Question about early aviation in career mode with J-20 jet engine

[Kerbalmann]

So Ive unlocked the earliest aviation node in career mode without anything else further the branch. I cannot work out a way to both attach J-20 Juno Jet Engine and 'Small Cirlular Intake'. If I put them together, I cannot attach them to the wings of my aircraft or anywhere else. If I attach J-20 engine at the end of the aircraft, the small circular intake wont fit in any other parts.

Yes I know I can use rocket engine, which I did, and my aircraft lifts off and fly ok. But how do I make it work with basic jet engine ?

 

 

 

 

Edited January 19, 2016 by Kerbalmann

[Vegetal]

Try using the mk0 fuel tank on the sides.

Also, that little craft doesn't have ANY pitch authority....

[Kerbalmann]

mk0 works wonder. Thanks

What is pitch authority ?

[Rocket In My Pocket]

Usually a plane has 3 groups of control surfaces.

A set on the wings to roll (Twist) the plane. [Aileron]

A set on the tail horizontally to control pitch (Point the nose up or down): [Elevator]

And one or possibly a set vertically on the tail to control yaw (Left and Right). [Rudder]

Authority is how well it can control these movements, since your plane only has Ailerons it won't have much pitch authority, and practically no yaw. You can right click each part to set what directions it will try and help control, by default all control surfaces try to help with every axis of movement, so your plane will in fact fly and be controllable just not very well.

Picture from google images to help visualize.

Edited January 19, 2016 by Rocket In My Pocket

[Snark]

Yes, the Juno generally doesn't make any sense in-line.  Well, not unless you're building something like this. 

Spoiler

On the plane you've shown:  not only don't you have a place to put the circular intake, but you're also going to have terrible aerodynamics on the back end because you've got that big flat surface facing back with no taper.

@Vegetal's solution is a great one:  mount the engines to the side of the fuselage.

Consider the following assembly:

• A Mk0 LF tank (this is the tiny 0.625m one that was added in 1.0.5).
• A small intake on the front
• A Juno on the back

That's a very convenient, small package-- and, most importantly, the fuel tank is surface-attachable.

So you can just stick a pair of those assemblies on the left and right of your fuselage, near the back (like a Learjet).  Or you could sling a pair of them under the wings.

Works great!

Edited January 19, 2016 by Snark

[Plusck]

"Authority" is the ability to apply a force to control the attitude of a craft. You have very little pitch, roll or yaw control. Roll is probably the axis with the greatest authority, but with the control surfaces so close to the body it will be much less than if they were further out along the wing. The other two look to be entirely controlled by the torque wheels in the cockpit.

Edited January 19, 2016 by Plusck

[swjr-swis]

1 hour ago, Vegetal said:

Also, that little craft doesn't have ANY pitch authority....

Not sure with that specific design, but aircrafts that small can actually have sufficient control authority purely with the torque supplied by the command pod's reaction wheels (or SAS unit if installed).

[Kerbalmann]

Thanks a lot for help guys. This is what I finally ended up with. Now with better pitch authority or so i hope. Is there anything else i can fine tune my air craft. It lifts off well and easy to control now. But I still have the problem when the first fuel tank runs out, the front part becomes heavier than the back thus pulling down the plane.

 

 

Edited January 19, 2016 by Kerbalmann

[Snark]

16 minutes ago, Kerbalmann said:

Thanks a lot for help guys. This is what I finally ended up with. Now with better pitch authority or so i hope. Is there anything else i can fine tune my air craft. It lifts off well and easy to control now. But I still have the problem when the first fuel tank runs out, the front part becomes heavier than the back thus pulling down the plane.

Are you sure you don't have it backwards?  I'd expect the front tank to run out first, causing the back end to become heavier and causing the plane to nose up.

In any case:  could you replace the two 2-ton fuel tanks with a single 4-ton fuel tank?  (I'm guessing you don't have it researched yet, or you'd be using it already, but it's only a little bit up the tech tree.)  That way, it drains uniformly.  The CoM of your plane is located right exactly where the CoM of a single 4-ton tank would be, so that your plane's CoM wouldn't be shifting around as the fuel is burned.

Another option:  Downsize.  Use one tank instead of two, use a Terrier instead of a Reliant. That's a little bitty plane, the Reliant seems like overkill.  Perhaps you're avoiding the Terrier, because you're thinking "it's a vacuum engine and is crappy in atmosphere."  And you'd be right.  However, the important thing to realize is that the atmosphere thins out a lot faster than you think.  That little plane ought to be able to fly up to an altitude of 10-12 km using just the Junos, with no problem. And at 10 kilometers altitude you're already most of the way to a vacuum.  Atmospheric pressure at that height is only just a very small fraction of sea-level pressure, and as a result, the Terrier works just great. So as long as you divide the responsibilities (Junos for low altitude, Terrier for high), then you'll be fine.

 

Edited January 19, 2016 by Snark

[Kerbalmann]

Hey snark, yes i checked and the fuel runs out from the back tank first. I think because its connected to the engine. Thanks for your solution, ill work it out later.

I also used your suggestion to use the Terrier. It ends up having not enough TWR to lift the plane off and I need 2 extra J 20 engines to lift it off. It costs me more in the end. The good thing is it slows down the fuel consumption.

 

[Snark]

11 minutes ago, Kerbalmann said:

Hey snark, yes i checked and the fuel runs out from the back tank first. I think because its connected to the engine. Thanks for your solution, ill work it out later.

I also used your suggestion to use the Terrier. It ends up having not enough TWR to lift the plane off and I need 2 extra J 20 engines to lift it off. It costs me more in the end. The good thing is it slows down the fuel consumption.

You shouldn't be running any rocket engines at all when you're taking off.  Those Junos have plenty of power to take off nicely and whisk you up to 10 km or more of altitude.  You shouldn't be activating any rockets until you're at high altitude.

In fact:  you don't even need that many Junos.  You've got four of 'em on there.  Two should be plenty.

Let me guess what your problem is taking off if you use just the Junos:  it goes fast down the runway but doesn't want to lift its nose and start flying, right?

This is because you don't have decent torque authority around the rear landing gear.  Simply going-fast-enough-to-fly isn't enough, for takeoff:  you also need some way of getting the nose up.

One very simple solution to this is just to use the "translate" widget in the vehicle editor to raise the rear landing gear a bit, so that they're higher than the front gear.  This will cause your plane to have a naturally nose-up attitude when it's sitting on the ground.  Therefore, to take off, all you need to do is just go fast; you don't have to lift your nose off the ground while your rear gear is still on the runway.

Another approach is to move your rear gear forward a bit, so that it's only slightly behind your CoM.  This will allow the elevators on the tail to generate more torque around the pivot point (i.e. the rear gear):  they can push the tail down, bringing the nose up and rotating you off the tarmac.  Just be careful not to rotate too fast and smack your tail on the ground.

Edited January 19, 2016 by Snark

[Vegetal]

Exactly what Snark said. Your rear landing gear is too far to the back, and the elevators are just above it: You have no pitch authority on the ground.

Look at real world airliners. Their main landing gear is right at the middle of the aircraft, just a tiny bit behind the center of mass. That way the elevators have an easy time controlling the aircraft's pitch - the pilot can point the nose where he wants. That's what we call control authority, the ability to point the craft to the direction we want. It's easy on spacecraft, you just put more reaction wheels or RCS, but on atmospheric flight the design process is more complicated.