INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Jobs

How to calculate force per unit length of a helicopter blade in hover

How to calculate force per unit length of a helicopter blade in hover

(OP)
Dear members,

I am trying to find out the force per unit length of a helicopter blade while in hovering. I know from blade element theory how to calculate the lift force (1/2*rho*v^2*....)generated by one blade. For example, if i have 4 blades, then, the total lift force=weight of the helicopter=4xone blade lift. Now, if the total weight of the helicopter is 20000 N, can we say that each blade is taking 1/4 of the of the weight ie, 5000 N? On the other hand, from the disk loading, we are getting the pressure and if we multiply that pressure by one blade's planform area, we are getting different lift value per blade. Does it mean that, while rotation, the lift force is distributed through out the disk evenly so that each blade is loaded lightly as can be seen from disk loading? Or the 1/4 sharing rule is correct (this is around 12-15 times greater than disk loading lift)? To calculate he force per unit length of one blade, which formula should we use? And if anyone of the two is selected, then how to calculate the force per unit length? Could you please explain? I appreciate your help.

Thanks

Pratik

RE: How to calculate force per unit length of a helicopter blade in hover

1 blade carries 1/4 of the load sounds reasonable.

using the disc area (ie the area swept by the blade) to derive a pressure, and applying that to the blade area sounds unreasonable. Calc the pressure from disc area and apply this to a quadrant (ie the area swept by a blade). Better would by to use disc area and factor the pressure by the activity factor (the area of the blades/disc area).

another day in paradise, or is paradise one day closer ?

RE: How to calculate force per unit length of a helicopter blade in hover

Centrifugal acceleration produces a much higher than lift. If it didn't the cone angle would be very steep.

I doubt the lift is evenly distributed; at least I haven't noticed a significant washout like is seen in propellers.

I will guess that there is some amount of washout to even the loading, but it makes most sense that that would be a cruise condition where efficiency is important, and that hover will not be ideal and will shift the load in some direction. One can assume that the AoA and section are constant, so the lift will vary as the square of the radius. One place I just searched to suggested 6 degrees of washout; you can look at the Cl/Cd charts to make an estimate on the size of the effect for your case.

RE: How to calculate force per unit length of a helicopter blade in hover

Seepratik..

Suggest downloading/reviewing documents from DTIC. Answer probably lies within...

http://www.dtic.mil/dtic/

Search AMCP engineering design handbook helicopter [or possibly the AD number listed]

AMCP 706-201 ENGINEERING DESIGN HANDBOOK. HELICOPTER ENGINEERING. PART ONE. PRELIMINARY DESIGN [ADA002007]

AMCP 706-202 ENGINEERING DESIGN HANDBOOK. HELICOPTER ENGINEERING. PART TWO. DETAIL DESIGN [ADA033216]

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close