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Percent power/performance chart question


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Urs, I think that people run out if fuel because they are trying to fly their calculated range in miles, which in our Manuals is a "no wind" calculation.

I fly my C based on time--each tank is good for 2-1/2 hours, regardless of how many or how few miles that takes me. My groundspeed envelope in level cruise at 7500-10,000 msl, WOT- a little, 2500, 50° ROP, is 68--186 knots, which will be a huge variation in 5-hour range (yes, IAS was the same, 140-145 mph). Actually, I've proven that my actual range with this power setting is more like 6 hours, if I fly one tank dry (flew 4:45 twice, refilled with 41 gallons or 1:15 reserve remaining).

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2 hours ago, Hank said:

Urs, I think that people run out if fuel because they are trying to fly their calculated range in miles, which in our Manuals is a "no wind" calculation.

True. Today there is really not much excuse for this, with today's flight planning possibilities it is however very important to have a vaild airplane profile. Sadly, with a lot of vintage planes for whom the POH was written by marketing departments, it is really necessary to make sure you get a profile which corresponds to the real airplane rather than just a type off the POH values.

Also a lot of flight planning profiles are made sloppily, i.e. people put values for the lowest and highest altitude and let the planner do the rest. That does not work. For our vintage Mooneys, you get 2500, 5000, 7500, 10000 and 15000 ft tables, so they need to be put properly and you need to fly the profile you choose.  Yes it is a lot of work to do it right, but for all those who think typing off figures and then testing and adjusting them to your airplane, try to do it for an airliner and see what happens :)

In most products today you can define indefinite numbers of cruise profiles. I usually do a high speed profile, long range profile plus 75, 65 and 55% power. For the same profiles, you need to produce power setting charts (or look them up in the POH) so you actually use the power settings your flight planner works with.

I attached mine which I did for my C model with powerflow exhaust. Obviously not to be used by anybody as reference for real world flight ;)

So to fly LRC at 7500 ft you'd have to fly 20 inches and 2300 RPM plus crosscheck the resulting fuel flow of about 9 GPH, at 10'000 ft you have the choice between 17 or 18 inches with almost similar results and around 8 GPH. With a good fuel totalizer you will also have a pretty good idea how much fuel you actually have at TOC and compare that with the FR-TOC figure.

 

performance.jpg

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23 hours ago, Hank said:

Above ~7500msl, I pull the throttle just enough to make the MP needle wiggle. Then I set 2500, lean to peak and advance anywhere from none to 50°.

I suggest flying one tank empty, or at least until it sputters. Switch tanks and fly on. When you land, fill the now empty tank first and confirm its volume. The 24 gallon placards make no sense.

My tanks were stripped and revealed, then filled to the brim with 52.2 gallons. Yours should be the same.

I have run 2.5 hrs on a single tank and added 23 gallons afterwards, and it sure looked like there wasn't much more than a gallon left in the bottom. But of course that can be very deceiving in a low, sloping tank.  I have never had the guts to run a tank dry in an airplane. I'd be a little worried to do so to be honest.

Do you guys routinely run a tank dry? Do your passengers ask questions when things get quiet out front?

I'll probably run it near dry and then drain the rest, then fill to brim to get an idea of what the true volume is. Thanks for the suggestion. 

 

6 hours ago, carusoam said:

Double check actual amount of fuel that fits in the tanks for any new 2U airplane...

Most short body Mooneys may get 52gals total.... if their fuel necks have been updated to the 65 or newer style...

The older Mooneys with a door over the fuel cap lost some capacity with that style... aka thermos bottle fuel cap...

 

For long flights with only 52 gallons...  consider getting a FF gauge with a totalizer... or those Ceis floats and a digital display...

Flying gets more comfortable when your math matches the read outs....

 

It only took me a decade to prove that to myself...

:)

Best regards,

-a-

I have standard caps without a door. I definitely want a fuel flow gauge with totalizer. I see JPI makes a decent one which should talk to my existing JPI 700, or there is a standalone option the FuelScan 450. Either option is cheaper than upgrading to a more modern engine monitor. The previous owner did such a great job on a really cool new carbon fiber panel I'm a little hesitant to rearrange it for the big displays of the 900 series. I'm leaning towards the FuelScan but might fly a little more before making any decisions. I've only just gotten through the first annual. 

 

All the advice is great and greatly appreciated. Thanks all!

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2 hours ago, Urs_Wildermuth said:

would certainly be interesting to see what kind of endurance record one can do like this.

I recall whale watching trips where I'd struggle to get the airspeed below 120 KIAS with fuel flow between 5-6 gph.  After one unsuccessful hour, my wife asked how much fuel we had left to continue.  I did some quick math and told her "9 hours."  She paused and said she was ready to go home.

So the answer is that your max endurance is specified by your spouse, not the POH :) 

2 hours ago, Philip S said:

I have run 2.5 hrs on a single tank and added 23 gallons afterwards, and it sure looked like there wasn't much more than a gallon left in the bottom. But of course that can be very deceiving in a low, sloping tank.  I have never had the guts to run a tank dry in an airplane. I'd be a little worried to do so to be honest.

Do you guys routinely run a tank dry? Do your passengers ask questions when things get quiet out front?

While it's technically safe, be warned that poo may come out.  First, the engine does NOT stop or go quiet when it's running low--the fuel flow becomes intermittent, but since the engine continues to spin, it just kind of starts slowing down, so the first "oh s--t" moment comes when you realize the tank has already been dry for a while.  The second moment comes when you switch tanks, because it seems like it takes FOREVER to restart smoothly, it seems like it sputters for an eternity before settling down again.

If you do it, do it at altitude near an airport, and bring some Depends... :unsure:

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30 minutes ago, jaylw314 said:

I recall whale watching trips where I'd struggle to get the airspeed below 120 KIAS with fuel flow between 5-6 gph.  After one unsuccessful hour, my wife asked how much fuel we had left to continue.  I did some quick math and told her "9 hours."  She paused and said she was ready to go home.

So the answer is that your max endurance is specified by your spouse, not the POH :) 

While it's technically safe, be warned that poo may come out.  First, the engine does NOT stop or go quiet when it's running low--the fuel flow becomes intermittent, but since the engine continues to spin, it just kind of starts slowing down, so the first "oh s--t" moment comes when you realize the tank has already been dry for a while.  The second moment comes when you switch tanks, because it seems like it takes FOREVER to restart smoothly, it seems like it sputters for an eternity before settling down again.

If you do it, do it at altitude near an airport, and bring some Depends... :unsure:

Not my experience. The first time, I was distracted and it coughed once then back to smooth. Then it coughed twice and I realized my mistake and switched. The second time I was ready, waiting and expecting a cough. It just went quiet. Both restarts were almost immediate. No drama at all. 

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3 hours ago, Shiny moose said:

How about almost 11 hours  in a 67F at older 172 speeds and 150 fuel burn. 

I think someone should try it

E1395DCE-3F47-41E1-9F8B-5D4BB94184A8.jpeg

Be careful there, Moose! Introducing your 200hp, fuel-injected, heavy airplane [2740 lb!] into a discussion about C-model performance [180 hp. carbureted, 2575 lb] can be misleading to readers who don't pay close attention!

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23 minutes ago, Hank said:

Be careful there, Moose! Introducing your 200hp, fuel-injected, heavy airplane [2740 lb!] into a discussion about C-model performance [180 hp. carbureted, 2575 lb] can be misleading to readers who don't pay close attention!

That's a good point, I wonder if restarting the IO-360 after fuel starvation is more poo-inducing than the carbureted version?

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10 minutes ago, jaylw314 said:

That's a good point, I wonder if restarting the IO-360 after fuel starvation is more poo-inducing than the carbureted version?

I almost induced wife-poo while troubleshooting weird EGT readings. Why was it going up during cruise? How could it go above redline? Something clicked in the back of my mind, and I experimented with the ignition switch. When I moved it to "Right," the engine went silent and the nose pitched down to maintain my trimmed airspeed at 9500 msl, indicating that the Right magneto had died. So when I was extending my range due to planned fuel stop having pump problems, I made sure to discuss it with my wife in advance, and she didn't freak out when the engine went silent. Three legs totaling 4.7 hours [6000, 3000, 9500 msl; all airports were well below 1000 msl], then I filled up with 41 gallons including the entire left tank [26 gal].

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2 hours ago, Hank said:

I almost induced wife-poo while troubleshooting weird EGT readings. Why was it going up during cruise? How could it go above redline? Something clicked in the back of my mind, and I experimented with the ignition switch. When I moved it to "Right," the engine went silent and the nose pitched down to maintain my trimmed airspeed at 9500 msl, indicating that the Right magneto had died. So when I was extending my range due to planned fuel stop having pump problems, I made sure to discuss it with my wife in advance, and she didn't freak out when the engine went silent. Three legs totaling 4.7 hours [6000, 3000, 9500 msl; all airports were well below 1000 msl], then I filled up with 41 gallons including the entire left tank [26 gal].

Ooof, you have a good partner if she still talks to you after that! :D

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+1 for keeping the SIC in the know before doing things...  some SICs still think the plane will fall out of the sky when the engine goes silent... any engine burble is assumed to be the beginning of the end...

 

+1 for running a tank dry... but only if your selector switch moves easily... if it is binding, get it fixed before running the tank dry...

+1 for acquiring a FF/totalizer...  ask Alan if he has any pre-flown ones available...

+1 for the really low power setting in the M20C POH...   when collecting hours, minimize the FF....

If you run the tanks very low, and your fuel gauges can’t tell you which tank has more.... it is quite possible that the fuel pick-up will get unported...  nose down, fuel runs away from the pick-up....

Switch tanks count to 10... power will resume...  10seconds in the traffic pattern, without power, on final approach.... doesn’t count as good fuel management... :)

PP thoughts only, not a mechanic...

Best regards,

-a-

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