Rotor Calculation

[alwynhartman]

Hello everyone, this is my first post!
Im an English teacher in Japan with some time on his hands and as an intellectual exercise would like to design a theoretical helicopter.

Does anyone perhaps have Excel based spread sheets with calculators for the following, (if not, then perhaps just a simple formula)?

How do you calculate (assuming STP),
a.The power required to turn a rotor of a given diameter at a given tip speed (at HIGE and then at some average flight speed not more than 100kts).
b.The total drag (induced and profile only) of above rotor.
c.The lifting force" at hover.

Im only looking for a calculation method not actual results.
Any help / ideas?

[Pilot DAR]

al,

Though there are probably many excellent formulae available to you, which are beyond my scope, I will highly recommend this Amazon.com: Helicopter Aerodynamics (9789991992167): R. W. Prouty: Books (http://www.amazon.com/Helicopter-Aerodynamics-R-W-Prouty/dp/9991992162) book.

It's very easy to understand, yet thorough explanations of such things. That said, the price on Amazon seems over the top, so it's probably worth a look around for it.

[puntosaurus]

And then you can look here (http://www.amazon.co.uk/Principles-Helicopter-Aerodynamics-Cambridge-Aerospace/dp/0521858607/ref=ntt_at_ep_dpt_1).

Somone who posts here has done what you're trying to do already and produces some very pretty pictures to boot, I'll have a search and try to find some of their results.

Here (http://www.pprune.org/showthread.php?t=98410&referrerid=110355) is some more help. Just do an advanced search on 'Blade Element Momentum Theory' and you'll get more, including the names of the usual suspects when it comes to this stuff (Dave Jackson, Matthew Parsons, Graviman)

Aha ! Delta3 is the name I was looking for with the pretty pictures see here (http://www.pprune.org/rotorheads/300955-helicopter-urban-myths-7.html).

[John R81]

I read those links and it went rightover my head.

Puntasaurus - is my training unfinished? Should I ask for my money back?

I blame my instructor!

[puntosaurus]

Possibly. We'll find out on Saturday though. :eek:

[Dave_Jackson]

alwynhartman

This is the link to the online book Basic Helicopter Aerodynamics ~ by J. Sheldon. Basic Helicopter Aerodynamics (http://www.scribd.com/doc/24151688/Basic-Helicopter-Aerodynamics)

The book gives the equations etc. for Momentum Theory and the more advanced Blade Element Theory.

This material will have to be entered into a spreadsheet or database for repetitive calculations. If you have and use Microsoft's Access Database, I can send you some forms and coding but they will need modification for use as a stand-alone program.

Hope that this is of some help.

Dave

[Graviman]

Alwyn,

I've edited my post after time to think about what you actually want. :\

What you need are some basic calculations which are nicely laid out in chapter 1 of Prouty (Imperial units) or Leishman (Metric). These can be used to approximate the ideal performance of a helicopter. You'd be suprised how far you can take some of these basic techniques.

As a starting point for your theoretical design in hover assume (in SI units):

Engine power = Weight^1.5 / (2 x Air_density x Rotor_area)^0.5 Watts

In practice the actual power will be about 1.4 times that calculated due to the 70% efficiency of a practical rotor system. This is because the same aerofoil section, twist and taper must handle many flight conditions, so ends up a least worst compromise.

For engineering design performance calculations the accepted method is to combine vortex panel aerofoil sections with blade element momentum theory. You use the vortex panels to calculate coefficients of lift, aerodynamic centres, and drag (boundary layer seperation). The momentum theory then calculates the performance in hover, climb, forward flight, etc. This gets more and more complicated as you try to capture inflow effects and tip vortices. Ultimately to capture the dynamics of vortex ring state you end up using computational fluid dynamics...

So you can see that the subject starts off easy but can become complicated. :uhoh:

Mart

PS: I genuinely hope you have not been badly affected by the Tsunami - the news images look terrifying.

[alwynhartman]

Thank you to all who took the time to reply!

I have indeed purchased copies of Prouty's work and Leishman's textbook (including the answer set to the questions).

The studying has been slow but very interesting!

In the end it appears more and more that it’s a case of "teaching a new perception" in that many of the flight mechanics may seem obvious at first but are then revealed to be deceptively different. After such a revelation it’s almost impossible to "un-see" what was learned and obviously true.

I either case, I would like to extend an apology to those I may have offended with my first posts. I was perhaps too confident and the weight of that confidence was more than the critical yield limit of my knowledge base at the time.

[Thomas coupling]

Japanese might be easier

ご多幸を祈る

[alwynhartman]

Ha Ha! Quite!