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How Fast Can An Aircraft Go With Reverse Thrust?  
User currently offlineLegoguy From United Kingdom, joined Jun 2006, 3313 posts, RR: 40
Posted (8 years 3 months 3 weeks 1 day 12 hours ago) and read 16618 times:

After messing around on Flight sim for a while, it occured to me, how fast can an aircraft go in reverse thrust? What is the maximum speed ever reached? etc etc

Infact, can an aircraft with engines on the wings even go backwards with reverse thrust without the tail lowering and hitting the ground?

EDIT-obviously I ment how fast can an aircraft go backwards whilst on the ground. Thought I would correct myself before I got some smart ass comments  Silly

[Edited 2006-07-11 20:35:01]


Can you say 'Beer Can' without sounding like a Jamaican saying 'Bacon'?
67 replies: All unread, showing first 25:
 
User currently offline777DadandJr From United States of America, joined Feb 2005, 1516 posts, RR: 12
Reply 1, posted (8 years 3 months 3 weeks 1 day 12 hours ago) and read 16564 times:

Quoting Legoguy (Thread starter):
how fast can an aircraft go in reverse thrust?

I'm not sure of actually how fast it would go. Eventually, once you got rolling, the mass of the aircraft would have a lot to do with how much speed you could gain.

Quoting Legoguy (Thread starter):
Infact, can an aircraft with engines on the wings even go backwards with reverse thrust without the tail lowering and hitting the ground?

I believe any plane with reverse thrust can go backward. I don't believe that the tail would fall to the ground. The biggest threat would be sucking debris into the wing mounted engines. That would sure stop the plane in a hurry.

Russ



My glass is neither 1/2 empty nor 1/2 full, rather, the glass itself is twice as big as it should be.
User currently offlineSwissy From Switzerland, joined Jan 2005, 1734 posts, RR: 4
Reply 2, posted (8 years 3 months 3 weeks 1 day 11 hours ago) and read 16496 times:

Quoting 777DadandJr (Reply 1):
I believe any plane with reverse thrust can go backward. I don't believe that the tail would fall to the ground. The biggest threat would be sucking debris into the wing mounted engines. That would sure stop the plane in a hurry.

Coming to a stop would be a risky task......

Cheers, Big grin Big grin Big grin


User currently offlineBirdwatching From Germany, joined Sep 2003, 3823 posts, RR: 51
Reply 3, posted (8 years 3 months 3 weeks 1 day 11 hours ago) and read 16476 times:

Quoting 777DadandJr (Reply 1):
The biggest threat would be sucking debris into the wing mounted engines

Why would that be any more probable than normal?

Quoting 777DadandJr (Reply 1):
the mass of the aircraft would have a lot to do with how much speed you could gain

Why?

Soren  santahat 



All the things you probably hate about travelling are warm reminders that I'm home
User currently offlineMicstatic From United States of America, joined Jul 2001, 781 posts, RR: 1
Reply 4, posted (8 years 3 months 3 weeks 1 day 11 hours ago) and read 16456 times:

I've always heard 60knots is the target for coming off the reversers. I know they instruct pilots to keep their feet on the floot and off the brakes so they don't inadvertantly step on the brakes after powerback and send the tail to the ground.


S340,DH8,AT7,CR2/7,E135/45/170/190,319,320,717,732,733,734,735,737,738,744,752,762,763,764,772,M80,M90
User currently offlineJetflyer From Netherlands, joined Aug 2009, 0 posts, RR: 0
Reply 5, posted (8 years 3 months 3 weeks 1 day 11 hours ago) and read 16435 times:

Quoting Birdwatching (Reply 3):
Quoting 777DadandJr (Reply 1):
The biggest threat would be sucking debris into the wing mounted engines



Quoting Birdwatching (Reply 3):
Why would that be any more probable than normal?

The engines would need to use high power setting to move the aircraft in reverse thrust mode, more than to taxi normally I should think, since only the air from the bypass duct is reversed. This increases the chance of damaging airport objects. Also, the air from through the reverse thrust doors is pushed forwards and outwards and would send any small objects from around the plane flying into the air which could be sucked back through the front of the engine.

Quoting Birdwatching (Reply 3):
Quoting 777DadandJr (Reply 1):
the mass of the aircraft would have a lot to do with how much speed you could gain

Why?

Well duh.... The aircraft needs a certain amount of thrust/weight ratio to even move, and the heavier the aircraft is, the more thrust it needs to move. The same reasons that mass affects takeoff acceleration, climb performance, etc..You need more of your thrust to move the aircraft when it is heavier than when it is very light.


User currently offline777DadandJr From United States of America, joined Feb 2005, 1516 posts, RR: 12
Reply 6, posted (8 years 3 months 3 weeks 1 day 11 hours ago) and read 16416 times:

Quoting Swissy (Reply 2):
Coming to a stop would be a risky task......

That's true. Stopping abruptly while reversing would change the center of gravity and could certainly send the nose skyward.

Quoting Birdwatching (Reply 3):
Why would that be any more probable than normal?

Because it would be blowing even more debris forward. That is the reason why for the most part, only planes with tail mounted engines will do a powerback.

Quoting Birdwatching (Reply 3):
Why?

Because the more mass the object has, the te more momentum it will gain.

Russ



My glass is neither 1/2 empty nor 1/2 full, rather, the glass itself is twice as big as it should be.
User currently offlineLegoguy From United Kingdom, joined Jun 2006, 3313 posts, RR: 40
Reply 7, posted (8 years 3 months 3 weeks 1 day 11 hours ago) and read 16414 times:

Quoting Birdwatching (Reply 3):
Quoting 777DadandJr (Reply 1):
the mass of the aircraft would have a lot to do with how much speed you could gain

Why?



Quoting Jetflyer (Reply 5):
Well duh.... The aircraft needs a certain amount of thrust/weight ratio to even move, and the heavier the aircraft is, the more thrust it needs to move. The same reasons that mass affects takeoff acceleration, climb performance, etc..You need more of your thrust to move the aircraft when it is heavier than when it is very light.

Im sure he ment momentum wise. Once the aircraft gets up to speed, it carries more momentum.

Quoting Micstatic (Reply 4):
I've always heard 60knots is the target for coming off the reversers. I know they instruct pilots to keep their feet on the floot and off the brakes so they don't inadvertantly step on the brakes after powerback and send the tail to the ground.

So switching from between reverse and normal thrust is where the danger of hitting the tail off the ground lies?



Can you say 'Beer Can' without sounding like a Jamaican saying 'Bacon'?
User currently offlineMatt72033 From United Kingdom, joined May 2005, 1617 posts, RR: 4
Reply 8, posted (8 years 3 months 3 weeks 1 day 11 hours ago) and read 16407 times:

Quoting Birdwatching (Reply 3):
Why would that be any more probable than normal?

because normally you have forward speed!

Quoting Birdwatching (Reply 3):
Why?

because for a constant power setting, if your heavier, you wont be able to go as fast as a light aircraft!


User currently offlineMatt72033 From United Kingdom, joined May 2005, 1617 posts, RR: 4
Reply 9, posted (8 years 3 months 3 weeks 1 day 11 hours ago) and read 16391 times:

Quoting Micstatic (Reply 4):
I've always heard 60knots is the target for coming off the reversers. I know they instruct pilots to keep their feet on the floot and off the brakes so they don't inadvertantly step on the brakes after powerback and send the tail to the ground.

i hope your not implying they get up to 60 knots on powerback??  Wink


User currently offlineLegoguy From United Kingdom, joined Jun 2006, 3313 posts, RR: 40
Reply 10, posted (8 years 3 months 3 weeks 1 day 11 hours ago) and read 16375 times:

So no one actually knows what the maximum backwards speed of an aircraft is  Silly

Another question would be, do either Boeing or Airbus ever test backwards speed with reverse thrusts when testing aircraft?



Can you say 'Beer Can' without sounding like a Jamaican saying 'Bacon'?
User currently offlineMicstatic From United States of America, joined Jul 2001, 781 posts, RR: 1
Reply 11, posted (8 years 3 months 3 weeks 1 day 11 hours ago) and read 16374 times:

Quoting Matt72033 (Reply 9):
hope your not implying they get up to 60 knots on powerback?? Wink

I'm not, but that would be thrilling!



S340,DH8,AT7,CR2/7,E135/45/170/190,319,320,717,732,733,734,735,737,738,744,752,762,763,764,772,M80,M90
User currently offlineMatt72033 From United Kingdom, joined May 2005, 1617 posts, RR: 4
Reply 12, posted (8 years 3 months 3 weeks 1 day 11 hours ago) and read 16338 times:

Quoting Legoguy (Reply 10):
Another question would be, do either Boeing or Airbus ever test backwards speed with reverse thrusts when testing aircraft?

what would be the point?


User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 13, posted (8 years 3 months 3 weeks 1 day 11 hours ago) and read 16331 times:
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Quoting Legoguy (Reply 10):
Another question would be, do either Boeing or Airbus ever test backwards speed with reverse thrusts when testing aircraft?

If so, I need to know where to buy tickets.




2H4





Intentionally Left Blank
User currently offlineTod From Denmark, joined Aug 2004, 1729 posts, RR: 3
Reply 14, posted (8 years 3 months 3 weeks 1 day 10 hours ago) and read 16254 times:

Quoting Legoguy (Reply 10):
ever test backwards speed

That would put one's tiller control skills to the test too.

Tod


User currently offlineTheSorcerer From United Kingdom, joined Oct 2005, 1048 posts, RR: 0
Reply 15, posted (8 years 3 months 3 weeks 1 day 9 hours ago) and read 16224 times:

Quoting 777DadandJr (Reply 6):
Because it would be blowing even more debris forward. That is the reason why for the most part, only planes with tail mounted engines will do a powerback.

Just to add to that, IIRC a lot of turboprops can do powerbacks, the Jetstream 31 for example, one A/C i know that powerbacks would pose problems for is the Dash 8, it's got something to do with the nose gear, sorry i can't really elaborate.

Dominic



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User currently offlineFlyMatt2Bermud From United States of America, joined Jan 2006, 563 posts, RR: 7
Reply 16, posted (8 years 3 months 3 weeks 1 day 9 hours ago) and read 16224 times:

Take it from me guys, tricycles were not intended to go backwards. At least not fast and I ended up getting some serious sidewalk rash about 45 years ago when I learned my lesson the hard way....I was 4.  Angry
All aircraft have the potential to move backwards if they have reverse thrust however many airframe and engine manufacturer's have limitations prohibiting such. There is great potential for problems, as mentioned above I think FOD and a potentially damaging and aircraft and engines top the list. Any reversing should be planned.



"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward" Leonardo Da Vinci
User currently offlineLegoguy From United Kingdom, joined Jun 2006, 3313 posts, RR: 40
Reply 17, posted (8 years 3 months 3 weeks 1 day 9 hours ago) and read 16196 times:

I was wondering where my thread had disappeared to!!! I thought it was deleted for a minute!  Sad

Quoting Matt72033 (Reply 12):
what would be the point?

I thought it might be a random useful thing to know  Smile I thought they tested every possible manourve possible with the aircrafts limits in testing...and reversing backwards is within the limits.

And this reminds me of another question!!! Im not sure If I should ask it in a new thread or ask it here.

Is there any other airliner that has flown upside down in a test flight? I saw a documentary and it showed a 707 flying upside down. Anyother airliner flown upside down before?



Can you say 'Beer Can' without sounding like a Jamaican saying 'Bacon'?
User currently offlineFilton From United Kingdom, joined May 2006, 51 posts, RR: 0
Reply 18, posted (8 years 3 months 3 weeks 1 day 9 hours ago) and read 16195 times:

Quoting Legoguy (Thread starter):
how fast can an aircraft go in reverse thrust?

Well, lets make some assumptions...

- You are in Concorde (nice bucket thrust reversers)
- You can apply 'reverse' thrust up to 10,000 lbs (44.5KN) before the buckets fall off
- The buckets send the thrust forward at and angle of 80deg to the horizontal
- Your Concorde is fully loaded and weighs 185,000 kgs.

Trig:
Total reverse thrust = 2 x 44500 x cos(80) = 15500 N

x 4 engines = 61800 N of reverse thrust.

In theory, you can go as fast as the amount of drag this much thrust will overcome, which is quite rapid.

However, lets assume the limiting factor will be runway length. Lets say you have 1 mile (1600m) to hand before you need to get on the brakes.

A 185,000 kg Concorde will accelerate backwards from rest at 0.334m/s (or 0-60mph in 1.4 minutes).

So, in one mile, you will be going SQRT(2 x 0.334 x 1600) = 33 m/s or 74 mph.

Sounds reasonable. Good luck steering though.


User currently offlineLegoguy From United Kingdom, joined Jun 2006, 3313 posts, RR: 40
Reply 19, posted (8 years 3 months 3 weeks 1 day 8 hours ago) and read 16180 times:

Quoting Filton (Reply 18):

Well Mr Filton. I have to hand it to you. Nice calculations there! We all know however that not everything works out as good as it does on paper  Silly

Thanks for the reply!! It would be interesting to know if any aircraft have actually tried it.



Can you say 'Beer Can' without sounding like a Jamaican saying 'Bacon'?
User currently offlineMarkC From United States of America, joined Apr 2006, 259 posts, RR: 0
Reply 20, posted (8 years 3 months 3 weeks 1 day 8 hours ago) and read 16175 times:

I have seen test results of a JT9D-7R4 that made 35,000 lb of thrust in reverse. The same engine did 47,000 forward. Goes to show you how large the contribution of the fan is to total thrust (JT9's do not have core reversers).

So, if you don't care about the FOD (min recomended reverser speed is 80 kts), and the landing gear can take it, you have quite a bit of power available.


User currently offlineN8076U From United States of America, joined Jun 2006, 425 posts, RR: 9
Reply 21, posted (8 years 3 months 3 weeks 1 day 8 hours ago) and read 16175 times:

Reverse thrust can be used to accomplish push back on certain aircraft, at certain places by certain airlines. One of note is the DC-9/MD-xx. However, the fact that the engines are up high on those particular aircraft makes the possibility of FOD ingestion far less of a problem.

Also, an aircraft like the DC-9 with aft-mounted clamshell type reverser deflectors, which deflect all of the engine's exhaust, will be more successful in being able to move backwards with reverse thrust than say a 747-400 with fan-only cascade reversers. Also, having a fan-only reverser allows the core of the engine to negate some of the reverse thrust from the fan because the core always provides forward thrust.

On some aircraft with under-wing mounted engines that have cascade-type fan reversers, the reverse thrust may disrupt the engine's incoming air at higher power settings if the aircraft is not moving or moving too slowly. This may result in surging. There is also a high possibility of FOD ingestion during these same conditions.

Chris



Don't blame me, I don't work here...
User currently offlineLegoguy From United Kingdom, joined Jun 2006, 3313 posts, RR: 40
Reply 22, posted (8 years 3 months 3 weeks 1 day 8 hours ago) and read 16166 times:

There is a lot of mention of FOD (foreign object debris). Is the risk of FOD higher just because the aircraft is moving slower than it would at take off speeds?


Can you say 'Beer Can' without sounding like a Jamaican saying 'Bacon'?
User currently offlineN8076U From United States of America, joined Jun 2006, 425 posts, RR: 9
Reply 23, posted (8 years 3 months 3 weeks 1 day 8 hours ago) and read 16157 times:

Quoting Legoguy (Reply 22):
There is a lot of mention of FOD (foreign object debris). Is the risk of FOD higher just because the aircraft is moving slower than it would at take off speeds?

Yes, at slow speeds, the reverser's exhaust can blow something that is on the ground up into the air where it will be sucked in by the incoming air. At higher speeds, the airflow from the forward movement of the aircraft cancels out some of the forward-blown reverser exhaust, so it won't affect objects as far out in front. It also means that if something does happen to be blown up at higher speeds, the aircraft will pass by it before it can even get close to the inlet.

Chris



Don't blame me, I don't work here...
User currently offlineMesaMXORD From , joined Dec 1969, posts, RR:
Reply 24, posted (8 years 3 months 3 weeks 1 day 6 hours ago) and read 16111 times:

All I can say is clam shell reversers work alot better than cascades for backing up. You can get them going fast but as mentioned there are issues with ass ending it when you go to stop

25 Vikkyvik : I believe that's because clamshell reversers reverse the bypass AND core flow, correct (like the 732)? Cascades only reverse the bypass flow. (I migh
26 Post contains images 2H4 : Tailwheel or conventional-gear aircraft....though, these days, they're anything but conventional. 2H4
27 Ilikeyyc : This is correct. examples: the JT8 on the 732 are clamshell and reverse everything. the CF34 has cascades and only bypasses fan flow. But now that I
28 Post contains images Vikkyvik : Thank you! Can't believe I couldn't remember that. Then again, the humidity is like 90% and I just played an hour and a half of tennis....yeah....tha
29 N8076U : Some aircraft with clamshell reversers (731, 732, 727, DC-9, MD-XX) do reverse both the fan and core exhaust. But there are exceptions. The DC-8 50 a
30 Bohica : At an airshow at ADW there was a demonstration of the C-17. After it landed it deployed the thrust reversers and left them deployed. The plane stopped
31 N8076U : That must have been quite a sight to see! I would guess with a military cargo aircraft, there's the possibility of landing in all sorts of places oth
32 FredT : The center of gravity remains where it is at. However, the forward acceleration tilts the total force acting on the aircraft so that the resultant fa
33 DH106 : Good answer FredT. I think in reality there would be a 'break out' force required to start the a/c moving that would be greater with heavier weights.
34 Post contains images N8076U : When pushing back an empty 747, it was very easy, even with a narrowbody tug. With a fully loaded 875,000lbs 747, it was sometimes almost impossible
35 Bri2k1 : IIRC, those air carriers who perform powerbacks instruct crews to place both feet firmly on the floor and stop the reversing only with forward thrust.
36 MarkC : The F117 has cascade reversers for the fan, and the same type of blocker door / cascade design for the core contained in the nozzle. Not a clamshell
37 MesaMXORD : All the engines I play with are rear engine high mount so you just have to watch your readings so the engine doesn't start ingesting hot air. RR AE300
38 Post contains images B52murph : For security reasons, I won't divulge a location...but...this is standard procedure for getting out of the C-17 parking spots at a certain location.
39 Vikkyvik : You do indeed remember correctly. They demonstrated this at an airshow at BED that I went to years ago. ~Vik
40 Sanjet : Aircraft like DC-9's can do power backs and back up pretty quickly and is certified to do so. Most aircraft are not as the problem is that the engines
41 Bri2k1 : That might be true on an air-cooled piston engine, but a high-bypass turbofan is going to suck in more air at idle than will ever be "RAM"med in at a
42 N8076U : I agree, an engine ingesting its own exhaust gas is not good, but with a typical high bypass engine, it will only ingest the fan air, which isn't hot
43 Post contains images Jetlagged : FOD stands for Foreign Object Damage, i.e. damage done by foreign objects. Foreign Object Debris (debris from foreign objects?) makes no sense. Befor
44 MarkC : For an engine that is more surge prone than others (not mentioning any names), this is more of a concern than FOD. Airflow disruption to the engine c
45 Post contains images Bri2k1 : Well, we know it's not the JT8D, given the (sadly, historcal) practice of powering back "Super" 80's and DC-9s...
46 Jetlagged : Even with a JT8D, if you apply full reverse with the aircraft stopped or moving slowly you run the risk of compressor stall due to exhaust gas re-ing
47 bri2k1 : I believe they do. The 717. To about 4 knots. For AirTran.
48 pmk : In regard to the C-17, at the Nellis Air Show I too saw the C-17 demonstration. The announcers of the team stated that the reverse speed of the C-17 a
49 Post contains links 747classic : Also the Saab Viggen was famous for backwards taxiing with reverse thrust : http://www.youtube.com/watch?v=zpxz_-ELi6U
50 Musang : Not quite. Using the wheel brakes while going backward is the problem. Even above idle, I can't imagine abruptly going back to forward thrust would t
51 747classic : This statement cannot be true. JT9D-7R engine full fwd trust 48.000 lbs (lowest certified value) Bypass ratio = 5 ,so 5/6 of the thrust is fan thrust
52 DH106 : Nitpicking, but wouldn't that be 1 / (SquareRoot(2)) = 0.707 (approx 70%) for 45deg, not 50% ?
53 alwaysontherun : Jajaja, classic stuff! He would have to be in a car, with the "Follow Me" sign posted in reverse! ƎM WO⅃ÃÂ
54 jetlagged : True, but 50% is probably nearer the truth as there are losses in the cascades to consider. Also in reverse the engine is limited to a lower N1 and t
55 bri2k1 : I have no idea how this happened, but that reply wasn't posted by me! My username is all lower-case; is it possible that they are permitting users wi
56 747classic : You are totally right, I was still dreaming. In this example max. possible (not certified) reverse thrust would be approx. 28280 - 8000 = 20280 lbs.
57 Musang : Excellent! Good to have some hard numbers to support our opinions! Regards - musang
58 Post contains images David L : That reply was made 3 years 7 months ago. Are you sure you haven't just forgotten about it? You may have logged on using capital letters when you mad
59 bri2k1 : If I'd forgotten about it, how could I be sure? Just kidding. Yes, it does sound just smart-assed enough to have been written by my past self. But to
60 tdscanuck : Temperature rise across the fan can be upwards of 100 degF...it's quite easy to surge an engine if it eats its own fan air. This is only true if the
61 bond007 : Is the conveyor belt also going backwards ... and at the same speed? Jimbo
62 bri2k1 : Right, as usual. I suppose I should have phrased it "minimize entropy generation."
63 rcair1 : All we need now is a myth to go with it - and we can submit it to Mythbusters and watch them back a 747 around the desert at high speed by remote con
64 alwaysontherun : Me too……… You deal with the plane, while I deal with Carry! Tom, how much water can a modern engine deal with? I believe they do test this, cor
65 Post contains links tdscanuck : Lots. I'm not sure what the exact figure is, but it's equivalent to flying through a monsoon. It's a *lot* more than you'd think the engine can handl
66 Post contains links Musang : Surely someone must have filmed the take-off? Love to see that. here's the only photo I've ever seen of the aftermath. http://www.flightglobal.com/pd
67 alwaysontherun : Interesting! Okay, but in the TACA case you posted this obviously could not be done! Well done by the crew, landing on grass! Yep, Mother Nature is a
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