Fuel economy

[Jet-A]

I have used the techniques in the AOPA article many times in the past and if you're not in any hurry to go anywhere, then flying 30% above Vy is fine. I guarantee that you'll be forced down to earth by your biological needs rather than your avgas ones. A little more bias towards speed, and I have seen fuel burn rates of about 9+/- gph at sea-level and 100 ROP still gets me about 105 KTAS. And I have VGs. Works great for me.

[210TC]

Cool pictures.

[klaas]

I use a little less than 9 gph doing 112 mph IAS at 12,500' in a M-7-235C with the IO-540. That is at full throttle (18"), 2100 rpm, and -7 flap, no VGs.

I spoke with someone who cruises at 1800 rpm, I'd like to give that a try but it's below the green range on the rpm (stops at 2050). I'm not sure if that should worry me: the manuals appear to warn about low rpm only for one specific prop/engine combination. Am I missing something?

Klaas

[210TC]

You may want to call lycoming and ask if it makes any difference at those altitudes.
I would try it and as long as you have no temp problems it should not hurt anything.
I think those RPM limits are for above the 75% power range. Check it out and let us know.
I think I have mentioned this. My Hot Rod I sold would burn 9.4 at 160 Kts indicated at about 10,000. Sure wood like to see a Maule get better mileage.

[benflyn]

If the optimum altitude for a non turbo plane is 1.3*Vy, would the same apply for a turbocharged airplane?

[210TC]

You got me. Never thought about it!!!!!!

[YELLOWMAULE]

Well, you guys have me beat. I've never flown by any formula but rather by "feel" and EGT. I don't have an engine monitor to give the exact amount of flow and temp.s so I do the next best thing I listen to the engine. I also only fly by the hobbs meter, not the fuel gauge. Ever.
So here's what I have watched. 50* ROP, 24"/2400 and below 5,500' = 9.3-9.7 gph like clock work above 5,00' and for any length of time (2 or more hours) it drops down to 8.6-8.8 gph. All the while flight planning for 10 gph.
Not scientific but reliable. Besides, despite carrying almost 6+ hours of fuel, my bladder never seems to be capable of more than 3 hours.
I'd love it if someone offered the last 6 cyl. engine monitor for me.

[Kirk]

I use a little less than 9 gph doing 112 mph IAS at 12,500' in a M-7-235C with the IO-540. That is at full throttle (18"), 2100 rpm, and -7 flap, no VGs.

I spoke with someone who cruises at 1800 rpm, I'd like to give that a try but it's below the green range on the rpm (stops at 2050). I'm not sure if that should worry me: the manuals appear to warn about low rpm only for one specific prop/engine combination. Am I missing something?

Klaas

My M5 with the O540 J1A5D and Hartzell prop, the 2050 RPM limit is not to exceed 23" MP below 2050 RPM (vibratory limit). That limit is listed in the AFM and is listed as required placard. Not sure what other engine/prop combinations are limited by that. If your airplane is affected you should have the placard and the green arc lower limit at 2050 RPM.

I've run at 1800 RPM with less than 23" but gave it up. It just seemed to slow me down too much.

KIrk

[Sam Rutherford]

I've been flying a few routes where endurance/range are of interest.

I'm now at 7,5-7,8 gph, 105 kts. MX7-180B - so I have a shade over 9 hours (with taxiing, a climb etc.), or almost 1000nm to fumes.

As already mentioned, the bladder is screaming 'full' long before the plane is screaming 'empty'!

Klaas, good figures on yours, I have traditionally heard that the 235s are nearer the 12 gph (but perhaps that's at 120 kts!)?

Sam.

[Jayson v Schalkwyk]

Does anybody have a copy of the original article? I cannot seem to open the link.

[Brenton C]

Does anybody have a copy of the original article? I cannot seem to open the link.

+1 on the broken link. I get a blank page and no article.