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spungey
08-01-2011, 12:07 AM
Hi all,

Since I don't see it yet ... please use this topic to continue the amazing "Beyond Streamlining" topic that John McGinnis started a couple of years ago and now exists only in the archives.

John's demonstrator aircraft is amazing (what we've seen of it.) Mayyyybe the Synergy discussion belongs in a new thread now. :-) The issues and discussion of aerodynamics, thermodynamics, synergy, syntropy, etc. remains relevant and deserves discussion. Maybe I'll even have something to add besides eyeballs this year.

danielfindling
08-01-2011, 07:31 PM
I second your request. John are you out there?

spungey
08-05-2011, 12:18 PM
John, what do you need in order to make it safely through GFC? We're EAA. We're broke, but we're collectively a genius. Maybe we can help.

hogheadv2
08-05-2011, 02:41 PM
The cost of a book, collectively would add up to a great deal. A GREAT Many of us have gleened much from Johns sharing his time and spin on how the fluid we breath works.
Pocket money from us can change the history of GA. http://www.synergyaircraft.com/ Be part of something that you look forward to, that challenges your brain, That has the Best Smile in the country :D

spungey
08-05-2011, 03:57 PM
First, I agree with Hoghead. Many hands (or pocketbooks) make light work.

Now, back to the real purpose of this discussion -- next-generation aerodynamics. Here are some thoughts brought about by post #192 in the archived thread "Beyond Streamlining...."

Here is John responding to a question about dynamic pressure. I shuffled the order around so it makes a bit more sense for my points.

In 1752 (!) Jean d' Alembert proved that an object in steady motion through a
perfect fluid (inviscid, which means free of viscosity) would in fact have no
drag at all. Modern experiments since the 1950s have shown this to be a fact,
as when we (correctly) use power to take away the influence of viscosity, drag
drops to essentially zero. This is what Goldschmied shouted from the rooftops
in the 80's.

This makes perfect sense to a physicist. It is only when we must do work against resistance that we need to apply power. We do similar things in the lab all the time with air tables (think air hockey) for less-friction experiments. On the other hand we only want to remove the viscosity right next to our skin. We need to air to drag other air along with it so that our wings work and throw big bunches of it at the ground. (That's induced drag though, not dynamic pressure.

Yet because of the 'impossibility' that total drag could be less
than the form drag revealed by the 'dynamic pressure', it was quite literally
not understood for a long, long time.

It's easier to just "do the math" than to actually understand a problem and the system where it exists.

As it turns out, the problem is found in the concept of dynamic pressure
itself. But taking only one-half of the circular kinetic energy of mass flow is
a mathematical sleight-of-hand that allows us to 'lock down' air movement long
enough to assign it a number. In the other branches of physics this is a no-
no. You can't know both the position and the the velocity of a particle at the
same time.

ummm ... when that particle is extremely tiny, extremely fast, or extremely energetic. We have a long way to go in terms of personal flight before we need to worry about the speed of light. (More's the pity, actually.) :-) Yes, dynamic pressure is sleight-of-hand. It got out of hand. A standing joke in the physics community goes like, "Today we're going to study milk. For our first-order approximation, we'll assume the cow is a sphere." John's point is valid. For a century we have split the "airplane in flight" system into tiny, bite-sized chunks we (thought we) could work on mathematically. We pretended that what happens in the airstream five feet from the wing no longer matters. It matters, but it's going to take some work to prove it other than empirically.

OK, with respect to your post #190, we need to separate subject matter.
Let's say we're flying in a neutral bouyancy airship so that there will be no induced
drag. Classically what we are taught is that the dynamic pressure (1/2 the
product of the air density and the velocity squared) times the area and drag
coefficient will yield the drag. Under this paradigm there will always be a drag
value that is approximately double what it would be if we used power to
eliminate boundary layer viscosity, instead of simply trying always to blast
our way through it. ... No physical mechanism corresponds to the '1/2' in the
equation (!) It is an assumption, long buried,


Whenever I see an equation of the form y = 1/2 aX2 and that equation is modeling a physical system, then we're most likely looking at one of the many forms of Newton's second law, F = ma (force = mass times acceleration.) The right-hand side of that equation is most (but not all) of Newton's law written with respect to velocity instead of acceleration. The whole equation of course being f = 1/2 mv2 + v0. The 1/2 comes from taking the instantaneous value of "change of position" (the first derivative, if you're math inclined.) On the other hand, we appear to have been waving our hands at and ignoring a meaningful value. None of this has anything to do with viscosity but only change of position. The whole "we can treat viscosity as if it were pressure" assumption has got to go though.




Even the 'neglible' low viscosity of our atmosphere can and does create major
havoc when circumstances allow persistence to develop. Just as a bullwhip
translates 'negligible' forces and velocities at the handle into supersonic
energies at the tip because it's a supple and transmissive medium of adequate
length....

Great John, introduce chaos theory. Wasn't this deep enough? :P

What is low induced drag? For our purposes it is low wake vortex.

So induced drag is not the energy we put into making lift, but something else? We certainly need to provide the impetus to do both. (I'm not--yet--schooled in aerospace engineering, but I am a physicist and systems scientist. The fun parts of John's ideas come with the systems more than the physics. If we can deal with boundary layer viscosity then we should see a change in drag. I'm curious if the measured changes are density-dependent.) (I wonder if we could beg our web provider for a Greek alphabet too ... ) :-)

. . .

Anyone want to talk about systems theory? Feedback, feed-forward, signals, control theory, etc. and digging into how Synergy sizes up with other aircraft?

John Bucknell
02-21-2012, 02:26 PM
This entry is for anyone who has been wondering why Goldschmied Propulsion hasn't taken over the world. I have collected many papers on the topic, and one was recently published by AIAA that may shed light on why nothing of note has appeared in literature in the intervening years.

I would point those who are curious at AIAA 2012-0866 "Computational Study of the Embedded Engine Static Pressure Thrust Propulsion System" which attempts to reproduce Goldschmied's wind-tunnel results in CFD (ie the Goldschmied body). The bad news is that the only discrepancy found is the pressure upstream of the embedded fan - CFD predicts far greater delta-P than the measured data. This directly relates to the amount of power required by the embedded fan to achieve static pressure thrust - and this power consumption is far higher than Goldschmied calculates, in fact so high that it is higher than that necessary for a non-embedded propulsor (ie conventional external propellor). It is unfortunate that the power used to drive the fan was not directly measured (or perhaps not reported since it would have been inconvenient) by Goldschmied - he back-calculated based on velocity and delta-P (ref. AIAA 1987-2935-856). I suspect that this one pressure port was somehow measuring some dynamic pressure instead of the static pressure it should have.

I can say fairly confidently now that with this datapoint as well as some independent simulation on my own largely confirms that the data presented by Goldschmied is erroneous. I suspect industry came to the same conclusion long ago.

However, there is one ray of hope on this topic. In the formal report to the Navy (DTNSRDC-ASED-CR-02-86 Wind Tunnel Test of the Modified Goldschmied Model with Propulsion and Empennage Analysis of Test Results - avail on DTIC), Goldschmied points to another body shape that should perform substantially better. This shape is called out as the R8 body from Smith, Stokes & Lee's "Optimum Tail Shapes for Bodies of Revolution", AIAA Journal of Hydronautics in 1981 (search AIAA.org). The bad news is the ordinates of this shape are not called out correctly in Goldschmied's report - the X and Y coordinates are the same for the first 26 datapoints, which is perhaps more example of his less-than-meticulous nature.

Best,

John

John McGinnis
03-11-2012, 08:38 PM
Hello all, glad to be back if only briefly. The renewed build continues (http://www.facebook.com/pages/Synergy-Aircraft/112353422181543), but I'll open a post to hopefully keep any Synergy Q&A (http://eaaforums.org/showthread.php?1563-Synergy-Q-amp-A) separate from this thread.

John, thank you for posting on this topic. Goldschmied really missed the point when he became enthusiastic about pressure thrust for propulsion. It just doesn't work.

In fact, I had to be shown that he was an advocate of this misapplication since I couldn't believe it. I always thought this mistake was from others re-interpreting the work. Pressure thrust should (only) be used to recover pressure drag.

Anyway, the Goldschmied result that is much less controversial is both demonstrated and duplicated, which is our ability to reduce the profile drag of a body to essentially zero by application of power. Several methods are considered better than Fabio's fan. One of the more recent works is that of Gerry Merrill and Sid Siddiqi at the Kirsten Wind Tunnel (U of WA). The study I have is a pre-publication version so I don't want to post it, but it lead to this patent (http://www.google.com/url?sa=t&rct=j&q=blpp boundary layer&source=web&cd=4&sqi=2&ved=0CDYQFjAD&url=http%3A%2F%2Fwww.google.com%2Fpatents%2FUS2008 0023590.pdf&ei=nlldT8a5JMTSiALSldCRCw&usg=AFQjCNEnMx3HBwsziaWg9GXSEvzFTB0Tmg&sig2=V-QTPZvpJoR8Sh5h5iKDMg) for boundary layer pumped propulsion.

I haven't found or read the CFD study you mention in the last five Journal of Aircraft... was it published in P&P? T&H? If you can forward a copy that would be great. My working conceptualization for the ideal BLC body would be difficult to expect from a typical CFD study and I'm very interested in the methods they employed.

As far as industrial disuse is concerned, the more likely cause is the ability of anyone with an aero degree to successfully argue the same points, as many have; along with the high cost of a practical application. I hold that our collective lightbulb has not yet been lit on this topic; if it were we'd stop imitating Goldschmied and derive our own ways to efficiently remove stagnant layers after letting them serve us in pressure recovery.

Just as elegant control of the electron opens an entirely new realm of practice (http://www.youtube.com/watch?v=Ws6AAhTw7RA), so also elegant control of the boundary layer changes everything in fluid dynamics. With all of the things we stick out in the airstream, general aviation is presently so far from that future that we barely have the credibility to engage in its pursuit. I hope we don't avoid the necessary setbacks along that journey just because they are inevitable.

John Bucknell
03-11-2012, 11:11 PM
John,

Thanks for the pointer to the patent (I need to digest it), as well as your commentary. As for your request - I get access to papers through work, but I can point you more directly:


Computational Study of the Embedded Engine Static Pressure Thrust Propulsion System

Paolo Nestore Peraudo Virginia Polytechnic Institute and State University, Blacksburg, VA; Joseph Schetz Virginia Polytechnic Institute and State University, Blacksburg, VA
AIAA-2012-866
50th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, Nashville, Tennessee, Jan. 9-12, 2012



There work is listed on Virginia Tech's site as well: http://www.tbw.aoe.vt.edu/papers.php

Keep up the good fight getting your plane done - I have a project vehicle still incomplete after ten years. It's not nearly radical as yours (but still radical :)), however getting asked constantly when it'll be done gets old after a while.

John

John McGinnis
03-15-2012, 12:09 PM
Thanks John. I'll enjoy that paper, I'm sure! I'd LOVE to see your project, as well!

rpickell
05-08-2012, 03:03 AM
I just had a small flash (Eurka moment) from my late night (ok, early morning now) coffee (caffeine) fix. This has to do with wake immersion propulsion.

For much of my life I have been interested and fascinated by ballistics. Especially rockets and bullets. Yet there was one thing I could not really grasp clearly until just now and that is 'bleed base' artillery projectiles. Without getting to deep into it by having a flammable solid burning at the base of the artillery projectile 'bleeding' gas into the wake stream you can nearly double the range of the projectile. Yet the amount of 'raw' energy produced by the flammable solid base burning is very small.

I could never wrap my head around how you nearly double the range for less then a 1% additional input of energy into a system !!!

Well it finally hit me. This is in essence the same effect you get in wake immersed propulsion. The real gain is due to using a small amount of power to prevent the drag from occurring in the first place. As such by almost eliminating the formation of drag from the movement of the body you no longer loose energy to it and your overall efficiency goes WAY UP !!!

If this can be done with cannons and projectiles I see no reason it will not be successful in GA.

John McGinnis
05-08-2012, 09:59 AM
Absolutely correct, sir.