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Are thrust reversers too powerful?


ExtremeSquared

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Oh so many problems.  I'd be most worried about the exhaust from the reverser being sucked back through the intake.  This is one reason you never see jets trying to back up.  Reversers only work with a headwind to keep the intake clean.  But a couple military transports do in fact use reverser in flight as a sort of active airbrake on steep decent.

Edited by Sandworm
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Apparently Concorde used mid-air thrust reversal to control its speed, and I have seen a C-17 moving itself backwards on the ground, but reverse thrust should not come anywhere near total forward thrust - at least for jets, I can see it being possible for variable-pitch prop thrust reversal, but even then I bet you'd get airflow and cooling problems at max power.

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The thrust reversers on most commercial aircraft divert most of the air out sideways and only a little bit forward, also commercial aircraft have a TWR below 0.5 at landing weights (worse at takeoff) and the reversers aren't meant to be used at full power.   However, the large volume of air coming out perpendicular to the wing enormously increases the drag coefficient of the airframe and disrupts residual lift so the wheel brakes work better.    They are very effective above 100 knots but are generally stowed below 60.

Rather than model this however, they just made reversers 100% efficient at redirecting the exhaust stream 180 degrees.  They also seem to have jet engines much more powerful than they should be, but have compensated to a degree, by making wings less effective.

 

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On 05/05/2016 at 9:08 AM, Sandworm said:

Oh so many problems.  I'd be most worried about the exhaust from the reverser being sucked back through the intake.  This is one reason you never see jets trying to back up.  Reversers only work with a headwind to keep the intake clean.  But a couple military transports do in fact use reverser in flight as a sort of active airbrake on steep decent.

 

On 05/05/2016 at 9:08 AM, Sandworm said:

Oh so many problems.  I'd be most worried about the exhaust from the reverser being sucked back through the intake.  This is one reason you never see jets trying to back up.  Reversers only work with a headwind to keep the intake clean.  But a couple military transports do in fact use reverser in flight as a sort of active airbrake on steep decent.

727s and MD-80s regularly pushback from the ramp using reverse thrust.

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3 hours ago, lrd.Helmet said:

I'm just going to leave this here: :P

 

Remind me to never fly Northwest. I used to be a push-back driver, when I was in my 20's - that aircraft is supposed to be attached to a tow-bar on the nose gear and pushed out with a "tug" tractor - pilots cannot see what's directly behind them, and that little stunt they just pulled was super-risky.

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13 hours ago, djnattyd said:

727s and MD-80s regularly pushback from the ramp using reverse thrust.

Yes, but some aircraft and reverser types are better-suited to it than others. You'll note all three aircraft noted earlier in this thread are high-engine, low-wing models where the wing will interfere with the circulation back to the intake. You're not actually so concerned about ingesting exhaust as you are about blowing up grit and debris from the ramp and ingesting that.

@Xyphos' comment is valid, but it's more of a "bad habits" kind of problem for ramp damage, not an issue with being bad for the engine itself. Fine for commercial concerns, but in a general aviation environment you may be in a situation where there is no tractor and still must back up. In those situations you may have no choice.

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9 hours ago, Xyphos said:

Remind me to never fly Northwest. I used to be a push-back driver, when I was in my 20's - that aircraft is supposed to be attached to a tow-bar on the nose gear and pushed out with a "tug" tractor - pilots cannot see what's directly behind them, and that little stunt they just pulled was super-risky.

To be fair, you can see a pair of spotters on the tarmac at around the level where the support vehicles are. But... yeah.

 

Keep it in until we get puller engines.

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I don't see what the problem is.  You're complaining about how unrealistic an engine's features are in a game that has magical reaction wheels and treats all wing shapes as ideal at whatever speed on a planet that is impossibly dense due to having the same gravity in 1/11th the radius of Earth.

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1 hour ago, regex said:

I don't see what the problem is.  You're complaining about how unrealistic an engine's features are in a game that has magical reaction wheels and treats all wing shapes as ideal at whatever speed on a planet that is impossibly dense due to having the same gravity in 1/11th the radius of Earth.

Don't forget a turbofan engine that pretends to be a SCRAMJET with a 23:1 thrust/weight ratio.  And 2kN ion engines.  And little tiny bolts that have more drag than a parachute.  And little green men who can live forever in space with no support at all. :wink:

 

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26 minutes ago, Renegrade said:

Don't forget a turbofan engine that pretends to be a SCRAMJET with a 23:1 thrust/weight ratio.  And 2kN ion engines.  And little tiny bolts that have more drag than a parachute.  And little green men who can live forever in space with no support at all. :wink:

 

...and a magical garden hose that defies the 2nd law of thermodynamics in which it can transfer unlimited amounts of fuel without restrictions.

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6 hours ago, ExtremeSquared said:

They aren't 100% thrust in reverse. Almost as strong. Probably 80-90%

I'll bet you that's configurable too, if you're willing to change it using ModuleManager.

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18 hours ago, Xyphos said:

...and a magical garden hose that defies the 2nd law of thermodynamics in which it can transfer unlimited amounts of fuel without restrictions.

I figure anybody who tries to use that much pressure with rocket fuel, even kerosene, through today's fuel systems is going to have an explosive surprise. But that is a bit of realism I am not feeling a pressing desire for with KSP. For one thing, I think it has been pretty much established that kerbals don't use Liquid Hydrogen and even LOX seems not necessary.

KSP is just to give us mundane folks an idea of how ballistic rocketry works.  Not actually give us the entire rocket science treatment. That would be a headache to simulate well.

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