Paul,
I would love to hear you opinion and the opinion of others on this
newsletter re: <http://www.synergyaircraft.**com/
<
http://www.synergyaircraft.com/
Sounds like a great potential platform for the TC-Turbonormalized
rotary.
Still Dreaming
Michael Francisco
Sounds good. Has it flown?
Paul Lamar
Another variation on the boxwing concept. Except this time with even
more intersections of flying surfaces and thus even more interference
drag. One word description: CRAP !
Lutz Strobel
Does this apply to the winglets on the EZ's?
Paul Lamar
That is a pretty dismissive statement (CRAP)! I have been following
this design for a while. While there is a lot of hype at this point,
the Engineering principles and design elements they are using are
sound. I will wait until they build and test the full size prototype
before I dismiss it as feces. Think of all the naysayers before the
Wright brothers flew!
One of the cooler aspects of this design is that it uses a smaller
diameter higher pitched pusher configuration. Can anyone say direct
drive rotary application?
James Osborn
I am going to join the nay sayers :)
You need 6 foot diameter to have a reasonably efficient prop. Props
are subject to induced drag so the tip vortices's are a major factor.
Think of a prop as two sail plane wings going around in a circle.
Way back when Paul McCready was attempting to win the Kramer prize
for the first man powered aircraft I was called in as a consultant. I
took one look at the low aspect ratio low diameter prop and said:
"that will never fly". :) Sure enough it did not until they put a
large diameter prop on it and flew the figure 8 and won the prize!
Paul Lamar
The bit difference is the the bulbous design of the fuselage. I don't
claim to fully understand or believe it, but I think it is supposed
to cause the air to hit the propeller disk differently than a
conventional propeller, with an inward pointing component. This
speaks to their point about putting all these design elements
together having a synergistic effect.
What about a ducted fan configuration with a rotary? Always thought
that would be cool for a personal hovercraft design.
James Osborn
I doubt the fuse has much effect on prop eff.
Ducted fans are real bad news in our speed range. Perry Mick tried
them for years before giving up and going with a gear box. Went 20 to
25 MPH faster.
Here is the data from Kuchemann & Weber.
Paul Lamar
I'm with you James, I have also been following this for sometime
now. When I posted it for evaluation on here the reply's were
somewhat narrow minded. However having read the discussion leading up
to the concept design I was not persuaded to accept the negative
comments. Just because it hasn't been done doesn't mean it can't be
done. It is always easier to default to tried and tested methods.
Paul Lipps proved that propeller design is yet to be fully
understood, though unfortunately he was not able to finish his work.
So if you want an education on aerodynamics read the discussion at
http://www.oshkosh365.org/ok365_DiscussionBoardTopic.aspx?id=1235&boardid=147&forumid=175&topicid=3339&page=1.
Ignore the pop-up and read on. It can be heavy going but John
McGinnis knows his stuff, Burt Rutan obviously thought so. You might
want to checkout John Roncz as well, another forward thinker. BTW,
it's not a box wing, it's a double box tail. Come on guys don't be
card carrying Flat Earth Society, Geocentrics. Remember what the "E"
stands for in eaa. Hope he finish's the prototype soon, I'm dying to
see how it goes.
Graeme Riley
Paul Lipps DID NOT not magically make a small diameter prop work. The
laws of physics are to be obeyed :) It is not just a good idea.....
ITS THE LAW.
Think about a helicopter. You need to study up a little bit on this
aerodynamic stuff.
Google is a great resource. Use it to educate yourself on aerodynamic
principles. Look up aspect ratio and interference drag.
Paul Lamar
Hi!: interesting info, thanks a lot. I have a booklet, by R. W.
Howey in 1982 (6th ed), obtained from Zenith Aviation Books, P.O. Box
One, Osceola, 54020 WI, and entitled 'Ducted-Fan for Light Aircraft';
this referencewas given to me by the 'Spanish Association of
Experimental Aircraft'.
This article or booklet included a chart on the propulsion efficiency of
Duct-Fans, Free-Props, Turbo-Fans and Turbo-Jets, probably Prop-Fans
were too experimental then, chart that in the vertical Axis has the
Propulsion Efficiency, from 0 to 100%, and inthe Horizontal, the Speed
in mph, from 0 to 600 mph.
Ducted-Fan efficiency starts quite flat around 80% at 0 mph, but
atairspeed faster than 100 mph, its efficicncy starts to drop
steeply,with an efficiency of some 65% at 150 mph, and 57% at 200 mph,
the chart doesn't go any faster for Duct-Fans, and just around 110 mph,
the Propulsion efficiency of D-F is surpassed by Free-Props with 81%,
efficiency of F-Ps that may have a top around 85% between 200-300 mph,
to fall down sharply after 300 mph; top speed for which efficiency data
exist in the chart for F-Ps is 400 mph, with a mere 60%.
Turbo-Fan propulsion efficiency data start around 43% at some 275 mph,
upto a maximum of 64% at 475 mph, to drop fast until 58% at 530 mph.
Data for Turbo-Jet Propulsive Efficiency start at 40% at 300 mph,
andfollow a near straight line, surpassing Turbo-fans with a 60%
efficiencyat 500 mph (You can watch in you tube the TurboProp version of
Republic F-84 Thunderstreak), and the chart ends for Turbo-Jets at 61%
efficiencyat 600 mph.There is, or was, a link in the Wikipedia Prop-Fan
article to a thesis in aCanadian University about Prop-Fans, that may be
interesting looking at, even when it has more than 10 years on it.
This publication by R. H. Hovey includes an expression for
Horsepower,that is H.P.= (Velocity in Ft/Sec) x (Thrust in Lb) the
figure resulting fromthis being divided by 550.
Thrust= (375) x [HP/velocity] result multiplied by (Efficiency)
Free-Prop Wake Velocity= Square root of 2 x Square root of
[(Thrust)/[(air density) x (Prop Area)]
Ducted-FanWake Velocity= Square root of [(Thrust)/(Air Density) x (Area
at Exit)]
The article by R. W. Hovey contains lots of info, but if I repeat it all
hereI'd be breaking the Copyright, and it would take too long.
Is this of help to anybody, or am I repeating Oldies?
Regards, salut +
Jose Gros-AymerichE-28033 Madrid, Spain
I think Perry Mick used that book.
Please scan the chart and send it to me.
Most books on the subject ignore the significant additional drag of the
duct it self.
Paul Lamar
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