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Help with F-14's - 4/24/2008 11:20:12 PM   
ravill



Posts: 1831
Joined: 1/24/2003
From: Redwood, CA, USA
Status: online 		Hello good folks!

I am determined to make an F-14 fly well at any wing position! Mostly, I'm interested in how to make one "docile" at "slower" (ie half throttle e.g.) with the wings swept.

My question:

How does the F-14 react with the wings swept and how to compensate for those bad tendancies?

Here are some of my thoughts,

Wings sweep back mechanically-> CG gets moved back mechanically

Strakes with wings swept?

How about keeping the ailerons functional with the wing swept??

I've bought two little foamies to make experiment before I try it with a turbine. I am determined to make a Tomcat and "everyday" jet!

Thanks guys!

< Message edited by ravill -- 4/24/2008 11:26:49 PM >

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RE: Help with F-14's - 4/25/2008 12:28:31 AM   
jetmech43


 

Posts: 571
Joined: 10/7/2003
From: Bartlett, TN, USA
Status: offline 		good luck. it will be quite a project why dont you go to the jet forum

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RE: Help with F-14's - 5/2/2008 4:41:23 PM   
victorzamora


 

Posts: 495
Joined: 10/16/2006
From: Mt. Airy, NC, USA
Status: offline 		One idea might be building one for G3.5/G4 and seeing how well it works. That's what I did for one of my planes, and I'm glad I did. The plane wasn't aerodynamically stable. Luckily I didn't build it just to destroy the plane. Go to Knifeedge.com and search the forums there for help! Make sure you keep us updated!!

(in reply to jetmech43)
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RE: Help with F-14's - 5/2/2008 8:54:43 PM   
Ron S



Posts: 992
Joined: 12/12/2001
From: Fort Worth, TX, USA
Status: offline 		Ravill,
I haven't built an F-14 (those that have built and flown one, please stand up! [)] ), but one thing you may want to consider is design the pitch/roll system with a rolling tail. Then, mix your aileron type control surfaces into the rolling tail for roll only. I have done this with my 14MZ, because I was not sure how my wing-mounted roll control devices (spoiler-slot-deflectors) were going to work on my recenty project. When you are happy with your roll control, you just modify the mix amounts to adjust what may need changing. There are a lot of neat things that can be done with the new radios out there.

If I wanted to address the wing sweep issue, this would be my first thought: Assuming the model is trimmed for normal flight with the wings forward, sweeping the wings aft will move the aerodynamic center aft. Not having flown an F-14 model before (another reminder! [)] ) I think we can predict the model will now be nose heavy (certainly more so than with wings fwd), and you will most likely need stabilator up trim, and the model will most likely feel sluggish in pitch. Certainly adding stab up trim would be an easy thing to accomplish as a function of wing sweep.

I have heard of people adding weight to the wingtips in an effort to "automatically" move the CG slightly more aft as the wing sweeps aft. I think it's a clever idea, but I wouldn't like the idea of adding dead weight to the wingtips, and can't comment how effective it is. What I would consider though, is using the swing mechanism to perhaps move something heavy that has purpose (ie, battery packs) fwd/aft as the wings sweep. How much weight and distance to be moved will depend too much on the specifics of the model - that would be my consideration though.

Lastly, if I were doing this, I'd consider flying the model initially with wings fwd. Once you get to the point where you are happy with it's flight characteristics, limit your wing sweep amounts initially and "creep" up to the eventual full sweep angle. Reason should be obvious - if you have a problem at the 45 degree sweep angle with balance, the amount of adjustments necessary will be less than going full bore to the 65 degree max sweep angle (or whatever max sweep is).

I'd like to work on a project like that, but I haven't developed any interest in flying a twin yet. I've been kicking around doing a Backfire bomber at some point, and setting it up as a single turbine. Too many other projects to decide upon, though.

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RE: Help with F-14's - 5/10/2008 7:07:44 PM   
BMatthews



Posts: 8796
Joined: 10/4/2002
From: Burnaby, BC, CANADA
Status: offline 		Keep in mind too that the idea in the full sized plane is that full sweep is used for high speed use only. It may not be realistic to expect low speed manners from the full swept position on your model any more than the pilots of the full sized one would on there craft. All planes have operating envelopes that need to be respected and models are no different.

At full sweep I think you'll find that the full sized uses very little or no aileron and relies on elevon action for roll. Go watch Top Gun again and study the control movements during the hard maneuver flight scenes. In the wings out hard maneuvers you can see the ailerons and elevators really crank over for the roll input.

..... writing from Paris France to kill a little time


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Proudly wasting balsa since 1965.

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RE: Help with F-14's - 5/10/2008 8:57:10 PM   
Fxrs_tim


 

Posts: 278
Joined: 4/4/2005
From: Austin, TX, USA
Status: offline
quote:

ORIGINAL: BMatthews

At full sweep I think you'll find that the full sized uses very little or no aileron and relies on elevon action for roll. Go watch Top Gun again and study the control movements during the hard maneuver flight scenes. In the wings out hard maneuvers you can see the ailerons and elevators really crank over for the roll input.




The full scale uses spoilers instead of ailerons, coupled with tailerons. The spoilers should be fairly effective if done to scale, as they're pretty large.

(in reply to BMatthews)
       Post #: 6

RE: Help with F-14's - 5/14/2008 9:44:36 PM   
DanSavage



Posts: 567
Joined: 4/17/2002
From: Trabuco Canyon, CA, USA
Status: offline
quote:

ORIGINAL: ravill
I am determined to make an F-14 fly well at any wing position! Mostly, I'm interested in how to make one "docile" at "slower" (ie half throttle e.g.) with the wings swept.

My question:

How does the F-14 react with the wings swept and how to compensate for those bad tendancies?

Here are some of my thoughts,

Wings sweep back mechanically-> CG gets moved back mechanically

Strakes with wings swept?

How about keeping the ailerons functional with the wing swept??

I've bought two little foamies to make experiment before I try it with a turbine. I am determined to make a Tomcat and "everyday" jet!

Thanks guys!


The design of modern variable geometry wings virtually eliminates any CG shift when the wings swing. According to those who've flown RC models, they get a little more nose-heavy with the wings all the back, but that's it.

IMO, you're better off sticking with tailerons. According to those who've flown models of the F-14, this works fine. (See Jet Hangar Int'l)

Strakes were originally meant for supersonic flight, but are unnecessary on the model. Looks cool, but adds little functionality.

You can put the ailerons on the wings, but as you note, their function will have to be shut down when the wings sweep. A modeler in England produced a wing-sweeper 'black-box' that would handle all of this and more. I'm not sure of his name, but you might check with JHI to see if they carry the product for their EDF F-14.

Dan

(in reply to ravill)
       Post #: 7

RE: Help with F-14's - 5/18/2008 3:27:28 AM   
culver


 

Posts: 131
Joined: 6/18/2005
From: TELFORD, PA, USA
Status: offline 		On the full size bird the stabilizers trim LE down as the wings come back. Remember the wing skins were milled out of planks of metal so have weight as they swing back plus they were filled with fuel. 20-55 degrees sweep the spoilers work with the stabs for roll, past 55 the spoilers are not in the loop and the stabs provide roll control. Deltas have a high drag rise at high angles of attack and slow airspeeds but low drag at high speed, the glove vanes ( strakes) that were on the airplane was to add some area up front when maneuvering with the wings swept but were disabled when they realized they didn't really help. I used to be a Tomcat Tweaker.

(in reply to DanSavage)
       Post #: 8

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