Forward thrust Q

[Ramapriya]

Hi again,

I have for a colleague a 30-yr old former Air Canada 737 pilot who
doesn't take too kindly to questions of my kind :( When I asked him
recently about how forward thrust happens, he said that the engine
blades simply turn the other direction. With nothing to back up my
hunch, I still feel something amiss and implausible in what he said,
but if true, I must confess it represents fantastic braking within the
engine to first get the blades to a stop spinning, and next spin the
other way!

Could someone please confirm or deny what my colleague told me? That
pilot, by the way, says he has not heard of 'chandelles' or 'phugoids'
or even 'angle of attack'. Leaves me thinking that either Denker's
book contains non-standard terminology (unlikely) or Canadians use a
different set of terms (likely). OR he's feigning to keep me away :((

Ramapriya

[John T]

Ramapriya wrote:
>
> When I asked him
> recently about how forward thrust happens, he said that the engine
> blades simply turn the other direction.

If by "forward thrust" you mean "reverse thrust" where the air is being
pushed toward the front of the plane instead of the back, then yes, the
propellers of some aircraft are capable of twisting enough to provide
reverse thrust. The C-130 Hercules cargo plane is a good example of this
and there are a number of civilian models that have this option, as well.

> With nothing to back up my
> hunch, I still feel something amiss and implausible in what he said,
> but if true, I must confess it represents fantastic braking within the
> engine to first get the blades to a stop spinning, and next spin the
> other way!

They don't stop spinning nor do they turn in the opposite direction. They
simply twist about their axis enough so that the air is pushed in the
opposite direction.

To demonstrate, drive down the highway with your arm outstretched and your
hand flat. Now twist your arm so that the front of your hand (the side
facing the wind) is angled up, Your arm will tend to rise. Now twist your
arm so that the front of your hand is angled down. Your arm will fall.
This is a very simplistic demonstration of what happens with
thrust-reversing propellers.

--
John T
http://tknowlogy.com/TknoFlyer
http://www.pocketgear.com/products_search.asp?developerid=4415
____________________

[Ron Natalie]

Ramapriya wrote:
> Hi again,
>
> I have for a colleague a 30-yr old former Air Canada 737 pilot who
> doesn't take too kindly to questions of my kind :( When I asked him
> recently about how forward thrust happens, he said that the engine
> blades simply turn the other direction.

If you're talking about reverse thrust, he's full of it. The engines
do not change direction. The exhausted air is redirected forward.
Different styles are used on different engine, but there's some sort
of device on the rear end of the engine that just mechanically redirects
it.

Here's sort of a simple "bucket" style:

http://sitemaker.umich.edu/thrust.reverser/files/deployed_2.jpg

The high bypass fans in the later 737's have doors in the cowl, not the
greatest but I found this picture of one deployed:

http://www.geocities.com/airliners_au/images/AN_737-300_reverse_0206.jpg

[G.R. Patterson III]

Ramapriya wrote:
>
> I have for a colleague a 30-yr old former Air Canada 737 pilot who
> doesn't take too kindly to questions of my kind :( When I asked him
> recently about how forward thrust happens, he said that the engine
> blades simply turn the other direction. With nothing to back up my
> hunch, I still feel something amiss and implausible in what he said,
> but if true, I must confess it represents fantastic braking within the
> engine to first get the blades to a stop spinning, and next spin the
> other way!

With propellor aircraft that have this feature, the blades can be tilted such that
they blow air towards the front instead of the back. I've not heard that this can be
done on fan jets, and it's impossible on true jets. The reverser feature with which
I'm familiar on jet engines is a sort of bucket that lowers down over the engine
exhaust and turns it around 180 degrees.

> Could someone please confirm or deny what my colleague told me? That
> pilot, by the way, says he has not heard of 'chandelles' or 'phugoids'
> or even 'angle of attack'. Leaves me thinking that either Denker's
> book contains non-standard terminology (unlikely) or Canadians use a
> different set of terms (likely). OR he's feigning to keep me away :((

I'd say that he doesn't want you to ask him questions. Another possibility is that he
actually has no pilot experience at all.

George Patterson
If a man gets into a fight 3,000 miles away from home, he *had* to have
been looking for it.

[lance smith]

I got this from the GE webpage:

Thrust Reverser: Thrust reversers serve as an aircraft's main brakes
on landing. There are three types of thrust reversers: translating
cowl, clam shell and turboprop reverse pitch. All three literally
reverse the engines thrust by closing in when deployed by the pilot
pushing the air out the front of the engine rather than the back. This
motion decreases the speed of the aircraft and is the loud noise you
hear when landing.

I'm assuming you're mostly concerned with 'jets', then you would be
wondering about the clamshell and translating cowl. Clamshells when
activated deflect the exhaust forward, and the translating cowl only
sends the bypass air forward.

A couple of discussions on thrust reversal:
http://www.airliners.net/discussions/tech_ops/read.main/54508
http://www.airliners.net/discussions/tech_ops/read.main/43007

-lance smith

[BTIZ]

maybe that's why he's a "former" 737 pilot...

the piston engine blades on propellers do not "turn the other direction",
but they do change pitch enough to create reverse thrust..

on a jet engine, it's a matter of thrust attenuators changing the flow of
the air around the engine or exhaust direction

BT

"Ramapriya" > wrote in message
om...
> Hi again,
>
> I have for a colleague a 30-yr old former Air Canada 737 pilot who
> doesn't take too kindly to questions of my kind :( When I asked him
> recently about how forward thrust happens, he said that the engine
> blades simply turn the other direction. With nothing to back up my
> hunch, I still feel something amiss and implausible in what he said,
> but if true, I must confess it represents fantastic braking within the
> engine to first get the blades to a stop spinning, and next spin the
> other way!
>
> Could someone please confirm or deny what my colleague told me? That
> pilot, by the way, says he has not heard of 'chandelles' or 'phugoids'
> or even 'angle of attack'. Leaves me thinking that either Denker's
> book contains non-standard terminology (unlikely) or Canadians use a
> different set of terms (likely). OR he's feigning to keep me away :((
>
> Ramapriya
>

[Andrew Sarangan]

Next time when you are flying commercial, take a look at the engine when
thrust reversers are applied. A deflector is used to reflect the exhaust
gases in the forward direction. You can clearly see the deflector being
activated if you sit near the engine nacelle. The blades do not change
rotation in most turbofan engines.

I am not too surprised about the chandelles. It is not a required
maneuver in the Canadian commercial checkride. But not knowing angle of
attack is surprising. This is basic concept everyone learns in primary
ground school. However, I am not sure how much aerodynamics a 737 pilot
has to know. At that level you are so far removed from the stick and
rudder flying that it is quite possible they have forgotten the basics.
I consider the heavy iron pilots as more like a systems manager than a
stick and rudder pilot.



(Ramapriya) wrote in
om:

> Hi again,
>
> I have for a colleague a 30-yr old former Air Canada 737 pilot who
> doesn't take too kindly to questions of my kind :( When I asked him
> recently about how forward thrust happens, he said that the engine
> blades simply turn the other direction. With nothing to back up my
> hunch, I still feel something amiss and implausible in what he said,
> but if true, I must confess it represents fantastic braking within the
> engine to first get the blades to a stop spinning, and next spin the
> other way!
>
> Could someone please confirm or deny what my colleague told me? That
> pilot, by the way, says he has not heard of 'chandelles' or 'phugoids'
> or even 'angle of attack'. Leaves me thinking that either Denker's
> book contains non-standard terminology (unlikely) or Canadians use a
> different set of terms (likely). OR he's feigning to keep me away :((
>
> Ramapriya
>


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[Peter Clark]

On 8 Nov 2004 22:54:58 -0600, Andrew Sarangan
> wrote:

>But not knowing angle of
>attack is surprising. This is basic concept everyone learns in primary
>ground school. However, I am not sure how much aerodynamics a 737 pilot
>has to know. At that level you are so far removed from the stick and
>rudder flying that it is quite possible they have forgotten the basics.
>I consider the heavy iron pilots as more like a systems manager than a
>stick and rudder pilot.

Opening can of worms and running, but don't a number of 737's have an
AOA meter?

[pickle]

Ramapriya wrote:

> Hi again,
>
>30-yr old former Air Canada 737 pilot

Yeah. Right.