Question for Kibort, Dangler and other aviation guys...
11-02-2009, 09:08 AM
#46
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Mark your observation is correct but with no airflow over the control surfaces, they don't do squat. The helicopter pic you attached seems to have a turbine outlet at the rear using vectored thrust instead of a tail rotor, no?
11-02-2009, 10:03 AM
#47
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Adrian, Sure, that's why NASA and Burt Ratan use R/C models to flush out new designs. There is this thing called the Reynolds Number that reflects the size of the airfoil compared to the size or air molecules. There is also the consideration of scale airspeed that makes them seem not quite so slow or floaty. There is a whole segment of R/C that builds true to scale R/C planes and they find they are very difficult to fly as the scaled down airfoil is just not up to the loading for the slower speeds needed for take off and landing the smaller scale planes.
There is a plane developed here in Oklahoma called the bush plane that amazingly flies at only 25 mph and can take off and land in only 75 ft.
I also think if you go look at the modern aerobatic planes (also developed and built here in Oklahoma, the EDGE) like those used in the Red Bull Air Racing you will find they are very light and "floatable" and have a very comparable power to weight ratio as R/C planes.
But when you go to indoor R/C planes, yes there are some foam r/c planes made for indoor aeribatics now that are insanely light and are flown in exhibitions in gymnasiums. I am anxiously awaiting the materials and radio controls to be sized down in both weight and size to be able to fly aerobatics slow enough to be able fly it around in my living room instead of a basketball court sized gymnasium. So far mini micro R/C are only rudder, elevator, and throttle control, no ailerons yet. They use the vibrator motors from pagers, watch batteries, and the radio equipment and servos weighs in at just 2 grams.
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There is a plane developed here in Oklahoma called the bush plane that amazingly flies at only 25 mph and can take off and land in only 75 ft.
I also think if you go look at the modern aerobatic planes (also developed and built here in Oklahoma, the EDGE) like those used in the Red Bull Air Racing you will find they are very light and "floatable" and have a very comparable power to weight ratio as R/C planes.
But when you go to indoor R/C planes, yes there are some foam r/c planes made for indoor aeribatics now that are insanely light and are flown in exhibitions in gymnasiums. I am anxiously awaiting the materials and radio controls to be sized down in both weight and size to be able to fly aerobatics slow enough to be able fly it around in my living room instead of a basketball court sized gymnasium. So far mini micro R/C are only rudder, elevator, and throttle control, no ailerons yet. They use the vibrator motors from pagers, watch batteries, and the radio equipment and servos weighs in at just 2 grams.
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. Or Boeing/Airbus wind tunnel models, or any other model of this class. And I think the guys that exemplified using R/C were not exactly thinking at high end true to scale models that might cost the equivalent of a good car.I can' t talk about the Oklahoma bush plane, since I know nothing about it, but I can tell you that here we have quite a few clubs of R/C airplane enthusiasts and I had the chance to watch competition models in action on quite a few occasions. All were incomparable with real aircrafts in term of specific weight.
Anyway, you're right with the fact that there are R/C models that do have similar specific weight as "real" airplanes, but that's exactly why I iniaitally said that most R/C planes don't.
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11-02-2009, 11:04 AM
#48
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Scaling has been used in aircraft since the Wright Brothers. They have EVERYTHING in common with their larger brothers. Now, do we see thrust to weight, or glide ratios like the models? no, not always, but sometimes.
The point here is nothing like the conveyor question. in theory, a plane could lift off if tied to a pole, if it was light enough and had enough thrust. I dont think the question was for a specific airplane. If it was, then yes, the answer would be "No".
The point here is nothing like the conveyor question. in theory, a plane could lift off if tied to a pole, if it was light enough and had enough thrust. I dont think the question was for a specific airplane. If it was, then yes, the answer would be "No".
I hope that everyone understands that most R/C airplanes have a specific weight that has little to nothing in common with any modern aircraft.
Only the very early designs (wooden frame covered with muslin ) come close. But due to size even those had to use much denser wood aso.
This doesn't necessarely translates in much higher power to weight ratio, but especially in much higher flotability (might be using the wrong english term here, but you get the idea). Many R/C models can glide with the engine cut off at very low speeds aso.
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Only the very early designs (wooden frame covered with muslin ) come close. But due to size even those had to use much denser wood aso.
This doesn't necessarely translates in much higher power to weight ratio, but especially in much higher flotability (might be using the wrong english term here, but you get the idea). Many R/C models can glide with the engine cut off at very low speeds aso.
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11-02-2009, 11:11 AM
#49
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And that was my point. air flow WOULD be over the control surfaces, and with enough thrust, it would work. counteracting engine torque, could be done SIMPLY by the use of full wing length alerons. (also a form of thrust vectoring). the tail section would have air flow over it and it certainly could produce a change in thrust angle for the prop by keepng the tail secton low and getting a better force vector from the prop. remember, we are talking theory here. NO airplane I know of in real life, could do this trick. 
Hey, im a firm believer that this wouldnt work with real, existing full scale airplanes. remember that discussion on the race list? someone said they did this in a cessna, and remember my comments? turbulent flow over the wings, not enough flow over enough of the wing, etc, were reasons that the plane couldnt have been flying at 0 indicated airspeed, and 0 ground speed (even for a moment) as he had thought he saw.
Hey, im a firm believer that this wouldnt work with real, existing full scale airplanes. remember that discussion on the race list? someone said they did this in a cessna, and remember my comments? turbulent flow over the wings, not enough flow over enough of the wing, etc, were reasons that the plane couldnt have been flying at 0 indicated airspeed, and 0 ground speed (even for a moment) as he had thought he saw.
11-02-2009, 01:10 PM
#50
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Scaling has been used in aircraft since the Wright Brothers. They have EVERYTHING in common with their larger brothers. Now, do we see thrust to weight, or glide ratios like the models? no, not always, but sometimes.
The point here is nothing like the conveyor question. in theory, a plane could lift off if tied to a pole, if it was light enough and had enough thrust. I dont think the question was for a specific airplane. If it was, then yes, the answer would be "No".
The point here is nothing like the conveyor question. in theory, a plane could lift off if tied to a pole, if it was light enough and had enough thrust. I dont think the question was for a specific airplane. If it was, then yes, the answer would be "No".
11-02-2009, 01:49 PM
#51
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11-02-2009, 01:58 PM
#52
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Mark, I guess that video proves your point. I would sure like to have a power to weight ratio like that in my airplane! Rather hard to do if one expects an aircraft to carry a pilot, passengers and fuel for several hours. Amazing video!
Now the question: could that (in the video) airplane lift off if it was held by a string attached to its tail?
Now the question: could that (in the video) airplane lift off if it was held by a string attached to its tail?
11-02-2009, 02:02 PM
#53
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Mark, I guess that video proves your point. I would sure like to have a power to weight ratio like that in my airplane! Rather hard to do if one expects an aircraft to carry a pilot, passengers and fuel for several hours. Amazing video!
Now the question: could that (in the video) airplane lift off if it was held by a string attached to its tail?
Now the question: could that (in the video) airplane lift off if it was held by a string attached to its tail?
Dan
'91 928GT S/C
475hp/460lb.ft
11-02-2009, 02:37 PM
#54
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It would depend on a few factors, mainly the shape of the airfoil. if it was assemtrical, it would lift off. if not, then Dan's point above could be a possiblity.
I think for the discussion, you have to nail down the question. are we talking cessna tied to a pole? No, it wouldnt get airborn. a prop plane, with an asymetrical air foil, and some crazy amount of power, sure, it would lift off the ground. anyone with a RC plane that was slightly overpowered could prove that it could be done.
I think for the discussion, you have to nail down the question. are we talking cessna tied to a pole? No, it wouldnt get airborn. a prop plane, with an asymetrical air foil, and some crazy amount of power, sure, it would lift off the ground. anyone with a RC plane that was slightly overpowered could prove that it could be done.
Mark, I guess that video proves your point. I would sure like to have a power to weight ratio like that in my airplane! Rather hard to do if one expects an aircraft to carry a pilot, passengers and fuel for several hours. Amazing video!
Now the question: could that (in the video) airplane lift off if it was held by a string attached to its tail?
Now the question: could that (in the video) airplane lift off if it was held by a string attached to its tail?
11-02-2009, 03:03 PM
#55
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Amazing skill for the pilot of that R/C aicraft.
That kind of model is pretty much what I had in mind when I said that the specific weight of the R/C stuff has nothing to do with real airplanes. Seems quite probable that the model in this clip could pull the "tied to the pole flight" trick.
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That kind of model is pretty much what I had in mind when I said that the specific weight of the R/C stuff has nothing to do with real airplanes. Seems quite probable that the model in this clip could pull the "tied to the pole flight" trick.
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11-02-2009, 03:46 PM
#56
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Note the size of the wings on the model compared to its weight. That wing loading is near to nil. Lots of drag obviously but that's desirable for a model designed to be flown in a confined space indoors. In the real world ... not so much.
11-02-2009, 04:32 PM
#57
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Most of the drag is due to lift, being lightly wing loaded, that is proportionally smaller than in the real world. being lightly wing loaded, it can fly considerably slower. If that pilot pushed the throttle, it would be a rocket!!
anywa, the wings are scale for its size and that of the full scale "Extra" its modeled after. notice the paper thin wings and fus. Its EXTREMELY low drag, but super lightly wing loading as you say.
Here is another BIG RC plane doing similar things. go to the 3:00 mark
http://www.youtube.com/watch?v=qMrUu...1&feature=fvwp
mk
anywa, the wings are scale for its size and that of the full scale "Extra" its modeled after. notice the paper thin wings and fus. Its EXTREMELY low drag, but super lightly wing loading as you say.
Here is another BIG RC plane doing similar things. go to the 3:00 mark
http://www.youtube.com/watch?v=qMrUu...1&feature=fvwp
mk
Last edited by mark kibort; 11-02-2009 at 04:48 PM.
11-02-2009, 05:25 PM
#58
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For the argument of liftoff purely from prop thrust and disregarding lift generated by the aircraft (wings fuselage…), liftoff possibility all depends on the attachment point of the constraining rope. If you draw a line which coincides with the thrust vector and it falls below the attachment point it is a possibility for it to lift off the ground, however if the line falls above the attachment point infinite thrust will still not cause lift off. This is due to the pitch moment generated by the trust and retention forces. The pitch moment can be figured about any arbitrary point with the same end result. For simplicity and ease of visualization we will use the attachment point for the restraining rope as the point about which we figure our moments.
As you can see in the first example the thrust will create a CCW torque causing the plane to nose down into the ground no liftoff.
As you can see from the second example the plane will tend to want to rotate clockwise and will increases its lifting component of the thrust and given an engine that could generate sufficient thrust would eventually liftoff.
As you can see in the first example the thrust will create a CCW torque causing the plane to nose down into the ground no liftoff.
As you can see from the second example the plane will tend to want to rotate clockwise and will increases its lifting component of the thrust and given an engine that could generate sufficient thrust would eventually liftoff.
11-02-2009, 06:45 PM
#59
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A couple of years ago the first home built jet engined plane flew in Australia, (scary!
)the builder did all his pre-flight ground testing with it chained from the back to a tree,I seem to remember it got off the ground, he would have had the tree frightened either way.
)the builder did all his pre-flight ground testing with it chained from the back to a tree,I seem to remember it got off the ground, he would have had the tree frightened either way.
11-02-2009, 07:17 PM
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A couple of years ago the first home built jet engined plane flew in Australia, (scary!)the builder did all his pre-flight ground testing with it chained from the back to a tree,I seem to remember it got off the ground, he would have had the tree frightened either way.
)the builder did all his pre-flight ground testing with it chained from the back to a tree,I seem to remember it got off the ground, he would have had the tree frightened either way.This could have ended very badly, but lucky enough he was completelly crazy, but not completelly stupid. So he decided to build first a scale model and do some testing. To cut this short, the booster test produced an explosion that shattered the windows of a few apartment buildings in the area, and sent the wannabe Werner von Braun straight to the hospital.
For those who might understand romanian this could be an entertaining lecture http://www.gandul.info/news/un-bucur...-marte-3436669
To somehow end the OT, this prooved that a booster tightened in a vice does not tale off, unless it has enough thrust to lift off the working table
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