My 13B engine configuration (tentative)

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rv7charlie

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I mean, I think I am? But mail lists seems to have died. I am on a FB group that never seems to have many posts.
As a test, for you, the most recent thread on the flyrotary list has been about 'exhaust broken again', and last post was on 6-16-21. If you're not getting the emails, I'll try to contact the list owner for you if you want. PM me the email address you registered with.

Charlie
 

dwalker

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As a test, for you, the most recent thread on the flyrotary list has been about 'exhaust broken again', and last post was on 6-16-21. If you're not getting the emails, I'll try to contact the list owner for you if you want. PM me the email address you registered with.

Charlie

Hmm... I thought I was on this list but apparently it is another list I am on. I'll sign up on this one.
 

Cardmarc

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It would be a step in the right direction for sure.
As Mistral was a Swiss company, perhaps the parts were made there or anywhere in Europe, or elsewhere. Some Mistral installations exist in USA even now and are flying.
BTW, the rotary engine list is alive and well. However, Paul Lamar’s rotary engine forum died when he did. The other list soldiers onward.
 

rv7charlie

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Thanks Lendo; 1st time I've seen good images of the Mistral internals. What's visible looks really nice (and really stout).
 

Lendo

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Thanks rv7charlie. they built the housing out of Magnesium for lightness and strength, some are concerned about that as it's the same metal used in Sparklers (highly combustible) but probably has a fire resistant coating on it.

I remember counting the Ring Gear teeth and Sun Gear teeth but can't exactly remember the Reduction Ratio, got it in my notes somewhere.
For those unfamiliar it's (Ring gear / Sun Gear +1) and like all Planetery gearboxes the Planets float a little which is an allowance for heat expansion, which results in some lash, but also allows the planets to centre themselves compared to the more stiff Powersport internal Gear system.

I'm impressed with the size of the system and how well it's designed and manufactured, compared to Automotive Planetary systems.
George
 

Cardmarc

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Is that the muffler that failed on Mistral’s test Piper Arrow and caused a forced crash landing?
 

Lendo

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There was one before this, I remember seeing it but can't find a photo. This looks far too robust to fail -if a little heavy. I will keep looking for the other photo.
George
 

Cardmarc

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Found it, They had cold air fed into the exhaust outlet, how that's configured internally I don't know, it, may have been too restrictive.
Hope that helps.
George
From my understanding, the Mistral Piper Arrow muffler collapsed internally, and restricted the engine output badly. Common failure mode, especially in a high temp, high frequency rotary exhaust. Stout and heavy appears best. Look at the RX7 mufflers! The rotary list has been experimenting with several muffler designs for years. The turbo versions of the 13B (13B rew tt) have a divider in the exhaust port; perhaps that allows the turbine wheel to last. But that engine also uses all Inconel hardware (all nuts and studs) and an Inconel manifold, so it’s a real consideration.
 

rv7charlie

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I believe the exhaust splitter is actually in the non-turbo 13B engines. It's there to break up the intense pressure waves caused by the opening of the peripheral exhaust port, to reduce noise and to modify/reduce the destructive pressure pulses on the exhaust system. The turbo engines want all the exhaust energy, unrestricted, to spin the turbo, and the turbo itself serves to break up the destructive pressure pulses & protect the downstream exhaust parts.

Even with the splitter in the exhaust port, there's still an incredible level of energy/pressure pulses in the 13B exhaust. The 'side' exhaust ports in the later Renesis engines reduce some of the destructive pulse levels by both the 90 degree turn out of the block, but even more significantly, the more gradual port opening of the side port, compared to the brutal near-instant opening of the peripheral exhaust in the 13B.
 

dwalker

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From my understanding, the Mistral Piper Arrow muffler collapsed internally, and restricted the engine output badly. Common failure mode, especially in a high temp, high frequency rotary exhaust. Stout and heavy appears best. Look at the RX7 mufflers! The rotary list has been experimenting with several muffler designs for years. The turbo versions of the 13B (13B rew tt) have a divider in the exhaust port; perhaps that allows the turbine wheel to last. But that engine also uses all Inconel hardware (all nuts and studs) and an Inconel manifold, so it’s a real consideration.
All 13b peripheral port exhaust engines use inconel sleeves. RV7Charlie is accurate that the non-turbo engines had the divider. All exhaust manifolds, turbo or not, were simple cast iron. The TT manifolds crack with regularity, and are stupid heavy, thus no one uses them for anything.
The hardware however, IS Inconel- studs and nuts- and should never be replaced with anything else.

Exhaust noise is always an issue, and the best method of dealing with it is to turbocharge the engine ;)

If not turbocharging the engine in a tractor configuration you are going to be pretty well stuck using an inconel manifold and muffler with turndowns. Everyone will hate you on taxi and take-off but once in the air it should sound pretty good. The problem with a short exhaust on a NA rotary is one of exhaust velocity and, as has been proven over and over, the more you treat it like a port-tuned two-stroke the better your results will be. If I were to go with an NA rotary in an aircraft I would construct an expansion chamber exhaust from inconel and 321SS using all the space I could, potentially using a "long nose" engine mount to give more room for the exhaust to wind around. Pictured is the exhaust from one of the Renesis race cars. Take note of the expansion chamber- not pictured is the back half which was the rear tapered cove back down to 3". With this exhaust the Renny made more power overall and more power and torque throughout the RPM band.
 

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thjakits

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Cardmac, From just looking at all the Photos, the Mistral PSRU looked bulletproof , if someone could just find out who did the Machining of components, it would be a good start, providing Mistral is no longer in business. Apart from that if someone has one to be copied, it originated in Europe somewhere. Perhaps parts were made in the US for the Certification process.
George

Switzerland...

Likely - machining was done locally - after all the Swiss have a reputation!

 

Lendo

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OK I counted the teeth for everyone - Ring Gear 93 teeth with Sun Gear 50 teeth = 1.86+1 - 2.86:1 Ratio. If the engine was running at preferred Cruise RPM of 6000 rpm=6,000/ 2.86= 2098 prop rpm and at 6,500 engine rpm = 2,273prop rpm. This pretty slow so maybe they were using higher Engine rpm, for more power - don't know. I would prefer a 2.5 to 2.7 range.
I agree maybe made by the Swiss. Anyone in Switzerland like to comment? I remember it was a development Project out of some University in Europe, maybe Switzerland..
 

Lendo

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OK I miscounted, it's 93/51= 2.82:1 (a bit better) with 6,000rpm =2127prop rpm and 6,500 = 2304 prop rpm, still a low.
The Planets are 93-51=42/2 =21 teeth each planet gear, good sized planets. That's how I picked-up my error as one can't have 21.5 teeth on each planet gear.

On teeth gear, did you know that each pair of engaged teeth must have a supporting pair of teeth and Tooth Tip Relief must not be so much in reducing that support. I don't know about you but I found that most interesting, as part of the Science of Gear Cutting. Naturally Tip Relief reduces the possibility of Teeth clashing.
Hope that helps budding gear designers, I'm no expert myself.
George
 

rv7charlie

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Yes, there was one up in the NW corner of the US. Coot amphib. He made is own belt drive, & used nitrous for an extra kick when getting off the water. Haven' t heard anything about it in years, and his website info seems to be gone now. You might find something on the Wayback Machine, searching through old iterations of the old rotary list run by Paul Lamar.

Wait; found a really old snapshot on the wayback machine. Built by Ken Welter; here you go:
https://web.archive.org/web/20030219024225/http://homepage.mac.com/rotarycoot/
You can play with later dates & see if there's any more info, but it seems to be dead in every snapshot I tried after ~2010.
 
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