Did your life come with instructions???!! I keep looking for mine but must have misplaced them...
Thanks, -- Chris.
ArrowCopter sets new speed record
- Thread starter ckurz7000
- Start date
Thanks, -- Chris.
Jean Claude
Junior Member
Registered by FAI makes sense to show the world an incontestable performance.
Registered by the ARC, the C30 performance is as reliable and can be compared.
So, the 131 km/h in 2007 was not really a technical achievement. But now 181 km/h is really a novelty !
Good work Chrs, congrats
Jean Claude
Junior Member
At this speed parasitic drag appears more clearly.
Therefore, now we best can clarify it.
I guess the speed was 185 km/h to account for the time lost in the half turn.
I also assume that the mass was 440 kg with only the pilot and 14 kg of gasoline.
In this case the drag of the rotor 8.6 x 0.2 m and 3 degrees was 420 N
I guess still the propeller thrust was 1150 N ie 100hp at 0.79 efficiency
Therefore the parasitic drag is 730 N and the parasitical drag coefficient of ArrowCopter C20 is 0.45 m2
It is only half of old Bensen without any fairing (0.9 m2) Yet the dress is nice.
Therefore, now we best can clarify it.
I guess the speed was 185 km/h to account for the time lost in the half turn.
I also assume that the mass was 440 kg with only the pilot and 14 kg of gasoline.
In this case the drag of the rotor 8.6 x 0.2 m and 3 degrees was 420 N
I guess still the propeller thrust was 1150 N ie 100hp at 0.79 efficiency
Therefore the parasitic drag is 730 N and the parasitical drag coefficient of ArrowCopter C20 is 0.45 m2
It is only half of old Bensen without any fairing (0.9 m2) Yet the dress is nice.
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To give you more accurate numbers: my average cruising speed was more like 200 km/h. The difference is for wind, turning and accounting for the climb. My take-off weight was 500 kg.
Your thrust looks OK.
-- Chris.
Jean Claude
Junior Member
The flight manual said empty weight 342 kg and fuel capacity 76 liters
You said a completely empty tank and half of the other. So, remaining quantity = 19 l or 14 kg. Then I assigned you a flat rate of 84 kg. Hence my 440 kg
How your 500 kg?
You said 25 km/h headwind on the way. Therefore back with 25 km/h on back. This has altered than 3.5 km/h your average speed back and forth.
Then half a turn angle of 45° represents a distance of 800 m to 180 km/h or 16 seconds lost on a 15 minute course. It is 1.8% increase required or 3.3 km/h
So we need real speed of 181 km/h (registred) + 3.5 km/h (wind effect) + 3.3 km / h (half turn effect) = 188 km/h
At last, taking in account the climb, you must also takes in account the temporary advantage of the two descents before the line. How much ?
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Well, I had a look at the flight recording made by the EFIS installed in the gyro. My average airspeed was 197.5 km/h. This is determined as the average from IAS readings taken once per second between passing the start gate and passing the finish gate. The maximum speed was 225 km/h, by the way.
Regarding weight. My empty weight is 372 kg. That's because I have all the options installed. 342 kg is the lightest possible empty weight. And I am 1,94 m tall and weigh 90 kg. With clothes and miscellaneous stuff (flight recorder, battery, documents, headset, etc.) I weighed in at 93 kg.
Greetings, -- Chris.
P.S.: You are a stickler for details, which I admire. How do you find the time to spend on this?
That is not symmetric because my best rate of climb speed is about 105 km/h and my average cruise speed is 198 km/h. I cannot go that much faster on descent as I can go slower on the climb.
Regarding weight. My empty weight is 372 kg. That's because I have all the options installed. 342 kg is the lightest possible empty weight. And I am 1,94 m tall and weigh 90 kg. With clothes and miscellaneous stuff (flight recorder, battery, documents, headset, etc.) I weighed in at 93 kg.
Greetings, -- Chris.
P.S.: You are a stickler for details, which I admire. How do you find the time to spend on this?
Jean Claude
Junior Member
I'm just trying to get a realistic coefficient of drag.
If I understand correctly, the weight for this flight was 372 + 93 + 14 = 479 kg right?
It is required for know the rotor drag.
Regarding speed, the anemometer is too imprecise because of the difficulty of the static pressure. I was hoping better by the stopwatch.
But I was wrong to think that your speed and power was constant.
If the climb was slower, and the power was 115 hp for 5min, then my calculation is distorted without knowing in what direction.
Remember, without quantifying, we know nothing.
If I understand correctly, the weight for this flight was 372 + 93 + 14 = 479 kg right?
It is required for know the rotor drag.
Regarding speed, the anemometer is too imprecise because of the difficulty of the static pressure. I was hoping better by the stopwatch.
But I was wrong to think that your speed and power was constant.
If the climb was slower, and the power was 115 hp for 5min, then my calculation is distorted without knowing in what direction.
Remember, without quantifying, we know nothing.
The ASI is actually pretty well calibrated. sttic pressure is derived from two static ports carefully located on each side if the gyro. We experimented a lot with this. Weight is higher because I carried more fuel than you assume. I can give you a better number once I check with the EFIS again. It also records fuel quantity.
What Cd do you get with the numbers I gave you?
A while ago we did a state-of-the-art CFD calculation of drag at 150 km/h cruise. I must see if I can get these data. Alternatively we can do a dedicated test flight.
-- Chris.
What Cd do you get with the numbers I gave you?
A while ago we did a state-of-the-art CFD calculation of drag at 150 km/h cruise. I must see if I can get these data. Alternatively we can do a dedicated test flight.
-- Chris.
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Jean Claude
Junior Member
From your text, Chris: " I emptied the left tank and about half of the right one to be as light as possible." For me this gives 14 Kg, not 35 kg
If 200 km/h at weight 500 kg, ie 4900 N, then I find a parasitical drag = 0.33m2
(assumed 397 rrpm, rotor drag = 465 N, propeller thrust = 1070 N)
If 185 km/h at weight 4650 N, then I find a parasitical drag = 0.43m2
(assumed 385r rpm, rotor drag = 460 N, propeller thrust = 1130 N)
Pitch at rest is not the same as in flight because the constraints. RRPM informs on that. How much read you ?
Computational Fluid Dynamics is very reliable when the flow is not separated from the walls. Unfortunately, on the ass of the pod the flow is largely separed.
So, a flight test dedicated is better, noting carefully rpm, weight, power, atmospheric density.
High sensitivity of the results requires be picky
Jean Claude
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The CFD code was not a simple Navier-Stokes solver. It also used some other algorithm (I believe particle-in-cell) which is supposed to capture the properties of turbulent flow well. In any case, its predictions matched our flight data almost to the "tee".
But I will try to measure the relevant flight parameters in another high speed situation. You'll get accurate numbers for weight, rrpm, speed, rpm and density altitude.
Greetings, -- Chris.
But I will try to measure the relevant flight parameters in another high speed situation. You'll get accurate numbers for weight, rrpm, speed, rpm and density altitude.
Greetings, -- Chris.
Jean Claude
Junior Member
I would be grateful
Seeing is believing, Alex. With this lightweight Rotax and 500 kg total weight for that flight I was able to cruise at 200 km/h.
Climb rate at the MTOW of 560 kg is still 900 fpm.
-- Chris.
OK, here are the numbers hot off the press:
Flight mass: 518 kg
Density altitude: 400 ft
Rotor rpm: 375
IAS: 203 km/h
Power setting: 5.500/35" (100% max continuous power, i.e., 100 hp)
I am not so certain about the 3° of disk AoA. It is probably more, because the stick was not at the forward stop. However, the result of the calculation of the effective drag area depends on it linearly. Change it to 6° and you get a much smaller area. So without measuring it, I am not sure that you will get a decent result...
Greetings, -- Chris.
Just for fun I did a back of the envelope calculation myself and got 0,20 m^2 with the above numbers. But I didn't use any kind of rotor model, just assumed that the aerodynamic drag of the rotor was W * tan(a), where W is the gyro weight and a the disk AoA.
Prop thrust: 1030 N
Rotor drag (estimated as discribed above): 266 N
Aerodynamic drag is the difference of the two: 764 N
Air density: 1.27 kg/m^3
Flat plate drag coefficient: 2
With these numbers I get for the equivalent area of the parasitc drag: 0,19 m^2.
There are two main uncertainties in this: the disk AoA and the error in the airspeed as measured by the ASI. If I use 190 km/h I get 0.23 m^2.
Greetings, -- Chris.
Prop thrust: 1030 N
Rotor drag (estimated as discribed above): 266 N
Aerodynamic drag is the difference of the two: 764 N
Air density: 1.27 kg/m^3
Flat plate drag coefficient: 2
With these numbers I get for the equivalent area of the parasitc drag: 0,19 m^2.
There are two main uncertainties in this: the disk AoA and the error in the airspeed as measured by the ASI. If I use 190 km/h I get 0.23 m^2.
Greetings, -- Chris.
Jean Claude
Junior Member
Chris, thank you for your answer.
If 203 km/h at weight 518 kg, ie 5080 N,
375 rrpm means blades pitch in flight = + 4.3° aerod. (more than the pitch setting because underbalancing), then according my spreadsheet: rotor drag = 454 N (less profile loss), and disk A.o.A = +5.1° Longitudinal flapping a1 = 4.2°
With 100 HP, propeller thrust = 1050 N
Difference= parasitical drag = 596 N
Because Drag = ½ ρ V² S Cd, we have S.Cd= 2 D/ ρ V² = 0.32 which is in m²
unrelated to the drag of a flat plate, but proximity gives a good mental picture.
Note: standard air density at 400 feet above see level is 1.17 kg/m3 .
If 190 km/h, then rotor drag = 485 N according my spreadsheet.
Disk A.o.A = +5.45° a1 = 3.85° Blades pitch in flight = + 4.12° aerod.
With 100 HP, propeller thrust = 1110 N
Difference= parasitical drag = 625 N
=> S.Cd = 0.38 m²
Main uncertainty is the airspeed.
Other point.
In my post # 26, I mentioned that my calculation is for a 8.6 x 0.2 m rotor, without being contradicted. Yet the autorotation limit would be reached before 210 km/h.
Since you said reach 220 km/h, this means an inconsistency.
Are you sure on the cord of 0.2 m? Not more ?
This hardly changes the calculated parasitic drag, but I am curious.
If 203 km/h at weight 518 kg, ie 5080 N,
375 rrpm means blades pitch in flight = + 4.3° aerod. (more than the pitch setting because underbalancing), then according my spreadsheet: rotor drag = 454 N (less profile loss), and disk A.o.A = +5.1° Longitudinal flapping a1 = 4.2°
With 100 HP, propeller thrust = 1050 N
Difference= parasitical drag = 596 N
Because Drag = ½ ρ V² S Cd, we have S.Cd= 2 D/ ρ V² = 0.32 which is in m²
unrelated to the drag of a flat plate, but proximity gives a good mental picture.
Note: standard air density at 400 feet above see level is 1.17 kg/m3 .
If 190 km/h, then rotor drag = 485 N according my spreadsheet.
Disk A.o.A = +5.45° a1 = 3.85° Blades pitch in flight = + 4.12° aerod.
With 100 HP, propeller thrust = 1110 N
Difference= parasitical drag = 625 N
=> S.Cd = 0.38 m²
Main uncertainty is the airspeed.
Other point.
In my post # 26, I mentioned that my calculation is for a 8.6 x 0.2 m rotor, without being contradicted. Yet the autorotation limit would be reached before 210 km/h.
Since you said reach 220 km/h, this means an inconsistency.
Are you sure on the cord of 0.2 m? Not more ?
This hardly changes the calculated parasitic drag, but I am curious.
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