Hg"/Prop RPM ?Curious

[John-Paul at GAMI]

"Do auto fuel mixtures work exactly the same when LOP or ROP? I assume that the laws of physics also apply to auto fuel."

Yes. The detonation margins will be different, but the principles will all be the same.

[a64pilot]

OK how about this. Being a non turbocharged aircraft, and at the altitudes I regularly fly at, I'm firewalled. I'll agree if I were at power setting that would allow me to increase manifold pressure to recover the power lost by LOP operation then I would not see any decrease in speed. However, my best fuel consumption per mile covered in my Maule is up around 10,000 ft. I believe it's so high because the Maule has just too much wing lift to be any kind of decent cross country machine and you have to get so high to loose some of the drag. Up there the power reduction of being LOP is just too much for me to tolerate. At 10,000 ft. about the most I can squeeze out of it is 65% power ROP. I don't care what a TN anything can do, I and the vast majority of Maules aren't TN.
I'm not beating on your product, I've already said that they were the best thing since sliced bread for our C-210, I just didn't see anything nearly as good for the Maule. I'm happy with my GAMI's, just from what I can tell the big Lyc. just doesn't respond nearly as well as the big Conti. I haven't gone to the trouble of having them "balanced", maybe that would show some improvement. I do have the fuel flow option on my analyzer and the data logging capability, so maybe even someone as stupid as I am could manage it.

[a64pilot]

"Do auto fuel mixtures work exactly the same when LOP or ROP? I assume that the laws of physics also apply to auto fuel."

Yes. The detonation margins will be different, but the principles will all be the same.

Is there an injected engine in a Maule that has an STC for auto fuel?

[a64pilot]

John-Paul,
Welcome to the forum. I think you will find that there are a lot of OWT's out there that you may help straighten out.

[BudG]

Hey there everyone,
Seems that I asked a HOT (metaphor) question. I am grateful for everyones input. Since originally asking about running the LOP/ROP question and receiving the resulting information I have been reading as much information as I can from GAMI, and Lycomings sites. My brain has really been energized. Since getting the GAMI's my starts have been so smooth, my runups smoother and even my wife said she thought that the engine sounded quieter. Temps are real close egt/cht and oil temps are good. I went flying and just for interest leaned the engine as I did before the injectors and edm700. I got to cruise and flew for about 5mins then, without looking at the fuel flow, started leaning until the engine ran rough then increased the mixture a quarter turn. The fuel flow was still 1.5@gals / hr. less than I used to run it, 10g/hr vs 11.5-12g/hr. The engine was running smooth too. I started enrichening the mixture and the egts increased for about 15-20 df. I forgot to look at the cht's...darn I'll have to go flying again. Anyway Thank you all for such great input! What a great web site.
BudG
Tailwinds2U

[John-Paul at GAMI]

"However, my best fuel consumption per mile covered in my Maule is up around 10,000 ft. I believe it's so high because the Maule has just too much wing lift to be any kind of decent cross country machine and you have to get so high to loose some of the drag."

You can lean so far that your "miles per gallon" will go back down. At that altitude your best economy might be right at peak EGT.

However, I've seen something similar to what you described on a float equipped 206.

At 10,000 ft, you are at such low power that your best Brake Specific Fuel Consumption (BSFC) may be very close to peak, or maybe at peak. There may be 2 or 3 percent HP difference between best power and best economy. That power loss may be enough to cause the airplane to fly at a higher angle of attack and "mush" through the air a little more. That would cause more drag and end up losing more airspeed than normal, so your "miles per gallon" stays the same. Maybe that is happening with the Maule as well.

That's all just a working theory I've been running around in my head, and not based on any data. It may be full of crap. I'd like to see some actual fuel flow vs TAS over a wide range of mixture settings for a few similar airframes, but I don't see that happening any time soon.

[Walter Atkinson]

I have a question about this information. Do all of the tests and results apply also to those of us who use auto fuel? Do auto fuel mixtures work exactly the same when LOP or ROP? I assume that the laws of physics also apply to auto fuel.

flyer

Flyer:

Please allow me to apologize for addressing you improperly, but you did not sign your post with your real name.

The answer is YES, auto fuel works in the combustion event like 100LL with one basic exception. Auto fuel has a shorter latency period (the time it takes for the flame front to become organized in response to the spark event) and as such will result in higher internal cylinder pressures and higher CHTs in most cases.

Other than that, as Sir Isaac Newton said, "the physics are everywhere the same!"

I used to use auto fuel in my Twin Beech (STC'd and approved), but discontinued the practice for the above listed reason. The other option is to retard the timing about 2 degrees. Since that is not an FAA/OEM approved option, recommending doing that is not appropriate.

[Walter Atkinson]

At 10,000 ft, you are at such low power that your best Brake Specific Fuel Consumption (BSFC) may be very close to peak, or maybe at peak.

JP:

Right.

The BSFC(min) at that power setting will be between about 10 and 15dF LOP. Peak won't hurt anything at that low power, but it will be slightly more efficient slightly LOP than at peak--and the engine will run cleaner and cooler; both good things to have happening.

A LOT of measurements over a wide range of aircraft always seem to result in about the same speed loss between Best Power and 10dF LOP------you'll lose about 2-3 knots TAS but will save 2-3 gph in fuel. Again, that's the physics. If you're losing more speed than that going LOP at that altitude, you're leaning too far LOP to be optimal. You won't HURT anything, but you give up some performance.

One other thing: Those of us not flying turbo-charged aircraft may not think we care about how things work in those engines, but they can be excellent examples of how things can work to our advantage where mixture management is concerned. What's the difference in operating a TC'd engine or a Maule engine at sea level WOT?? Something to ponder, right?

[a64pilot]

For me and my M-6 10,000 + or - 1,000 or so gives me my highest true A/S, so she's not at the point where she is wallowing around yet. Depending on gross weight, that doesn't happen until around 15,000 or so. Most other N/A recip aircraft I've flown are fastest around 7,500. The Maule has this flat bottom / high lift wing and the newer ones a -7deg. flap setting to try to reduce the lift some what for a better cruise speed. Any way for me at my best altitude for speed, the difference between 50 ROP and peak is .5 gph, and I lose a couple of knots at peak. LOP, the speed reduction is even greater and the fuel burn is down about 1 gph, because at 10,000 or so my fuel burn is about 11 gph. For me 1 gph in light of the speed loss isn't worth it. I haven't done the math, but I don't think the mpg is much better due to the speed loss. Maybe it's ignorance, but running at peak just doesn't seem smart and .5 gph just isn't worth it.
I theorize the best altitude for the airframe as far as the lift to drag ratio is much higher than the altitude that a N/A engine is efficient at, so in that way it's not a good match, but a Maule is not a cross country machine, it's a STOL machine and that big high lift flat bottomed wing is good for that.
There were a few turbo Maules built and those I would think would do real well at the flight levels. I would love to see a TN Maule that would have a critical altitude around FL180 or so, but that kind of sophistication is probably not in the best interest of the average bush / back country pilot, to say nothing about what a TN system might weigh.
As far as running WOT at sea level LOP, I'm sure it could be done safely as long as you kept it so lean that the power was down enough not to hurt it, but if you were that stupid pilot that Lycoming talks about, or if the weather is getting bad or etc. and didn't see it getting close to peak because it got colder or you climbed a little or anything else to affect air density and you have at best an expensive repair bill. One that you would never save enough fuel to pay for.
For me it's the cost / benefit thing that worries me. I believe the risk is managable, but the savings isn't but around a gallon an hour or so.
Now on the IO-520 in the C-210 we have the mpg can go from 10 at ROP to as much as 14 LOP if you don't mind losing 10 kts. What it does in fuel range for the 210 is phenomonial. Depending on the length of the trip you may get there faster in it going LOP because you can skip a fuel stop.

[Walter Atkinson]

Those are all very good points.

If you're losing 10 knots at altitude in the C-210, you're further LOP than optimal for the best economical tradeoff in speed vs. fuel burn.

[Maule 9V]

In my M-5 with a Cont. IO-360 @ 7500', WOT, my mpg goes from 12 to 16 when I go from 100 degrees ROP to 30 degrees LOP. I am being perhaps too extreme on both ends. My air speed drops about 8 mph when I do this. I will try using 10 degrees LOP next time.

[Walter Atkinson]

In my M-5 with a Cont. IO-360 @ 7500', WOT, my mpg goes from 12 to 16 when I go from 100 degrees ROP to 30 degrees LOP. I am being perhaps too extreme on both ends. My air speed drops about 8 mph when I do this. I will try using 10 degrees LOP next time.

Best power is approximately 80dF ROP, so that may be a tad rich at 100dF. Unlike when ROP, the difference between 10 and 30dF LOP will be significant because when LOP, HP is ONLY related to FF. A change in FF when ROP has little to sometimes no effect at all on HP. The HP curve ROP is very flat in the commonly used mixtures.

[a64pilot]

Those are all very good points.

If you're losing 10 knots at altitude in the C-210, you're further LOP than optimal for the best economical tradeoff in speed vs. fuel burn.

Your probably right, but by losing those 10 kts, I get 4 mpg greater, which unless I do the math wrong is a 40% increase. The fuel saved is nice, but sometimes the greater mileage enables me to get to where I'm going without a fuel stop. Of course I can turn up the FF and go faster, but sometimes it's a case of getting there in less time by going slower because of not stopping.
It's just I can't get those results with the Maule, I wish I could.