enigmatic-j

I always wondered why no one ever built or put into production a model jet with working exhaust "turkey feathers."(the engine's tail component that changes as the thrust changes) I recall there was a gentleman on this forum who claimed he was working on one, and in fact had posted photos of his 1/5th scale prototype,but I haven't seen any updates or heard from the builder since his last post. I would think that for the ultra scale modeler and flier, this feature would be a significant part that rarely, if ever, gets touched by the companies or even private builder. Does anyone know of any company or individual that does or did provide a working tail/exhaust feathers as an alternative to the simple molded add ons?

scaleMan

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http://details4scale.com/

FalconWings

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Bob Fiorenze used to have scale working turkey feathers made for the 1/9th Yellow Aircraft F-16 (Ducted Fan)
I saw them and they were truly a work of art.

Details 4 Scale

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We are currently working on a set for the 1/6th Skymaster F-16. The system will hopefully be completed by the end of the month. Hard to say for sure though, it's just been crazy trying to keep up this year. Thanks for the interest.

Dan

Jgwright

I saw working set up at Ohain Whittle meeting in Germany back in 2004 it combined both afterburner and moving exhaust turkey feathers. It was servo operated and a clever bit of engineering. They also had a very good afterburner working and flying. I have not heard anything else since. There would be little point in making the tailfeathers move without squeezing the exhaust down to speed up the gas flow. However with our engines that is the last thing you would want to do so it would only ever be cosmetic unless combined with an afterburner. Also from a model point of view it adds considerable weight at the rear of the plane making C of G difficult to achieve.

John

B1Driver

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Why is this? Why not squeeze the flow increasing thrust without afterburner? I can only think that our engines cant handle the preasures or the EGT would spike out of tolerances. Just trying to learn more of these little gems.

Luis

Jgwright

Louis

The exhaust gas from the engine accelerates as it expands and draws cold air into the jet pipe. In a full size military engine the engine has a tailpipe that is all one piece with the engine and that usually incorporates an afterburner.

If you squeeze the tailpipe on our engines it will not allow the gas to pass through it as efficiently and you will lose thrust. I did do some experiments with a long tailpipe that was fixed directly on the back of the engine. It made a lovely sound and it had the benefit of a very small outlet. I used a divergent convergent section. Thrust levels were comparable with a standard pipe. The drawback was increased weight as it had to be made from thick stainless steel. The pipe got pretty hot and in a plane installation would need another tube around it. It is possible that working exhaust feathers could be used with such an arrangement. All in all there is no advantage only disadvantages.

John

enigmatic-j

I do see what you mean by the disadvantages, but I'm sure a clever or knowledgeable builder will find ways around them, especially for the sake of 100% scale realism. You may or may not be a scale enthusiast, but I sure am, and to date, none of the models offered for sale to the public are "100% scale." In my humble opinion, for something to be considered scale, like ARF composite, and others seem to advertise, the model would have to be very very close to the real thing, and I don't see how neglecting a major component of modern fighter aircraft makes the present models "100% scale." I'm sure other scale modelers will agree with me. There are those who build just to fly, and there are those who build for both realism/scale and flight, amongst these enthusiasts are those who place scale to higher standards than others. That's me.

On a sidenote: It is possible to have working "exhaust feathers," since there have been a few people who've already built working versions for their jets.

Details 4 Scale

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The nozzle we are working on is to only visually enhance the realism of the model. It is not a functional set of convergent/divergent nozzles. In our size models, it would be very impractical from a fuel standpoint. Take the real F-16. It burns more than 800lbs/min in full afterburner. Thats about 123 gallons per minute. OUCH!...The weight difference between the stock Skymaster F-16 tailcone and our working model is only about 1.5 ounces (the weight of the operating servo). THat's it! Since the entire molded assembly is made from carbon fiber, it is very light and very strong without a bunch of weight being added. It's really meant to add to the "cool" factor more than anything. It will come completely pre-finished, ready to install. No additional paint weight. Everything is done in the mold except the "Hot" section details and they weigh nothing! I hope this dispells the negatives of having a working scale nozzle.

Dan

bela

I couldnt agree more. I was thinking exactly the same thing when someone earlier stated that putting functional leading edge flaps on the new feibao f-16 was "overkill". Statements like those are pretty presumptuous. Anyway, increase of backpressure and resultant loss of thrust could possible be a valid point, but would only be so when the nozzle is deployed. this period would be limited to a couple seconds tops in flight and maybe 5 on the ground. just long enough to demonstrate the scale effect. Ive done some experiments with an experimental rig/electric fan setup to answer some questions about the mechanicals, (no thermodynamics) and had some successes. enough that warranted further work, however what i quickly found was the problem wasnt going to be the obvious.... it would in fact be how to form high temperature SCALE functional parts. again, form vs function. Case in point, the 3 axis thrust vectoring systems used on rc today,are awesome for the "just go fly guys". but for the "true scale guys", thrust vectoring hasnt even been invented yet.

F-15 Fan

The engines on a full-scale F-16 are also turbofans, turbofans generally move more air. The more power you give a turbojet (your little turbines), the more air it moves, and the faster it moves. The nozzles only close as the throttle is increased. I see how this would create a bit of backpressure, but I believe it would not affect thrust, the outlet diameter on the engine itself is usually less than that of the actual diameter of the nozzle. To get the same effect as the full scale F-16, you would need a model turbofan, which I see that some modelers have already created for their own use.

tulz161

Maybe I'm mistaken... but aren't the tail cones on the scale jets all just for looks? Working tail feathers or not? The exhaust pipe is doing most, if not all the work. So adding functional tail feathers would only add to the realism...which is what details4scales is trying to do.

Details 4 Scale

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Yep, that's the idea. Realism is all we're after. Now combine the scale operating turkey feathers with the AB lighting, water spray and colored pulse light system and that's pretty darn real looking.

Dan

Here's what we're hoping to achieve.

[img][/img]

tulz161

What do you mean by water spray? Looking forward to seeing the AB lighting kit... I saw a great one on youtube in a skymaster F-16's.

Shok

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I remember those, they were awesome!

Henry Chua

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Hi Ronnie,

Your are absolutely right....they are outstanding and certainly enhances the looks. This was mine many years ago and I kind of regret selling off the falcon.

Best regards
Henry

tulz161

Now that's a tail cone. The one that comes with the Skymaster is rather cheesy IMO.