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vertical drag on underslung load

sudhir kumar

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While calculating the power requirement during underslung operations, there obviously seems to be a requirement to cater for the vertical drag due to the rotor downwash on the area of the load projected to the downwash in hover.

Any rough and ready method u guys use to cater for the additional power required???

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  • 2 weeks later...
It's negligible. It may not even exist, depending on the winds, and it will vary in any case. Don't worry about it.

Did a bit of calculations.

Considering a 1 Sq M projected area of the load with a Cd of 1 (a flat plate area like an underslung jeep etc), the drag would at, say sea level, be 1/2 * 1.225* V^2*1.

The downwash velocity,v at the load would be a function of the length of the sling and would be quite high for a helo with a high disc loading.

For my current helo the drag penalty works out to almost 4% torque per sq M of area projected to the downwash. Quite high you'll agree!

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dont hook equipped helicopters have load cells to let the pilot know what weight he has on the hook? If so? would be simple to verify the weight difference----ALL ya gottah do is check the difference in weight w/ the ship hovering w/ & w/out the blades spinning ! B) you get the point anyhows :rolleyes:



this thread reminds me of the one about the flying chickens,,, i wish i could remember where it was,,,

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  • 3 weeks later...

In switzerland we have a marshaller syllabus course and inside you will find the informations you need. easy to say is that downwash of course is not the same just below the choper as 2-5-etc. meters and the value of the pressure in kg change all the time also with the lenght of the cable you use.

On the B3, Lama we can count with 20-30 kg pro square meter with a line of 30 feet.

On the AS 332 Super Puma it goes up to 40 kg.


But yes definitely we count with the vertical drag. That is why we always have long line to fly containers, etc..

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  • 4 weeks later...



It is a way better idea to put the load on a 100' long line or if you can't get the vertical ref down, put it on a 50 footer and go from there . if the load is flying attach a small pine tree to it that will screw up its aero dynamic properties. This is what we do when we fly small boat and canoes that seem to want to fly undetr the belly.


Good luck.



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