Certainly there's a relationship between these two important issues. I'm also sure they vary from model design to model design, as they should.

My C-101 airframe is close to that of the GFK L-39. The GFK L-39, to which I refer, some modelers use the Wren 44 successfully.

The L-39 airframe is not "on the money," but really close. Close enough so I could model the turbine angle and wing incidence this model uses in my design of the C-101.

Does anyone know the wing incidence/angle of attack used on this model? The GFK L-39.

Does anyone know the turbine thrust angle used on this model? The GFK L-39.

I could set the wing at zero, but placement and angle of the turbine has to be considered and determined.

Thanks in advance.

Charles

OK! OK!,

79 hits and not one reply.

Lets do it differently. Forget the L-39. No longer an issue.

Just tell me how many degrees your turbine sits at?

Thanks,

Charles

Hi Charles, if you copy the wing incidence of the full size casa , as well the turbine thrust line it will be ok.

This airframe has the thrust line on the low side of the fuselage profile. If this thrust line is set parallel to the airplane fuselage it would tend to pitch up at full thrust .. so aircraft designers tilt the exhaust down canceling this effect and even adding a little more so in case a novice jet pilot gets near a stall and then go to full power the airplane tends to pitch down helping to get out of this potentially dangerous situation.

Something from 5 to 10 degrees would be tipical for a plane like this.. but as I said above, just copy the full size one and you are going to do fine.


Enrique

OK,

I can understand the 5 to 10 degrees. Is the thrust tube set at the same degrees as the turbine?

Or is the turbine and thrust tube set at the same angle?

Charles

Hey Charles,

As far as I know the tailpipe and turbine must always be in line. The exhaust gas must be directed down the center of the pipe.

OK, and thanks for that.

Actually what I expected, but I choose not to guess these issues.

I just checked my drawings and a cross section. It appears as though the actual aircraft's turbine is set at 8 degrees. (If at 12" each .125 of an inch equils one degree.) Anyone else ever use this method?

I'll dig further to confirm this.

Now I have to determine the location of the turbine in relation to the thrust tube. Not to mention which tube to use?

My guess is the turbine placement is critical. One must take in consideration achieving the correct CG without adding additional weight to accomplish this.

I now need the turbine location so I can move forward and design, draw and cut my plywood pieces needed for the turbine cradle. Do they call the turbine mount a "cradel?"

Charles

Yes as mentioned the pipe should always be aligned with the turbine, so both things should be set looking downward at the same angle. About the turbine it is not critical at all, as it is always installed near the cg. Installing the batteries, uat,etc.. somewhere between it and the nose will probably balance the plane in the case of the C101 without any lead.

Hey Charles

Nice subject, always liked the Avio jet C-101

My F-4 (Jet Legend) has had two engine setups.

1. Twin about 8 degrees. No pitchup at full throttle
2. Single about 4 degrees slight pitchup at full throttle

Enrique and Pete have some great suggestions for thrust lines and wing incidence.

My thoughts on incidence washout (I have designed a couple of airplanes and have flown since 1976, but no scratch built jets.... well one F-18 df that had one take off and no landing . So take my suggestions as that sugesstions)

I would guess that most fast aircraft of this type would have around .5 to 1 degree of incidence. Of course it really depends on the airfoil, and how much incedence you will need on the elevator. Also this will effect your fuselage angle during flight so if you go with a too low incidence you fuselage will be nose up during flight and causing drag.

The wing thickness looks pretty good and it is straight so you might get away without washout, which makes for better aerobatics, but more critical landings.

Good luck and please post your progress!!

Duke,

Thanks for the note and interest.

I take it you looked at my photos?

I already have 1.5 degrees of washout in the wings. These were cut and sheeted 20 years ago. [sm=bananahead.gif]

I won't cut another set of wings, so this will have to do.

I may set the wing at zero. There was a time when we set everything at zero. Not jets though.

Charles