Incorrect Cruise Performance Data?

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JC150

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JC150
Hello, first timer here, forgive me if I posted in the wrong section. I apologize in advance for the long question.

I bought a Cessna 150L for the purpose of time building. I chose the C150 for economic reasons, and the performance figures I saw in the POH looked favorable. However, after I bought the plane, I noticed quickly on the first flight how wrong the data was. My biggest concern here is range. My question is A) Is there something I'm doing wrong, B) Is there something wrong with my plane or C) Is the POH wrong?

A little background info: I trained in a 2012 C172S and was taught to plan my cross countries with the data in the POH and trust them.

According to the data in my C150 POH, on a no wind situation, I should be able to go 380mi/330nm including fuel for start, taxi, runup, takeoff, climb, descent and 45 minute reserve at 2500rpm and 58% bhp at 7500 feet. 535mi w/o reserve.

Recently I flew TOL-AGC (191NM) at 7500 feet/2500RPM with a nice tailwind. Since I had a good 20 knot tailwind, the math calculated I'd land with about half tanks, since it is about half of the max range according to the POH. When I landed and checked the tanks, I had burned 17 gallons, and had about 1 hour reserve left, far more than I should have burned. So, as you can see, even though the POH says I should be able to fly 330NM legally in a no wind situation, I would have run into fuel exhaustion had I tried to do so, even with the 20 knot tailwind.

I've been trying to figure out why I'm running into this issue. About 99% of my flights are solo - long cross countries, so it's important to me to figure out why my aircraft performance isn't matching up with the POH. Let me mention that when I fly solo, i'm no where near max gross weight.

The POH say that at 7,500 feet @ 2500RPM (58% BHP), I'm supposed to get 105 MPH TAS (91 knots). In those conditions, I'm getting around 90 mph, about 15mph short of what the POH says. My aircraft has a new propeller, flap gap seals, wheel fairings, and I wax it often. I have a digital tachometer so I know I'm at 2500rpm.

However, I don't have any issues with fuel leaks. I keep the aircraft and engine clean and well maintained. The engine is a Continental O-200. I have a EGT and CHT gauge, which I use to help with leaning ROP. Also, I do compression checks monthly, which always shows good results.

So, I guess my question is, how come I'm not getting the speed and range performance I should be getting as shown in the POH? I'm getting about half the range, and about 10-15MPH slower in cruise flight.

I went from a new plane to a C150L twice my age, so I'm wondering if it has to do with the age of the aircraft?

I also noticed that Cessna advertised this for the Cessna 150 which shows two adults, two children, and two suitcases. Now, it could be me but that seems a little optimistic. So, I'm wondering, is it possible that the POH data was exaggerated a little to sell aircraft?
1966-Cessna-150-2page-Ad.jpg


Or is there something I'm doing wrong from an operators point? I'm new to the aviation game, so I figured I'd ask those with more experience. Thanks, and sorry for the long message!
 
Trust the data that is reality not the POH. But ya it could go faster

Do you have a climb prop installed ?

My 150 was good for about 95 knots, after overhaul more like 100 on a standard day around 4500. Leaned out at 2500-2600 rpm even with that said the Cessna POH is optimistic , you'd probably be surprised to see how those planes in those ads are actually equipped..bare bones.
 
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What is your actual average fuel burn per hour ? Running hard should not be more than about 6.3 - 6.5 GPH
 
I have a quick-and-dirty program that I wrote for fuel use calcs about 15 years ago and decided to put your parameters into it and see what it came back with. Fuel flow figures seem a little high based on what I remembered from my 150 time 40 years ago, but it said: CLIMB: 1.25 gallons @ 7.6 gph over 11.5 nm and 9.5 minutes + 13 gallons @ 5.9 gph over 180 nm and 1:54 CRUISE + .9 gallon for start, taxi, runup, T/O for a total of 15.2 gallons --- so, my calc isn't too far off from what you saw.
Just sayin ...
 
Check the tach - even a digital tach can be wrong.

increased fuel burn could be caused by improper leaning.

Improper rigging can slow you down, increasing fuel burn.

From your post, it seems like this is a new airplane to you. Learn what its fuel burn/speeds really are.

btw - winds aloft can be significantly different than forecast.

(and btw 2, enjoy the airplane....owning can be so much fun)
 
POH numbers do not reflect the real world, although they should. They were developed using a new airplane with a new engine flown by a professional pilot. You can't replicate those conditions.

Develop your own performance numbers as best you can, and always allow a healthy fudge factor.

Bob Gardner
 
And that 90 MPH vs. 105 MPH at 7500 feet is suspiciously close to the difference between IAS and TAS. Just checking....
 
Thanks for the replys everyone! I initially bought the plane for the sole purpose of time building, but it's been so much fun that I'm hoping to upgrade in the near future.

@ Dean V, I had a McCauley 1A101/PCM6948 prop put on. The previous propeller wasn't in the TCDS, and came off a Cessna 120, so I had that changed.

@ Taters, I'm usually burning around 6.5 gph, nothing near the 4.0-4.8 gph seen in the cruise performance charts. I knew it was a little optimistic!

Legally, I know I should plan to land with a 30 minute reserve (day), which would be 3-4 gallons. But, lets say you're approaching the airport and had 5 gallons remaining. Should I be concerned about having such little fuel in the tanks? By that I mean, if I did a maneuver such as a steep turn, could it be possible for the fuel to slide to one side of the tank and not continue to flow to the engine? Also, since there's no way to cross feed, or select tanks, what would happen if for example you had 4 gallons in the right tank but the left tank went dry?

I don't usually ask "what if" questions, but I've always tried to land with at least an hour reserve. The thought of landing with 3-4 gallons, and watching the some-what accurate fuel gauges bouncing close to E is a little concerning.

@GWEN, if you don't mind me asking about your fuel calc program, is that something you made on a computer? I was wondering how I could make something similar?

@Bob Noel, yes this is a new plane for me, many firsts. First time flying steam gauges, first time using a directional gyro, first time using a carburetor, etc.. But its a lot of fun to fly! I'm always up for learning something new!

Also, I use the winds aloft data from xm wx.. But, now i'm wondering if those could be way off too? I never questioned xm wx winds aloft until now.

@ Bob G, Thanks for the advice. At the university I went to, they taught us to trust the POH numbers even if they seemed off. I can't remember exactly why, but something to do with liability. Regardless, if I had followed the numbers in the POH and attempted a 250NM+ flight in no-wind conditions, I'd probably be looking at a fuel exhaustion situation.

@ MAKG, I use the sportys E6B app on my ipad to calculate my true airspeed. I also fly the g1000 C172, and the value I get on my ipad matches the TAS value depicted on the G1000, so, I just assumed it worked. What do you think about the possibility of a CG issue? I took my golden retriever flying with me last week in the back, and remembered at 5500 feet we were getting about 103MPH true, when I average 97 true at 2500 RPM. Could it be too much forward CG causing this slow speed problem? When I do W+B, it's within limits, but shows a forward CG.
 
Fly 4 cardinal directions on your heading indicator, measure and average the GS using GPS to determine your TAS.

Do timed flights with careful fuel data to determine fuel burn.

Check the continental specs on fuel burn. Your POH numbers could have specified Best Power or LOP operations for the data given, they use "clever" terminology sometimes, a careful reading will determine the test conditions when the data was obtained. Review the TCDS, which you can find on the FAA website.

After you're done, you will know how YOUR airplane performs. Use THAT data and watch for deviations to suspect issues.
 
Lean, lean lean
Have the rigging professionally done
Understand the limitations of the factory data
 
Thanks for the advice Jaybird. I will certainly try that. I see you're also from the DC area, I'm on the Virginia side though.
 
You can have the plane weighed and CG done anytime. That will affect performance and most (all) airplanes gain weight over time.
 
@ Duncan, I was so used to lean assist in the G1000, when I bought the C150 i had to learn how to do it the old fashion way. I had an EGT gauge put in, but it didn't seem to work too well. Now I just lean the mixture until I see a slight rise in RPM, then turn the mixture 2 turns in. I also heard the method of leaning until roughness, then rich slightly until it smooths out. If you don't mind me asking, which way would you recommend?
 
I agree with other check your TAS with a GPS or flight computer , are you leaning until it runs rough then mix back in until, smooth ?

Might have your carb air box checked to make sure the c. heat valve is closing all the way..this can cause a loss of power and more fuel burn...made a noticeable difference on my 150 once that was rebuilt this last December.
 
JC150 said:
@ Duncan, I was so used to lean assist in the G1000, when I bought the C150 i had to learn how to do it the old fashion way. I had an EGT gauge put in, but it didn't seem to work too well. Now I just lean the mixture until I see a slight rise in RPM, then turn the mixture 2 turns in. I also heard the method of leaning until roughness, then rich slightly until it smooths out. If you don't mind me asking, which way would you recommend?
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You are running very rich that way,

Sans EGT the standard is was taught was lean to rough, enrich to smooth.
 
@ Taters, good point. I noticed a change in the EGT/CHT gauge when I pushed and held in the carb heat knob. When I let go, the knob sticks out slightly, and the temp dropped on the EGT/CHT gauge. I'm pretty sure it was the CHT side... could that have something to do with it?
 
JC150 said:
Legally, I know I should plan to land with a 30 minute reserve (day), which would be 3-4 gallons. But, lets say you're approaching the airport and had 5 gallons remaining. Should I be concerned about having such little fuel in the tanks? By that I mean, if I did a maneuver such as a steep turn, could it be possible for the fuel to slide to one side of the tank and not continue to flow to the engine?.
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If you are using the foot rests to keep the aircraft coordinated, why would the fuel slide to one side of the tank?

On the other hand, if you are doing a forward slip, in some aircraft it is possible to un-port the low wing tank. Dunno what would happen to your aircraft in that case - likely it would not be an issue since if you are slipping you are typically at a low fuel flow.
 
JC150 said:
@ Taters, good point. I noticed a change in the EGT/CHT gauge when I pushed and held in the carb heat knob. When I let go, the knob sticks out slightly, and the temp dropped on the EGT/CHT gauge. I'm pretty sure it was the CHT side... could that have something to do with it?
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The knob should stick out slightly,

Honestly, stop running so pig rich and you will likely see a big improvement.
 
JC150 said:
@ Taters, good point. I noticed a change in the EGT/CHT gauge when I pushed and held in the carb heat knob. When I let go, the knob sticks out slightly, and the temp dropped on the EGT/CHT gauge. I'm pretty sure it was the CHT side... could that have something to do with it?
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Has everything to do with it , once you apply the kit your carb heat valve will behave like its supposed to , You can get the kit from aircraft spruce , but some of the parts have to be braised on..not a fun/easy job.
 
If you want to maximize duration, lean to peak EGT, and fly high enough where that won't cause detonation (watch the CHT -- probably 5000 feet) or run at lower power. Recommended lean is a bit richer than that.

150s don't have rudder trim (except perhaps for ground-adjustible tabs). Make sure you're coordinated in cruise!

An aft CG can make a difference, and it will be bigger in a 150 than a larger aircraft. But 15% seems a bit hard to swallow.
 
Skylane81E said:
The knob should stick out slightly,

Honestly, stop running so pig rich and you will likely see a big improvement.
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I agree but it shouldn't cause a performance increase with forward pressure.
 
Skylane81E said:
The knob should stick out slightly,

Honestly, stop running so pig rich and you will likely see a big improvement.
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YEAH

I flew a lot in a 152 for awhile. For best range -

Climb to 6-8000 feet, throttle wide open. If lower, set throttle for 65% power (I just guess) Lean until RPM starts dropping and gets rough. Then enrich until the rpm rises a little and the roughness goes away.

You should burn about 4.5 GPH this way
 
JC150 said:
@ Duncan, I was so used to lean assist in the G1000, when I bought the C150 i had to learn how to do it the old fashion way. I had an EGT gauge put in, but it didn't seem to work too well. Now I just lean the mixture until I see a slight rise in RPM, then turn the mixture 2 turns in. I also heard the method of leaning until roughness, then rich slightly until it smooths out. If you don't mind me asking, which way would you recommend?
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There's your issue for the fuel burn.
 
@ Taters, thanks. I'll look at aircraft spruce for it.

@ Ren, thanks for the advice. Would you say 6-8,000 is the optimum cruise altitude? I've been using 7,500-10,500 mainly. Even been up to 11.5 a couple times to avoid some weather. But i guess the slightly lower fuel burn doesn't make up for the extra fuel burn to climb to that altitude?

@ i, Thank You. I will start leaning that way from now on. I learned to lean using the Lean Assist on the MFD of the G1000, so it was new to me. When I looked on the internet, someone had said they were leaning that way, which is why I used that method. But I will use the other method now
 
To summarize - you've been running with the mixture set for best power. The cruise tables are written with mixture set for best economy.

For the purposes of leaning a normally aspirated, carbureted engine, I'd forget about the EGT gauge, especially if it is a single value only instead of reading all cylinders.

Lean till it gets rough, slowly enrichen till it just barely smooths out. None of this "two twists of the knob" business, mixture knobs aren't calibrated that way. My plane has all cylinder EGT/CHT and fuel flow, and I've found that this method is the quickest, most consistent way to achieve the POH performance numbers.
 
JC150 said:
Should I be concerned about having such little fuel in the tanks? By that I mean, if I did a maneuver such as a steep turn, could it be possible for the fuel to slide to one side of the tank and not continue to flow to the engine?
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If your turn is coordinated, the fuel will stay centered at the lowest portion of the tank. Kind of like Bob Hoover pouring iced tea in a coordinated barrel roll. http://www.youtube.com/watch?v=pMWxuKcD6vE

Also, since there's no way to cross feed, or select tanks, what would happen if for example you had 4 gallons in the right tank but the left tank went dry?
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In coordinated flight, no big deal. The fuel gravity flows to the engine even if one wing is empty.

It is certainly possible to unport a fuel tank in uncoordinated flight. For example, a long slip with the empty tank high.

FWIW, the 150 has a "balance tube" between the two tanks which is supposed to let the fuel equalize between the tanks. I've found that it does not work very well, I suspect because only one of the tanks is vented.
 
JC150 said:
@ Taters, thanks. I'll look at aircraft spruce for it.

@ Ren, thanks for the advice. Would you say 6-8,000 is the optimum cruise altitude? I've been using 7,500-10,500 mainly. Even been up to 11.5 a couple times to avoid some weather. But i guess the slightly lower fuel burn doesn't make up for the extra fuel burn to climb to that altitude?

@ i, Thank You. I will start leaning that way from now on. I learned to lean using the Lean Assist on the MFD of the G1000, so it was new to me. When I looked on the internet, someone had said they were leaning that way, which is why I used that method. But I will use the other method now
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Just depends on so many things.

Headwinds - stay low and fly at higher power

Tailwinds - climb as high as reasonable for the trip

So I would use 6-8k feet as a starting point. On a light wind day I would typically cruise at those altitudes
 
For no winds, look in the performance chart where your power setting intersects full throttle, and go there.
 
JC150 said:
@ Duncan, I was so used to lean assist in the G1000, when I bought the C150 i had to learn how to do it the old fashion way. I had an EGT gauge put in, but it didn't seem to work too well. Now I just lean the mixture until I see a slight rise in RPM, then turn the mixture 2 turns in. I also heard the method of leaning until roughness, then rich slightly until it smooths out. If you don't mind me asking, which way would you recommend?
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The latter. Your leaning method will leave you somewhere way rich of peak -- nowhere near the leaning necessary to get book fuel burns.
 
JC150 said:
However, after I bought the plane, I noticed quickly on the first flight how wrong the data was. My biggest concern here is range. My question is A) Is there something I'm doing wrong, B) Is there something wrong with my plane or C) Is the POH wrong?
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The C-150 is a nice plane.

I don't trust the fuel gauges or the dipsticks you can buy from Sporty's or whoever.

Best way to solve that uncertainty would be to fly, refuel, fly refuel, etc. and record the results.

A C-150 should burn 5.5 to 6 GPH at cruise power.

If you're burning way too much fuel, have a mechanic check the carb.
 
What everyone else has said plus

Wheel pants installed?

Flight controls rigged correctly?


Everything stated will affect performance, and added together, it can be significant.
 
JC150 said:
@GWEN, if you don't mind me asking about your fuel calc program, is that something you made on a computer? I was wondering how I could make something similar?
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Yeah, sort of. I did that program to simplify my preflights about maybe 10-15 years ago? I don't remember how it was coded (iAPX86, ForTran, or BASIC), so all that I have is the executable (vs source). I can forward a copy, if you'd like.
======================
I should probably mention -- it was intended for use ROP. Has no provision for estimating LOP operation

It is intended for use as a CommandLine / Terminal operation --- it doesn't work in Windows (or X-Windows)

====================
Given that I also had a fuel-challenged experience in a 150E (due to winds aloft vastly different from forecast), I can assume that the routine was written with "Best Power" vs "Economy" in mind
 
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JC150, I trained in 152's and Sparrowhark 152's. The mix setting(s) you've already heard about ... one thing we found is that by retarding the throttle slightly from WOT resulted in almost no change in RPM but DID make a difference in fuel burn. Try retarding 1/4" and then 1/2" and check your results (RPM, ground speed, time, burn rate).
 
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