prop formula

Thu Oct 21 21:42:37 AKDT 2004

The Wrights had a few things figured out scientifically, as well as 
practically.  They specifically picked Kill Devil Hill at Kitty Hawk, NC 
because they could usually count on strong winds and could use the dunes to 
launch their kite and glider tests.  They knew that the strong headwinds 
would also be an essential ingredient in getting a powered airplane 
airborne, considering that they could not afford the weight of an 
undercarriage and had to use skids on a track.  Had their 21st century 
imitators been more focused on duplicating the conditions that the Wrights 
had on 12/17/03 vs. hitting an exact to-the-day 100 year milestone, they 
might have gotten it off the ground too, i.e., they should have flown when 
there was a good, stiff breeze blowing.

They were lucky in the sense that the winds were strong enough to test the 
contraption before going home to Ohio for Christmas that year, otherwise, I 
think they deserve a little bit more credit for their achievement.

Ed

----- Original Message ----- 
From: "Jeff H. Snider" <jeff at snider.com>
To: <discussion at nsrca.org>
Sent: Friday, October 22, 2004 12:02 AM
Subject: Re: prop formula

>I don't want to try and decide what portion of any endeavor is art
> and what is science.  The Wright brothers were dilettantes very short
> on art but long on luck.  Any less lucky and physically talented
> people would have failed to fly that contraption of theirs.  A great
> deal of money and time was recently spent demonstrating that fact,
> unfortunately for all the people involved.  (If you ever have a
> chance to visit the Curtiss Museum in Hammondsport NY, along with
> a huge and wonderful display of aviation history there's an infectious
> undercurrent of distain for all things Wright.)
>
> I'm in favor of art, and I believe a good scientist is just a kind
> of artist who keeps good notes and follows a very strict methodology.
> What I said was "Maybe by then science will have more fully displaced
> art."  Meaning with a full molecule-by-molecule simulator a scientist
> could create and test a new airfoil in under a minute, instead of
> weeks painstakingly crafting a model and testing it in a wind tunnel,
> so we can accumulate a lot more facts and rely less on intuition.
> Science never eliminates art, but I'd rely on facts and technology
> in place of guesses any day of the week.
>
> I haven't in fact seen a good Analog Engineer.  I didn't know they still
> existed.  But then I've been a software guy too long and all that
> hardware stuff just appears on the loading dock courtesy of FedEx.
> Nobody actually builds it, do they?
>
> I am indeed flying Intermediate next season.  I'm desperately trying
> to remember all the maneuvers in the correct order before competing
> this weekend at BARKS.  Thank heaven for the simulator.  It has
> paid for itself in YS 30% fuel alone by now!
>
> -Jeff
>
> P.S.,
> In terms of progress and a by-the-molecules simulation of air, the
> numbers don't leave much room for error.  Take the number of molecules
> in a liter of air (3e22), the radius of the space a molecule has
> to itself at an instant of time (30 angstroms), the speed of the
> molecules (3e12 angstroms/second), and you find the need to do 3e33
> calculations per second.  Today we can do 3e9 calculations per
> second, so we need to get our computers 1e24 times faster to compute
> this liter of air in realtime.  Of course it takes more than one
> calculation per molecule, and conversely of course really smart
> algorithms can reduce the number of necessary calculations by maybe
> a factor of billion.  But just to keep things simple, if computers
> double in speed every 18 months, and it takes 80 doublings to reach
> 1e24, that's 120 years.  If I'm off by a factor of a billion, it
> takes 75 years.  And unless we forget the "supercomputers", the
> supposed fastest in the world was running at 36 teraflops in
> September: 1000 times faster than today's desktop computers, meaning
> the scientists get there 15 years ahead of us desktop computer guys.
> If I live to be a really old scientist, maybe I'll see it happen.
> For now I'm just trying to leave myself enough space for a half
> decent cobra with half rolls and get my outside loop to end anywhere
> near the same altitude where it started.
>
> P.P.S.,
> To take the fun out of a seemingly silly assertion and simultaneously
> demonstrating my analytical bent one last time:  Supposing I stretch
> my fuel to get 60 minutes flight time out of a gallon (this is a
> 140DZ we're talking about), and supposing I get a great deal of
> $16.50 per gallon on my fuel (this is YS 30% fuel we're talking
> about), I only need to have flown 12 hours on the simulator to equal
> its cost in fuel.  I would guess I average at least 20 minutes a
> day, so it pays for itself in fuel alone in 36 days.
>
>
> John Pavlick writes:
>> Jeff,
>>  Science displacing art? Obviously you haven't seen a good Analog 
>> Engineer
>> design and test an RF circuit. The only thing missing is the Dragon's 
>> Blood
>> and Eye of Nute. Your method of studying problems is refreshing though. I
>> wish some of the Engineers that I have worked with subscribed to this 
>> method
>> of thinking, rather than "Plug and Pray". You will be a formidable 
>> adversary
>> next year (I suspect that you will be flying Intermediate). If only I can
>> turn you to the "Dark Side"...
>>  I was thinking of trying a 3-blader myself. For now I just want to get
>> something reliable / proven to practice with. I have to re-train myself 
>> to
>> fly the 2 meter planes s-l-o-w-l-y. My lasting impression of Pattern 
>> comes
>> from watching Tipo's and Curare's with retracts and pipes. I still can't
>> believe these new planes don't tip stall when they're landing as slowly 
>> as
>> they do. I have to make a conscious effort to concentrate on a new
>> technique. I don't think the prop will be a major concern yet.
>>  As far as technology / progress goes, you might be wrong on that
>> calculation. Some of the things we do on desktop computers today were not
>> even possible on super computers a decade ago. Besides, all of this CAD 
>> CAM
>> stuff is nice but keep in mind that the Wright Brothers didn't have any 
>> of
>> this. You can't wait for technology to catch up with your creativity - 
>> come
>> on, get out your slide rule...
>>
>> John Pavlick
>> http://www.idseng.com
>>
>>
>> > -----Original Message-----
>> > From: discussion-request at nsrca.org
>> > [mailto:discussion-request at nsrca.org]On Behalf Of Jeff H. Snider
>> > Sent: Thursday, October 21, 2004 6:18 PM
>> > To: discussion at nsrca.org
>> > Subject: Re: prop formula
>> >
>> >
>> > Thanks for the feedback.  Nothing that can be done with paper
>> > and pencil, or keyboard and cpu, replaces going into the field
>> > and making some real world observations.  But having an
>> > analytical brain and being a former student of Math and Physics
>> > I really like being able to calculate my way through a problem.
>> > Plus having a theory to support what I see happening in the
>> > air does a world of good for my rate of improvement as a pilot.
>> >
>> > I missed reading about Jim Woodward and his 18x10 prop.
>> > Where was that?
>> >
>> > About multi-blade props.  APC's website says they roughly weigh:
>> >  17" 2 blade .07 lb
>> >  16" 3 blade .10 lb
>> >  15" 4 blade .46 lb!
>> > Is that a typo?  Does a 4-blade add over 6 ounces to your
>> > nose?  I'm ready to give this multi-blade bandwagon a test
>> > ride, but no one is flying a half-pound prop!  Are they?
>> >
>> > As Dean says, this is fun stuff!  I need to read up on
>> > that guy Renard.  Anyone have a suggestion for a good book
>> > on the subject?  I have "Model Aircraft Aerodynamics" or
>> > something similarly titled, which gave me my first exposure
>> > to the amount of art pervading the science of aerodynamics.
>> > (By my calculations, at the present rate of improvement
>> > in technology we're 120 years away from being able to use
>> > our desktop computers for a full and complete molecule by
>> > molecule realtime simulation of air flowing over a wing.
>> > Maybe by then science will have more fully displaced art.)
>> >
>> > -Jeff
>> > =====================================
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