C 170B climb fuel burn chart ??

[dj2790]

I have just purchased a 170B model. It's my first 170 and I would like to know (for flight planning) the fuel burn in a climb at full throttle. I know there are charts for cruise, but can't seem to find any for the climb. Are there any or is it just a WAG? Thanks in advance.

[bagarre]

I WAG everything at 9 gallons an hour so I'm never disappointed

[Bruce Fenstermacher]

This is the second time in as many weeks someone asked that question and the second time I've tried to figure out how to use the chart on page 12 of the C-145 operators manual (X30015 - PDF available here: http://www.cessna170.org/forums/viewtop ... 39&t=10364)

Can anyone explain how to use this chart which we could then read to swag takeoff fuel consumption?

X30015 pg 12 figure 2.jpg

BTW I noticed the 0-300 chart is different and will render a different result once one knew how to work the chart, but the result shouldn't be different than the shown C-145-2H chart.

[Bruce Fenstermacher]

That's a pretty good stab Arash. Makes sense anyway.

I'd been looking at the Spec. Fuel Cons - Lbs/BHP/Hrs and coming up with the formula .50/129/HR. That equation of course doesn't work and I couldn't see any other way to do it.

[Bruce Fenstermacher]

So climbing out at sea level at 2400 RPM then the formula would be .51*102=52.02 lbs. /6 = 8.67 gal hour.

[sfarringer]

My recollection is that my fuel flow gage reads about 11 to 11.5 gph at full throttle climb at low altitude.
Of course, I don't really spend much time looking at the fuel flow gage during climb......... But I'll look again next time out and see how bad my memory is........

Update:
-10C temperature today.
Full throttle climb at 80 MPH indicated, fuel flow shows 10.7 GPH.
Full throttle straight and level, fuel flow shows 11.5 GPH

[KS170A]

My recollection is that my fuel flow gage reads about 11 to 11.5 gph at full throttle climb at low altitude.
Of course, I don't really spend much time looking at the fuel flow gage during climb......... But I'll look again next time out and see how bad my memory is........

My home field elevation is about 1500', and I believe my O-300 is also in this neighborhood. Also going from memory, though...

[Bruce Fenstermacher]

Of course the chart posted is not a climb fuel burn chart. It is a sea level performance chart. It is however one of the few charts that has a fuel burn. Perhaps we are interpreting the chart wrong.

I would think fuel burn in a full throttle climb near sea level with a standard prop would be about 11 or 12 gph.

I thought Arash's numbers looked Ok except for one thing. I can't get 2600 rpm on climb which he used (best I remember anyway ). Thats why my example used a lower RPM of 2400 rpm. I seem to remember RPM closer to 2500 so if the chart can be used for this purpose and we are working it correctly, fuel burn would be between 8.6 and 10.7 gph.

[Bruce Fenstermacher]

One of the reasons I don't know better what my climb fuel burn is is that it really doesn't matter that much in the big scheme of things. As David pointed out for planning purpose I use 9 gph. I rarely climb higher than 1500ft AGL so my climb is not that long and of course I figure I'm burning much less fuel on decent which evens burn rate out.

[hilltop170]

My fuel flow computer shows 10 to 10-1/2gph at full throttle, full rich.

[DWood]

I have finally had a chance to study this graph for awhile and i remember similar ones in college. I believe I have it figured out and feel confident enough to post it. There are actually three graphs on this chart and the bottom two are needed for fuel consumption.
The Bottom graph is Specific Fuel Consumption in LBS/BHP/HR vs RPM
The Center Graph is BHP vs RPM
The Top Graph is Manifold Press vs RPM
Throttle is a Full open
The RPM is a function of Propeller Loading and is at max at 2700 RPM.

So here is the data as I see it:

Propeller loading
Spec Fuel Cons Cons
RPM LB/BHP/HR BHP Hr Lbs/Hr Lb/Gal Gal/Hr
2700 0.52 145 1 75.4 6 12.6
2600 0.5 128 1 64 6 10.7
2500 0.55 113 1 62.15 6 10.4
2400 0.51 100 1 51 6 8.5
2300 0.52 90 1 46.8 6 7.8
2200 0.53 78 1 41.34 6 6.9

I can't seem to get the matrix to spread out

2700 RPM 12.6 GPH
2600 RPM 10.7 GPH
2500 RPM 10.4 GPH
2400 RPM 8.5 GPH
2300 RPM 7.8 GPH
2200 RPM 6.9 RPM

[DWood]

Arash
Please try it this way.

The throttle is wide open and BHP & Fuel flow is a function of RPM. RPM is a function of Prop Load. This is demonstrated on departure where your RPM increases as you level off.

At 2400 on the bottom prop load is approx .51 LBS/BHP/HR
At 2400 on the center chart prop load is producing 100 HP

.51 LBS/BHP/HR * 100 BHP * 1 HR / 6 LBS / Gal = 8.5 Gal / HR

[Bruce Fenstermacher]

Well I couldn't figure it out at all.

Still not sure which line to use except for one point, 2700 RPM

[DWood]

Arash

As the propeller is loaded the RPMs drop.

The one point on the chart that convinced me that the Throttle Curve isn't used is the center chart. If the throttle is for throttle position then at idle position it shows the BHP to be 115 BHP which doesn't make sense.
It does make more sense that the Prop load shows ~72 BHP. I can buy that.

Now this is also a C-145-2H which probably has the Aeromatic prop.

Also the fuel flow is based on engine RPM and not throttle position.

I see we are crossing posts so I will look at the o 300 curve which says FULL throttle.

[DWood]

O 300

2600 RPM .47 LB/ BHP/HR * 127 BHP * 1 HR / 6 LBS per Gal = 9.9 Gal per Hr