Just got this notification from Rotax this morning. Rotax recommends minimum 5200 RPM on WOT climbout. Less RPM is said to overload the engine and possibly induce pre-ignition/detonation, particularly at higher OAT's. So....... I was wondering what all the other RV-12 flyers were seeing for RPM on cimbout. My propeller is set to 71.4 degrees using the Van's pitch setting procedure. This setting yields a static RPM of 4850 and 5000-5100 WOT @75 knots( this was 2 days ago with OAT 60 F). Field elev is 1280 MSL and density alt was 1100, gross weight 1170# initial climb rate was 1000 FPM. Summertime numbers are similar but slightly lower with DA around 3000-3500. I understand this topic has been discussed before, but not in the context of a factory recommendation. Just to let you know, I have 25 years experience building, dynoing, racing and maintaining roundtrack racing engines from GSXR 1100 Suzuki's to Daytona 500( unrestricted and restricted). Not bragging , just want you to know I thoroughly understand many aspects of high performance internal combustion engine operation. I might have to do a plug check soon just to see if my engine shows signs of detonation. Anyway, I'd love to hear from other RV-12 guys about this.
Van's Air Force
Don't miss anything! Register now for full access to the definitive RV support community.
Rotax SL-912-016R1
- Thread starter DBRuth
- Start date
SL-912-016 has actually been around for a long time, but this is the first time I have ever seen Rotax publish a power chart (at least part of the R1 revision I imagine).
I find it very interesting that they imply that the 75% power setting is 500 RPM below the max. continuous power setting (5500 RPM). This smells fishy and I will be doing some research with the Rotax reps.
Meeting the recommended RPM minimum (5200) on a clean / fast airplane that has a fixed pitch propeller is pretty much impossible unless you are willing to severely limit the airplanes cruise performance.
This is not a problem with a slower / higher drag airplane because a lower prop pitch is already being used because of the lower speeds.
If the PAP procedure for propeller pitch adjustment on the RV-12 is followed, for most owners it results in a Vy climb engine RPM of about 5100 and a WOT static on the ground of about 4950-5000 RPM depending on ground elevation, DA, etc. (this is assuming the engine is at full normal operating temp).
I find it very interesting that they imply that the 75% power setting is 500 RPM below the max. continuous power setting (5500 RPM). This smells fishy and I will be doing some research with the Rotax reps.
Meeting the recommended RPM minimum (5200) on a clean / fast airplane that has a fixed pitch propeller is pretty much impossible unless you are willing to severely limit the airplanes cruise performance.
This is not a problem with a slower / higher drag airplane because a lower prop pitch is already being used because of the lower speeds.
If the PAP procedure for propeller pitch adjustment on the RV-12 is followed, for most owners it results in a Vy climb engine RPM of about 5100 and a WOT static on the ground of about 4950-5000 RPM depending on ground elevation, DA, etc. (this is assuming the engine is at full normal operating temp).
Last edited:
I know, but if I remember correctly (and now a days I often don't) it was never referenced to a specific manifold pressure. Without that variable, there is no meaningful correlation of HP to RPM.
This is something that Dynon has to choose to do. They have chosen not to do this for the 912 engine on the D-180, Skyview, or HDX
RFSchaller
Well Known Member
Doug, I usually see about 5050RPM climbing at 75KIAS. I've never seen 5200 at Vy. My WOT in level flight at 8000 ft is just shy of 5500 RPM.
Phantom30
Well Known Member
Scott...am I correct assuming I want 75% power (5000 rpm), I am pitched properly if I see 26" manifold psi @ my normal cruise altitude and DA (if there is such a thing as normal).
I haven't flown in awhile, but if memory serves me correct, I've never seen 26", more like 24"s. Just wondering?
Performance numbers
Rich, your perf numbers are almost exactly the same as mine. I haven't done a Vx climb since phase 1 testing so I don't have those figures memorized. My prop was pitched at about 71deg during phase 1 so those numbers aren't valid anymore, but it could climb at 1300 FPM at that time. Cruise at 5500 was 112knots, now I see about 116-118k at 5500 after repitched to 71.4 deg. Maybe one day I'll work another outage at PVNGS and I'll give you a call.
Rich, your perf numbers are almost exactly the same as mine. I haven't done a Vx climb since phase 1 testing so I don't have those figures memorized. My prop was pitched at about 71deg during phase 1 so those numbers aren't valid anymore, but it could climb at 1300 FPM at that time. Cruise at 5500 was 112knots, now I see about 116-118k at 5500 after repitched to 71.4 deg. Maybe one day I'll work another outage at PVNGS and I'll give you a call.
RFSchaller
Well Known Member
Doug, sad to say I don't remember running into you at PVNGS. I'm retired out of the business of converting matter to energy. We were the modern day alchemists --- I'm sure one or two of those fission products was gold!
Rich
Rich
Whilst we experiment, are high power/WOT static run-ups detrimental to the undercarriage with all that energy the gears and fuselage are being subjected to? I'm thinking save WOT testing for high speed runway ground runs and put less repeated stress on the gear and fuselage, even with the SB to bolster the gear attachments. Also, save the prop from FOD/picking up loose small stones. Having said all that, I obtained 5000 and as the plane was bucking to be turned loose I thought this has to be stressing the old girl. Just a thought.
Driftdown
Well Known Member
What is your WOT at 2500-3000 ft.?
The bucking and shaking you speak of is the result of sitting on rather soft tires.
The loads that are induced on the airframe are nothing even close to what is induced by some peoples landings occasionally.
DaleB
Well Known Member
Hey, now watch it. I resemble that remark.
A 912 with CP or VP prop fits the Rotax model pretty well. We who are limited to GA or FP props are stuck with compromises.
My Flight Design CTSW takes off with 15 deg flaps and rotates at about 5000 rpm. To get up so 5200 more quickly, I modified my takeoff to use zero flaps where possible. Rotation is still about 5000 or a little over. After clearing the 50' obstacle, I push the nose over and accelerate to 5200 rpm then pull the nose up. I'm doing 80-90 knots then. It's a flatter climbout profile. I quickly get to 100 nmph and go to -6 flaps, then climb at about 5300 or better.
I don't know if that will work for an RV or not.
My Flight Design CTSW takes off with 15 deg flaps and rotates at about 5000 rpm. To get up so 5200 more quickly, I modified my takeoff to use zero flaps where possible. Rotation is still about 5000 or a little over. After clearing the 50' obstacle, I push the nose over and accelerate to 5200 rpm then pull the nose up. I'm doing 80-90 knots then. It's a flatter climbout profile. I quickly get to 100 nmph and go to -6 flaps, then climb at about 5300 or better.
I don't know if that will work for an RV or not.
Harvey rv12
Well Known Member
research
Scott McDaniel;
Did you manage to do any research on this subject?, it seems if we follow the recommendation from Rotax on rpm/throttle/map we are limiting the output of our engines, especially in an RV-12.
thx
Scott McDaniel;
Did you manage to do any research on this subject?, it seems if we follow the recommendation from Rotax on rpm/throttle/map we are limiting the output of our engines, especially in an RV-12.
thx
No
The next time I have an opportunity to talk with one of the guys at Kodiak I plan to ask them about it.
The recommendation of the 5200 RPM climb minimum has always been in place. It just seems they are putting more emphasis on it now for some reason.
RFSchaller
Well Known Member
OK, I hope I don't embarrass myself with a bonehead miscalc, but I remember an equation for Power= Force X Velocity.
At 120 miles per hour and 100HP that works out to a max theoretical drag force of about 312 pounds. Seems like that would be the max force at WOT runup and would actually be something less when inefficiencies are accounted for.
At 120 miles per hour and 100HP that works out to a max theoretical drag force of about 312 pounds. Seems like that would be the max force at WOT runup and would actually be something less when inefficiencies are accounted for.
Harvey rv12
Well Known Member
static rpm
I should know this, but am deferring to the experts.
regarding static rpm, with all other things being equal, if I performed a max static rpm runup on a 30 deg f day, and then did the same max static rpm runup on a 90 deg f day, which would yield the greater rpm ?. I know the engine will develop more horsepower on the cold day, but isn't it also more difficult to swing the prop through that cold thick air ?
RV-12, 912uls, standard elsa build.
thx
Tom O.
I should know this, but am deferring to the experts.
regarding static rpm, with all other things being equal, if I performed a max static rpm runup on a 30 deg f day, and then did the same max static rpm runup on a 90 deg f day, which would yield the greater rpm ?. I know the engine will develop more horsepower on the cold day, but isn't it also more difficult to swing the prop through that cold thick air ?
RV-12, 912uls, standard elsa build.
thx
Tom O.
RFSchaller
Well Known Member
I think a better measuring rod would be density altitude.
