John any updates on the 915? Do you have it flying yet?
John any updates on the 915? Do you have it flying yet?
May I ask a newb question? I see that the 915 has the same exact bore and stroke on its pistons as the 912/914 engines. Does this mean the only way the new 915 is making more HP is that it's going to higher RPM's versus the 912/914? Hence your statement that a fixed pitch prop wouldn't take advantage of the engine's HP because it's essentially the same engine and has roughly the same HP/torque curves at the lower RPM's as the 912/914? The only way to take advantage of the higher horsepower at higher RPM's is to keep the engine spinning at the high RPM's and adjust the pitch of the prop for max thrust during takeoff and max forward speed at cruise? I did read an article on the SeaReys that said cruise RPM was 4800? So that actually seems lower than normal cruise RPM? If it's making more power due to higher boost/more oxygen in the fuel/air mixture, then why isn't a fixed blade prop going to work if the RPM range is the same? That's where I'm getting confused. Is it due to the changed reduction unit? Why would they change that if so?
Thanks,
Brandon
Last edited by brandonschmit; 06-07-2018 at 06:19 PM.
The constant speed prop keeps the rpm the same. It’s the manifold pressure that is showing how much power the engine is making. Similar to if you were biking turning the pedals at 120rpm. If you went up a slope you could still keep 120rpm but you would have way more force on the pedals to do that.
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Josh Esser
Flying SS7
Rotax 914iS
AirMaster Prop
Edmonton, AB, CWL3
I don't believe the 915is runs at any higher RPM than the 912/914. The extra power comes from the turbo boost (packs in more air/oxygen to burn more fuel) AND the intercooler which cools the hot boosted air so even more dense air can be packed into the cylinders.
Jim Ott
Portland, OR
Kitfox SS7 flying
Rotax 912ULS