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Old Jun 08, 2012, 06:23 AM
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Quote:
Originally Posted by Warren B View Post
A little update on my Windbag.
I had 3 reasonably successful flights, a bit quick on roll response and a bit slow on elevator, requiring most fo the available "up" to keep flying.
My 4th flight was a prang as I over-rolled a turn, ended up inverted and ran out of ideas and altitutude at about the same time.
Made a big bang (it's a very hollow resonant structure) but zero damage.

I then replaced the original silver PAW 55 screamer with a slightly milder red head version with exhaust manifold.
I also rebalanced to move the CG back, to hopefully cure the need for so much up elevator.
And I calmed the aileron (actually taileron) function a little.

The result has been much slower flying and almost no control.
I think maybe the much reduced slipstream over the tailerons may have been the problem.

So it retired to the shed for a rest whilst a played with other things.

Just recently I scored yet another PAW 55, so I shuffled 3 motors/planes to put the screamer back in the Windbag -time for another go!!!

Warren B.
So, Just where is the CG location on the "Wind Bag"? I dont seem to find it on the plan. Also, it looks like formers F4 & F5 are the same.
~Fred
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Old Jun 08, 2012, 07:44 AM
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Hi Fred
That's part of the problem.
No CG marked and no mention in the article.
I guessed about 30% of the length.
But seems nose heavy so I have moved it back a couple of inches for the next try.
If/when I get it right I will update.
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Old Jun 08, 2012, 08:05 AM
pd1
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Planeman posted a plan of the Roy Clough design, post number 28, it shows the CG.
Should be close.
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Old Jun 08, 2012, 09:28 AM
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Hmm.......
The outlines of the wing...sorry...fuselage..(or should it be 'hull'..?), form a fully symmetrical "wing section" (although very thick), with a totally neutral stab shown on plan, i.e. no decalage at all, thus requiring a slightly raised nose when flying level.
As this nose-up attitude makes the "thing" fly, we cannot do anything about it, though by raising the stab T/E a little, thus providing an initial decalage of couple of degree or so, wouldn't trimming be easier...?...and the airflow over the stab getting more "clean" as well....?..."flying wing-wise"....


Thinking loud, again....
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Old Jun 08, 2012, 11:03 AM
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Continuing with the fiddly bits....
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Old Jun 08, 2012, 02:44 PM
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un-orthadox.or new concept in thinking?

Quote:
Originally Posted by brokenspar View Post
Continuing with the fiddly bits....
Great construction job! How would one figure "hull/wing" loading? for rescaleing.
~Fred
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Old Jun 08, 2012, 09:31 PM
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Originally Posted by Vrated View Post
Great construction job! How would one figure "hull/wing" loading? for rescaleing.
~Fred
I wish I knew the answer, Fred. "Hull" area is about 1.6 square feet. The plans indicate a flying weight of 6 ounces. Mine, with the RC gear and e-conversion will be at least 7 ounces, for a wing loading of maybe 5 ounces/sq foot. That's super light for a conventional wing but of course this thing is anything but conventional. All the traditional rules of thumb assume a reasonable aspect ratio (ie 5 or 6). The Space Ship has an aspect ratio of less than one.

Power-wise, the original design flew with a sport type 1/2A engine, such as a Baby Bee 049. If memory serves, those put out about 1/20 of a horsepower on mild fuel and a 6 x 3 prop, or around 37 watts. Allowing for motor inefficiency, I'll need about 50 watts of input power to get that. And my high altitude location (5300 feet above seal level) might be another factor. So many variables...
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Old Jun 08, 2012, 11:26 PM
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Originally Posted by earlwb View Post
I think these planes are pretty neat. I never got around to building one myself, but mayube one of these days. I sometimes wonder if some NASA engineers had made them when they were young and that led them to the lift bodies and Space Shuttles later on too.
Interesting thought. I was working at NASA in the lifting body (and later Shuttle) days, but never heard of the Martian Space Ship until I saw Skip Ruff fly his in about 1990.

The lifting body concept was a logical development in which engineers tried to design a reentry vehicle which maximized volumetric efficiency and yet had sufficient gliding capability to land like an airplane rather than landing by parachute. A round ball has the greatest ratio of volume to surface area, and the Russians did indeed use the round ball shape at first. Not only does the round ball have optimum volumetric efficiency, but it also is most immune to localized heating during re-entry. Sharp edges, corners, fins & wings get hot much faster than a blunt, rounded shape.

The Americans quickly went to the shape of a missile nose cone. The nose cone isn't quite as efficient from a volume standpoint, but it takes advantage of the existing shape of the missile nose. But it was necessary to turn the nose cone around backwards for reentry.

Both the sphere and the nose cone have a glide ratio of essentially zero. So the lifting body is the minimum modification to a nose cone which would have an adequate lift to drag ratio so it could be landed without a parachute. The first lifting body flown by NASA was really nothing more than one half of a missile nose cone shape. Theoretically, you could have put two lifting bodies back to back on top of the booster and they would become the nose cone.

The invention of thermal protection materials (such as tiles) was a game changer. Now we could put wings on a re-entry vehicle and not have them burn off. So the Space Shuttle was made possible by the advent of high temperature insulation. Prior to having high temperature insulation it would have been necessary to cover a vehicle with an ablator, which burns away on re-entry and unfortunately changes the shape of the vehicle and gives it a very rough surface.

By the way, virtually all of the key lifting body engineers were or had been modelers. And some of the first "proof of concept" lifting bodies were stick and tissue paper free flight models.

Sorry for being so long winded,

Dick
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Old Jun 09, 2012, 05:05 AM
RFJ
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Quote:
By the way, virtually all of the key lifting body engineers were or had been modelers.
Like these guys.

Ray
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Old Jun 09, 2012, 01:38 PM
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The saga continues....
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Old Jun 09, 2012, 05:07 PM
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Have you given any thought on an "access hatch"? BTW, looking good. A fun project for sure, even the head scratching part. Thanks for the info guys.
~Fred
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Old Jun 09, 2012, 08:24 PM
Visitor from Reality
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Dick - not long winded at all, a great inside look at a fascinating era. Thank you indeed.

An 'Access Hatch'? First off, let's figure out where the 'Top' and 'Bottom' are!

D
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Old Jun 09, 2012, 10:26 PM
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For anyone who would like to see a video of the very first lifting body model airplane, take a look at the youtube below. The video has some factual errors, leading one to believe that the first model was radio controlled and was dropped from a larger RC model. But that "first" model was strictly free flight and was towed aloft by a conventional powered model which did have rudder and tow release control. Remember, this as 1962 and radios were not simple, not small, and certainly not cheap. Short clips can be seen at about 1:45 to 2:00 and is B&W 8mm film. The red and yellow "mother ship" seen there is a later development, from about 1967. By then we had a little more budget and proportional radios (wow ! Into the big time).

The fellow speaking, Dale Reed, built that first model (and the towplane) at home on his own time and with his own money. His wife took the 8mm movie at a local dirt strip airport.

Dick

NASA Destination Tomorrow - Lifting Bodies (5 min 21 sec)
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Old Jun 10, 2012, 01:27 AM
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FASCINATING!!! Thanks, otrcman!!!
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Old Jun 10, 2012, 12:26 PM
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That is indeed interesting and it's surprising to find that this lifting body project was the brain child of a single engineer. Must have been quite a ride, with a sink rate of 3600 feet per minute.

Not sure about a hatch yet, but I've had good luck with magnetically held hatches in the past.
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