Old JHH F-4 airframe conversion
 

Hi all,
Just managed to get a hold of an old JHH F-4 airfare that i want to convert to a turbine.
i have a RAM500 laying around that needs a new home and thought that this one would be perfect for it.
i saw that this airframe can be converted using a P-60, the RAM500 have approximately the same thrust as the JetCat - 12lbs

this airframe was (for some reason, dont ask me why) initially converted to a prop and flew once or twice, since then it just gathering dust for years.
i will build a new nose for it.
currently, without noting installed, it weights 7.54lbs (3.45kg).
the airframe will go though some reinforcements and the wing will get a new spar for strength.
i intend to fully overhaul the plane, sand its old paint and repaint it in Israeli camouflage scheme (see pic)

unfortunately the horizontal stabilizer is not a monoblock, is there an easy way to convert it to one?

because i am trying to save as much weight as possible, and trying to avoid any thrust losses, i am considering using a single tail pipe that will be mounted at a certain angle that will cause a moment that will cancel the moment created by the single exhaust offset from the center.
did some calculations and found that in order to cancel the yawing moment that will be caused by the offset, the exhaust should be angled at 3.17deg outboard (basic trigonometry).

is it even possible to use a single tailpipe using this configuration?

i would be glad to hear your thoughts and ideas on this one.

best regards,
Raviv.

RE: Old JHH F-4 airframe conversion
 

looks like you have your work cut out fr you. I see what you mean by the mono black horizontal stab. Does it still have the scale airfoil?

RE: Old JHH F-4 airframe conversion
 

Unfortunately no, it doesnt have any airfoil to it.
as i go along i see that i will have to rebuild the stabilizers, using the correct airfoil.
can someone direct me to the correct airfoil that is been used on this kit ? i can use the "Profili" software to layout the ribs for the flying stabilizer, no problem there, just need the airfoil's number.

Thanks.

RE: Old JHH F-4 airframe conversion
 

contact JHH, thye are great help

RE: Old JHH F-4 airframe conversion
 

Give me a call, i will be happy to assist you: 054-7879636
I already did this modification many years ago including the monoblock stabs.

RE: Old JHH F-4 airframe conversion
 

Hi Offir, thank you for your reply and will to help, will contact you.

already mailed Larry at JHH, hope to get this project in gear as soon as i close all the above issues.

RE: Old JHH F-4 airframe conversion
 

Hi Raviv, contact Yellow Aircraft,their f-4 stabaliser has the scale airfol shape and is covered with balsa,no carving sanding and shaping required.You should be able to get every thing you need to get your stabaliser working from them.

RE: Old JHH F-4 airframe conversion
 

well, it seems that this project goes on,
would like to thank Ofir Babish for his help.
emailed larry a few times and it is sure is a good thing to know that you have someone to point your questions to, two thumbs up for that.

after many considerations, it seems that the RAM500 with its 12 lbs of thrust will be a tad marginal for that airframe so i decided to go with the Kingtech K80E, which seems to be a good turbine (people's opinion here on RCU), it has approx. 18lbs of thrust (8Kg) that will fly this airframe well.

any other ideas and thoughts will be appreciated.

p.s
i would like to thank I3DM (Lior Zahavi) for putting up with me in the last few days [sm=49_49.gif]

RE: Old JHH F-4 airframe conversion
 

I am just finishing up my JHH F-4. It is powered by a super bee. Just need to check the CG and do some last tests.

babish, can you tell me where you ended up installing your fuel tanks? I had to put mine just in front of the intakes.

I would also be curious in your flight experience with the model...

Jim

RE: Old JHH F-4 airframe conversion
 

You're most welcome my dear friend ! any time.

RE: Old JHH F-4 airframe conversion
 

Hello Jim

My main fuel tank located in front of the intakes too, the CG change during flight is minor, you can see the home made Carbon fiber thank under the blue ECU at the picture.

I started with this jet (my first model jet) approximately 10 years ago. I flew it with POTECH PT80 (very heavy turbine).

I built this model together with my friend Gilad Olinki. He decided to enlarge the wing area by 10% (which was a very good idea in order to compensate the turbine weight).

The result: A very stable model, Easy to control, Very friendly with crosswinds and looks great.

I think that today with the light weight and good performance turbines in the market this model should fly excellent with no wing enlargement.

Wish you to enjoy it (I'm sure you will).

Ofir.

RE: Old JHH F-4 airframe conversion
 

babish, thanks for the information! Your F-4 looks great in the pics.

I was worried about the CG change with the tanks in that area, and I appreciate your feedback on that.

Do you remember if you stuck with the recommended CG of 9" back from the LE of the wing root?

Do you know of any bad tendencies when landing this bird? I talked to Larry at JHH about the plane previously, he mentioned to use 30 deg of flaps on takeoff, 60 deg flaps on landing. Plus he said a 14lb turbine was more than enough to fly this plane (although the above info says otherwise). If it is lacking I may upgrade my bee to a super bee 2 for more thrust.

Jim

RE: Old JHH F-4 airframe conversion
 

This is quite the project you have here! Replacing the nose is a simple process and we have an E nose conversion for the airplane also.

18lb thrust seems a bit over kill. What is the size/weight of the Kingtech engine? A Wren 70 at 15.5lb thrust (or if you want 18lb thrust, a Wren Supersport!) would be more ideal and is a pretty light install as those things go. Just as a comparison, this design has flown with a P60 and had a RTF weight of about 17 lbs which is heavy. The airplane was very fast with plenty of power, but landed fast too. If you can get the dry weight in at about 12lb give or take, that would be ideal.


Chris

RE: Old JHH F-4 airframe conversion
 

Chris,

have you flown it with a 12lb turbine ?

RE: Old JHH F-4 airframe conversion
 

i3dm,

I have not and I'm not aware of any that have at the moment. I'm only aware of the one F-4 with the P-60 though I know there are others out there. It seems to me that 12lb thrust should fly the airplane decently, though may require a little higher power setting to keep the airplane in the groove. 14lb thrust certainly would fly it better and give you that extra thrust margin should you need it.


Chris

RE: Old JHH F-4 airframe conversion
 

Sorry Jim, I don't remember where the CG was located on my Phantom. Besides, my wing is deferent then yours.

No bad tendencies when landing this bird, Larry recommendations are very good!

I think that 14lb turbine will do the Job, even though I'm going to use my Wren Super sport on it.

The T/O weight (2.6 liters of fuel) with my old heavy turbine was 27.5lb, so my opinion is that 18lbs turbine will be suitable.

Ofir

RE: Old JHH F-4 airframe conversion
 

Deferent =different

RE: Old JHH F-4 airframe conversion
 

Hi Chris,
Yes, i know its quite a project but i am not afraid of a little hard work and some elbow grease.
The E conversion nose sound great, because i am doing an israeli phantom, this conversion will have two birds in one shot - a new nose and a scale one.
can you further elaborate on this conversion? how does it connect to the rest of the fuselage? where do i cut the it?
how much does one cost?
if you can, please post some pictures of it, will sure love to have one.

as for the turbine selection - i will probably decide as the project goes on, will have a better weight estimation once i get my stabilizers done and tail-pipe installed.
when ill have the total weight, i will decide on what turbine to use,
currently, i have the RAM500 just sitting on the shelf but if it will not suffice ill order the kingtech.

Thank you all for your help and opinion.

RE: Old JHH F-4 airframe conversion
 

Ravivos,

The E nose is installed by cutting the C/D nose off essentially at the scale location of the radome and is the glued on such that the E nose overlaps the fuselage slightly. So on, a little filler to blend it all and you're good to go. I don't have a picture off hand and I'm not sure the price. I will find out and get back to you via PM.

I'm glad you're excited about the project. No doubt with a little work this will shape up into a beautiful representation of the F-4. [8D]


Chris

RE: Old JHH F-4 airframe conversion
 

Hi Chris

Thanks for that, your input regarding the nose conversion made my day (the little things that makes us happy [sm=regular_smile.gif])

waiting for your price estimation.

Raviv.

RE: Old JHH F-4 airframe conversion
 

Hi,

Well I just finished up my JHH F-4. I am thinking of taking it out for a maiden. I have checked everything over, CG is around the 9" mark from LE (its nose heavy right now - which I prefer for maiden flights). Set all the control throws to the recommended range for ailerons, elev, flaps. Air system is holding nicely. New BVM brakes work well. Dry weight is 14.6lbs, turbine is super bee. I expect with 66 oz of fuel the T/O weight to be about 18 lbs.

This is the first airframe I built up from the beginning (other than gear and some mounts already installed). So it was a good learning experience for myself.

Any advice from members? I havent flown an F-4, just my F-16 and boomerang to date.

Thanks!

RE: Old JHH F-4 airframe conversion
 

Ravivos my dear friend a lot of work ahead of you![sm=thumbs_up.gif]
Good luck!

RE: Old JHH F-4 airframe conversion
 

Hyperdyne,

The F-4 looks GREAT! I'd recommend calling the shop and talking with my dad about first flight pointers. He's the most familiar with the airframe by far. I'll talk with him too to get his thoughts.


@Raviv, Just an FYI, I sent a pm yesterday with pricing, etc. for the E nose.



Chris

RE: Old JHH F-4 airframe conversion
 

A lot of work but trust Ravivos (and his helper i3dm :D) that she will be a beauty once done !
You know why ? cause thats the way we ride brotha' ......

RE: Old JHH F-4 airframe conversion
 

Chris,
Saw your PM, thanks for that... emailed Larry (your dad, apparently:) ) for shipping quotes, your input about the E nose was great.

Jim,
Your F-4 looks fantastic, please feel free to share some more pictures and build experience.
dont forget to update when she's airborne.

Lior,
True... True... ;)