Most efficient rpm?

[Lior]

Hello, Drifterites. A question if I may.

 

I'm still a bit new to the Drifter 582 flying business, and have noticed that fuel calculations change dramatically with the added weight of a passenger, hilly terrain and winds, even on "there and back" flights. My Drifter is a Maxair model put together in 1994.

 

So what is the best cruising rpm to conserve fuel and maximize range assuming one is in operating limits? I can stay up to enjoy the view at 4700 rpm/ 50 mph IAS and take on Middle Eastern headwinds at 5200 rpm / 60 mph IAS, but still don't know how to max my range on 60 liters. A pleasure flight over Nazareth during the weekend nearly would have my Drifter into a glider after 2 hours 40 minutes had I not monitored fuel levels carefully. Landed with a modest reserve after that experience. Was hoping to get 15 liters an hour :( One theory that I had was that increased angle of attack in a fully laden Drifter with its fat ultralight camber results in a dramatic increase in induced drag compared to when flying solo. I'm no expert yet but I don't intend to stop learning any time soon.

 

Helpful tips will be welcome.

 

 

[M61A1]

Can't speak for the others, but in the last Drifter I spent much time in, cruise was around 65 kts at 5400 rpm and around 15 litres per hour with two on board. What are the temps and altitudes like where you're flying, meaning is it hot and/or high?

 

 

[Lior]

Last time I flew I calculated a density altitude at field level of 2500 feet, and I was flying at a mean density altitude of 4500 feet (e.g. 2000 feet ASL). Few are the days in which the temperature here is that of a standard atmosphere, but my field's altitude is 200 feet ASL. M16A1, Your fuel burn sounds good!

 

 

[damkia]

Obscure general answer, but the most volumetrically fuel efficient engine RPM is that at which the peak torque is developed. This is the point at which it will produce the most power for the least fuel consumption.

 

Have a look at your engine specs and check the peak torque RPM.

 

 

[Tex]

I concur with damkia! You get best distance in the right RPM band (2 strokes and all) which is mid 5 thousands in a 582 (with the right prop pitch). You need to work out what fuel burn you get at 5800 (max cont) but 18l should be MORE than required for planning purposes (though I always used 20l in the 582).

 

Running at between 5200-5600 you should be able to get close to 60kts avg IF you can fly the lift well. Plan 55kts.

 

Personally I never found any great fuel savings by running lower RPM in a 582... they are on song around 5500 generally...fuel saving at 5000 were negligible (and temps harder to manage).

 

A GOOD pilot uses the air masses to save fuel over distance by running the speeds according to lift encountered. For example: I struggled to get away from an early model 582 WB Drifter (slim pod) with me in a in a 912 Drifter poking along because the pilot in the 582 is an excellent glider pilot. He could wind it up and follow good lift lines/air and maintain 65kts.... at times though getting to 3 times my height!

 

 

[Lior]

Thanks for the tips. I've been soaring a bit in Grob Twins, so I do try to stay on the windside of any slopes and find thermals (even of the blue variety). 65 knots is a tad fast in my drifter with its diminutive pod. Even in a Flycom Helmet one can feel that the aircraft is not happy, and without an elevator trim tab a lot of forward stick pressure is needed to maintain straight and level.

 

 

[Tex]

No trim tab... that would be my first mod!

 

 

[Guest Maj Millard]

My 582 WB with 4 blade Brolga like 5000-5200 most of the time and would usually get 17-20 Lts per hr. Always flight planned for 20 L per hr burn....Fairly consistent for the 600 Hrs I did in her.........Maj..

 

 

[facthunter]

Your plane would have a best cruise speed for weight and height. The prop then has separate considerations and then we get to the motor where the needle taper and main jet affect things and then there is the tuned exhaust to consider as it works best at certain revs and not so good at others. It would be easier to work it out on a C-130. Too many unknowns. Nev

 

 

[farri]

Hello Lior, There are too many variables to answer your qustion correctly!

 

My aircraft is an Austflight WB Drifter with the standard small nose pod. I`ve had four Rotax 582, grey head engines ( all used for flight training ). I used the standard jets and jet needle that were fitted to each engine. The prop for each engine was a Brolga, four blade 60 inch diameter with 17 degrees pitch blocks and the gearbox was the E type, 2.62:1 reduction. I used unleaded fuel and the fuel consumption for each of them was 12/14 lts phr.

 

My current engine is a Rotax 503 DCDI with E type box, 2.62:1 reduction, Ivo 3 blade 60 inch Diameter prop and fuel consumption is 15 lts phr, average.

 

Unfortunately, you will have to find what works best for your situation but keep in mind that it is better and safer to have the engine running a littl rich ( using too much fuel ) than to have it too lean and risk destroying it.

 

Frank.

 

 

[Lior]

Well my current engine has 15 hours of life left in it before I replace the short block. Prop here is a three bladed Warp Drive as we don't have the right way up Austflight engine mounts here. The idea of a trim tab is appealing, even of the ground adjustable variety. While I agree that there are great many variables involving power plant, even the Austflight manual does not have a drag / speed plot. That said, I'm not sure if best range speed and best glide speed (49 kts per the Austflight manual) are the same.