# Some thoughts on cross wind takeoffs.

#### dabkb2

##### Dave Bacon
With ELA 07 100 hp at 450 kg, pre-launched at 220 rpm, my calculation gives a run of 250 feets with a 20 Kts headwind.

View attachment 1153600
That is most probably true with an ELA, With my Bensen and a AUW of 500LBS it is almost a vertical take off at 20 Kts (mph)

#### Jean Claude

##### Junior Member
It depends on the diameter of the rotor.

With 22 feets in a 20 kts headwind, we would only get 295 rpm at standstill, for 20° of disk A.o.A . The vertical climb is then impossible and would 90 fts of run to leave the ground.
Hover is only possible in a head wind of 22 kts and A.o.A 30 degrees with the help of propeller lift (nose up).

#### Burrengyro

##### Gold Supporter
That is most probably true with an ELA, With my Bensen and a AUW of 500LBS it is almost a vertical take off at 20 Kts (mph)

It depends on the diameter of the rotor.

With 22 feets in a 20 kts headwind, we would only get 295 rpm at standstill, for 20° of disk A.o.A . The vertical climb is then impossible and would 90 fts of run to leave the ground.
Hover is only possible in a head wind of 22 kts and A.o.A 30 degrees with the help of propeller lift (nose up).

View attachment 1153604
Hi Jean Claude,
Thank you for the calculations and the graphs. Could I ask you to publish your formula for the ELA07 with 8.5m rotors for different wind speeds? I would be very interested to learn how to calculate the expected distance to take off for different head wind speeds at MTOW of 500kg using normal pre-rotation of 220 rpm before releasing brakes and adding full throttle? I am operating at sea level? I am trying to calibrate safe take off distances and safe abort distances for a short runway. Many thanks your generosity in sharing this information. John H.

#### Vance

##### Gyroplane CFI
Staff member
Hi Jean Claude,
Thank you for the calculations and the graphs. Could I ask you to publish your formula for the ELA07 with 8.5m rotors for different wind speeds? I would be very interested to learn how to calculate the expected distance to take off for different head wind speeds at MTOW of 500kg using normal pre-rotation of 220 rpm before releasing brakes and adding full throttle? I am operating at sea level? I am trying to calibrate safe take off distances and safe abort distances for a short runway. Many thanks your generosity in sharing this information. John H.
My system is no substitute for Jean Claude’s calculations.

I would take my gyroplane to an airport with a long runway and experiment with takeoff roll and distance to climb over whatever obstacle might be in place.

Your technique or your particular gyroplane may make it operate outside what the calculations suggest.

When doing short field takeoffs I feel it is also important to consider ground obstructions and their effect the wind and your ability to climb out.

The lee side of a ridge, tree line or building may create turbulence that will limit your climb.

The wind at ground level is often very different than it is twenty feet (three meters) above the ground.

A cross wind component will also influence your lift off and climb out distances.

#### Jean Claude

##### Junior Member
Hello John
I don't use algebraic formulas for these results, but two EXCEL spreadsheets that I designed.
- One to simulate rotors by entering their geometry (diameter, chord, pitch, drag coef) and forward speed, then adjusting the angles a1, b1, disk A.o.A and rpm to cancel the calculated moments (pitch, roll, and spin)
- The other one to calculate step by step the forward speed and the rrpm of the gyrocopter, taking into account the static thrust of the propeller, the supposed parasitic drag coefficient, the supposed rolling coefficient, then entering at each instantaneous speed obtained the values of drag and rotating torque obtained in the first spreadsheet.
This method is precise but too tedious for you.
Perhaps, I could however help you by calculating the case of the only gyro you are interested, and with no wind. Then you can simply use these results for each wind by the formula: distance with wind = distance without wind - (Wind speed* run duration)
A little less accurate, due to the parasitic drag error, but easier to you.
Let me little times for checker this possibility.

Launch 220 rpm with 8.5 m rotor ? Is not with the 8.26 m ? Engine power 100 HP ?

#### Abid

##### AR-1 gyro manufacturer
I was taught to prerotate with a flat disk to about 100rpm at the hold short line, then move onto the runway and tilt back away from the wind till I get to about 220, then commence the takeoff roll. I have never had any issue with a gust surprising me using this technique, despite lots of takeoffs (and landings) in very blustery conditions, often with a lot of crosswind.
Flat or slightly tilted. it works. By the time you get to 100 RPM you can flatten it out anyway. Its when they are slow you can possibly start a flap in initial spool up, the same way you when taxi too fast after landing and a gust and start a tiny pulse of flap and you need to slow down or stop the gyro and tilt into the wind to let it die off

#### Abid

##### AR-1 gyro manufacturer
My system is no substitute for Jean Claude’s calculations.

I would take my gyroplane to an airport with a long runway and experiment with takeoff roll and distance to climb over whatever obstacle might be in place.

Your technique or your particular gyroplane may make it operate outside what the calculations suggest.

When doing short field takeoffs I feel it is also important to consider ground obstructions and their effect the wind and your ability to climb out.

The lee side of a ridge, tree line or building may create turbulence that will limit your climb.

The wind at ground level is often very different than it is twenty feet (three meters) above the ground.

A cross wind component will also influence your lift off and climb out distances.

My rule of thumb is, if you are calculating numbers to clear an obstacle, you already have your answer. You can only push your luck from there. Murphy's law dictates that anything that can go wrong, will at some point go wrong and then all your calculations flush down the toilet. We all push our luck sometimes but doing it as a pattern is just a numbers game and they always catch up to us

#### All_In

##### Gold Supporter
This forum changed my rule of thumb for the gyros to be much different (mindset) than taking off in FW's over obstacles!!
Gyros are too easy to just, push, trailer, or tow it to a better location. No wings and very lightweight make little need to cut it close with a gyro.

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#### Burrengyro

##### Gold Supporter
Hello John
I don't use algebraic formulas for these results, but two EXCEL spreadsheets that I designed.
- One to simulate rotors by entering their geometry (diameter, chord, pitch, drag coef) and forward speed, then adjusting the angles a1, b1, disk A.o.A and rpm to cancel the calculated moments (pitch, roll, and spin)
- The other one to calculate step by step the forward speed and the rrpm of the gyrocopter, taking into account the static thrust of the propeller, the supposed parasitic drag coefficient, the supposed rolling coefficient, then entering at each instantaneous speed obtained the values of drag and rotating torque obtained in the first spreadsheet.
This method is precise but too tedious for you.
Perhaps, I could however help you by calculating the case of the only gyro you are interested, and with no wind. Then you can simply use these results for each wind by the formula: distance with wind = distance without wind - (Wind speed* run duration)
A little less accurate, due to the parasitic drag error, but easier to you.
Let me little times for checker this possibility.

Launch 220 rpm with 8.5 m rotor ? Is not with the 8.26 m ? Engine power 100 HP ?
Hello Jean Claude,
Thank you for your reply. My ELA07S is the 914 turbo version with an 8.5m diameter rotor. A simplified version of your formula would be very helpful to me. I have no problem with a very short take-off with a headwind in the runway direction. However, crosswind and 45-degree crosswind, and zero wind conditions for a short runway is my research. Thank you for any rough guidelines you can offer me. Best regards from Ireland. John H

#### Burrengyro

##### Gold Supporter
This forum changed my rule of thumb for the gyros to be much different taking off in FW's over obstacles!!
Gyros are too easy to just, push, trailer, or tow it to a better location. No wings and very lightweight make little need to cut it close with a gyro.
Hi Abid, Vance and John,
I try to avoid using the trailer if at all possible. Our runway options are often limited due to grass surface or unfavourable weather. If our grass runway is too wet, we are grounded, even though the weather may be perfect for flying. Our grass runway is prone to waterlogging. We practice short takeoffs and short landings all the time in all wind conditions on any portion of the runway that is serviceable after rain. A short hard surface runway 250m in length is a possibility. We want to make sure the runway length is adequate for safety reasons for one pilot and a half tank of fuel for ELA07S and Magni M16 gyros. Finding suitable sites for such a hard runway is a problem. Very often, the sites have slopes of up to 6% which can be a big factor. The limited takeoff distance and the danger of overspeeding on a downhill runway before the rotors are up to flying speed is a big concern, even with no obstacles at the end of the runway. You guys with access to hard surface long, wide and level runways are sooooo lucky! John H

#### Abid

##### AR-1 gyro manufacturer
Hi Abid, Vance and John,
I try to avoid using the trailer if at all possible. Our runway options are often limited due to grass surface or unfavourable weather. If our grass runway is too wet, we are grounded, even though the weather may be perfect for flying. Our grass runway is prone to waterlogging. We practice short takeoffs and short landings all the time in all wind conditions on any portion of the runway that is serviceable after rain. A short hard surface runway 250m in length is a possibility. We want to make sure the runway length is adequate for safety reasons for one pilot and a half tank of fuel for ELA07S and Magni M16 gyros. Finding suitable sites for such a hard runway is a problem. Very often, the sites have slopes of up to 6% which can be a big factor. The limited takeoff distance and the danger of overspeeding on a downhill runway before the rotors are up to flying speed is a big concern, even with no obstacles at the end of the runway. You guys with access to hard surface long, wide and level runways are sooooo lucky! John H

I hear you. US has likely the biggest general aviation infrastructure available in the world with Europe behind it and then the rest of the world. We are indeed lucky in the US. I am sure you know you are taking more risk than normal doing this every time you have to takeoff. May be grading the grass so it does not get water logged is a possibility?

#### Burrengyro

##### Gold Supporter
I hear you. US has likely the biggest general aviation infrastructure available in the world with Europe behind it and then the rest of the world. We are indeed lucky in the US. I am sure you know you are taking more risk than normal doing this every time you have to takeoff. May be grading the grass so it does not get water logged is a possibility?
Hi Abid,
We walk the runway when it is wet to identify the sections dry enough and safe enough to use. The main problem is soil saturation. If it rains for more than 2 days, the runway may need 2 or 3 days of dry weather to be usable. While the rain may not be heavy, we may not get enough dry days in a row for the runway to dry out. As a result, we end up being grounded even when the weather is good for flying. Hence my interest in a dry hard core runway to use during those precious flyable days during our mainly wet winters. A safe runway is the first priority. John H.

#### Abid

##### AR-1 gyro manufacturer
Hi Abid,
We walk the runway when it is wet to identify the sections dry enough and safe enough to use. The main problem is soil saturation. If it rains for more than 2 days, the runway may need 2 or 3 days of dry weather to be usable. While the rain may not be heavy, we may not get enough dry days in a row for the runway to dry out. As a result, we end up being grounded even when the weather is good for flying. Hence my interest in a dry hard core runway to use during those precious flyable days during our mainly wet winters. A safe runway is the first priority. John H.

looks like you guys need to spend some \$\$ on either a hard surface or a helicopter

#### Burrengyro

##### Gold Supporter
Hi Abid,
We walk the runway when it is wet to identify the sections dry enough and safe enough to use. The main problem is soil saturation. If it rains for more than 2 days, the runway may need 2 or 3 days of dry weather to be usable. While the rain may not be heavy, we may not get enough dry days in a row for the runway to dry out. As a result, we end up being grounded even when the weather is good for flying. Hence my interest in a dry hard core runway to use during those precious flyable days during our mainly wet winters. A safe runway is the first priority. John H.
Apologies if my posts have diverged from the original post re crosswind takeoffs. Crosswind takeoffs problems can be magnified for those of us stuck with using short runways for a lot of the year. I am hoping to learn as much as possible from the forum contributors to keep safe. John H

#### dabkb2

##### Dave Bacon
It depends on the diameter of the rotor.

With 22 feets in a 20 kts headwind, we would only get 295 rpm at standstill, for 20° of disk A.o.A . The vertical climb is then impossible and would 90 fts of run to leave the ground.
Hover is only possible in a head wind of 22 kts and A.o.A 30 degrees with the help of propeller lift (nose up).

View attachment 1153604
There must be something wrong somewhere, can you change the graph for MPH instead of KM/H. And I do have a 22' x 7" rotor

#### Jean Claude

##### Junior Member
1 km/h = 0.62 MPH
Take off at airspeed 65 km/h is 40 MPH
1m = 3.3 fts
Take off at 27 m is about 90 fts

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#### dabkb2

##### Dave Bacon
Thank you. That is about what I thought it said. I am taking off way ahead of that, more like 25.

#### All_In

##### Gold Supporter
Question to my brother Dave. Are you hanging on the prop when you takeoff like that?

#### All_In

##### Gold Supporter
Hmmm, seen Dave takeoff with a 20knt headwind in what from a distance seems like 20 or 25 feet.
One way to test the program might be to ask Dave. At what headwind is required to appear to be hovering and not hanging on the prop.
= No, take run required headwind speed! That should be a fixed headwind and remove the pilot technique and hanging on the prop???
Can you calculate that?

#### loftus

##### Super Member
Hmmm, seen Dave takeoff with a 20knt headwind in what from a distance seems like 20 or 25 feet.
One way to test the program might be to ask Dave. At what headwind is required to appear to be hovering and not hanging on the prop.
= No, take run required headwind speed! That should be a fixed headwind and remove the pilot technique and hanging on the prop???
Can you calculate that?
We have not seen Chris with the Arrowcopter on this forum for a long time. It's a pity, his testing skills would have a lot to contribute.

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