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Reverse Thrust In-Flight On Dash 8  
User currently offlineDogfighter2111 From United Kingdom, joined Nov 2004, 1968 posts, RR: 1
Posted (8 years 3 weeks 19 hours ago) and read 15504 times:

Hi all,

Well this afternoon i flew EDI-MAN on a BA Connect Dash 8-300. The flight was great, and i loved the final approach. We were being bounced about a lot  Smile

Anyway we were coming in to land and when we were about 3000ft from the ground suddenly the engines sounded as though they were powering up. I thought we were perhaps too slow but as soon as i had heard the power up i was pushed forward out of my seat as though we were slowing down! The way it felt made it obvious that the engeins had been put into reverse and i was unaware that this aircraft was capable of doing this whilst in-flight.

Can anyone just confirm this, even though i think it is obvious i still have that feeling in the back of my mind that it may have been something else.

Thanks
Mike

46 replies: All unread, showing first 25:
 
User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 1, posted (8 years 3 weeks 19 hours ago) and read 15497 times:
AIRLINERS.NET CREW
DATABASE EDITOR



I think, more likely, the push forward was created by the increased drag of the flaps being lowered. The higher power setting would have been selected to compensate (partially, at least) for the increased drag from the flaps. That's my guess, anyway...




2H4





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User currently offlineStarlionblue From Greenland, joined Feb 2004, 17015 posts, RR: 67
Reply 2, posted (8 years 3 weeks 18 hours ago) and read 15488 times:

Quoting 2H4 (Reply 1):
I think, more likely, the push forward was created by the increased drag of the flaps being lowered. The higher power setting would have been selected to compensate (partially, at least) for the increased drag from the flaps. That's my guess, anyway...

Having been self loading cargo on the Dash-8 a lot, I would say this increase in power is indeed very common, and comes at flap lowering.


After touchdown, the props do reverse.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineSkookum From Canada, joined Jul 2006, 115 posts, RR: 0
Reply 3, posted (8 years 3 weeks 17 hours ago) and read 15466 times:

The changing of the prop pitch could also create similar sounds to a power increase, and the resultant drag of the flat pitch of the blade is usually felt in large turboprops.


Good flying
User currently offlineLimaFoxTango From Antigua and Barbuda, joined Jun 2004, 784 posts, RR: 1
Reply 4, posted (8 years 3 weeks 17 hours ago) and read 15461 times:

Actually, what you felt was the condition levers or props being moved from the cruise position of 900 RPM to the MAX setting of 1200 RPM. The propellers are moved to a position where they're basically flat against the oncoming air which adds quite a bit of drag and thus slows the aircraft down. Placing the aircraft in reverse while inflight is prohibited. The warning sticker in the photo below to the left of the FO's airspeed indicator reads "Positioning of the Power Levers below the flight idle stop during flight prohibited. Such positioning may lead to loss of aircraft control......." you get the idea.


View Large View Medium
Click here for bigger photo!

Photo © Stefan Zahn




You are said to be a good pilot when your take-off's equal your landings.
User currently offlineKELPkid From United States of America, joined Nov 2005, 6370 posts, RR: 3
Reply 5, posted (8 years 3 weeks 16 hours ago) and read 15457 times:

You would have known if the props were in beta. Propellers in beta make a very distinct, low frequency "growling" sound...(for lack of a better description). It almost sounds like a C-130 taxiing around on the ground  Big grin


Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlineEMBQA From United States of America, joined Oct 2003, 9364 posts, RR: 11
Reply 6, posted (8 years 3 weeks 15 hours ago) and read 15433 times:

Quoting Dogfighter2111 (Thread starter):
The way it felt made it obvious that the engeins had been put into reverse and i was unaware that this aircraft was capable of doing this whilst in-flight.

No Turboprop that I know of can go into reverse in flight. VERY-VERY BAD things happen if they do. Most all aircraft that I know of have a Beta Stop to prevent the crew from pulling the power levers too far back when in flight.



"It's not the size of the dog in the fight, but the size of the fight in the dog"
User currently offlineHAWK21M From India, joined Jan 2001, 31679 posts, RR: 56
Reply 7, posted (8 years 3 weeks 13 hours ago) and read 15403 times:

Shouldn't the Reverse Pitch be Air-Grd Sense Related.
regds
MEL



Think of the brighter side!
User currently offlineAvt007 From Canada, joined Jul 2000, 2132 posts, RR: 5
Reply 8, posted (8 years 3 weeks 12 hours ago) and read 15401 times:

The reverse in the Dash8 can be selected in flight, but it is prohibited, and there is a screamingly loud warning horn that goes off if it is accidently done. LimaFoxTango has it right, the noise and deceleration is the rpm being increased in preparation for a possible go around, also the reverse is more effective on the ground with the condition levers at max rpm.

User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 9, posted (8 years 3 weeks 12 hours ago) and read 15399 times:
AIRLINERS.NET CREW
DATABASE EDITOR




Quoting EMBQA (Reply 6):
No Turboprop that I know of can go into reverse in flight.

I know of only one:





Powerplant - Pratt & Whitney PT6A-25C
Horsepower - 750
Propeller - Hartzell 3 blade composite, 100� diameter
Wingspan - 24 feet
Length - 22 feet, 4 inches
Height - 8 feet, 9 inches
Wing Area - 100 square feet
Seats - 1
Empty Weight - 1,600 pounds
Fuel Capacity - 150 gallons / Jet-A
G Limits - 12 positive / 12 negative
Take-off Distance - 200 feet @ performance weight
Landing Distance - 800 feet (using reverse thrust)
Max Climb - 10,000 fpm @ 120 KIAS
Cruise Climb - 4,500 fpm @ 215 KIAS
Service Ceiling - 30,000+ feet
Fuel Consumption - 45 gph @ cruise power
Range - 800 nm (VFR reserves)
Endurance - 3 hours (VFR reserves)
Vne (never exceed) - 300 KIAS
Vs1 (stall) - 65 KIAS
Vref (approach) - 80 KIAS
Top Speed @ 3,000 feet - 260 KIAS (300 mph)
75% Power @ 3,000 feet - 230 KIAS
Sustainable Vertical Speed - 60 KIAS, 5,000 fpm, straight up!
Exhilaration Factor - "10"




2H4





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User currently offlineInbound From Trinidad and Tobago, joined Sep 2001, 851 posts, RR: 2
Reply 10, posted (8 years 3 weeks 12 hours ago) and read 15388 times:

yes that's right, that sound you heard was the condition levers being moved from either 900rpm or 1050rpm to 1200 for landing.

you may also hear it when some hotshots are screaming around to base turn at about 200KIAS and need to create some quick drag to get down to gear and flap extension speeds :p

LimaFoxTango, how are things in antigua tonight? A bit wet??
Caribbean Star has left a few planes in Piarco tonight due to the storm passing thru antigua.



Maintain own separation with terrain!
User currently offlineLimaFoxTango From Antigua and Barbuda, joined Jun 2004, 784 posts, RR: 1
Reply 11, posted (8 years 3 weeks ago) and read 15297 times:

Quoting Inbound (Reply 10):
you may also hear it when some hotshots are screaming around to base turn at about 200KIAS and need to create some quick drag to get down to gear and flap extension speeds

I know that one!!! Especially accepting the visual overhead TRI at 4100'.

Quoting Inbound (Reply 10):
LimaFoxTango, how are things in antigua tonight? A bit wet??
Caribbean Star has left a few planes in Piarco tonight due to the storm passing thru antigua.

It was pretty quiet. No wind and hardly any rain just like any other evening.



You are said to be a good pilot when your take-off's equal your landings.
User currently offlineVikkyvik From United States of America, joined Jul 2003, 9907 posts, RR: 26
Reply 12, posted (8 years 2 weeks 6 days 23 hours ago) and read 15291 times:
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Quoting 2H4 (Reply 9):
I know of only one:

Christ, that is some serious performance!

In going from 900 up to 1200 RPM and changing the pitch to create more drag (is that coarse pitch or the other one?), is this because in a go-around situation, it is much faster to change the pitch back (thereby quickly increasing thrust) than it is to spool the engines up?

Thanks.

~Vik



"Two and a Half Men" was filmed in front of a live ostrich.
User currently offlineT prop From United States of America, joined Apr 2001, 1028 posts, RR: 1
Reply 13, posted (8 years 2 weeks 6 days 20 hours ago) and read 15243 times:

Interesting that the Turbo Raven above is in this thread. It crashed at an airshow oct 99 when the pilot was using reverse inflight and was atempting to switch back to forward thrust at about 800 feet. The pilot says that when he wanted to come out of reverse and pushed the power lever up there was no response from the engine and he continued to sink till he crashed.

BTW, on the Dash 8 reverse is in the beta range. Part of the beta range is available inflight, not reverse though.

T prop.


User currently offlineBri2k1 From United States of America, joined Dec 2004, 988 posts, RR: 4
Reply 14, posted (8 years 2 weeks 6 days 20 hours ago) and read 15230 times:

Quoting Vikkyvik (Reply 12):
it is much faster to change the pitch back (thereby quickly increasing thrust) than it is to spool the engines up?

Power is still set with the thrust levers. The condition levers control the propellor RPM which is only indirectly related to power. The faster the engine turns, the more power it produces. By setting a fine pitch, the blades take a smaller bite of air, and can spin faster. This allows the engine to turn faster, which produces more power. In cruise flight, less power is needed, and by turning the engines slower, less fuel is consumed, so a more coarse pitch can be selected.

It sounds like it would be possible to operate at a coarse propellor setting with a high thrust setting, but in practice this is damaging to the engines.



Position and hold
User currently offlineN231YE From , joined Dec 1969, posts, RR:
Reply 15, posted (8 years 2 weeks 6 days 17 hours ago) and read 15206 times:

Quoting 2H4 (Reply 1):
I think, more likely, the push forward was created by the increased drag of the flaps being lowered. The higher power setting would have been selected to compensate (partially, at least) for the increased drag from the flaps. That's my guess, anyway...

I know the SAAB 340 (SF340) has a similar occurance; when the landing gear is lowered, I always hear a sudden change in the pitch of the propellers, as if they are throttling up (engines)/ changing the prop's pitch slighly to compensate for the increased drag of the extended landing gear.


User currently offlineDogfighter2111 From United Kingdom, joined Nov 2004, 1968 posts, RR: 1
Reply 16, posted (8 years 2 weeks 6 days 9 hours ago) and read 15140 times:

Hiya all,

Thank you all so much. I never even thought that it could be the props being moved although i was wondering about them moving in-flight whilst i was on the ground in EDI.

Well i am just going away now to catch my return flight.

Thanks
Mike


User currently offlineAjd1992 From , joined Dec 1969, posts, RR:
Reply 17, posted (8 years 2 weeks 5 days 4 hours ago) and read 15027 times:

If they had engaged reverse pitch inflight, you may notice a wing falling, with you in pursuit Big grin Think of the Lauda 767 over Thailand.

User currently offlineDogfighter2111 From United Kingdom, joined Nov 2004, 1968 posts, RR: 1
Reply 18, posted (8 years 2 weeks 5 days 3 hours ago) and read 15021 times:

Quoting Ajd1992 (Reply 17):

Yes, i understand that but every aircraft is different and every aircraft has it's won capabilities.

Obviously from that experiance a B767 cannot use Reverse thrust in-flight (That was only one side remember, which also never helped the situation) but the Trident was able to do so.  Smile

Thanks
Mike


User currently offlineBri2k1 From United States of America, joined Dec 2004, 988 posts, RR: 4
Reply 19, posted (8 years 2 weeks 5 days 3 hours ago) and read 15017 times:

I believe the C-17 Globemaster can use at least idle reverse on at least the two inboard engines (and possibly more) in flight for incredible descent performance. It shares engines (under a different designation) with the P&W-powered 757s, so it seems in-flight reversing capability is really a function of airframe design moreso than of the engine. The C-17 also has a unique reverser design where most of the air is deflected straight ahead or upwards to minimize FOD, which allows it to safely powerback even with wing-mounted engines.


Position and hold
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17015 posts, RR: 67
Reply 20, posted (8 years 2 weeks 5 days 2 hours ago) and read 15007 times:

Quoting Bri2k1 (Reply 19):
i2k1 From United States, joined Dec 2004, 681 posts, RR: 1
Reply 19, posted Fri Aug 4 2006 16:17:42 UTC+2 and read 7 times:

I believe the C-17 Globemaster can use at least idle reverse on at least the two inboard engines (and possibly more) in flight for incredible descent performance. It shares engines (under a different designation) with the P&W-powered 757s, so it seems in-flight reversing capability is really a function of airframe design moreso than of the engine. T

Indeed. Also several older jets have had idle reverse in flight capability. For example the DC-8. And I'm pretty sure I remember postings from a 747 captain who left the boards a while a go about idle reverse on the 747 for the purpose of emergency descent. Apparently the noise and vibrations are something else.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineMeister808 From United States of America, joined Jan 2000, 973 posts, RR: 1
Reply 21, posted (8 years 2 weeks 4 days 1 hour ago) and read 14908 times:

Quoting Bri2k1 (Reply 14):
Power is still set with the thrust levers. The condition levers control the propellor RPM which is only indirectly related to power. The faster the engine turns, the more power it produces. By setting a fine pitch, the blades take a smaller bite of air, and can spin faster. This allows the engine to turn faster, which produces more power. In cruise flight, less power is needed, and by turning the engines slower, less fuel is consumed, so a more coarse pitch can be selected.

It sounds like it would be possible to operate at a coarse propellor setting with a high thrust setting, but in practice this is damaging to the engines.

You've got the right idea here, and I know what you mean, but I'm going to clarify a little bit for those people out there who don't know how constant-speed propellers work.

The condition levers control RPM. The power levers control torque. When the RPM is pulled back, the propellers will move to a higher pitch(coarse) so that the same thrust can be produced with less revolutions of the propeller (the prop needs to take a bigger bite out of the air, since it is moving slower). In addition, the high pitch condition produces less drag, so the airplane can go faster with less fuel burn.

What really changes blade pitch is the power lever. Given a constant RPM, an increase in torque will increase pitch (coarse) so that more thrust will be produced. A decrease in torque will decrease pitch (fine) so that less thrust will be produced.

The reason high RPM is selected for takeoff and landing is because, at lower RPMs, the propeller may hit maximum pitch somewhere short of maximum torque, so there will be engine power that is unused (at maximum torque)because the prop can't take any bigger bite out of the air. By increasing RPM to maximum, you ensure that there is adequate blade pitch to use all torque available when the power lever is moved fully forward.

You are also correct in saying that, even if you don't run out of pitch, it is still bad to operate at high torque with the RPM decreased, as it strains the engine components. It would be akin to accelerating your manual-transmission car from 5 to 20 mph in 5th gear with your foot on the floor. It works, but common sense dictates that it will be better on the vehicle (and faster) to match engine RPM with tire RPM slightly better by downshifting a few gears. Every engine and prop combination will have limits published to dictate how much power can be used at certain RPM settings.

-Meister



Twin Cessna 812 Victor, Minneapolis Center, we observe your operation in the immediate vicinity of extreme precipitation
User currently offlineBri2k1 From United States of America, joined Dec 2004, 988 posts, RR: 4
Reply 22, posted (8 years 2 weeks 3 days 19 hours ago) and read 14866 times:

Quoting Meister808 (Reply 21):
What really changes blade pitch is the power lever. Given a constant RPM, an increase in torque will increase pitch (coarse) so that more thrust will be produced. A decrease in torque will decrease pitch (fine) so that less thrust will be produced.

The reason high RPM is selected for takeoff and landing is because, at lower RPMs, the propeller may hit maximum pitch somewhere short of maximum torque, so there will be engine power that is unused (at maximum torque)because the prop can't take any bigger bite out of the air. By increasing RPM to maximum, you ensure that there is adequate blade pitch to use all torque available when the power lever is moved fully forward.

...

It would be akin to accelerating your manual-transmission car from 5 to 20 mph in 5th gear with your foot on the floor. It works, but common sense dictates that it will be better on the vehicle (and faster) to match engine RPM with tire RPM slightly better by downshifting a few gears.

Good explanations -- better than mine  Smile



Position and hold
User currently offline3DPlanes From United States of America, joined Apr 2006, 167 posts, RR: 0
Reply 23, posted (8 years 2 weeks 3 days 17 hours ago) and read 14841 times:

Quoting Bri2k1 (Reply 19):
The C-17 also has a unique reverser design where most of the air is deflected straight ahead or upwards to minimize FOD, which allows it to safely powerback even with wing-mounted engines.

They also reverse the core discharge, rather than just the bypass air... Do any of the commercial engines do that?



"Simplicate and add lightness." - Ed Heinemann
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17015 posts, RR: 67
Reply 24, posted (8 years 2 weeks 3 days 17 hours ago) and read 14840 times:

Quoting 3DPlanes (Reply 23):
Quoting Bri2k1 (Reply 19):
The C-17 also has a unique reverser design where most of the air is deflected straight ahead or upwards to minimize FOD, which allows it to safely powerback even with wing-mounted engines.

They also reverse the core discharge, rather than just the bypass air... Do any of the commercial engines do that?

Not the newer ones in general. Most of the air is in the bypass duct anyway. On older engines, it is pretty common. The Jurassic 737s have core and bypass reverse, for example.

[Edited 2006-08-06 02:36:43]


"There are no stupid questions, but there are a lot of inquisitive idiots."
25 Post contains links LPLAspotter : Absolutely correct my friend, and here's the video to prove it: http://flightlevel350.com/Aircraft_B..._Untitled_Aviation_Video-5025.html LPLAspotter
26 Av8trxx : The sound change from the props has nothing to do with compensation for the increased drag from the gear. It just happens that the flow that goes wit
27 N231YE : Having never flown in an aircraft with constant-speed propellers until recently, I noticed one of the items on the checklist (at least for an PA-28 &
28 FLY2HMO : And for that matter all planes with JT8Ds.
29 Post contains images KELPkid : My first complex/high performance landing (I took care of both signoffs at once) with an instructor, I neglected the "P" in GUMP. Well, after flaring
30 Post contains images Meister808 : Doubtful - its a purely mechanical system, so unless the guys at Saab tied the landing gear hydraulics into the prop control cables somehow (I can th
31 EMBQA : Nope... landing check list items. 1) Gear Down.... 2) Props to max.
32 N231YE : So that makes sense. On landing, the pilots put the gear down, then they put the props to fine pitch (high RPMs). The main reason I speculated that t
33 ThirtyEcho : i was pushed forward out of my seat Next time, Cappy, pay attention to the seat belt sign and announcement. The DC-8 could use reverse thrust inflight
34 Post contains images Jetlagged : The Trident could also use in flight thrust reverse as a means to make rapid descents. It was possible to select reverse in flight on the 727, but I d
35 Starlionblue : Well, it was a long time ago and my memory may be hazy. Perhaps Captain Squares can set the record straight.
36 Post contains links and images N231YE : Just to add, some of the early DC-10s with the CF6's had core reversers, but those were removed as well. Note the "paddle" in the core flow of engine
37 Access-Air : This is exactly what is going on.....The power levers are not moved..only the propeller pitch levers taking the props out of their Wide open pitch to
38 Flyboy80 : When I used to work dash 8s we would just come screaming in (apply that definition as you well with this particular aircraft) to some airports, guys u
39 Post contains links 71Zulu : Very bad things indeed http://www.airdisaster.com/reports/ntsb/AAR88-08.pdf
40 DashTrash : Most of the time, we're pushing the power levers forward at the same time the non-flying pilot is pushing the condition levers forward. Maintains a r
41 Cdekoe : Can anybody here tell me what the engine RPMs are during the cruise, descend, approach and landing phase of the Dash 8 flight profile? Thanks!
42 LimaFoxTango : Normally 1200RPM for take off, 1050RPM for climb, 900RPM for cruise, descent and approach and 1200RPM for landing.
43 Cdekoe : Thanks for the quick reply! Would you happen to know related core engine speeds? I'm looking for the variation in accessory gearbox drive - AC genera
44 CF188A : Someone correct me if I am wrong, but the Buffalo can and does engage reverse thrust before they touch down. I witnessed it several times.
45 WrenchBender : It can be selected but requires weight on wheels switch to be made to actually activate. Like most DHC products 'Prop discing' is used as a speed bra
46 DashTrash : "Discing" is the same as beta in the Dash 8. You can't do it in flight. The beta lockout system prevents it. If you lift the triggers to bring the pow
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