Best range settings 160HP largely stock Cub?

Hi all,

I am going to be undertaking a 2100NM trip across Australia at the end of next week. I've never really looked at fuel flows in detail before and I don't have a fuel flow monitor.

I have standard 36 gallon tanks
O-320A2B with high compression pistons, 160HP. Low time. Doesn't use much oil at all.
74-54 Sensenich
Sutton exhaust
29" Bushwheels and Scott tailwheel
Vernier mixture control, so I can actually lean it accurately now

Am interested in people's thoughts on best strategy for range.

Thanks in advance.

David

The trip:

My 160 hp Super Cub burns about 7 gph with the McCauley prop and 8 plus with the Sensenich metal prop. 4:20 is the longest I have sat in my Cub and still had fuel reserves, no fun.

That's a long trip using a climb prop. Do you have another prop with more pitch available?

skywagon8a said:

That's a long trip using a climb prop. Do you have another prop with more pitch available?

Click to expand...

Unfortunately not! I fly very slowly.

Averagely speaking, according to Wolfgang

Using rule of thumb (1.5 * Vs1), the best range is ~71 mph. Really slow.

The problem with best range speed may be sticking valves - these engines are happiest at 65% -75%


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What might be the prevailing seasonal winds for your trip, especially as they vary by altitude?

Edit: Bellengin NSW > Broome WA; E>W. http://www.bom.gov.au/climate/averages/wind/selection_map.shtml

Gary

I fly a Cub Cruiser with a 160hp engine - an O-320 B2C - and a 82/43 Borer prop. I find that the best power setting is around 2450-2500 because the engine seems happiest at that rpm and the aircraft seems to be on the step so to speak. I have tried lower settings but always seem to be losing height or getting very slow. I have read about people burning as little as 4 gallons an hour properly leaned and throttled back to 2200 but mine seems to be in the 7.5 -8 range (I calculate on 30 litres/hour and plan on 95 knots although the ASI is in mph and shows 110-115 at that rpm). I never plan legs longer than 3.5 hours for proper reserves and unforeseen circumstances.

In your shoes I would be filling her up, going for an hour’s flight at 2450 out and back and filling her again to note the burn and checking the GPS for ground speeds and relating that to the winds and ASI readings. Then plan the flight around that data. You could do another flight at a lower power setting and see how that compares. You are then working with real information on your plane.

I am no expert but I have found that this approach has kept me from embarrassment on my cross country flights.


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For range:
Power into headwinds; unpower with tail winds; side wind use relative wind vector
Load aft CG for lower drag; CG moves forward as fuel is burned
O-320 lowest fuel vs power produced 2450-2550; Also see sea level power vs pressure altitude charts in O-320 Owner's Manual Sec 3
Lean at favorable altitude for winds aloft
Which is why flow meters vs GPS data like fuel consumption and range are available

Gary

When doing long range/duration wildlife surveys, the 160hp w/Dodge 30.5 tanks (+headers) would go for 8.5 hours...As mentioned above, 7gal/hr is a good number.

Absolute best range is likely always very slow and engines are usually NOT that happy. The Japanese in WW2 almost doubled the range of the A6M but as I recall needed to develope special spark plugs to do it. Lindberg likewise stretched the range of the P38 and engines were not always happy. That said remember Gary's caution to power into headwinds.....

I seem to recall that the guys from OZ went hunting for a Japanese carrier that didn't exist, they could not believe they were attacked by land based aircraft.

I certainly don't envy 11-12 hour missions in a single seat fighter nor do I do well for over 3-4 hours in a Cub or about 1.5 in a Pitts. When Marcia was along, better find a place to land in 2 hours:smile:

Jack

As always the first question is do you have a 4 cylinder get/cht? If you do it is very simple to pick a RPM and lean properly. It is very easy to to get CHT'S too hot any time you go above 2400 and do aggressive leaning especially with high compression pistons. The big question is how far apart are your fuel stops. If I am alone on long trips I will put 36 gal in the back in cans/bags. If you have fuel every 4 hours you should be fine. Look at Lycoming instructions on leaning, you can get aggressive when you stay below 65% power if I remember correctly.
DENNY

I heard the exact same thing about running low rpm's, when I got my first Rotax 12 years ago, "don't lug it." I failed to pay attention to this advice, but easily made the 2000 hour TBO with ZERO issues of any sort. I have no idea if my experience translates over to a Lycoming, but I do know when the subject comes up among the Rotax crowd, to this day the advice remains the same as per low rpm's. I continue to ignore it, and get insanely low fuel burns and double digits duration, but yes I'm talking in the mid to high 70's mph, indicated.

The Rotax is a special case, the intakes are horribly asymmetric. Rotax says don't cruise below 5000, but you won't suffer anything but EGT spread.

If you have a full engine monitor with fuel flow I would go high 10K-13K and lean to 6-7 gph at a normal cruise RPM. I regularly burn 6-6.5 gph at 92 mph true with a big flat Catto, 35s, bare gear, safety cables and 7 degrees incidence at high altitude.

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Skywalker said:

The Rotax is a special case, the intakes are horribly asymmetric. Rotax says don't cruise below 5000, but you won't suffer anything but EGT spread.

Click to expand...

The majority of my 2680 hrs Rotax time has been below 5K rpm, just saying.They are ultra conservative near as I can tell, which I like. This rpm recommendation is one example, at least based on my experience.

My experience with lugging on the 6 cylinder Lycomings is that fuel consumption does go down but oil burn goes up exponentially. I run a BMW built GO480 in a Focke
Wulf Piaggio 149 and generally it burns about one pint of oil in 4 -5 hours but I tried the Lindbergh approach of low revs and high manifold on a 3 hour flight and ended up with a 3 quart oil burn and an oily belly! I thought I had damaged the engine but then after refilling did an aerobatic flight at high rpm for half an hour and burnt virtually no oil at all. That was 40+ hours ago and with normal operation the oil consumption has been back to normal and no oil on the belly!


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I did 25 litres per hour one time. Not in a hurry. 150 hp Super Cub with Sensenich 74-52 prop. Probably 2200 rpm, leaned it, wasn't that high. Speed was 80 or 90 mph. Didn't have bushwheels.

Good trip to do before it gets too hot in the Western Island.

Cheers,
Andrew.