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Author Topic: Flying on the Edge?  (Read 1368 times)

Offline Joe Messinger

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Flying on the Edge?
« on: October 12, 2006, 10:29:30 PM »
Hello,

I guess I'm too curious about stuff.  I wonder about things like "Why do we call apartments, apartments, when they're all bunched up together?"

Anyhow,  I've never understood how an airplane can fly on it's side?  Seems any lift generated by the wings wouldn't help at that attitude.  Is engine thrust the only factor that keeps the plane flying?

I know c/l planes don't do much flying with wing tips pointing up and down.  Maybe for a few moments during a wing over or during overhead maneuvers.  A good many r/c and real planes seem to have no trouble with flying on their side.

Maybe some knowledgable reader can satisfy my curiosity. (Don't worry about the apartments.)

Thanks,

Joe
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Offline RC Storick

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Re: Flying on the Edge?
« Reply #1 on: October 12, 2006, 10:36:33 PM »
Kinda like we dirve on the Parkway and Park on the diveway.
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Offline Dick Fowler

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Re: Flying on the Edge?
« Reply #2 on: October 13, 2006, 06:32:29 AM »

Joe you're right abut the wings not providing any lift in the overheads. I believe that the thread on line tension covered most of the reasons. The simple answer without getting caught up in terms... the model is flying fast enough that the "centrifugal" force is large than the pull of gravity in the overhead in order to stay out there.

I would image we are getting some lift from the fuselage and vertical stab  but not enough to do the job.(assuming proper leadout location). Full size aircraft and RC models usually have to input large amounts of rudder to keep the nose up during knife edge maneuvers.
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Offline Russell Shaffer

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Re: Flying on the Edge?
« Reply #3 on: October 13, 2006, 09:46:31 AM »
The nose may be up, but the aircraft is on a ballistic trajectory.  We have a lot of F-15's flying here, and when they are in a vertical bank on landing approach, the sink rate is amazing.  Of course, if the nose is up, the power to weight ratio lets them do almost anything.   Just like an Akromaster with a 19 pulls me out of foolish moves like getting the stooge line over the control lines on takeoff.
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Offline Ted Fancher

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Re: Flying on the Edge?
« Reply #4 on: October 17, 2006, 09:26:14 PM »
Joe you're right abut the wings not providing any lift in the overheads. I believe that the thread on line tension covered most of the reasons. The simple answer without getting caught up in terms... the model is flying fast enough that the "centrifugal" force is large than the pull of gravity in the overhead in order to stay out there.

I would image we are getting some lift from the fuselage and vertical stab  but not enough to do the job.(assuming proper leadout location). Full size aircraft and RC models usually have to input large amounts of rudder to keep the nose up during knife edge maneuvers.

Close, Dick.  but not exactly right, at least as far as the overhead eights are concerned.  As long as the airplane is flying at an angle of attack (positive or negative) to the air mass in which it is moving the wing will be producing lift.  It just won't necessarily all be directed perpendicular to gravity as it pretty much is in level flight.  It's the lift, after all, that provides the energy to track the halves of the eight.

A perfectly straight wingover is a better example of the possibility of the wing producing zero lift.  The perfect wingover would be the result of the tail driving the wing to a positive angle of attack until the flight path is exactly vertical (of course on the surface of a sphere which almost immediately starts putting the side of the fuse into play regards to producing a small amount of lift,  more or less like knife edge free flight).

Once the flight is vertical the ship depends primarily on thrust and inertia for the path to the top and then you have to start back pedaling because now gravity is urging it on instead of holding it back.  Ergo, we need good stunt engines!

Ted

Offline Bill Little

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Re: Flying on the Edge?
« Reply #5 on: October 17, 2006, 10:30:14 PM »
I'm just so happy that these models of ours fly as good as they do!!!!!!   ;D

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Offline steve pagano

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Re: Flying on the Edge?
« Reply #6 on: November 27, 2006, 04:46:06 AM »
rudder control !!!!!!!!
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Offline Shultzie

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Re: Flying on the Edge?
« Reply #7 on: January 09, 2007, 02:22:53 PM »
No problemo what so ever.....this one holds beautifully out on the lines..turns waaaay inside it's own wing tips...snap stalls, like it'S nailed to a wind wall, grooves like its on rails....

Perhaps we could just buy a piece of foam core board, paint an outline of an old Nobler on the side...mount a engine up front....and GO FOR IT!
Don Shultz

Offline Paul Smith

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Re: Flying on the Edge?
« Reply #8 on: January 15, 2007, 11:23:32 AM »
I've seen some RC airplanes and helicopters do a lot things that would be impossible in the "real world". 

The answer is simple: Lots of thrust and very little weight.  Up until the latest generation of fighters: F-15, 16, 18 ,etc, they didn't have the 1-to-1+ thrust to weight ratio.  Now, as long as you have airflow over the controls, you can point to any way you want as long as you want.

The T-38 was, and still is, a hot fighter-trainer.  But it weighed 10,000 pounds with half a tank of fuel and put out 4,000 pounds of thrust in full burner.  It would go straight up only until the initial airspeed was depleted. 

Lots of CL & RC models  will take off vertically and accelerate.
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Offline L0U CRANE

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Re: Flying on the Edge?
« Reply #9 on: January 17, 2007, 01:06:49 AM »
Ted,

>"A perfectly straight wingover is a better example of the possibility of the wing producing zero lift.  The perfect wingover would be the result of the tail driving the wing to a positive angle of attack until the flight path is exactly vertical ...

Comment: The climb and dive in the Hourglass are also no-lift great circle paths, aren't they?

>"...(of course on the surface of a sphere which almost immediately starts putting the side of the fuse into play regards to producing a small amount of lift,  more or less like knife edge free flight).
..."

Comment: The fuselage side area should only come into play in Wingover or Hourglass long straight-lines IF the model yaws further from the perpendicular to the pull force than it is in level flight or other maneuvers. If it stays tangent to the hemisphere in the RWO and 'glass long lines, the fuselage and its side area are just as aligned to the path of motion as for any other path in the pattern, no?
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Offline Mark Scarborough

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Re: Flying on the Edge?
« Reply #10 on: January 17, 2007, 01:10:45 PM »

..."

Comment: The fuselage side area should only come into play in Wingover or Hourglass long straight-lines IF the model yaws further from the perpendicular to the pull force than it is in level flight or other maneuvers. If it stays tangent to the hemisphere in the RWO and 'glass long lines, the fuselage and its side area are just as aligned to the path of motion as for any other path in the pattern, no?
[/quote]
In theory this would seem logical, however I think that if you were to diagram it out physically you would find that the aircraft when aligned perfectly tangent to the arc of motion still has  positive angle of attack on the  nose. It is outside the cirlce (arc of motion) and as such is moving laterally  ID there is air hitting inside surface of the nose. At least thats what I see when I draw it out. For the air not to be interfacing with the inboard side of the fuse the nose would have to be pointed exactly in line with the direction of travel, which would dictate the fuse be yawed inboard.To visualize this imagine your plane was infact say ten feet long and moving with the cg tangent to the circle, think about where the nose would be and how it would be moving in relation to the line of flight.
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Offline W.D. Roland

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Re: Flying on the Edge?
« Reply #11 on: February 08, 2007, 11:03:33 AM »
knife edge flight(flying with airplane on side)with r/c scale planes i have built
Art Chester Jeep--good and level with 1/2 rudder movement--will climb with full rudder.
Gee Bee R-2---real good with very little rudder.havent flown it much-seems like it will do it forever(real one to)
cap 21--heavy but will maintain level flight for fairlylong distance extreme angle of attack
lazer 300--real good--almost knife edge loop.
pt-19-- yes but silly and dihedral fights it

side area-shape-light weight-hp

just a thought---use less line rake and more rudder so that as lines slaken in overhead rudder points nose out and we have knife edge flight?
in c/l cetrifical force is probably largest factor

David
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Offline L0U CRANE

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Re: Flying on the Edge?
« Reply #12 on: February 08, 2007, 11:29:24 AM »
To Mark's Post #10...

Agreed. Remember also that the effect - right-turning yaw tendency (for the most usual kind of flying, CCW upright) - includes the fin/rudder aft of the CG.

If we could transform the circular path to straight, and curve the fuselage to keep the same relationship to that path as it has in the  real world, this would be easy to see.

There's a lot of other air disturbance going on from just in front of the prop to aft of the whole model... Inflow fields to the prop and the wing; propwash spiral flow; wash over the wing, fuselage and tail, etc.

I consider the least yaw attitude to be when the imaginary straight line from the handle to the CG is perpendicular to the fuselage centerline. Another way to say that is that the path of the CG is tangent to the flight circle.
\BEST\LOU

Offline Jim Thomerson

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Re: Flying on the Edge?
« Reply #13 on: February 08, 2007, 11:49:15 AM »
OK, I know that centrifugal force is a myth, but so what? ::).  If your airplane has a pull of three g's in level flight, as some people say it should, then it should have a pull of 2 g's at the top of the circle, assuming airspeed is the same as level flight.  We don't need no steenking lift. ;D

Offline bob branch

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Re: Flying on the Edge?
« Reply #14 on: February 08, 2007, 05:41:22 PM »
Rc planes and 100% scale fly in knife edge flight by flying with a positive angle of attack and that makes the fuselage create lift. This is done by applying top rudder, ie rudder in the direction of the side that is up when in knife edge flight. The amount of rudder required decreases with increased fuselage area, and speed. Very good aerobatic planes with adequate power can do knife edge loops and almost any other maneuver you can think of from any other attitude including knife ege flat spins... very cool looking but mostly the modern 3D genre of planes are the ones that can do that.

A trimming point of interest, most aircraft when in knife edge will try to turn one way or the other, either towards the belly or towards the canopy. Superbly designed aerobatic aircraft will do niether or so little that very little correction is required. Most folks will trim that out by mixing an elevator correction that occurs automatically when they are in knife edge flight in their radio transmitter. There are several ways to do it, depending on the radio and pilots preferences.

Just as an asside, I am working at being able to fly the full modern CL stunt pattern in RC. The most difficult maneuver is the wingover because there are no control lines to regeign the plane in. Flying a consistant large diameter arc thru knife edge is a real toughie, coming around the circle and repeating the maneuver in the same place is a regular killer. I have just recently maidened a plane that I think will let me do it. I've worked on a couple of different types of planes and its pretty demanding. My current solution is a very large side area full bodied 3D very long tail momented .46 size ship with a hot .60 in it. We'll see. Everything around here is solid ice, wind chills in the minus teens and wind over 20 knots for the last 2 weeks.

Bob Branch
Harsens Island, MI

Offline W.D. Roland

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Re: Flying on the Edge?
« Reply #15 on: February 09, 2007, 09:21:10 AM »
Bob
that sounds like someting i would try.
let me know how the wing over comes out
5ft recovery!?
 
 David
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Offline bob branch

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Re: Flying on the Edge?
« Reply #16 on: February 11, 2007, 04:05:57 PM »
David

If I can do it with 100 ft recoveries I'd be doing good  LL~..... Don't hold your breath for a 140 diameter circle either.  Its alot tougher without the strings.  HB~>That's why RC pattern went and did its own thing and didn't try to copy CL pattern.

bob


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