Gimballed nozzle thrust vectoring VS fixed nozzle thrust vectoring

[Spacescifi]

 

Which is better? I guess the real answer is it depends on the engine and fuel source.

Engine: Nuclear thermal reactor. We are doing an open cycle nuclear reactor to heat the oncoming air coming into the intakes as propellant by running it over the reactor. No this would never see the light of day in real life, but this is the engine required to come to conclusions with this study. Plus this is the only known plane that can stay in the air until it's parts wear out (besides weak solar), since running out of fuel is not a concern.

Fuel: Air.

Gimballed nozzle vectoring analysis: Put them at rear corners of plane and you can use them to pitch, roll, and even yaw. Less nozzles required for maneuvring. The disadvantage is like all moving parts, it will need maintenance from routine movement and from all the air resistance pushing on them, especially when doing sharp turns.

Fixed nozzle vectoring analysis: The advantage here is no moving parts on nozzles so less maintenence and more durability. The disadvantage is you need more nozzles on the ship, at different areas so the ship can thrust vector. So less maintenence but more nozzles and ways required to channel the air to the reactor. Assuming you built the nozzles into the body of the ship rather than have them stick out, you would get the added advantage of a more streamlined airplane, which means less air resistance than thrust vectoring gimballed nozzles provides.

 

Which is better in this scenario to you? You can even cite your experiences in kerbal as a reason or guide.

 

 

Edited May 26, 2019 by Spacescifi

[kerbiloid]

(He is building a SLAM in backyard.)

Spoiler

 

[DDE]

3 hours ago, kerbiloid said:

(He is building a SLAM in backyard.)

  Reveal hidden contents

 

@Spacescifi is Rogozin’s account, confirmed.

8 hours ago, Spacescifi said:

Gimballed nozzle vectoring analysis: Put them at rear corners of plane and you can use them to pitch, roll, and even yaw. Less nozzles required for maneuvring. The disadvantage is like all moving parts, it will need maintenance from routine movement and from all the air resistance pushing on them, especially when doing sharp turns.

Fixed nozzle vectoring analysis: The advantage here is no moving parts on nozzles so less maintenence and more durability. The disadvantage is you need more nozzles on the ship, at different areas so the ship can thrust vector. So less maintenence but more nozzles and ways required to channel the air to the reactor. Assuming you built the nozzles into the body of the ship rather than have them stick out, you would get the added advantage of a more streamlined airplane, which means less air resistance than thrust vectoring gimballed nozzles provides.

You need at least one gimbaled nozzle for pitch and yaw, versus four fixed ones. Two gimbaled nozzles give you pitch, yaw and roll - whereas no amount of fixed prograde engines can, forcing reliance on RCS.

What you’re mission is that both gimbals and throttling are major engineering challenges. Rocket engines, both chemical and nuclear, respond poorly to operation at anything but rated mass flow; it’s even more nightmarish for nuclear reactors because of how propellant is also usually a neutron moderator and sends your neutron flux askew in a self-sustaining cycle of doom. Gimbaling large pieces of machinery, complete with flexible links for propellant feeds or, worse, the combustion chamber throat, is also non-trivial. Not to mention that gimbals need space for nozzles to move.

The two forms of throttle direction control you’ve missed are various parasite nozzles for roll control of a single-gimbal system (e.g. gas generator exhaust, verniers) and injection into one side of the nozzle to induce asymmetric thrust (solid motors use a dedicated fluid, and the Yuzhmash engine used rerouted preburner exhaust in combination with dedicated roll control nozzles)

[KerikBalm]

1 hour ago, DDE said:

You need at least one gimbaled nozzle for pitch and yaw, versus four fixed ones.

Technically you could do pitch and yaw with 3

[Spacescifi]

12 hours ago, kerbiloid said:

(He is building a SLAM in backyard.)

  Hide contents

 

Even if I did have the materials to do it, I would have been arrested long ago LOL.

[magnemoe]

11 hours ago, KerikBalm said:

Technically you could do pitch and yaw with 3

Guess starship plan to do this, as in trajectory control during burn. You could also add an slow spin who let you reduce trust on engine at position. You will use RCS for spin control and major changes and also then not under trust but it makes sense during burns. 
 

4 hours ago, Spacescifi said:

Even if I did have the materials to do it, I would have been arrested long ago LOL.

Yes, both the weapon licence and environmental impact study will be kind of hard even if the nuclear weapons was dummies. 

[radonek]

If it's atmospheric vehicle, why not use ordinary aerodynamic control surfaces?

[DDE]

On 5/28/2019 at 2:13 AM, radonek said:

If it's atmospheric vehicle, why not use ordinary aerodynamic control surfaces?

They tend to get eroded pretty quickly at hypersonic velocities. Some people postulate that things like Avangard use forcefield (electromagnetic, specifically) steering.

People who would know, however, say it’s drag flaps:

[kerbiloid]

Spoiler

48 minutes ago, DDE said:

 

According to the shape, with CoM displacement.
Hits in ground and keeps rolling.

Like the famous rubber bomb, which hits in ground and keeps jumping and stomping.