RE: What stops vertical flight?  
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RE: What stops vertical flight? - 12/23/2003 9:51:50 PM   
Frankenthumb



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RE: What stops vertical flight? - 12/23/2003 9:55:45 PM   
JimRoss



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Gravity is actually measurable. It is taken in units called "Gals" after the man, Galileo, who is credited with having the idea that there was such a thing. One is able, with the right equipment, to accurately measure the difference in the effect of gravity over a span as small as two or three feet. The change over a given change in altitude is only several microgals or millionths of a Gal.

Now, having inundated you with all this useless trivia, the difference in gravitational pull from sea level it say 10,000 feet is negligible, as far as an aircrafts weight is considered.
Gravity is, after all is said and done, the limiting factor that keeps us and our airplanes from flying off into space but it is not the only thing that stops airplanes from vertical flight. It is a slightly limiting factor but other forces come into play long before gravity effects anything.

The main reason is loss of lift/thrust to overcome the aircrafts weight, which is determined by gravity, and the drag imposed on it by the atmosphere.
Picture a rocket, it has enough thrust to overcome the Earths' atmosphere and gravity and put it into orbit. Our tiny little planes are not capable of producing that amount of thrust. Now if you strap a Titan Booster onto it, you have a whole new ballgame. But then you get into a cost vs benefit situation that makes it totally out of reason to do.

BTW, there is no such thing as gravity, the Earth sucks.


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RE: What stops vertical flight? - 12/24/2003 12:43:21 AM   
destructiveTester


 

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Status: offline 		ok here's another theory -

Your Magic hovers at less than full power right? - but when you pull into a vertical climb it starts falling back after a while.

I think the engine tuning idea has validity. And I also think the perspective of height idea has validity.

However - you did not mention falling revs or a dying engine - most engines set to lean either gradually or quickly cut out.

Also I don't think you would bother to post a message because you had trouble judging height, so I think the perspective theory is unlikely to apply here too.

How about this for a theory:- when you are hovering your magic, is the plane at a strictly 90 degrees angle, or are you slightly nose forward/tail backward? I was watching a wmv of a small fun fly model (.25 size) doing some slow speed/prop hanging, and it was not at 90 degrees, more like 45 degrees.

Therefore, even though the wing is not moving, the relatively large diameter (small pitch) prop of the plane was blowing over some of the wing. Now I expect this was creating a bit of lift. Not enough to hold the model, but enough to add a vertical force component to augment the upward/vertical component of the engine's thrust.

Could it be that strictly speaking you are not totally prop hanging the magic to start with, and its only when you do that you rely on the full power of your engine? i.e. when you pull up into a 90 degree climb from a 70 degree hover?

I could be totally wrong but just thought I'd put my 2 cents in

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RE: What stops vertical flight? - 12/24/2003 12:45:51 AM   
cirrus


 

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Status: offline 		These guys are right. The change in gravity between ground level and a few hundred feet is so negligible you would have a very hard time measuring it even if you were properly equipped. In fact the change in G between the surface and 100 miles up is also negligible. Yes Martha, the astronauts float because they are in free fall. Another point to consider is propeller efficiency.

cirrus

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RE: What stops vertical flight? - 12/24/2003 1:45:45 AM   
JimRoss



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quote:

ORIGINAL: cirrus

These guys are right. The change in gravity between ground level and a few hundred feet is so negligible you would have a very hard time measuring it even if you were properly equipped. In fact the change in G between the surface and 100 miles up is also negligible. Yes Martha, the astronauts float because they are in free fall. Another point to consider is propeller efficiency.

cirrus


To this I must add my other two cents.
100 miles up yields a significant difference in effect of "G". 100 miles up I would weigh nothing, on the ground I weigh 255 pounds.
So, for all you fat people out there who want to lose weight, it's really easy. Climb a step ladder and you have just lost about one tenth of an ounce. No pills, no diet, no sweat, no exercise, except for climbing the ladder.
See, we can put all these fad diets and pills right out of business.


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RE: What stops vertical flight? - 12/24/2003 2:06:30 AM   
Jim Thomerson



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Status: offline 		Actually, as I calculate it, JimRoss at an altitude of 100 miles would weigh @ 242.75 pounds. Now I made a D in algebra the second time through and failed Geophysics, so you might want to do your own figuring.

Jim

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RE: What stops vertical flight? - 12/24/2003 2:25:07 AM   
BMatthews



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quote:

ORIGINAL: MHawker

...To clarify, I was concerned with strictly vertical flight and not the momentum carried into the climb. If I had a plane with, let's say a 1.5 power to weight (but the ratio is not important), it would accelerate vertically to a point and then stop. What causes it to "stop"? ....


With that power to weight it will not stop until it's well out of sight of you.

BUT....

The speed in the vertical climb will be limited because 2/3 of the thrust is being used to negate the weight of the model. That leaves only 1/3 to accelerate the model until the air drag stops it from going any faster. At that point it's like flying your model level at only 1/3 the maximum thrust. It'll be slow and less snappy but it'll still fly.

And while I know it's already been taken care of that bit about the gravity fading with distance to where at 100 miles there is no weight left didn't make sense. If that was the case what holds the moon in orbit or the earth in orbit around the sun? The tiny fraction of 1 ounce makes a lot more sense.

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RE: What stops vertical flight? - 12/24/2003 2:25:25 AM   
Boss248



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RE: What stops vertical flight? - 12/24/2003 2:42:01 AM   
michpittsman


 

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< Message edited by michpittsman -- 12/23/2003 9:45:40 PM >

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RE: What stops vertical flight? - 12/24/2003 2:46:36 AM   
JimCasey



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Status: offline 		JimRoss, you are not weightless at 100 miles altitude. Weightless reports at 100M altitude come from spacecraft that are traveling at around 17000 mph, in effect doing a 1G outside loop; just countering gravitational effect so they feel "weightless". IF you were real clever and could be stationary in space at 100 mi, you would feel hardly ANY lighter. Gravitational force is distance dependent, but the distance is from the center of the earth. The Earth's diameter, rounded off, is 8000 mi. THe gravity at 100 mi would be (4000/4100)squared, or 95% of surface gravity.

Vertical flight of your airplane stops because of the increasing distance from your wallet. As we ALL know, MONEY is what makes airplanes fly.

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RE: What stops vertical flight? - 12/24/2003 2:47:46 AM   
JimRoss



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quote:

ORIGINAL: Boss248

Did JR just call us fat???


Absolutely did not call anyone fat. That is unless you secretly are! Just remember, climb only as high as necessary to lose the weight you want to.

How high are the satellites orbiting the Earth? They are weightless or they would fall back to Earth.


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RE: What stops vertical flight? - 12/24/2003 2:54:03 AM   
JimRoss



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quote:

ORIGINAL: JimCasey
Vertical flight of your airplane stops because of the increasing distance from your wallet. As we ALL know, MONEY is what makes airplanes fly.


BY GOD, I think he has hit upon the only real truth in the universe.
It has been said that money is the root of all evil. I don't believe so. I think lack of money is the root of all airplanes limitations, to say the same thing Jim Casey said in another way.
I defer to your higher wisdom.


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RE: What stops vertical flight? - 12/24/2003 2:54:52 AM   
Boss248



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Status: offline 		The sattelites that are in low orbit are constantly corrected but the geosynchronous sattilites are 22,000 miles...give or take a little.
I hate gravity...it makes my knees hurt

< Message edited by Boss248 -- 12/23/2003 9:55:06 PM >

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RE: What stops vertical flight? - 12/24/2003 3:34:02 AM   
Tall Paul



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quote:

ORIGINAL: JimRoss

quote:

ORIGINAL: Boss248

Did JR just call us fat???


Absolutely did not call anyone fat. That is unless you secretly are! Just remember, climb only as high as necessary to lose the weight you want to.

How high are the satellites orbiting the Earth? They are weightless or they would fall back to Earth.

.
Satellites are continuously falling around the earth.. at their altitudes the direction of fall matches the curve of the surface of the earth.
Stuff like that is "weightless", but the mass is still there. "inertia".. That's what makes things "interesting" when orbiting stuff meets other orbiting stuff.
In a stable orbit, the gravitational force on the satellite is equal to the centripetal force for that orbit.
Average orbital speed is 18,000 mph.
A geosynchronous satellite is about 39,000 km above the surface.
And, there's no way to keep fat a secret!

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RE: What stops vertical flight? - 12/24/2003 4:28:39 AM   
BMatthews



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Status: offline 		....A geosynchronous satellite is about 39,000 km above the surface.

[/quote]

And to elaborate a bit...

That altitude was specially selected because at that altitude the time to orbit at the proper speed matches the rotation of the earth. It's not that the satelite is just sitting up there but rather that it's going 'round at the same speed WE are so it looks like it's just sitting there.

None of the satelittes just "sits" there. If they did they wouuld fall to earth just like Newton's apple.... but thanks to air friction it would be a baked apple by the time it hit's your upheld fork...

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