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Reverse thrust

Started by Hardy Heinlin, Sat, 9 Apr 2011 15:50

Hardy Heinlin

Interesting phidget.

They say "... outputs a number between 0 and 1000".

But is every step 1 unit?

Jeroen Hoppenbrouwers

Good question. I don't have such a unit at hand right now, but it could be. 256 is pretty low for a 300 degrees pot, it is clearly a leftover from game controllers.

Blake H

Hi again, so your saying that I can have a dedicated pot to GO throttle :) and reverse throttle, is that correct, if so that is what I will build.

The only reason why I say that I was going to use one pot is beacause I was going to use a 10k linear 300 degree pot if you look at flight simulator FSUIPC SDK throttle rangle is -16384 (or max reverse, usually nearer -4096) to +16384.

-+0 thrust (60 degrees) -4096 is full reverse (300 degrees) and 16384 is full thrust (300 degrees)

farrokh747

#23
hello -

many of us use phidgets cards for various systems in the deck -

This one is for all analogue (pot) sensors - http://www.phidgets.com/products.php?category=0&product_id=1018

this will take any pot input  -  i use a set of sensors (pots, really) scavenged from the -200 quadrant (used by the Flight Data Recorder i think) and made by Penny & Giles

I also use the above linked (jeroen) pot for spoiler and aileron sensing - they also have a linear (slider) sensors  http://www.phidgets.com/products.php?category=7&product_id=1112

If you want to up the ante on pots:
http://www.precisionsales.com/potentiometers/singleturn/index.htm
http://www.precisionsales.com/potentiometers/linearmotion/index.htm

Most of us use Alan Dyer's wonderful FS2P, which lets us configure and assign each input as required. FS2P also controls Relays, Encoders, Digital in and out, amongst others.

I've found the Phidgets cards and sensors very stable and hardy (no pun intended!) I haven't had a card fail in 7 years - I believe the primary use for these cards are battlebots...?

Moreover, FS2P lets me set logic conditions for outputs (EG: relay for spoiler deploy) using a set of conditions (Squat Switch, levers 1, 3  at idle, etc)

With PSX, I believe much of this logic writing will not be needed, as it will probably have variables for all functions that the builder needs.

I've done some tests with the OEM sensors and phidgets 8:8:8 cards, and with an original 744 throttle quad and 744 thrust lever sensor assy - the values are rock steady. Values for the flap detents, for eg, are within +/- 10 units (out of 1000) each time I move the lever out of the gate and back again. Another thing is to watch out for any RF interference, or power line proximity.

I've found that the mechanical linkage from the levers to the sensors is critical. any play here will send errors to FS (in this case), and forces you set wider dead zones.

Apart from null zones, FS2P lets you set pot range of travel, reverse sense (in case you've got your wiring inverted) and much more.

Relay cards: http://www.phidgets.com/products.php?category=9&product_id=1014

My final system will be:
Analog inputs (from all pots - flt controls, toe brakes, thrust levers, etc) to Phidgets 8/8/8
Intermittent power related functions (Shaker, spoiler deploy, etc) to Phidgets Relays

All digital in and out (switches and leds) to FDS Sys cards - the GUI is REALLY very easy to use and highly recommended - it took me just under 2 hours to assign the entire overhead) - FDS also had a relay card

Sorry if I've gone on a bit,

cheers!

Farrokh.

tl1975

Quote from: Hardy HeinlinGood question, Will.

Re thrust reversers again: Just learned something new. The reversed exhaust gas generates an almost irrelevant force. (I have always wondered anyway how this thrust vector that goes nearly sideways could have such a big effect, compared to the remaining forward components). Now it's clear: In reverse configuration with high RPM, the braking force comes from the intake drag. When windmilling, the drag is low, when powered up, the drag is high.

http://yarchive.net/space/thrust_reversers.html


|-|

Well, sort of.... the C-17 can taxi backwards on reverse thrust. Some thrust is present. Of course very little.

dutch57

Hi All,

On reverse thrust,
When an Fan engine is operating in fwd thrust, the air of the fan is flowing backwards , relatively un obstructed.

During reverse , we open blocker doors, to direct the airflow in a custom patern forward, by doing this you create a force on the blocker doors wich goes against the forward force and so decelerating the aircraft.
If you try to put full reverse on a loaden B744, you might loose your reverser doors due to the force impact they are not designed for that force.

That a C17 can reverse and backup that is the strenght of those doors In the past Eastern used reverse on their B757 to do pushback, please note their B757`s had RR engines , that reverse design is much different than GE or PW

sincerly,
Bob

John H Watson

Quote from: dutch57If you try to put full reverse on a loaden B744, you might loose your reverser doors due to the force impact they are not designed for that force.

Bob, are you saying that Boeing didn't design full reverse thrust for RTO?

dutch57

John ,

Boeing prohibits backing up using reverse thrust as they write in th FCTM.

For an RTO full reverse thurst is used, but be aware that full reverse thurst is NOT the same as full Forward thrust due to engine limitations/controlling.

Bob