rv7charlie
Well-Known Member
Andrew makes some good points. Some of the other posts seem to be from people who've heard from other people who heard from their wife's brother-in-law's uncle who heard from someone that rotaries are {fill in your choice here}. 
I haven't flown my rotary, but the Renesis is on the motor mount and could fly within a few months, if I could just get 'life' out of the way. I've been around rotary powered a/c and their builders for a couple of decades now.
Conventional wisdom: Rotaries are almost impossibly tough on reduction drives.
Fact: Tracy Crook (founder of Real World Solutions) now has hundreds of hours on a Renesis in his RV-4 (wood prop) using his RWS 2.85-1 drive, with no torsional isolation whatsoever. Now, he will tell you that it's not possible to do this in every scenario, but it certainly blows that myth out of the water.
Cooling: It's an internal combustion engine. Its conversion efficiency of fuel to power is roughly the same as any other IC engine. It's got to be cooled, just like a Subaru, or a Continental, or a Lycoming. Cooling a Lyc should be a piece of cake, especially on a cookie cutter a/c like an RV, right? Search VAF for 'oil cooling' or 'cylinder head temp'. Even an RV/Lyc can be done wrong, and very often is. If someone starts out knowing nothing, and has no template to work from (as is available with an RV/Lyc), then odds of success are even poorer.
3 rotor all-aluminum engine: I'm aware of exactly zero examples that have actually flown. I'm aware of exactly one 2 rotor all-aluminum example that's actually flown (though there may be others). That one likely has less than 50 hrs on it (used to set a time to climb record), before being retired. So impossible to even speculate on odds of success. And honestly, if it *does* work, your market size could likely be estimated using just your own personal appendages, since the price of an aircraft-prepped turbo'd all-aluminum 3 rotor with reduction drive and cooling system will be very close to (possibly higher than) the price of a Lyc/Conti with the same HP.
Uncertainty on one or two turbos: What's the logic for twin turbos, on a rotary in an a/c? And FWIW, assuming that the custom aluminum end housings can survive continuous high output, a 3 rotor engine (if P-ported) will make ~300HP without turbos. Cooling it will be another matter entirely, turbo or not. (Aluminum end housings will not make a significant difference in the ability to cool the engine.)
Auto-PSRUs: I spoke with them at SNF several years ago. Tread very carefully. Find a real mechanical engineer with at least a couple of decades of power transmission experience, and pay him several thousand dollars to evaluate it, before investing in one. Here's one 'tell' on their design: their torsional decoupler (clutch) they use approaches the weight of an entire RWS reduction drive, *including* its decoupler mechanism. Based on my conversation with them several years ago, they knew literally less than nothing about rotaries. Several things their rep tried to tell me about them was just...wrong. At that time, all they had was a dummy engine with their drive bolted over the end of the engine; it had never even run on a rotary. Unless things have changed radically in the past few years, I wouldn't consider flying with one. While reduction drives are not *easy*, they aren't rocket surgery either, for a qualified engineer. The RWS design, probably the most-flown reduction system ever, is effectively open source now; anyone can get a copy of the drawings. Just something to consider....
Noise: With straight pipes, the 13Bs really are painfully loud, due primarily to the high frequency harmonics caused by the exhaust port snapping open (on the 13B), very much like a 2-stroke engine's sound. But I'm aware of at least three flying examples that are no louder than a Lyc (though the *noise spectrum* might make them sound louder to some ears). One example (13B), in an SQ2000 pusher, used the stock cast iron exhaust manifold (~12 lbs) coupled to a short stack pointed aft through the prop. It sounded eerily similar to a small block V-8 with straight pipes. In another example (Renesis, still flying), you can barely hear the engine at all; virtually all noise is from the prop, very similar to a turbine. The entire exhaust system on that plane, from engine block to tailpipe, is around 20 lbs. A properly engineered muffler system could be significantly lighter. Perhaps Billrsv4 will chime in, or you can search here for his posts to see an example.
Strongly advise signing up for the Flyrotary email list; that's where you will find guys that are actually flying the engine.
Charlie
I haven't flown my rotary, but the Renesis is on the motor mount and could fly within a few months, if I could just get 'life' out of the way. I've been around rotary powered a/c and their builders for a couple of decades now.Conventional wisdom: Rotaries are almost impossibly tough on reduction drives.
Fact: Tracy Crook (founder of Real World Solutions) now has hundreds of hours on a Renesis in his RV-4 (wood prop) using his RWS 2.85-1 drive, with no torsional isolation whatsoever. Now, he will tell you that it's not possible to do this in every scenario, but it certainly blows that myth out of the water.
Cooling: It's an internal combustion engine. Its conversion efficiency of fuel to power is roughly the same as any other IC engine. It's got to be cooled, just like a Subaru, or a Continental, or a Lycoming. Cooling a Lyc should be a piece of cake, especially on a cookie cutter a/c like an RV, right? Search VAF for 'oil cooling' or 'cylinder head temp'. Even an RV/Lyc can be done wrong, and very often is. If someone starts out knowing nothing, and has no template to work from (as is available with an RV/Lyc), then odds of success are even poorer.
3 rotor all-aluminum engine: I'm aware of exactly zero examples that have actually flown. I'm aware of exactly one 2 rotor all-aluminum example that's actually flown (though there may be others). That one likely has less than 50 hrs on it (used to set a time to climb record), before being retired. So impossible to even speculate on odds of success. And honestly, if it *does* work, your market size could likely be estimated using just your own personal appendages, since the price of an aircraft-prepped turbo'd all-aluminum 3 rotor with reduction drive and cooling system will be very close to (possibly higher than) the price of a Lyc/Conti with the same HP.
Uncertainty on one or two turbos: What's the logic for twin turbos, on a rotary in an a/c? And FWIW, assuming that the custom aluminum end housings can survive continuous high output, a 3 rotor engine (if P-ported) will make ~300HP without turbos. Cooling it will be another matter entirely, turbo or not. (Aluminum end housings will not make a significant difference in the ability to cool the engine.)
Auto-PSRUs: I spoke with them at SNF several years ago. Tread very carefully. Find a real mechanical engineer with at least a couple of decades of power transmission experience, and pay him several thousand dollars to evaluate it, before investing in one. Here's one 'tell' on their design: their torsional decoupler (clutch) they use approaches the weight of an entire RWS reduction drive, *including* its decoupler mechanism. Based on my conversation with them several years ago, they knew literally less than nothing about rotaries. Several things their rep tried to tell me about them was just...wrong. At that time, all they had was a dummy engine with their drive bolted over the end of the engine; it had never even run on a rotary. Unless things have changed radically in the past few years, I wouldn't consider flying with one. While reduction drives are not *easy*, they aren't rocket surgery either, for a qualified engineer. The RWS design, probably the most-flown reduction system ever, is effectively open source now; anyone can get a copy of the drawings. Just something to consider....
Noise: With straight pipes, the 13Bs really are painfully loud, due primarily to the high frequency harmonics caused by the exhaust port snapping open (on the 13B), very much like a 2-stroke engine's sound. But I'm aware of at least three flying examples that are no louder than a Lyc (though the *noise spectrum* might make them sound louder to some ears). One example (13B), in an SQ2000 pusher, used the stock cast iron exhaust manifold (~12 lbs) coupled to a short stack pointed aft through the prop. It sounded eerily similar to a small block V-8 with straight pipes. In another example (Renesis, still flying), you can barely hear the engine at all; virtually all noise is from the prop, very similar to a turbine. The entire exhaust system on that plane, from engine block to tailpipe, is around 20 lbs. A properly engineered muffler system could be significantly lighter. Perhaps Billrsv4 will chime in, or you can search here for his posts to see an example.
Strongly advise signing up for the Flyrotary email list; that's where you will find guys that are actually flying the engine.
Charlie
