Fuel burn on AR-1

Abid

AR-1 gyro manufacturer
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Oct 31, 2011
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Tampa, FL
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AR-1
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4000+ 560 gyroplanes. Sport CFI Gyro and Trikes. Pilot Airplane
On a cross country to South Carolina and back was a good time to observe the fuel burn and average it for AR-1 912ULS powered gyroplane with 2 people and some luggage for 2 people to spend a weekend there. Basically close to gross weight.

It seems that AR1 powered by 912ULS burned 4.1 GPH at 75 knots cruise. It has a fuel tank with useable fuel capacity of 16.8 gallons (US gallons). That would mean with 30 minute reserve, making it able to fly 3.5 hours with reserve at cruise near gross weight.

Any MTO, Calidus or Tagna owners confirm if they get similar numbers at gross? Appreciate the info.
 
The Cavalon with a 914 burned a little over four gallons an hour unless I was running along at 85kts.

I used five gallons an hour for cross country planning.

I feel a half hour reserve is not enough for a gyroplane and use an hour reserve for flight planning.

I have not put much time on anything with a 912.
 
Abid, all Rotax powered gyros I know cruise reasonably at 75% power or so. At that setting, the 912 burns 20 l/h which is close to 5 gph. 4 gph seems too little for a decent cruise.

-- Chris
 
Abid, is your Rotax on diet? It sounds like I am joking but I am not.
 
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75% power on a 912ULS would be 5.4 GPH roughly.
No our 912 is not on diet. It burned this 4+ at 75 knots averaged over a pretty decent sized cross country flight. We did not go 85 knots which would have burned actually more closer to 75% or perhaps even a tad higher. The way the fuel burn was calculated was starting with a full tank and on each stop filling it back up and noting how much fuel it took. Pretty simple.
This is with Averso Stella blades 8.5 meters and Sterna 70" prop setup.
For comparison our LSA airplane burns 2.7 GPH at 75 knots with 912 ULS and only 2 GPH with 912iS. Our trikes burn about 3.5 GPH at the same speed 2 up.

I will do another test run to verify again and check speed calibration again with GPS.
 
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My Cavalon burn 4.1 solid gallons per hour. 2 up and full fuel. Cruising at 75 knots.
I have 25 gallons and do all my planning at 6 gallons/hr. Plenty of power.
Love that engine !!
 
What rpm setting was giving you 75 Kts? I would guess around 4600 based on the 4.1 gph fuel flow. Does the AR-1 have static ports? Have you done an airspeed calibration?

Thanks

Jim

Yes airspeed calibration was done. GPS ground speeds verify the general speeds as well.
Danny Kelly who was flying one up in his Tagna gyroplane next to AR1 which was two up, burned also about the same fuel from what I am told at the same speed roughly. So 75 knots at 4.1 GPH was not just AR1, it was also the same with Tagna gyro. Though AR1 was carrying an extra person.
 
You forgot to mention what fuel you're using. Some people might be using 100LL, others E10, others E0.

They used usual car gas 93 octane (E10) but on the way back used 100LL on a 150 mile leg once I believe. E10 does worsen fuel burn a little but may be by 2 or 3%. Not a lot.
 
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5,200 rpm 75Kts

RPM without manifold press. does not really tell much about power setting. In absence of manifold pressure, one can use the fuel burn as a percentage of fuel burn suggested at full power to gain approximate power setting. Usually 912ULS would be around 5000 RPM but at 27 "Hg manifold. That all depends on prop pitch and planform and twist. Usually you will find that people cruising at 5000 RPM are not at 75% power in fixed pitch props.
 
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That number seems low to me but good for you if that's what you're getting.
 
I am no engine expert by a long stretch but it seems to me that 5000 rpm will be 20 lph as per the manual.

-- Chris.
 
I'm also not an expert but I'd assume different fuel burns at same engine RPM for fine and coarse prop ;)
 
I am no engine expert by a long stretch but it seems to me that 5000 rpm will be 20 lph as per the manual.

-- Chris.

Hi Chris.
No actually. The manual calculates fuel burn by setting the prop pitch such that at WOT you can reach a max 5000 RPM. That is how they come up with manual numbers as I understand it. But when we set the prop to reach 5650 RPM. The fuel burn at 5000 is going to be different and it won't be 75% power. What it will be depends on the prop and manifold that the engine reaches. On an adjustable prop you could get there but not on a fixed pitch prop
 
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Hi Chris.
No actually. The manual calculates fuel burn by setting the prop pitch such that at WOT you can reach a max 5000 RPM. That is how they come up with manual numbers as I understand it. But when we set the prop to reach 5650 RPM. The fuel burn at 5000 is going to be different and it won't be 75% power. What it will be depends on the prop and manifold that the engine reaches. On an adjustable prop you could get there but not on a fixed pitch prop



What??????
 
Some thought on fuel consumption.

Some thought on fuel consumption.

One of the things that can be measured on a dynamometer is pounds of fuel per horsepower hour.

It is measured at different rpms because the efficiency of an engine may vary at a specific rpm.

Put simply; make more power and you burn more fuel regardless of the RPM.

The Cavalon consistently burned slightly over four gallons per hour flying at 75kts because of how much power we were using, not how many rpms we the engine was turning.

The manifold pressure and engine rpm can give a rough idea of how much power the engine is producing and how much fuel it should use if properly tuned.

My guess is they were using around 55 horsepower to burn 4.1 gallons per hour at 75kts.
 
What happens at even lower fuel burn rate?

What happens at even lower fuel burn rate?

Fara and Vance, for a two up gyro at gross 1250 lbs, 55HP for 75 knot is pretty good.

Based on power and drag relation:
85knots ~97mph @75% (75HP)
75 knots ~86 mph
So, 75HP*(86/97)^3 ~ 52HP.

Based on fuel burn ratio:
4.1gph*75HP/ 5.5gph(@75HP)~ 56HP

52 & 56 are pretty close.
Can a linear fuel burn be assumed for the 912 ULS to produce ~41 HP @3gph fuel burn?

I ask because the drag & power equation give ~80mph at 41HP and I do not think that only 41HP can get you to 80mph at 1250lb gross.

Anyone can shine some more light on this?
 
Fara and Vance, for a two up gyro at gross 1250 lbs, 55HP for 75 knot is pretty good.

Based on power and drag relation:
85knots ~97mph @75% (75HP)
75 knots ~86 mph
So, 75HP*(86/97)^3 ~ 52HP.

Based on fuel burn ratio:
4.1gph*75HP/ 5.5gph(@75HP)~ 56HP

52 & 56 are pretty close.
Can a linear fuel burn be assumed for the 912 ULS to produce ~41 HP @3gph fuel burn?

I ask because the drag & power equation give ~80mph at 41HP and I do not think that only 41HP can get you to 80mph at 1250lb gross.

Anyone can shine some more light on this?

I suspect the drag and power equation you are using is flawed.

I have not flown a gyorplane that will reach 80 miles per hour on forty one horsepower at 1,250 pounds.

I have found it difficult to predict the aerodynamic drag on a gyroplane so I don’t know where you are going with this.

In my opinion there is a lot more involved in determining power required for a gyroplane than simply weight and speed.

Based on the engines I have run on the dynamometer I would expect the pounds of fuel per horsepower hour to go up as manifold pressure goes down at the same RPM.

If I reduce the rpm to where I have the same manifold pressure at a lower rpm I would imagine the specific fuel consumption to be closer to linear.
 
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