Forum: F-35 Lightning II

When the F-35B hovers, is the engine limited to MIL power, or is it possible to have a rocketlike vertical takeoff in afterburner?

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mil_hobbyist wrote:

When the F-35B hovers, is the engine limited to MIL power, or is it possible to have a rocketlike vertical takeoff in afterburner?

Yes, the F135-PW-600 will be limited to MIL when in hover. I suspect whenever the 3BSN is moved beyond 0* there will be no AB possible.

For a "rocket-like" takeoff, one would have to pull the nose up sufficiently to move the nozzle back for horizontal flight, much like the Harrier does at airshows.

REF: http://www.youtube.com/watch?v=w-OnJIkWftU

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TEG

That makes me wonder. Would the pilot be able to keep the nose pointing straight up with the right power settings? I mean hover in a verticle position.

pushoksti wrote:

That makes me wonder. Would the pilot be able to keep the nose pointing straight up with the right power settings? I mean hover in a verticle position.

Hover in a vertical attitude; NO.

There wouldn't be enough authority from the control surfaces to keep the aircraft pointed in the right direction.

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TEG

Most definitely not and STOVL controls would never allow it to begin with. STOVL operation on the JSF is not like the Harrier. To ascend, you simply pull back on the sidestick. Pushing forward on the throttle in STOVL mode does not increase power, but instead increases forward velocity.

Which apparently fixed wing pilots love but those with helicopter experience hate.

I personally find the proposed set up counter intuitive.

You KNOW the thrust is pointing downward, so increasing the throttle SHOULD increase your altitude by increased thrust. I would hate to be doing control inputs during the 'transition', i hope the FCS lock the pilot out for a bit.

I have heard the same complaint numerous times, but after you spend a few minutes in the SIM it is incredibly simple. Sounds a little crazy, but you just have to forget that the throttle controls thrust. This setup allows for unified controls across the variants and a common cockpit. No extra handle like the harrier, just a button.

nam11b wrote:

To ascend, you simply pull back on the sidestick. Pushing forward on the throttle in STOVL mode does not increase power, but instead increases forward velocity.

I found the controls logical. Once the STOVL button is ''on'';
- To ascend ''touch'' the stick's front.
- To descend ''touch'' the stick's back.
- ''Touch'' the stick's leftside/rightside for coasting starboard/port (???).
- No roll or pitch input allowed, they will be controlled by computer (???)

And
- Pedals for yaw.

Throttle controls are;
- Push throttle to reduce ''vectoring'', pull back to increase ''vectoring''. Thus the throttle will give a special kind of pitch command of course automated & corrected by the computer. This is also OK.

Questions:
1) What is the default throttle position? Perhaps when the STOVL button is ''on'' the throttle will move to a predetermined position?
2) How to go back? No need for reverse movement?

You got it a little backwards. To ascend, you pull back on the stick. To descend, you push forward. Same idea as nose up to climb, nose down to dive.

To control heading you can use stick input and rudder input. The flight control system limits you to about 20 degrees of roll in the hover so you can't roll the a/c over.

1) What is the default throttle position? Perhaps when the STOVL button is ''on'' the throttle will move to a predetermined position?

The throttle doesn't move to a position and doesn't have to. The throttle is not connected by linkage, it is essentially throttle by wire. The pilot will have a detent that sets the throttle so that thrust is directed at 90 degrees down.

2) How to go back? No need for reverse movement?

When your angles is >90 you will negative velocity (ie reverse), when your angle is less than 90 you have forward movement. I know it sounds reversed, but this is how the symbology is. The way I understand it, it isn't the angle of the nozzle in relation to the aircraft, it is the angle of the thrust. 0 degrees is no nozzle movement, 45 degrees is still providing forward thrust, but also compensating for lack of lift. Keep in mind the lift fan is running by this point.

Thank you for your answers...

Quote:

You got it a little backwards. To ascend, you pull back on the stick. To descend, you push forward.

Well, actually I've tried to say the same thing. ''Touch at the frontside'' of the control-stick so that it will ''move backwards'' and that is ascending...

Quote:

To control heading you can use stick input and rudder input. The flight control system limits you to about 20 degrees of roll in the hover...

If so (i.e. 20deg limited roll command via control-stick) how is the coasting command given? Or isn't there a coasting maneuver?

Quote:

The throttle doesn't move to a position and doesn't have to. The throttle is not connected by linkage, it is essentially throttle by wire. The pilot will have a detent that sets the throttle so that thrust is directed at 90 degrees down.

Well, I still think there has to be a default throttle position.
IMO, the throttle must move to a default pos.n automatically once the STOVL mode is selected OR the pilot is to move the throttle to a predetermined position and then activate (be able to activate) the STOVL mode.

Quote:

When your angles is >90 you will negative velocity (ie reverse), when your angle is less than 90 you have forward movement.

Sorry, it is because of my poor English again; In fact I was asking how the command for reverse movement will be given by the pilot.

i found the youtube link i was thinking of, during the sim demonstration the controls are mentioned but sorta in passing, have a look

http://au.youtube.com/watch?v=SbnWg4v6iHk

Quote:

If so (i.e. 20deg limited roll command via control-stick) how is the coasting command given? Or isn't there a coasting maneuver?

No coasting maneuver that I know of. If you release the stick, the a/c will automatically stabilize and you can set velocity via autothrottle.

Quote:

Well, I still think there has to be a default throttle position.
IMO, the throttle must move to a default pos.n automatically once the STOVL mode is selected OR the pilot is to move the throttle to a predetermined position and then activate (be able to activate) the STOVL mode.

The STOVL aircraft will have a detent for 90 degree thrust, but as far as I know the a/c does not have a "default" throttle position. IMO I see this as becoming part of a checklist, but as far as I know it is not a function on STOVL operation.

Quote:

Sorry, it is because of my poor English again; In fact I was asking how the command for reverse movement will be given by the pilot.

When the pilot retracts the throttle and his nozzles are pointed forward (>90 degrees) the result is reverse velocity
quote]

Afterburner operation in the hover would give massive pitch changes so it is not an option.

This was identified as a risk issue when the BS100 for the P1154 was designed and tested in the mid sixties, I had the pleasure to be the test engineer on one of these beasts years later (mid 70's) when we were using it for some thermal effect testing.

The AB exit air temperature was about 2,060 degrees F at 36,000 pounds of thrust and 490 lb/sec of airflow; it was a beast.

I do not have my copies of the flight clearance documents for the Harrier at hand right now but I recall that the AV8A airframe was cleared to travel backwards at 35 Kts. The Sea Harrier has a nozzle nudge feature which allowed the pilot to adjust the lateral position of the aircraft relative to the deck spot without adjusting the engine thrust.

Here is a 1994 NASA techbrief on the design of VSTOL HUD symbology, as you can see it is a highly complex activity to program well.

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Forum: F-35 Lightning II

Afterburner in hover mode?