I need advice...

I'm working on my new jet model Galeb G2.
My friend made drawings in 3D program, and yesterday when we start working on fuselage find small problem.
I want to put position of turbine as far forward as possible, to avoid later problems with CG.
Last rib on fuselage and fuselage axis dictate position of engine and exhaust tube. If I made it to be parallel turbine touch a wing in rear position...



That made me two problems, first engine can't come more forward, and second if someone want to put bigger turbine it must come even more backward...

But, if I pick up angle of engine and exhaust pipe for one degree with regard to fuselage axle, I solved the problem...



How much that bigger angle may have an effect on the flight characteristics?

Thanks in advance on answers...

Mirce

If it's only one degree or so I would not worry, more important to keep turbine and thrust tube in line as you are obviously aware of.

I doubt you would notice any difference in flight imo.

Gary.

It's not a big deal to put the engine back some. Remember... you need to put your electronics somewhere too... and they normally counter the weight of the engine. Also... it's more important to put your fuel on the CG.

Hi Mirce,
I would go with option 1 and look at getting the fuel as near the centre of gravity as possible. This will reduce any trim change as you burn fuel. Also any possible throttle to elev interaction caused by the thrust angle of the turbine and pipe. You have enough nose on that model to counterbalance the slightly rearward turbine. Better still.. Make the plane bigger
Regards Al

I'd move it back a little more, so the longer inlets allow fuel between. Nose unit will counter the vertical fin weight and radio/valves etc the tail. Tail moment and nose length with cockpit etc will be fine. Ali is right fuel near the balance point is more important and any angle on the tube could mean big pitch changes with power on/off. Depends how you are rigging the wing/tail incidences

Dw

Thank you all for quick answers...

Ali, maybe you don't need to tell me twice to made bigger model...
Maybe 1/4 scale...

OK, but back to this G2.
I don't want to be "smart", I'm just talking about experience I have with my Ziroli F9F Panther. Here is a picture of Ziroli Panther and my Galeb (1/5 scale)...



...and as we can see Galeb is longer behind. Also exhaust tube is much longer than on F9F.
If I put turbine on place like option 1, from my first post, engine is almost on same place like in Panther. In my F9F model I need to add 500 gr ballast in the nose to made CG on right spot.

Second, fuel tanks on Panther is slightly in front of CG, because plastic inlets...



CG is in the middle of the tube in the wing, and rear part of fuel tanks are in that line. Should not be forgotten, engine is P 80, and I fly with 2 liter of fuel.
I haven't some big difference in flying capabilities with full and almost empty tank...

Galeb is much longer in the rear of the fuselage, and exhaust tube is almost 40 cm longer. Noses and wings of both airplanes are in the lines.
That is main reason why I want to put engine as far forward as I can...

After this explain more opinions please...

Regards

Mirce

I think in this model is better to put the engine as forward as possible, and even so you will need some ballast. (or some big and heavy batteries at the nose cone).

About the tank position, Ali is right. The nearer the CG the better. Some airplanes like your Panther are trimmed to land well with the tanks half or almost empty. Try to land this plane with full tanks and you will notice a difference.

The best way to counter this is with twin conformal tanks at the turbine sides, this will make a better handling plane.

By the way, cool project. This plane has everything to be a great flier.

Enrique

1/4 Scale.. Now we are talking !

Its a game of trading off potential issues. For me on a model like this I would rather add nose weight than deal with fuel away from the centre of gravity, and an angled tailpipe. I also like as short a tailpipe as possible. I am no genius when it comes to tailpipe designs, I just know through experience that the shorter tailpipes ( for a given diameter ) have proven to work better/ more efficiently in planes that I have flown.
Many years ago I remember a company called Jet Welt came out with a model called a Jet Provost. They showed it to us at the jet masters in Thailand. The full size has a very short nose and long tail so for the model they put the turbine right forward in the cockpit, with a long pipe... Just so they can reduce nose weight. I saw it fly and it looked awful. Sounded not so nice either. When they came to production the turbine was more in the normal spot and the model needed lots of nose weight, flew great and I owned three of them over the years.
Keep it simple Mirce.
Regards Al

Am I missing something but surely the wings don't pass through the fuselage, assuming they don't the turbine can sit below the outline of the wing root profile and sit 'down' more than your drawings show? Naturally the wing joiners etc need to pass through the fuz but these are usually below the wing top level.

marcs

Marc, my plan with this project (model) is to offer relatively big scale jet model in kit form, build from traditional material, for smaller turbine.
My goal is to made this Jet model not heavier than 12 -13 kg.

Knowing that, construction will be like on big warbird model, two piece wing with wing joiner. Modeler can choose will he made wing from one or two pieces. Wing will have pins in front an with two bolts on the rear trough which be fix on the fuselage.
That mean, wing will come from the bottom of the fuselage.
Advantage of that construction is that in wing hole, on the bottom of the fuselage, can be installed turbine, tanks, and other parts.
Front part of the fuselage will be removable, and that will be second area for installation heavier parts (batteries for example).
That will be only two holes on fuselage, and that will help to fuselage be strong, but simple for making...

More about this project you will find here: http://www.rcuniverse.com/forum/m_10...mpage_2/tm.htm

Regards

Mirce

Thank you Ali, I'll have to remember all your advice. Finally you will be a future dealer for this kit...

Regards

Mirce

There is a lot of fuselage mass behind the balance in the Panther...
500 gram with or with a Cockpit and Pilot? I have pilots that weight 500 grams!!

Dw

Mirce, OK understand - thanks.

marcs

Dave 500 gr is without full cockpit and pilot.

http://www.rcuniverse.com/forum/m_10..._3/key_/tm.htm

Total weight, without fuel, is 10,5 kg

Regards

MIrce