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Old Jul 02, 2012, 10:54 PM
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Final post for today - a shot of the nose leg and wheel. I was given this leg - I think it is from a Yellow kit, but not the F-4. It's slightly too long but I can't shorten it much more without compromising its strength, so the airframe will sit nose high. The wheels are also a little oversize, which means I needed to cut the wheel well a bit longer. I don't mind - it should roll better on bigger wheels, although I hope the nose high attitude on the ground won't affect take off behaviour adversely.
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Old Aug 13, 2012, 07:07 PM
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Hi
I am converting my YA f4 to turbine... did you finalize yours? is it possible for me to get some pictures? I cant find them at your link of the build.
I have a P60 and a Rabbit and would like to know your opinions. Also ordered custom jet-tech tanks with 76 oz.

Thanks
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Old Aug 22, 2012, 01:53 AM
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Hi 1alonso, the only photos I have at the moment are on this thread. The build has slowed up again due to work and life, etc, but I hope to have another big push within a month or so, and maybe get most of it finished then. I'll take more photos as I go.
A P-60 sounds like a good choice - I've also read about people putting in lots of different engines, right up to a P-120, in this airframe.
I think the best choice depends on a few things - for mine the issue is the extent of the thrust loss via the bifurcated tailpipe, and that I want to make the jet as light as possible to help with getting it off and on my fairly short landing strip. My engine has 13.5 lb thrust.
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Old Sep 14, 2012, 06:27 PM
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A final fairly big push to get things done sees most of it built now. The elevator linkages turned out to take much longer than hoped in order to make them rigid and strong. Installing the turbine ancillaries was tight but they eventually went in. Just one air tank should be OK for both the brakes and the Spring Air retracts for a few cycles of each. The use of Jettronic valves for retracts and brakes saved space, complexity and weight (although they are a touch pricey). The fuselage was reinforced on its sides with carbon fibre, around the area between the intakes and under the canopy.

I have put a first coat of paint in the Vietnam camo colours like the Phantoms the RAAF leased in the 70s. It's rough but it can be progressively improved.

The all up weight will be a bit over 7kg dry.

I think I've tried to solve most of the things that were going to be a problem and known issues, but I can't tell until it's flown and landed. Basically it's ready for a decent taxi test. If that goes OK, then I guess it'll be rerady to fly at the Temora jet meeting next weekend.
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Old Sep 19, 2012, 12:04 AM
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A final fairly big push to get things done sees most of it built now...
Been watching the build. Looks really good. Can't wait to see the maiden.
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Old Sep 25, 2012, 05:27 AM
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Here is a walkaround of the basically finished model,

Yellow F4 turbine walkaround. (4 min 5 sec)
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Old Sep 25, 2012, 05:54 AM
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And here is the take-off at Temora jets last weekend. Plenty of power, but....

Yellow F4 Phantom turbine (0 min 55 sec)


Sadly, the model didn't even complete one circuit before dropping its nose in a turn back upwind and planting itself hard. Nothing is left of the airframe though I have hope for most of the components.

Opinions differ about what happened - at first I thought it was just a basic pilot induced stall but I now I think that's only a part of it - the model was severly nose heavy and I was fighting with the aircraft the moment I got it to rotate (the take-off was long). I had time to add three clicks of up - which did absolutely nothing.

The seeds of its demise started with my decision not to use saddle tanks in the engine bay and go for a 1.5L tank in front of the CG. That in itself was not the whole issue either - the real issue I think is that I balanced the aircraft with the tank empty. That's the normal practice, I know, but in a small model like this one the mass of the fuel is around 15-20% of the aircraft's weight. So when it was fueled it was wildly nose heavy. I was worried about this and I asked around, but I was told by pretty experienced modellers that a tank empty CG is the way to go. With 50/50 hindsight I now don't agree. Balancing the 1.5L tank with, say, 50% fuel might have been much better, but saddle tanks were the crucially missing bit (and also the difficult bit to build, which is why I avoided doing it - lesson learned).

In flight and attempting a flat shallow bank the nose just dropped which made the roll worse, which made the nose tuck further and then it was uncorrectable, and all over.
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Old Sep 25, 2012, 06:17 AM
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Some nice "before" photos, and a sad "after" photo.
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Old Sep 25, 2012, 06:31 AM
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So, back at the pits, a friendly and generous chap offered me his partially built Yellow F4 airframe if I wanted another crack at this model. I reckon I know what happened to mine, and I know what I'd do differently. Definitely saddle tanks and keep the whole weight as light as possible (and on that, maybe plan for a shorter flight time, thereby having less total fuel weight on board). Temora was such good flying weather, and other guys were having a ball with their easier ARF known-to-fly-really-well jets while I was moping around and glum, so I've been left wondering about the effort to do it all again... but a big part of me wants to recover from this by starting again and getting it right.
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Old Sep 26, 2012, 12:00 PM
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You mentioned you used a JetJoe turbine in this and your previous plane.
What are your impressions on it ?
Any problems you encountered ? Did it work well out of the box or did you have to modify it ?
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Old Sep 26, 2012, 08:36 PM
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The JJ's are a budget turbine. You get what you pay for here. Mine has been ok, but not great. I've experienced 4 main issues. The fuel injectors can burn out (replaced once in 20 starts), the NGVs crack ( two in 45 starts), rpm sensor interference (hours spent rerouting then testing the sensor cable to avoid this) and finally I needed to dial back the accel delay to avoid odd flameouts when going full throttle from idle. If you are happy to fiddle and fine tune they're OK, but not otherwise really. Put it this way, mine has helped me learn about turbines more than I had planned.
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Old Sep 27, 2012, 12:33 PM
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...but a big part of me wants to recover from this by starting again and getting it right.
Just checked out the new videos. Sorry to hear of the crash. Of course you have to build another one so contemplating that further is a non starter.

Would it help to make the next one an EDF first so that you can get used to the CG location and such first without risking another turbine for the initial flights?
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Old Sep 27, 2012, 03:55 PM
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EDF's not a bad idea, but I've stripped down the turbine and the damage is pretty minimal so if I go again I'll repair it and use it. I'd also want to see if I could get the total aircraft weight down by a couple of pounds from the last one.
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Old Oct 10, 2012, 08:37 AM
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Beautiful girl the old f4
Bought myself a GoPro
How do I transmit to a receiver for POV flying????
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Old Oct 30, 2012, 12:13 PM
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Hi

I am finishing my project of this same airplane from YA. I am using jettech tanks and a rabbit. But I am just not sure jet where the CG should go. Can you tell me where do you suggest to be?

thanks
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