"Helicopter Aerodynamics" - remarks & questions

[LGNYC]

Hi, I am a private pilot, working towards my commercial, new to this forum, and I have a couple of remarks and questions regarding helicopter aerodynamics in general, and more particularly about "helicopter aerodynamics", Ray Proutty's wonderful book.

I will start with the remarks:
- I had a hard time finding this book. It has been out of print for a while (mid 80s I guess!) so I bought it used. I wish it was re-edited so more pilots could have access to it.
- I believe it is essential reading if you want to understand helicopter aerodynamics. I read Leishman's "principle of aerodynamics" and Stpniesky's "rotary wing aerodynamics" but I wish I had read's Proutty's book before. By simplifying everything and making it so clear, I believe he actually gives the reader the best foundation to then read the more advanced texts (as opposed to a more general but technical aerodynamics book like Anderson's "Intro to flight").
- On this forum and a few others, there are always these questions about dissimetry of lift, flapping, etc... Then usually, some experienced test pilots dispel all doubts about how things work. Well, I think in most cases first reading Proutty's little book would answer all these questions.

Now my questions:
- Has anybody read the sequels "More helicopter aerodynamics" and "even more helicopter aerodynamics"? I heard a rumor that they did not add much to the first book (maybe a lot of the stuff was recycled). Can anybody confirm that? Should I try an get these books too?
- In the fourth chapter of "helicopter aerodynamics", Proutty introduces flapping/dissimetry of lift. He refers to de la Cierva's first autogyro which had a rigid rotor and "rolled over and thrashed its blades into toolpicks" on first takeoff. However, to me, if that gyro rolled over it is not directly due to dissimetry of lift. On a rigid rotor, dissimetry of lift in forward motion will create a pitchup moment as the blades flap (but since it is a rigid rotor the whole rotor is tilted). So maybe some transverse flow effect created a rolling movement, but I do not see this crash as a direct illustration of dissimetry of lift.

And a final side note, about what appears to me as an unfair situation:
at the NTPS (National test Pilot School), they offer all kinds of interesting courses for test pilots and flight engineers. In my opinion, some of this stuff could be beneficial to all pilots, not just test pilots. The fixed-wing people at NTPS seem to agree with that, since they offer a series of courses about spins, inverted flight and so on for all pilots. On the helicopter side, however, there is no such training offered. Would it not make sense for the NTPS to offer courses on unusual attitudes in helos? Show how helos behave at the limits of their flight envelopes?

[Dave_Jackson]

All three of these books are excellent. Others have tried to get old copies. It is unfortunate that they have not been reprinted. Each book (and chapter) covers a different subject, but the subjects in the latter books are of a slightly less significant nature.

Since you have read textbooks by Leishman and Stepniewski, you might like Prouty's major book ' Helicopter Performance, Stability and Control'.

[[email protected]]

LGNYC, as a helicopter or autogyro moves into forward flight it experiences disymmetry of lift due to differences in the airspeed between the advancing and retreating blades which causes flapback and the nose to pitch up. Also there is a difference in the direction of the flow between the front and the rear of the rotor disc (a reduction of induced flow at the front) which makes the aircraft roll towards the advancing side ( this is inflow roll or transverse flow depending on which side of the atlantic you live on).



Did anyone mention the Rugby World Cup? It's not often we get to say that England are the world champions at anything so forgive me for gloating over our colonial bretheren!

[ShyTorque]

LGNYC,

Yes, all three books are excellent, the second gives some more general theoretical info and the third goes into design and historical information including some interesting type specific and experimental stuff.

Shame you didn't ask before. I ordered a set of all three books a few years ago (via Rotor and Wing, I think). After some weeks had gone by they hadn't arrived so I got in touch with the magazine and they sent a second set. The "lost" originals turned up on the same day as the replacements!

I gave the "free" set away a while back to someone who possibly hasn't even looked at them since ...... sorry :\

Cierva's full-sized aircraft rolled over because unlike his models, which used flexible materials of cane and feathers, he deliberately but mistakenly made a rigid rotor system (blade bracing wires from a kingpost).

He had not given the pilot a sufficiently powerful method of overcoming the effects of inflow roll and flapback, that's why it rolled into a ball. He subsequently used flapping blade hinges which allowed flapping to equality and this relieved feedback forces to the airframe, so the aircraft became more stable and controllable.

Ray Prouty also dispels the theory (sometimes expounded not far from here) that a helicopter is controlled by precessing its "gyroscopic" rotor system. That might get a bite LOL :E

[LGNYC]

All - You convinced me. So I now have a bid for the two other books in the series - "More Helo Aerodynamics" and "Even more helo aerodynamics". Anybody who's not reading them anymore want to sell?

Regarding Cierva's unfrtunate gyro here is what I meant - as forward speed increased the gyro's rotor should have tilted aft (and that would be, more or less, an illustration of dissimetry of lift). Since it was a rigid rotor, the whole gyro tilted aft. So my remark was -- why say that it "rolled over"? in itself this fact does not illustrate the whole issue with flapping/dissimetry of lift.

Now, the gyro probably did roll over, but I think this is because when there was a sudden and strong pitchup moment, then the gyro's rotor did act as a gyroscope and rolled on the side (and the whole autogyro with it).

BTW Im French so I think the remark on England winning the world cup is out of place.

And regarding Proutty's book on stability and control -- yes, I had been thinking about buying it but it kind of seemed expensive, relative to Leishman's and Stepniewsky's. But I know that is a relatively stupid reason so I'll probably get t soon.

[NickLappos]

LGNYC,

Please don't take that world cup comment personally, nobody knew you were French!

Normally I recommend using abe.com for book ordering, but they have none of the Prouty soft cover books. Ray is an acquaintence, and a great engineer. I strongly recommend his works.

[Mike Hardy]

LGNYC,
The courses at NTPS are open to anyone and would benefit all helicopter pilots, not just those in the test community. However, the syllabus is designed to offer most to that group. The RW courses do take the students to the edges of the envelope in controlled situations, demonstrating the methodology of how the envelope is defined. Examples of this are the low speed envelope (sideways and rearwards flight) and H-V. It depends which course you choose that determines the depth of the investigation.

I don't intend demonstrating or instructing inverted flight in a helicopter!!:D


If you want to discuss our curriculum, email me: [email protected]

[Genghis the Engineer]

I'm another Prouty fan. I'm sorry to say I've not met the gentleman, but have read all 4 of his books and found them all very clear, and the big-silver volume incredibly thorough (apart from this strange American habit of dropping ½ when calculating helicopter coefficients that confuses Brits and Europeans.)

The big-book is written for Engineers, or at-least people with a deep love of higher mathematics, and I wouldn't recommend it from a piloting perspective. The three "popular" volumes however I've yet to hear anything but praise for from either Engineers or Pilots.

Of the other three, I never managed to get hold of a copy of the first one "helicopter aerodynamics" but do have the other two. So, if anybody out there has a spare copy, I'd be delighted to buy, steal or swap.

G

N.B. At least the French entered the world cup - when are the Americans going to learn how to play Rugby properly, on grass and without constantly changing players in the middle of the game ?

[LGNYC]

Nick - I was kidding about the world cup. I wish France had won, but in the end the best team wins.

Mike - I am just a private pilot, so I need to gain a lot more experience before I think about taking courses at NTPS. But from what you say, that'd be exactly what I'd be looking for. Be sure I'll talk to you when I have the hours.

Genghis - The big book you refer to is "stability and control" I assume. Though I am a pilot I dont mind the math (phd in stochastic calculus so I can handle a few equations). This one at least I can buy on amazon. Also, I understand you have the two books I am looking for and I have the book you are looking for. Maybe we can work something out, like I make a copy of the one I have and send it to you, you make a copy of the ones you have and send that to me, and we send a check to Ray Proutty (Nick must know where he is at) for our fair assessment of the books' value. This way everybody wins.

[The Nr Fairy]

Of course, modernisation comes to everything, it seems.

Check out http://www.helobooks.com/ - the first book seems to be a reprint of all three Prouty books in one convenient cover !

[Genghis the Engineer]

I think so, it's some years since I was near a copy.

As I recall, the cover price of Prouty's "Helicopter dynamics" books was somewhat less than I'd consider a fair assessment of the value. Anyhow, NRF seems to have solved the problem for us both anyway.


Since you are clearly happy with maths as a descriptive language, I would also strongly recommend Simon Newman's "Fundamentals of Helicopter Flight". I'll admit a personal bias - Simon is a friend who has taught me much in the dozen years I've known him - including most of what I know about helicopter aerodynamics. But, despite that, I'm still sure you'd find it both readable and very informative.

G

[[email protected]]

LGNYC, back to the autogyro - the pitch up is caused by the disc flapping to equality because of differences in lift between advancing and retreating blades. The roll over is caused by the disc flapping to equality because of differences in lift between the front and rear of the disc. Flapback and inflow roll are both examples of the rotor disc flapping to equality.

Lets not go anywhere near gyroscopic precession and rotor systems or I shall have to taunt you a second time about the Rugby!!!!

[LGNYC]

Genghis - would you recommend "Fundamentals of Helicopter Flight" over Leishman's book or Stepniewsky's book? (cause I already have these).

NRF - thanks a million times for the link!

[Genghis the Engineer]

I'm afraid I don't know Leishman's, but yes I did find it much more up-to-date and friendly than Stepniewsky's.

G

[CRAN]

Leishmans book is specifically aerodynamics based and is a lot more technical. Much more maths capability is assumed on the part of the reader. Simon's book is great, much more readable and is not limited to soley aerodynamics as it includes some dynamics and performance stuff too.

From a pilots point of view buy Simon's book, from and from a design engineers point of view, read simons book and buy Leishman's! Hope this helps!

CRAN

[Dave_Jackson]

LGNYC,

In addition, you might consider 'Helicopter Theory' by Wayne Johnson.
Very informative at 1089 pages, and very inexpensive at $24.47. [Amazon.com] (http://www.amazon.com/exec/obidos/tg/detail/-/0486682307/102-0310046-0185745?v=glance) Originally published in 1980, but it might well be considered the bible of rotorcraft theory.

Don't buy a used one. :eek: The book's only weakness is its binding; 'cause it's so thick. :D

[LGNYC]

I have just ordered Newman's Foundations of Helicopter Flight, as well as Prouty's Helicopter Aerodynamics (the new edition with the three books in one). I will read these, before reading Leishman's again. Then I will consider getting Prouty's bigger book on stability and control. That will keep me busy for a while. To all the parties concerned - Thank you very much for all the advice.

Genghis, if you are still interested in completing your collection, I now have a redundant copy of the original "Helicopter Aerodynamics".

Crab: I am biting my tongue so I wont reply to your post on the flapping & gyroscopic effect. Too much has already been said on that.

[Genghis the Engineer]

I would very much like to, but I think negotiations on a public forum would be frowned upon, I'll Email you privately.

G

[LGNYC]

GG, I emailed you back.