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Author Topic: Vectored Thrust  (Read 912 times)

Offline Dick Fowler

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Vectored Thrust
« on: October 24, 2006, 11:04:47 AM »
A few days ago I watched a program about the newest jet fighter the F22 Raptor. It uses vectored thrust to improve the turning rates.

 Considering we have been having discussions about SFG's... what do you think? Would we be closer to the 5 foot radius corner with this technology? How about using it to kill adverse yaw or improve tension at critical times?
« Last Edit: October 24, 2006, 02:54:53 PM by Dick Fowler »
Dick Fowler AMA 144077
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Offline RC Storick

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Re: Vectored Thrust
« Reply #1 on: October 24, 2006, 04:45:15 PM »
Electrics would be a good use for this technology however I don't think with the current judging system you would fair well (Impression points and all).
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Re: Vectored Thrust
« Reply #2 on: October 25, 2006, 12:33:28 AM »
Dick and Sparky,

I'd be concerned with the time delay it takes to get the things working. As with a poorly setup Fox 35, the boost can come in and shut off at the wrong time,

Where we really face a crucial problem is in the "square" corners. Things happen too fast, there, for any kind of external throttle driver to handle, Tuned pipes and GOOD 4/2 break engine-setting-setups respond to maneuver load, IMHO, when and as required.

As with shifting weight to keep a bicycle upright, there are many things that need "muscle-memory" instead of pages of dubious calculations... If it works, and we can refine how well it does, we're on the way.
\BEST\LOU

Offline Dick Fowler

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Re: Vectored Thrust
« Reply #3 on: October 25, 2006, 06:23:33 AM »
Lou, I was think more along the lines of the motor mounted in a gimballed system. If use for corners then a single axis "pivot" could be linked to the bellcrank to swivel the engine in the pitch axis. The engine would pivot exactly at the same time as the elevator input is applied.

If yaw is the concern then change the pivot to act in the yaw axis. Kind of like a wiggle rudder but wiggle the engine instead. Use a full gimballed system for both!
Dick Fowler AMA 144077
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Offline Jim Thomerson

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Re: Vectored Thrust
« Reply #4 on: October 25, 2006, 05:13:14 PM »
I've seen this sort of system pictured a couple of times in "hints and kinks" columns  back in the 40's and 50's.  Interesting to contemplate.  I think only a few degrees of change would be necessary,

Offline phil c

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Re: Vectored Thrust
« Reply #5 on: October 25, 2006, 05:40:16 PM »
The F-22 probably has a wing loading of 200 lb/sq.ft.(?? or more) on a low aspect wing, and something like twice its weight in thrust.  It needs the engines for lift.  It's quite possible to build a stunter, with or without flaps, that can get close to the 5 ft. radius.  What you can't do is speed up anyone's reflexes to be able to accurately fly the corner in the time allowed.  A 5 ft. radius corner is only 7.8 ft. long.  At a typical 52 mph that is barely a tenth of a second.  Nobody but a hyperactive junkie on speed can come close, much less fly it with precision.  On a more typical 15 ft. radius corner the actual corner is about 24 ft, or 1/3 of a second, well within reach of most flyers.  Doesn't really matter how you get the corner radius, vectored thrust, wing loading, or rockets in the fuse, the pilot still has to be able to fly it.
phil Cartier

Offline Dick Fowler

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Re: Vectored Thrust
« Reply #6 on: October 25, 2006, 06:45:02 PM »
Just think Phil... we can achieve in stunt what the real world has been able to do for years. Build airplanes that exceed the pilots' physical capabilities.
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Offline Ralph Wenzel (d)

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Re: Vectored Thrust
« Reply #7 on: October 25, 2006, 11:45:51 PM »
Just think Phil... we can achieve in stunt what the real world has been able to do for years. Build airplanes that exceed the pilots' physical capabilities.

We've been able to do that for years, Dick. That's one reason why AMA Combat uses such huge planes now; for lift and turn without a great speed loss, but also to tame the horrendous speeds possible. Can you imagine just how fast a Quicker would be with a fire-breathing Nelson? If it didn't blow the wings off, I caneasily imagine 140 - 150 mph. Might be faster after blowing the wings off . . . <Grin>
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Offline Dennis Moritz

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Re: Vectored Thrust
« Reply #8 on: October 26, 2006, 05:45:12 AM »
A corner with a flip flopping engine or some vectored thrust surges? Maybe you guys experience a corner differently than I do. It's bad enough trying to cut a corner at a poky 52 miles an hour without a sudden burst of extry power blowing me around. Certainly the raptor is a fly by wire, has a super fast computer balancing the forces out. Stunt is old fashioned and outdated a throw back to simpler times. We should resist any and all calls for technological innovation. (Aside from electric power, Mike Palko's a pall.) j1

Offline Dick Fowler

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Re: Vectored Thrust
« Reply #9 on: October 26, 2006, 03:06:48 PM »
Dennis..."Stunt is old fashioned and outdated a throw back to simpler times."

I don't know Dennis, stunt has been using fly by wire since the '40's! <=
Dick Fowler AMA 144077
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Online L0U CRANE

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Re: Vectored Thrust
« Reply #10 on: October 28, 2006, 12:51:54 PM »
Dick, (to your reply #3...)

My log-on timed out while I was trying to compose another thought on this...

My concern is that the force shifted 90 by gyroscopic precession - it acts "later" in the disk's rotation - is quite powerful. Your gimbals would have to withstand that, while also standing up to engine vibration, thrust, and the rest of the model's motions. Quite a task!

There are other unknowns that might work really well, but could make things confusing:

Control force you'd need to input to meet the precession loads directly (without the help of the entire model's inertia)?

Aiming the thrust differently in regard to the model?

Prop blast changes in the middle of a violent change of lift and drag in a turn?

Swing the tank along with the engine? ...or find a tank position that suits all engine positions?

Not dissing the idea, just musing about things that might need to be sorted out, or might not be a problem at all.

If/when you move the idea along, I'd sure be interested to hear how it goes! (edit spelling)
\BEST\LOU

Offline Steve Helmick

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Re: Vectored Thrust
« Reply #11 on: October 28, 2006, 07:16:23 PM »
I once built a '60's type combat model that had some upthrust. It would turn amazingly well insides, and barely do outsides. It gave me some ideas about this. I thought that something like a K&B Series 64, mounted solid, put a boat U-joint on the shaft and run an articulated prop shaft, hooked to the bellcrank. I don't think we'd be able to deal with more than 5 degrees movement each way, but came to the conclusion that our control system couldn't adequately 'power' the 'vectored thrust' addition. It would also make starting kinda weird, unless you had a lockup pin. I'd like to see somebody actually try it, tho. :X Steve
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Offline Jim Pollock

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Re: Vectored Thrust
« Reply #12 on: January 14, 2007, 07:43:51 PM »
Speaking of lined flight, I believe Oba StClair was the first and I think it was at least in the '30's if not in the '20's.

Jim Pollock   ::)

Offline Matt Spencer

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Re: Vectored Thrust
« Reply #13 on: March 16, 2007, 03:30:00 PM »
Lou, I was think more along the lines of the motor mounted in a gimballed system. If use for corners then a single axis "pivot" could be linked to the bellcrank to swivel the engine in the pitch axis. The engine would pivot exactly at the same time as the elevator input is applied.

If yaw is the concern then change the pivot to act in the yaw axis. Kind of like a wiggle rudder but wiggle the engine instead. Use a full gimballed system for both!

 You'd need power steering ! !

  How about pylon mounted engines, 1 over , 1 under , with the throttles linked to the bell crank.

  Have a look at so W.W.1 Gothas and dornieers, for some 'unusual' configurations,
  theres some really wierd seaplanes.

  there were a few bombers with vertically stacked engines,
 when they opened up the top engines the pilot ended up wearing the aero plane , as it stood on its nose.

 which is where they'd put the pilot. ~^

 you need to keep an eye on some of these designers !


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