C85 vs A65 fuel consumption

[Robert Lees]

Many of you will know that I put a C85 engine, with shall we say, "O-200 mods" into my 1946 Taylorcraft back in January 2009.

Since that time, I've had an opportunity to compare the fuel consumption with the C85 against the old A-65.

The results are quite surprising:

Between Jan 1997 (start of A-65 measuring) and Jan 2009 (removal of A-65), the average fuel consumption was 4.33 USG per hour (spread over 836 hours).

Between Feb 2009 (start of C-85 measuring) and end Dec 2012, the average fuel consumption was 4.39 USG per hour (spread over 295 hours).

So to all intents & purposes, the fuel consumption is the same, despite the much more sprightly performance of the 85.

Rob
(I love figures & statistics).

[Hank Jarrett]

Re: C85 vs A65 fuel consumption

The difference is how much you pull the throttle back after going to high power. The additional fuel consumed by an 85 when producing 60 HP is insignificant compared to a 65 putting out 60 HP. I am hardly EVER in a hurry and tend to pull my 65 back to 70% or less except when I really need it. I burn around 3.5 gallons per hour. I would bet my engine gets slightly better efficiency at the lower power settings, but probably not measurable.
Hank

[Laz]

Re: C85 vs A65 fuel consumption

Having actually flown in Rob's "85" I can say that it gets up and go's. I did all the 85 mods on mine and probably should have put a 85 on it. The actual cost of rebuilding one is the same and you can actually by new cylinders for it instead of chrome or oversize. Rob's instillation is really nice. Ask him his Pint per hour consumption is at Camp Sholler?

[Robert Lees]

Re: C85 vs A65 fuel consumption

Hank is quite right...in the cruise, I used to fly the 65 at 2250 rpm, just the same as the 85, so one would expect the consumption to be similar, and the airspeeds are similar too.

But one thing to remember is "excess power", i.e. the excess power that the aircraft has above that necessary to overcome weight & drag.
If one was to assume that my 1946 BC12D takes 50hp to actually overcome the laws of physics to fly, with an A65 I have 15hp to play with. With an 85 I have 35hp to play with....that's 133 percent more "excess power". (Assuming max rpm's).

The nice thing with the 85 is that on the occasions when one is faced with strong headwinds, I can use that excesss power and wind the engine up to 2500 and get 120mph indicated for those "get home before dark" moments, and I have used that ability on several occasions. And it's also great getting off those short, boggy fields that I tend to land on!

And spending 20 minutes in the circuit (pattern) doing touch-and-goes without going above 50' or outside a 1000' radius is much greater fun with the 85.

[Hank Jarrett]

Re: C85 vs A65 fuel consumption

All true, but I think you would be very surprised at how LITTLE power is needed to maintain flight with a Taylorcraft. I hope to actually test it later, but I suspect you can fly on a reasonable day using less than 25 HP! You aren't going to take off with that, or do any reasonable climbing, but it is amazing how little power is needed to maintain flight and altitude. I used to love to pull the power back to idle and thermal. Got to remember to clear the engine once in a while if you don't want the full soaring experience! Landing out isn't that fun when the plane isn't designed to be taken apart and trailered.
Hank

[Robert Lees]

Re: C85 vs A65 fuel consumption

...to maintain flight...

Yes, but one has to get airborne first!

I've been soaring in mine, albeit not for long.

[Hank Jarrett]

Re: C85 vs A65 fuel consumption

The problem with getting airborne is there is no easy way to drop the tow rope. ;-)
Hank

[cvavon]

Re: C85 vs A65 fuel consumption

Just a quick post the c85 on my plane does 4.70 gl per hr most of the time doing cross country a little less when doing flight training

[Ragwing nut]

Re: C85 vs A65 fuel consumption

I have not been so lucky to have that low fuel burn. Then again, I have no speed limit in the air so other than pulling the throttle back to land, I usually rested my foot on it. never liked how sluggish a "B" felt in the air with power pulled back.

[N95334]

Re: C85 vs A65 fuel consumption

Hank, I know what you mean the Taylorcraft is a great sailplane. Living here in Florida during the summer you can have a ball going from thermal to thermal and have the power pulled way back. Always wanted to turn the engine off and see how long I could stay aloft. But no starter made me think twice. Humm, can you restart a 65hp Taylorcraft by diving the get the prop to start turning again? what airspeed?

[Pearson]

Re: C85 vs A65 fuel consumption

Humm, can you restart a 65hp Taylorcraft by diving the get the prop to start turning again? what airspeed?

Yes you can! I think the best procedure is to keep the airspeed up so the prop doesn't stop. But if the prop stops you can get it going again by diving to about 75-80 indicated. It may be different depending on your prop and density altitude.

[3Dreaming]

Re: C85 vs A65 fuel consumption

Yes you can! I think the best procedure is to keep the airspeed up so the prop doesn't stop. But if the prop stops you can get it going again by diving to about 75-80 indicated. It may be different depending on your prop and density altitude.

The speeds I found were quite a bit higher than that. A nice tight 65hp with a 72-44 wood prop took 125mph and about 1000 feet to get the prop turning. I did it right over the airport ,and started the dive at 2000 AGL. I figure I would give it 1000 feet, and if it didn't start I would have a 1000 feet to set up in the pattern.

[3Dreaming]

Re: C85 vs A65 fuel consumption

The problem with getting airborne is there is no easy way to drop the tow rope. ;-)
Hank

I have heard out west they used to fly them to a sailplane meet, remove the prop and install a tow release in its place. I don't know if there was any truth to this or not.

[Pearson]

Re: C85 vs A65 fuel consumption

[QUOTE=3Dreaming;75231]The speeds I found were quite a bit higher than that. A nice tight 65hp.......QUOTE]

Tom, that is why I qualified my post with "depending on your prop and the density altitude. Even if we had the same prop, and the density altitude was the same, all of these planes are individuals. You can't with, any certainty, say that what works for one of them will work with another. My engine is past mid time, so maybe that makes a difference. I have also learned that if you want the prop to turn over right away, you do need to dive to a higher speed. But on my plane if I push it over to 80 indicated and just wait a little bit, the prop will spool up and start the engine. I don't do it unless I am at least a couple thousand feet up. And I don't do it very often. I can't imagine it is very good for the engine.