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  • Overheating motorglider

    From Doug Bailey@21:1/5 to All on Sun Mar 5 02:22:34 2023
    I had to work all week so my only chance to take in the Reno show was Saturday. I left at 2:30am and was there in time for breakfast - followed the snowplow over the hump. Back home at 10:30pm before the next dump trapped me.

    One of the presentations I managed to see was by two German guys - maybe AS - where they were discussing an overheating problem with the rotary motor that seemed to get much worse at 6000rpm. They said that the problem was with cooling and airflow that
    just happened to be bad at that point in the rpm vs speed curve for the glider/engine combo.

    Neither of those guys looked old enough to have played with 2 stroke motorcycles, but that curve looked a lot more like exhaust pipe resonance than a cooling problem. I don't know if a rotary engine worries about back pressure - the exhaust pulse is
    famously strong, but it's not a 2 stroke cycle. The ADHD engineer in me is churning on this one - dog with a bone. Did anyone else think that the cooling explanation looked unlikely? If these guys are wrong and just increased the cooling, I'd be worried
    about the life of the rotor tip seals if the hot gas is being pressurised by a resonance in the exhaust pipe. 6000 rpm would be about right for a short pipe in a tight space. If a tip seal fails, the motor may leave someone in a crappy place - 1000ft
    above pointy stuff a long way from home, for example.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Charlie M. (UH, Pi & 002 owner/pilo@21:1/5 to Doug Bailey on Sun Mar 5 06:44:40 2023
    On Sunday, March 5, 2023 at 5:22:36 AM UTC-5, Doug Bailey wrote:
    I had to work all week so my only chance to take in the Reno show was Saturday. I left at 2:30am and was there in time for breakfast - followed the snowplow over the hump. Back home at 10:30pm before the next dump trapped me.

    One of the presentations I managed to see was by two German guys - maybe AS - where they were discussing an overheating problem with the rotary motor that seemed to get much worse at 6000rpm. They said that the problem was with cooling and airflow that
    just happened to be bad at that point in the rpm vs speed curve for the glider/engine combo.

    Neither of those guys looked old enough to have played with 2 stroke motorcycles, but that curve looked a lot more like exhaust pipe resonance than a cooling problem. I don't know if a rotary engine worries about back pressure - the exhaust pulse is
    famously strong, but it's not a 2 stroke cycle. The ADHD engineer in me is churning on this one - dog with a bone. Did anyone else think that the cooling explanation looked unlikely? If these guys are wrong and just increased the cooling, I'd be worried
    about the life of the rotor tip seals if the hot gas is being pressurised by a resonance in the exhaust pipe. 6000 rpm would be about right for a short pipe in a tight space. If a tip seal fails, the motor may leave someone in a crappy place - 1000ft
    above pointy stuff a long way from home, for example.
    Curious idea,decades ago, I played with 2 stroke exhausts on dirt bikes.
    Doing some searching prompted by your post, I found a lot, but mostly Mazda rotary Road cars.
    There is this....https://www.eng-tips.com/viewthread.cfm?qid=264735
    Read the posts, especially the link in the first post.
    I did a search using"exhaust tuning a rotary engine".
    Piqued my interest a bit, but I fly with an electric ASW-24e.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Eric Greenwell@21:1/5 to All on Sun Mar 5 08:09:27 2023
    On Sunday, March 5, 2023 at 6:44:42 AM UTC-8, Charlie M. (UH, Pi & 002 owner/pilot) wrote:
    On Sunday, March 5, 2023 at 5:22:36 AM UTC-5, Doug Bailey wrote:
    I had to work all week so my only chance to take in the Reno show was Saturday. I left at 2:30am and was there in time for breakfast - followed the snowplow over the hump. Back home at 10:30pm before the next dump trapped me.

    One of the presentations I managed to see was by two German guys - maybe AS - where they were discussing an overheating problem with the rotary motor that seemed to get much worse at 6000rpm. They said that the problem was with cooling and airflow
    that just happened to be bad at that point in the rpm vs speed curve for the glider/engine combo.

    Neither of those guys looked old enough to have played with 2 stroke motorcycles, but that curve looked a lot more like exhaust pipe resonance than a cooling problem. I don't know if a rotary engine worries about back pressure - the exhaust pulse is
    famously strong, but it's not a 2 stroke cycle. The ADHD engineer in me is churning on this one - dog with a bone. Did anyone else think that the cooling explanation looked unlikely? If these guys are wrong and just increased the cooling, I'd be worried
    about the life of the rotor tip seals if the hot gas is being pressurised by a resonance in the exhaust pipe. 6000 rpm would be about right for a short pipe in a tight space. If a tip seal fails, the motor may leave someone in a crappy place - 1000ft
    above pointy stuff a long way from home, for example.
    Curious idea,decades ago, I played with 2 stroke exhausts on dirt bikes. Doing some searching prompted by your post, I found a lot, but mostly Mazda rotary Road cars.
    There is this....https://www.eng-tips.com/viewthread.cfm?qid=264735
    Read the posts, especially the link in the first post.
    I did a search using"exhaust tuning a rotary engine".
    Piqued my interest a bit, but I fly with an electric ASW-24e.
    I've owned an ASH26E with the Wankel rotary engine for 28 years, and exhaust tuning has never come up in any discussions with the factory or other owners. It's a "four stroke" combustion cycle, so perhaps exhaust tuning isn't as useful as it is on two
    stroke engines. The engine rpm varies smoothly with throttle setting. It's had two very different muffler designs, with no apparent change in performance.
    Eric

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From jfitch@21:1/5 to Doug Bailey on Sun Mar 5 08:34:59 2023
    On Sunday, March 5, 2023 at 2:22:36 AM UTC-8, Doug Bailey wrote:
    I had to work all week so my only chance to take in the Reno show was Saturday. I left at 2:30am and was there in time for breakfast - followed the snowplow over the hump. Back home at 10:30pm before the next dump trapped me.

    One of the presentations I managed to see was by two German guys - maybe AS - where they were discussing an overheating problem with the rotary motor that seemed to get much worse at 6000rpm. They said that the problem was with cooling and airflow that
    just happened to be bad at that point in the rpm vs speed curve for the glider/engine combo.

    Neither of those guys looked old enough to have played with 2 stroke motorcycles, but that curve looked a lot more like exhaust pipe resonance than a cooling problem. I don't know if a rotary engine worries about back pressure - the exhaust pulse is
    famously strong, but it's not a 2 stroke cycle. The ADHD engineer in me is churning on this one - dog with a bone. Did anyone else think that the cooling explanation looked unlikely? If these guys are wrong and just increased the cooling, I'd be worried
    about the life of the rotor tip seals if the hot gas is being pressurised by a resonance in the exhaust pipe. 6000 rpm would be about right for a short pipe in a tight space. If a tip seal fails, the motor may leave someone in a crappy place - 1000ft
    above pointy stuff a long way from home, for example.
    If you are the guy who "the motor may leave ... in a crappy place", then you need to rethink owning a motorglider. These motors aren't intended as an insurance policy, and should not be used that way - even the operators manual warns against it. Like a
    pee tube, they are convenience, not safety equipment.

    The overheating problem referred to is peculiar to some of the injected engines which share the same exhaust as the carbureted version (which does not seem to have the problem). The injection system is 'mapped' with no feedback as you'd expect on any
    automobile or motorcycle engine. So, hard to get right for every conceivable condition. Being a certified aircraft powerplant, you can't just get in there and fart around with it willy-nilly. I think AS is working on the problem.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)