rv6ejguy
Well-Known Member
EGTs and fuel burn would go through the roof with this strategy. Not a good idea. Simply limit MAP with the throttle.
limit throttle or revs?
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Protech Racing
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You correlate the Fuel table to match the engine needs. Reduced timing results in lower map and corresponding fuel.
Trim as needed . If the ECU is tunable of course.
Trim as needed . If the ECU is tunable of course.
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Yes.
This is an Otto cycle engine, not a turbine or a diesel, and talking about limiting it to around 65% power. If the throttle is mechanically driven, WOT with fuel trim would be an AFR around 23:1 at sea level. The literature tells us Otto systems either won't run at all that lean or will run really really rough while likely having some short lived internals.
Now if the throttle valve is drive-by-wire and programmable within the ECU, you could limit throttle valve opening based upon engine rpm and redundently based upon MAP and/or atmospheric pressure and/or MAF sensor.
You will still need to know what that limiting air condition is to set all this up properly.
At Ford and at FIAT-Chrysler we had a fuel flow and engine torque output in the ECU's, and they always had significant errors. The trans calibrators could use them for starting points in calibrating clutch-to-clutch shifts, but had to really rely upon speed sensing and adaptive schemes to make good calibrations.
Billski
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rv6ejguy
Well-Known Member
At WOT and a given RPM, you have X airflow which requires X fuel flow to maintain X AFR. Reduced timing has nothing to do with MAP or AFR. Timing highly affects engine efficiency, detonation margins and EGTs.
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So we have a high performance airplane with (essentially) a fixed pitch prop, and limited throttle so the gearbox doesnt fail? Flying this configuration seems like a good idea to some of you?
Might be time to take a BIG step back and re evaluate the scenario here.
Might be time to take a BIG step back and re evaluate the scenario here.
In the 1990's, the auto industry was using spark retard (mechanical throttle) for energy management during autotrans upshifts. Even ZF trannies used in high end cars. It reduced power for a brief period to allow the shift to be made with less bump and less clutch energy. From the perspective of the clutch engineer and calibrator, it worked OK, but the catalyst got a pulse of feed gas high in HC's/CO/O2 which the cat then has to convert - raising temps and NOx risk too. Lots of folks in all the companies did not like it - It was hard on exhaust valves, catalysts, exhaust gas O2 sensors, carried emissions risks, and was noisy in some products too. And this was for a three 300 millisecond pulses per trip up through the gears. Better schemes were to just go zero fuel and/or close throttle for a couple hundred milliseconds. With fast actuators on throttle valve and suitable programming, both are doable and are widely in use for decades now.
You do not want to do fuel reduction nor spark retard for steady state operations. Even though we do not have catalysts and emissions to worry over, all that stuff Ross said above I second. It is real and has significant consequences...
MUCH better to manage the throttle valve, either manually, or electronically.
Billski
You do not want to do fuel reduction nor spark retard for steady state operations. Even though we do not have catalysts and emissions to worry over, all that stuff Ross said above I second. It is real and has significant consequences...
MUCH better to manage the throttle valve, either manually, or electronically.
Billski
In post 16 the OP indicates he has done some running and reinstalled the governor.
On top of that, I recommended fitting a partial flow filter to the system so any particles generated get a chance to leave the system before silting up places in the system or imbedding in bearings and such.
I assume the commentary on setting the low pitch stop is to leave some power available for emergency mode management, not for nominal use.
I do understand that loss of governor oil pressure in singles causes the prop to go to min pitch. It seems prudent to me to set that min pitch stop where the system can hold altitude somewhere around Vy and approach speed. Is there a reason not to do that? It might not give max rpm in the first couple seconds of takeoff, but that hardly seems needed for anyone but the STOL contest guys.
Billski
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Extra bracing is placed in the frame and all the skins from about the cockpit forward are replaced with thicker sheet. (The skins are bonded to the frame in a T-51, so it forms a strong unit.) In none of the "incidents" with T-51s has the cockpit area deformed. And the wings were tested to 10-12gs at 1650 weight.
Yes, this is just to make the plane flyable if your prop goes minimum pitch.
Some info / data points / calculations:
Owners leave the prop at cruise pitch when landing. If you go to minimum pitch the plane loses speed and altitude at a "remarkable" rate. It has a very thick wing, so the airframe is very draggy. So the fear of not being able to stop the plane once down unless the prop is minimum pitch is probably not real.
With the prop governor functioning, the plane cruises at 160-180 mph at 3000-3200 rpm at 19-22” at 3000 ft.
With the prop minimum pitch stop set to 14-16” at 1800-2000 rpm static, the limiting factor is the ability of the brakes to hold the plane at that setting and the need to ride the brakes when taxiing at 800 rpm idle
Using the GM Performance data for torque numbers (which are higher than my plane will have, with its short stacks exhaust) and 263 ft-lbs torque as our limit, we can use
22.5” at 2000 rpm
21” at 3000-3200
20.4” at 3600
20” at 3800-4000
18.3” at 4500
I find it interesting that the 21" at 3000-3200 rpm is what pilots use when cruising. So just by the seat of their pants they came upon the max safe sustained power?
I plan to fly at 7000 ft to allow for generous glide distance or plenty of bailout height. I assume this is also higher than C172s and similar GA planes fly, so less traffic. Yes? (The plane has emergency canopy releases, so getting out is easy.)
At 7000 ft, only 23” will be available anyway- but you could use it in an emergency.
Actually, this sounds pretty good to me.
No?
Jim
Good.
There are a lot of airplanes with constant speed props where you move the prop lever full forward and then adjust power to get the level in downwind and then descending to the runway. Sounds like you have a lot of prop for the airplane weight and approach speed. If you plan to leave the prop at cruise for the traffic pattern, you should also do tests to make sure that you have plenty of climb available by just pushing up throttle for missed approach. If climb is lethargic in the go-around with cruise prop setting, I suggest that that you figure out what prop setting gives you a good go-around response and use that from pattern entry to landing...
The knowledge that full forward prop and reduced throttle brings you down steeply is good information for the hair-on-fire descent. Again, do some data collection and establish your emergency descent power settings. This is just some of the things you should be establishing during the 40 hour test phase.
I do not know any details on your engine, so I can not check your work. If other folks are getting durability using those settings, that is a good thing.
It is good to know that other owners have converged on the same settings.
I fly up to 10,000 feet frequently in a Cherokee. Keep your head on a swivel and check the iPad for traffic too. You can not count on altitude to keep you clear of other traffic.
Billski
rv6ejguy
Well-Known Member
Seems nonsensical to install a heavy 430-480hp engine in any airframe and then de-rate it to half HP to make the marginal PSRU live.
Probably related to cost and reliability. Are there any other engines out there you can buy brand new for $7K and will loaf along at half redline at 160mph?
It's really not that heavy. No additional weight had to be added to the rear of the plane to be within CG range. In fact with a passenger you are getting close to the rearward limit. I don't know how they flew these planes with those little Rotax engines.
The plan is to have Elliot Seguin fly the plane. Initially the goal will be to see if the minimum pitch setting is set for too much pitch to take off and climb well.
He has quite a bit of experience with a Stewart Mustang and a loss of prop control with it.
Interestingly, that prop goes to max pitch rather than min if it fails.
He has quite a bit of experience with a Stewart Mustang and a loss of prop control with it.
Interestingly, that prop goes to max pitch rather than min if it fails.84" four blade prop, TOW w pilot alone about 1750 lbs, approach speed 70-80 mph.
Standard in single engine airplanes is for hydraulic prop to go low pitch on loss of oil pressure to hub. Standard in multi-engine airplanes is to have the hydraulic prop go into feather or high pitch on loss of oil pressure to hub. In singles, the theory is a failed governor and a running engine can still be flown to an airport. In multi-engines, the theory is the good engine can still take you to an airport if the dead engine is feathered.The plan is to have Elliot Seguin fly the plane. Initially the goal will be to see if the minimum pitch setting is set for too much pitch to take off and climb well.
He has quite a bit of experience with a Stewart Mustang and a loss of prop control with it.
Electric props are another topic... Some aerobatic aircraft run feathering style props for responsiveness. I do not fully understand the topic. Maybe others can help.
Billski
My mechanical in flight adjustable Hoffman prop has three positions (takeoff, cruise, feather). I don't see any problem staying in low pitch the entire flight. I do it often when looking for a thermal. It is controlled with throttle like any fixed pitch.
Just check the static rpm and don't exceed a predetermined prop rpm using the throttle. Of course then the prop rpm in climb will be about 200 more without moving the throttle. And the rpm in level flight will be about another 200 rpm without moving the throttle. To land just close the throttle.
Just check the static rpm and don't exceed a predetermined prop rpm using the throttle. Of course then the prop rpm in climb will be about 200 more without moving the throttle. And the rpm in level flight will be about another 200 rpm without moving the throttle. To land just close the throttle.
Is my thinking correct?
For the LS3 430 powered Titan T-51 Pilots use 3600 rpm at 20" to take off and 3000 rpm at 20" at cruise
The LS3 engine makes so close to 400 ft-lbs torque between 3000 and 5500 rpm at WOT you can use that for all those revs.
Correcting for the 263 foot lbs torque the gearbox was designed for yields 263/400 x 30" = 19.7" MAP maximum should be used.
Using the torque produced at full throttle and correcting for the 236/400 ft-lbs at 20" the LS3 engine makes these hps at these rpms:
2000 100
2500 125
3000 150
3200 160
3500 175
3600 180
4000 200
4500 225
5000 250
5500 275
So pilots are using 150hp at cruise and 180 to take off.
Which leaves about 100 hp for "emergency" use.
Is that correct, or am I misunderstanding something?
Thank you,
Jim
For the LS3 430 powered Titan T-51 Pilots use 3600 rpm at 20" to take off and 3000 rpm at 20" at cruise
The LS3 engine makes so close to 400 ft-lbs torque between 3000 and 5500 rpm at WOT you can use that for all those revs.
Correcting for the 263 foot lbs torque the gearbox was designed for yields 263/400 x 30" = 19.7" MAP maximum should be used.
Using the torque produced at full throttle and correcting for the 236/400 ft-lbs at 20" the LS3 engine makes these hps at these rpms:
2000 100
2500 125
3000 150
3200 160
3500 175
3600 180
4000 200
4500 225
5000 250
5500 275
So pilots are using 150hp at cruise and 180 to take off.
Which leaves about 100 hp for "emergency" use.
Is that correct, or am I misunderstanding something?
Thank you,
Jim
The "typical" aerobatic C/S prop and governor use the counterweighted "auto feather" scheme used on multi's. This is used so that the prop does not go flat during times of transient oil pressure loss during aerobatic flight. The typical aircraft engine will handle transient oil pressure loss much better than a propeller system will handle a transient overspeed.
