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Multi engine aircraft
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Miken



Joined: 24 Dec 2012
Posts: 273

PostPosted: Tue Nov 11, 2014 9:39 am    Post subject: Multi engine aircraft Reply with quote

Im reading a book at the moment about Short Stirling glider tugs and a thought occured to me that I dont know the answer to.
On old cars and motorbikes the rev counters are driven by a revolving cable from the engine to the dashboard instrument.
On a big aircraft did they have very long cables waggling away down the length of the wing back to the cokpit?
Surely they weren't electrical back then?
Presumably they would also have to split off through a junction box somewhere to be duplicated at the flight engineers position.
Any thoughts?
Mike
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peter scott



Joined: 18 Dec 2007
Posts: 6179
Location: Edinburgh

PostPosted: Tue Nov 11, 2014 11:11 am    Post subject: Reply with quote

Hi Mike,

Where it wasn't sensible to use direct mechanical drives they still used the same type of instrument but the engines had a small 3 phase generator connected via a short flexible drive and the outputs from these drove a synchronous motor connected to the usual alloy disc and magnetic drag arrangement within the instruments.

Peter
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Peter_L



Joined: 10 Apr 2008
Posts: 2323
Location: New Brunswick. Canada.

PostPosted: Tue Nov 11, 2014 3:23 pm    Post subject: Reply with quote

Further to the above reply by Peter S.

Quote Wikipedia "A synchronous electric motor is an AC motor in which, at steady state,[1] the rotation of the shaft is synchronized with the frequency of the supply current; the rotation period is exactly equal to an integral number of AC cycles. Synchronous motors contain electromagnets on the stator of the motor that create a magnetic field which rotates in time with the oscillations of the line current. The rotor turns in step with this field, at the same rate."

Wouldn't the supply have been a single phase, rather than 3 phase ?
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peter scott



Joined: 18 Dec 2007
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Location: Edinburgh

PostPosted: Tue Nov 11, 2014 4:27 pm    Post subject: Reply with quote

peterwpg wrote:
Further to the above reply by Peter S.

Wouldn't the supply have been a single phase, rather than 3 phase ?


Not according to "Aeroplane Maintenance & Operation, Instruments" by Molloy and Knott
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47Jag



Joined: 26 Jun 2008
Posts: 1470
Location: Bothwell, Scotland

PostPosted: Tue Nov 11, 2014 4:41 pm    Post subject: Reply with quote

Jaguar used on their later XK twin-cam engines a single phase AC generator and the dash gauge is a voltmeter with a rectifier. 12 volts equals 2400 RPM. I would have thought that this was not a particularly new idea and could have come from the aero industry. I can't think of a reason for three phase other than redundancy IE 3 parallel outputs. Question

Art
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Peter_L



Joined: 10 Apr 2008
Posts: 2323
Location: New Brunswick. Canada.

PostPosted: Tue Nov 11, 2014 11:23 pm    Post subject: Reply with quote

What is truly great about this forum is the diversity of questions and information.

I found some information on engine tacho's here.

http://www.theairlinepilots.com/forum/viewtopic.php?t=927

I have flown, as passenger, quite a lot and in a wide range of aircraft over the years but next time I will view the engine speed indicator/s in a whole different light.

........ next question..... I understand that aircraft engines push or pull a plane through the air and the difference in air speed above and below the wing enables it to fly. But when it is on the ground, how is the drive transferred from the engines to the wheels. Question

(answers on a post card please) Wink
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peter scott



Joined: 18 Dec 2007
Posts: 6179
Location: Edinburgh

PostPosted: Wed Nov 12, 2014 2:00 am    Post subject: Reply with quote

peterwpg wrote:
= But when it is on the ground, how is the drive transferred from the engines to the wheels. Question

(answers on a post card please) Wink


Ah yes but aircraft tyres have special treads that cup the air flow from the props or turbines but only where they contact the ground. The air flows over the top of the tyres unimpeded.

Sometimes I think I talk complete nonsense!

Peter Laughing
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ka



Joined: 03 Dec 2007
Posts: 600
Location: Orkney.

PostPosted: Wed Nov 12, 2014 7:55 am    Post subject: Reply with quote

So, moving on from this slightly, I understand about jet reaction,(I was in the Fire Service and hung onto a branch delivering 500 gallons a minute), but do propellors work on the same principle?
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KA

Better three than four.
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Peter_L



Joined: 10 Apr 2008
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Location: New Brunswick. Canada.

PostPosted: Wed Nov 12, 2014 2:08 pm    Post subject: Reply with quote

ka wrote:
So, moving on from this slightly, I understand about jet reaction,(I was in the Fire Service and hung onto a branch delivering 500 gallons a minute), but do propellors work on the same principle?


Courtesy of Boeing

http://www.boeing.com/companyoffices/aboutus/wonder_of_flight/propeller.html
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Miken



Joined: 24 Dec 2012
Posts: 273

PostPosted: Wed Nov 12, 2014 10:56 pm    Post subject: Reply with quote

peter scott wrote:
Hi Mike,

Where it wasn't sensible to use direct mechanical drives they still used the same type of instrument but the engines had a small 3 phase generator connected via a short flexible drive and the outputs from these drove a synchronous motor connected to the usual alloy disc and magnetic drag arrangement within the instruments.

Peter

Thanks for the description Peter.
MN
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