Calling All Savants...

[Chas]

Guys
We have got our knickers in a twist over Pitch Speed. Anyone care to comment? One contributor suggested that there are plenty of savvy guys who "hang around" this streetlamp, so here's whistlin'!
http://www.rcgroups.com/forums/showthread.php?s=&threadid=149125&perpage=30&pagenumber=1

Thanks
Chas

[Viper Pilot]

Wouldn't touch this with a ten-foot pole.

VP

[Sparky Paul]

There's more than enough information to thoroughly confuse the issue in the other thread, why add to it?

[Chas]

Thanks for the input guys!

[Ollie]

I highly recommend Chapter 14 of Martin Simon's MODEL AIRCRAFT AERODYNAMICS. This 16 page, illustrated exposition, of propeller theory will answer most modelers propeller questions authoritatively.

[e-geezer]

Yep. Look at p187 section 14.5. Martin uses 14 column-inches to explain the factors that influence pitch speed but doesn't say what it is.

My guess is that if a prop has a pitch of 8 inches and it's going round at 100 times per second then its pitch speed is 800 inches per second.

Based on this guess, I've derived the following formula:

Pitch speed (MPH) = (RPM * PITCH) / 1056

where pitch is in inches.

[Chas]

Exactly! Mother Nature does lots of hard sums, real fast!

Actual Pitch Speed accounts for all factors - (prop aspect ratio, blade profile, viscosity, temperature!!)

At Actual Pitch Speed Thrust Is Zero!! Is the plane flying? Yes!!
Chas


Illustarted??!! Fornicate in Hades!!!

[Chas]

Sparky.

Clearly you think that we have over-complicated the issue. Obviously, you have it sorted! So, why not give us the benefit of your opine, and clear it up for us?

Chas

[Chas]

e-geezer
In my book 14.5 occurs at Page 203.
It says
""the aerodynamic zero line represents the angle of attack at which this part of a real propeller blade would produce zero lift and hence no thrust." ... " Beyond this negative angle the propeller becomes an air brake".

So - back to square one -

Static = Max Thrust
Actual Pitch Speed = Zero Thrust
Excess over Pitch Speed = Negative Thrust

Why are people arguing about this? What could be %&**&%*&
simpler?

Chas

[e-geezer]

I should have said - fourth edition.

[Chas]

Doesn't matter really about the page. What's the argument??

Chas

[Sparky Paul]

Originally posted by Chas
Sparky.

Clearly you think that we have over-complicated the issue. Obviously, you have it sorted! So, why not give us the benefit of your opine, and clear it up for us?

Chas
.
Chas, your quotes from text show you're prepared.
Setups, IOW.
Personally, I have no interest in "pitch speed" computations, preferring to let the plane tell me whether it has the correct prop, not some calculation which may be seriously wrong, as I have found.

[e-geezer]

Anyway, I note that in section 14.12, Martin ends up with the same formula as me (Fig. 14.12) but complicates it no end with an unnecessary (but impressive-looking) graph which would only be relevant for someone without a calculator.

So pitch speed is what you think it is. A prop with a pitch of x inches going round at y revolutions per second has a pitch speed of x * y inches per second. It screws itself (ideally) that far into the air every second. Divide by 12 to get feet per second then by 5280 to get miles per second, and then multiply by 3600 to get miles per hour.

So pitch speed in MPH = Pitch in inches * RPM / 1056

[Chas]

Sparky,
I'm not spoiling for an argument, far from it. I'm just trying to defend myself against the criticisms which were, unsolicited, levelled aginst me.
I agree with you entirely. Such as pitch speed matters, and that's all I've ever said, it is to help you match to the motor/airframe. The "asymtotes" can jump in the lake.
I'm not "prepared". The guy asked me to consult that particular book.

As to this "flight with zero thrust" garbage, God save us from Literal Engineers.

C PS What is "IOW"? I only know Isle of Wight.
Chas

egeezer

This whole thing is nonsense because someone decided to take a turn of phrase literally. Of course, pitch speed is "about" PitchxRevs divided by 1056. Say.
The Poindexter Approach is to take an everyday phrase like "zero thrust" (which does actually exist) and independently add a phrase like "constant" - then proceed to harangue. I'm sorry I won't play, but also won't ignore the travesty.

Chas

[Aio_1]

Chas,

Not a fair interpretation of the other thread in my opinion.
I'm a lot more interested in having a discussion about WHAT is correct rather than WHO is correct. I for one never 'levelled criticisms against you'. I did disagree with your assertions. If you are going to take such offense when people disagree with your opinions then I don't know why you got into the discussion at all.
You seem to feel victimised because no-one was agreeing with you. It's a discussion not a competition.
I refuse to agree with you because I think your argument is flawed OR mis-stated. Not because I'm being argumentative.

As for your criticisms of me (I presume this was aimed at me?).
Tell me, if you're not to be taken literally in a technical discussion
then what the hell are words for???
I asked you several times if I correctly understood your position and you refused to help clear up the confusion. Then you've accused me of not reading your posts properly!
The whole discussion started out interesting and still is, but it seems to have turned slightly nasty.

That's enough for me.


Aidan

[steve lewin]

Guys if you want to talk about modelling science, feel free. If you just want to be rude to one another then please resist the temptation.

Steve

[Ollie]

Chas,

I gave the book recommendation for those who want to understand the basic principles involved. This understanding can help to guide the necessary flight testing of various commercial propellers to arrive at the best choice without overloading the propulsion system and possibly damaging a component. I consider my minor contribution constructive for those who don't already know the principles involved. I did not intend my recommendation to be taken in any other way.

Here's another recommendation. If you are deeply involved emotionally in this thread, take a few deep breaths and be cool.

Best regards, Ollie

[Aio_1]

Ollie,

Thanks for the reference.
I may take a look when I get the chance.

Aidan

[Chas]

Aidan
I was not speaking of you when I mentioned the criticsms of me - anyone can disagree with my ideas, that's why we're posting here.! My defence was against comments like

"If you want to re-define terms to suit the correctness of your arguments..." et seq

or

"Ability to write creatively [!!] is no substitute for an engineering degree"

or

"[try].. " a humbling experience for those who participate in Modeling Science discussions without having all their technical details in order".

Hardly objective?

As for your own participation Aidan I have objected to the insertion by you of words which completely redefine both the issue and my position ( most distracting of these was "constantly" for flying at zero thrust). Otherwise I think we have been quite cool and objective?

Far from refusing "to clear up the position", I have re-posted to every one of your suggestions (some seem to think ad nauseam)
and I can't think of a single word or concept which is presently in doubt.

Nothing nasty from my side and I hope no offence has been taken. I even asked you if you fancied a pint in the Ormond on 16 June 2004!!

Chas

Sorry for edits my keyboard keeps clicking out. Bad luck gents it's not permanent! :-)

(I've just had to edit that again - it printed as "bad luck gits"!!!!
See how these things happen)

[Dave Hederich]

>> "[try].. " a humbling experience for those who participate in Modeling Science discussions without having all their technical details in order".

I'm the one who said that, and it's the same advice I'd give to anyone who's never before participated in Modeling Science. I would also offer to anyone the advice that those who are easily distracted from the technical to the personal may have a different experience here from the norm.

[Chas]

??????

[steve lewin]

O.K. this thread has no modeling or science content, it's entirely about personalities. It's also now closed.

Steve
Moderator Modeling Science