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