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best range speed and rpm

H

hikouka

Registered User
Japan / New Zealand
Gidday Gidday,

Sorry for another fuel question. I wonder what RPM settings and IAS you guys fly when crusing cross country when you don't care about arrival times.

In a stock 150 horser what's the best airpseed and rpm setting to fly for maximum range at full fuel (36gals)?

On Wednesday I've all day to make a 200 mile hope and want to do it using the least possible amount of fuel.

Imagine you've all the time in the world to fly and the last of the world's remaining fuel in your tanks and a prize beyond words awaiting your liesurely arrival 200m away.

What RPM and IAS would you fly?

-------

PS - Bonus bromie points if someone also answers :
In a stock 150 horser what's the best airpseed and rpm setting to fly for maximum endurance if you're full fuel and all alone?
 
Your question is impossible to answer without knowing winds aloft. You will be more efficient with less power with a tailwind and with more power with a headwind. With no wind, probably TJ is right 14-1500 rpm will keep her flying and probably use the least amount of fuel for distance.
Set it on 2200 and call it good. If you get vibration there, adjust accordingly.

I fly my 125 horse cub at 2350 because that is where the engine likes to run, it is less noisy and smoothest. I push the power up to 2500 and get more noise, a bit more vibration and maybe 7 knots more speed.

I flew a RV6 alongside a cub for 600 miles last winter at 1600 rpm and a notch of flaps. I didn't like the cool oil temps, so would cranker up and fly a couple circles around the cub every half hour.
 
rpm

You don't want your tail dragging down so to low rpm is harder on gas,
you went her straight like an arrow, less drag 2150 is a good rpm also
make sure to load baggages accordingly it will save you gas
 
Hikouka

There are three types of aircraft in simple terms. Gliders, power producers(props) and jets. All aircraft become gliders if the engine(s) fail. Gliders have two important speeds. Min sink and L/D max. Min sink gives the longest time aloft and L/D max gives the longest distance in a glide.
There are four important speeds in engine aircraft. Max angle of climb, max rate of climb, max endurance, and max range. All of these speeds vary by weight but not by AOA which is why it would be nice to have a good, well calibrated AOA gage.

Max range in a power aircraft is at L/D max. This is where the drag polar is at a minimum. I don't know what L/D max is in a Supercub but I would guess between 65 and 70. Increases directly with weight.

Max endurance will be at the lowest point on a power required polar. Similar to the min sink part on a glider. It will be lower than L/D max but above the stall speed. I would guess in the range of 50 to 55. Also increases directly with weight.

Max angle of climb for a SC will be just above the stall...."hang it on the prop"

Max rate of climb faster than L/D max, need charts and or test pilot data again.

Bill

PS.... this is the simplified version, all you aero engineers don't jump on me please, I'm just trying to help.

So.....if you can get a drag polar for a SC and a power required polar you are in there. Anyone have these plots from the test program at Piper.
 
BEST RPM

Bill that was very interesting, i alsow think the best gas milage will be achieved with the wind at your back,witch can be difficult to achieve
at low altitude
 
I run about 2450 rpm I might get a little better fuel burn if I dropped the rpms a little but then I would feel like I am sitting still. I would be burning less fuel a hour but putting more hours on the engine and my sore butt. Leaned out I burn about 8.5 gallons a hour at this setting. Leaning your engine is just as important as rpm if you dont have a digital egt gauge you might want to think of upgrading. I am rigged with a 41 pitch bore prop, VGs and 31" bushwheels I have spent many hours twiking the wings to have the plane fly hands off(well sort of). No two plans are alike you need to figure your own plane out and except speed over fuel burn or fuel burn over speed.

Hope this helps.

Cub_Driver
 
endurance

This is for a 56 pitch prop. 2100 rpm will get you about 65 mph and 5 hours + reserve. Thats the best I've done. About 6.1 gph
Good luck on your trip.
 
Taking Bill Rusk's summary of the relationship between minimum power speed, Vx and best range, Vy, L/D max, the theoretical max range on a Super Cub 90 is in theory quite impressive. This also assumes no wind conditions.

i would suggest that best glide, or L/D max as might be published in a POH, will typically be calculated for max gross and a windmilling propeller. The windmilling prop will move the bottom of the drag curve up and to the left (increased non lift dependant or parasite drag), which suggests that at power the optimum long range speed will be faster than best glide. Perhaps around 10-15% faster than best glide speed with a windmilling prop. Conversely, as fuel burns off, the speed will reduce as less lift dependant or induced drag results, and best glide reduces as it is the point on the drag curve where induced and parasite drag are equal (ie minimum).

The Super Cub 90 best glide is typically stated as IAS 60mph, the 150 emergency procedure states IAS 70mph.

One up and half tanks the best glide speed might be 10% lower, but in turn least drag under power is likely to be 10-15% higher, so to maximise range one up in a Super Cub 90 you might start at IAS 70mph and work your way down to IAS 60mph as fuel is burned, for an average of 65mph. This results in minimal fuel burns, possibly as low as 2 1/2 to 3 gph (1900 to 2000RPM, or an estimated 35% power). Arguably the lower speed results in some improved propeller efficiency.

With 30 USG available, and 5 USG in reserve, taxi, climb (unlike a turboprop, max range for piston prop in no wind shouldn't require climb), this provides a theoretical range of around 750 statute miles, with reserves, but requiring 11 to 12 hours of flight.

On a fine day may attempt London to Milan, or London to Barcelona, non stop just to check this out!

As above any aerodynamic engineers please correct if anything looks wrong.
 
Jack Norris wrote a good book about this very subject....Jack was the mission director on the Voyager 'round the world flight. It's piggy backed on his propellor design book....
http://www.propellersexplained.com/
He has a "unique" way of writing....stick with it....it's worth it. He's a SMART guy!

It boils down to....fly at best L/D and as high altitude as you can tolerate.....best altitude is where you can just fly at best L/D at FULL THROTTLE leaned to best power!....In a Cub you'd be well up where you'd need O2....
DaveG


L18C-95 said:
Taking Bill Rusk's summary of the relationship between minimum power speed, Vx and best range, Vy, L/D max, the theoretical max range on a Super Cub 90 is in theory quite impressive. This also assumes no wind conditions.

i would suggest that best glide, or L/D max as might be published in a POH, will typically be calculated for max gross and a windmilling propeller. The windmilling prop will move the bottom of the drag curve up and to the left (increased non lift dependant or parasite drag), which suggests that at power the optimum long range speed will be faster than best glide. Perhaps around 10-15% faster than best glide speed with a windmilling prop. Conversely, as fuel burns off, the speed will reduce as less lift dependant or induced drag results, and best glide reduces as it is the point on the drag curve where induced and parasite drag are equal (ie minimum).

The Super Cub 90 best glide is typically stated as IAS 60mph, the 150 emergency procedure states IAS 70mph.

One up and half tanks the best glide speed might be 10% lower, but in turn least drag under power is likely to be 10-15% higher, so to maximise range one up in a Super Cub 90 you might start at IAS 70mph and work your way down to IAS 60mph as fuel is burned, for an average of 65mph. This results in minimal fuel burns, possibly as low as 2 1/2 to 3 gph (1900 to 2000RPM, or an estimated 35% power). Arguably the lower speed results in some improved propeller efficiency.

With 30 USG available, and 5 USG in reserve, taxi, climb (unlike a turboprop, max range for piston prop in no wind shouldn't require climb), this provides a theoretical range of around 750 statute miles, with reserves, but requiring 11 to 12 hours of flight.

On a fine day may attempt London to Milan, or London to Barcelona, non stop just to check this out!

As above any aerodynamic engineers please correct if anything looks wrong.
Click to expand...
 
My fuel flow meter is tied in to my GPS. With my Cub, I get the same miles per gallon between 2250 RPM to 2400 RPM. The MPG goes up below 2250 RPM and down above 2400 RPM.
 
myskyjeep,

How many degF rich of peak are you running below 2250 and above 2300? Unless you are consistent with with fuel mixture ratio, your numbers may not include the full picture.
 
(How many degF rich of peak are you running below 2250 and above 2300?)

Dogday
I have only checked the FFM while changing throttle settings and leaning for cruise. Fuel flow goes up with throttle nut MPG stays pretty constant. I'm breaking in 9.5:1 pistons now and I'm looking forward to see what changes it makes.

Dave
 
Chapter 19, "The working speeds of an airplane" in the old standard Stick and Rudder covers this subject coincidently using a 100 mph airplane. If I understand him correctly, Bill Rusk's explanation just about mirrors what Wolfgang Langewiesche wrote 70 years ago.
 
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