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samira.h(at)shaw.ca
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threein60(at)yahoo.com
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 Posted: Tue Jan 17, 2012 8:11 am Post subject: fuel range of a stock CJ? |
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I think you should find out Scott Andrews' secret. He has a CJ with an M14P and always lands with more fuel than he departed with! On long journeys he has to crack open one fuel cap to vent the excess fuel. All this while cruising a 175kts and the engine just above idle :0P
Just giving Scott some crap!
Larry Pine
--- On Tue, 1/17/12, Elmar & Manuela Hegenauer <samira.h(at)shaw.ca> wrote:
| Quote: |
From: Elmar & Manuela Hegenauer <samira.h(at)shaw.ca>
Subject: Yak-List: fuel range of a stock CJ?
To: yak-list(at)matronics.com
Date: Tuesday, January 17, 2012, 8:37 AM
--> Yak-List message posted by: Elmar & Manuela Hegenauer <[url=/mc/compose?to=samira.h(at)shaw.ca]samira.h(at)shaw.ca[/url]>
I have read Brian's recent posting about
the fuel range of a stock 285hp CJ.
As far as I am understanding is that 42 US gal.
would give you 3.5 hrs of flight time + 30 min.
reserve, but these numbers differ from the ones
stated in my handbook and my own experience 
What exact speed, rpm and MP would translate
in that kind of range? Photoshare, and much much onics.com/Navigator?Yak-List" target="_blank">http://www.matronics.com/Na - MATRONICS WEB -Matt Dralle, Listm/contribution" =======
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[quote][b]
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brian(at)lloyd.com
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| Posted: Tue Jan 17, 2012 9:17 am Post subject: fuel range of a stock CJ? |
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On Tue, Jan 17, 2012 at 7:37 AM, Elmar & Manuela Hegenauer <samira.h(at)shaw.ca (samira.h(at)shaw.ca)> wrote:
| Quote: | --> Yak-List message posted by: Elmar & Manuela Hegenauer <samira.h(at)shaw.ca (samira.h(at)shaw.ca)>
I have read Brian's recent posting about
the fuel range of a stock 285hp CJ.
As far as I am understanding is that 42 US gal.
would give you 3.5 hrs of flight time + 30 min.
reserve, but these numbers differ from the ones
stated in my handbook and my own experience
What exact speed, rpm and MP would translate
in that kind of range?
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I found that the CJ6A with a stock engine, is most efficient around 11,500'. I used to operate at full-throttle, 1950 RPM, and leaned to peak EGT. I would have opted for lean-of-peak operation but the engine would surge. (I suspect that the carb was out of adjustment but without a flow-bench to test it, I couldn't verify.) The resulting fuel burn was 11.5 GPH. Assuming a usable fuel load of 40gal, this results in a duration-to-empty of 3 hours and 28.7 min. (My apologies for stating as 3.5 + 0.5. The 3.5 stuck in my head.) So the actual number is 3hr + 30 min reserve. TAS is 130 kts yielding a no-wind range of 390nm. With a reasonable tailwind of 20kts flying eastbound I would regularly fly 450nm legs. By flying this way and carefully picking my fuel stops, I could usually eliminate two stops in a coast-to-coast flight. I could also do many flights non-stop where otherwise I would be making an intermediate stop.
So, even though you are flying about 10kts more slowly, eliminating a stop makes a big difference by eliminating lost time allowing you to arrive at your destination sooner.
Caveat: you have to verify your own fuel burn over several hops to confirm you are getting consistent results with these power settings. I also recommend using these hops to verify the accuracy of your fuel gauge. I found that mine appeared to be stingy by about 7%, i.e. the fuel in the tanks was about 7% more than what the gauge read. What this does is make you nervous about mid-way through the flight as you think you are going to be about 15min short on fuel. But as you press on (making sure you have intermediate landing spots) you will find that your fuel burn according to the fuel gauge is converging on your original calculation. (You do carry an E6B and do fuel-remaining-at-destination calculations, don't you?) Part of this is due to the increased fuel-burn during initial climb. Regardless, the goal is to accurately determine the average fuel burn at maximum range.
It is truly amazing what you can learn about your airplane if you are diligent about doing your own flight testing and data collection. I find that most pilots do no know their own airplanes very well and leave a lot of performance on the table when flying them. Knowing your airplane's real performance can provide you a substantial safety factor you didn't know was there.
--
Brian Lloyd, WB6RQN/J79BPL
3191 Western Dr.
Cameron Park, CA 95682
brian(at)lloyd.com (brian(at)lloyd.com)
+1.767.617.1365 (Dominica)
+1.916.877.5067 (USA)
[quote][b]
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yakjock(at)gmail.com
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| Posted: Wed Jan 18, 2012 1:48 am Post subject: fuel range of a stock CJ? |
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When it comes to range I find altitude is my friend (and it doesn't hurt for going over our mountain ranges either). I have the M14P with the Performance Airflow injection carb that is leaned manually. At 13,500' I am typically flying wide open throttle lean of peak (WOTLOP) at 154 kts TAS, around 20.8", 2100 RPM and 12.6 GPH. since it takes a bit of fuel to get up there, my duration is about 5 hrs to empty on 72 gallons with an indicated no-reserve range of about 700+ nautical miles (however, my bladder is more constraining). Flying in the 15,500 to 17,500 range gives a little higher TAS with a bit lower burn rate.
I have flown a lot of cross country with Tom Elliott in his stock CJ, and we are usually pretty close to each other on fuel burn. For cruising the stock CJ handles altitude quite well. On a trip together to Kalispel, Montana from Portland, Oregon, we were cleared into Class A airspace to stay VFR on top over the mountains. We were climbing pretty well through 18,640' as we approached the Kalispel airport (KGPI is 2,977'). The descent was one of those times when it is just great to have a warbird!
I have also flown quite a bit with Brian, and can attest to the fact that he is very adroit at milking a CJ for performance.
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brian(at)lloyd.com
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| Posted: Wed Jan 18, 2012 7:35 am Post subject: fuel range of a stock CJ? |
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On Wed, Jan 18, 2012 at 1:45 AM, Hal Morley <yakjock(at)gmail.com (yakjock(at)gmail.com)> wrote:
| Quote: | --> Yak-List message posted by: Hal Morley <yakjock(at)gmail.com (yakjock(at)gmail.com)>
When it comes to range I find altitude is my friend (and it doesn't hurt for going over our mountain ranges either). |
Hal is right on the money with this comment. I did experiment with different altitudes and its effect on max range. I too have had the CJ6A up to 18,000' (but then I was measuring the actual climb performance of the aircraft). In cruise I have operated from about 6000' to 15,000' which is how I came to the conclusion that right around 12,000' is the most efficient altitude.
But Hal aludes to a little secret: if you have tailwinds that increase with altitude, your most efficient altitude goes up (to a point). The actual efficiency of the aircraft may go down but the increased groundspeed changes the effective efficiency (ground distance covered per unit of fuel) in your favor.
And I would expect Hal's airplane to be more efficient higher up due to the excess available horsepower at higher altitudes. My seat-of-the-pants guess would put the most efficient altitude for his plane up around 15,000'. It would be interesting to gather data to see. I bet he has the instrumentation (fuel flow) to collect that data quickly. I had to get my data points on a per-hop basis at the gas pump which takes a bit more time.
--
Brian Lloyd, WB6RQN/J79BPL
3191 Western Dr.
Cameron Park, CA 95682
brian(at)lloyd.com (brian(at)lloyd.com)
+1.767.617.1365 (Dominica)
+1.916.877.5067 (USA)
[quote][b]
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