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N1 Monopole  
User currently offlineDiego From Italy, joined Apr 2001, 135 posts, RR: 0
Posted (9 years 1 week 4 days 17 hours ago) and read 4257 times:

Hi folks one quick question : reading a falcon 50 manual I read that N1 inputs are supplied by a monopole. What is it? Some sort of trasducer that transforms the rotational velocity of the turbine shaft in current then forwarded to the motor of the N1 indicator?
Thanks

9 replies: All unread, jump to last
 
User currently offlineDougloid From , joined Dec 1969, posts, RR:
Reply 1, posted (9 years 1 week 4 days 15 hours ago) and read 4232 times:

Quoting Diego (Thread starter):
Hi folks one quick question : reading a falcon 50 manual I read that N1 inputs are supplied by a monopole. What is it? Some sort of trasducer that transforms the rotational velocity of the turbine shaft in current then forwarded to the motor of the N1 indicator?
Thanks

Aha! a 731 question! I knew working for Garrett was good for something. It's just a small sensor that detects N1 rotation and provides a signal, where the signal goes is anyone's guess but I am sure there is an input to the computer... I have a mental picture of what it looks like but it's been 20 years since I was inside one but I believe it's in the removable engine tail cone. There's a metal cover that is removed, then the monopole cover plate is secured with 5 or 6 bolts that has the monopole on the back side of it, there's a removable cup shaped rotor with teeth on it that provides the signal....the actual monopole itself is about the size of a chapstick.
As I recall the lead has to be carefully straightened out so as to remove the entire assembly. It's delicate and expensive.


User currently offlineFrancoflier From France, joined Oct 2001, 3790 posts, RR: 11
Reply 2, posted (9 years 1 week 4 days 12 hours ago) and read 4218 times:

Hehe,

The TPE 331 has the same thing in the prop governor. It gives an RPM signal that's more accurate than the tachometer's to the EGT and starting computers.

On the 331, it also looks like a chapstick, (smaller I guess) and has a flat surface that is the sensing part. It's so freaking sensitive that even a millimetric scratch or crack on it will throw it off.

I don't know exactly how it works, but I guess it counts the number of times the shaft or gear in front of it goes by and then it is compared to a time signal or something....



Looks like I picked the wrong week to quit posting...
User currently offlineDougloid From , joined Dec 1969, posts, RR:
Reply 3, posted (9 years 1 week 4 days 12 hours ago) and read 4211 times:

Quoting Francoflier (Reply 2):
The TPE 331 has the same thing in the prop governor. It gives an RPM signal that's more accurate than the tachometer's to the EGT and starting computers.

Can't say I ever had to change a prop governor on a 331 or ever had any trouble with the rpm sensing or had it meddle with any of the startup stuff...must be something new as the last one I worked on was in 87....
are you working on -14s?

The 731 N1 monopole is in the relatively hot end...gets toasty in there.

if you're working on anything up through a -12, remind me to tell you about the secret check valve....


User currently offlineG4Doc2004 From United States of America, joined Feb 2004, 123 posts, RR: 0
Reply 4, posted (9 years 1 week 4 days 11 hours ago) and read 4192 times:

If I recall correctly, the N1 information is sent to the DEEC (digital electronic engine control) that in turn controls the fuel control solenoids. Hence the term "N1 DEECS".....the DEEC can be downloaded by a PC by an engine trend monitoring program called ECTM that Honeywell distributes. It is an excellent program that allows you to track every engine parameter, see exceedances, and also troubleshoot. I used it recently to track down a bad engine wiring harness....it had an intermittent short at the "A" solenoid.

Not to correct Dougloid, but I think the N1 monopole is mounted on the accessory gearbox. I changed one once or twice on a Hawker 800XP that had the -5BR engine. You had to verify the proper distance between the face of the monopole and the gear in the AGB it was looking at with a depth micrometer and shim it accordingly....



"Failure to prepare is preparing to fail"--Benjamin Franklin
User currently offlineDougloid From , joined Dec 1969, posts, RR:
Reply 5, posted (9 years 1 week 4 days 7 hours ago) and read 4157 times:

Quoting G4Doc2004 (Reply 4):
Not to correct Dougloid, but I think the N1 monopole is mounted on the accessory gearbox.

I believe that's the N2 monopole...the N1 monopole is accessible through the hubcap sized cover that you can see looking up the tailpipe....I remember shimming the N2 monopole one time.


User currently offlineDougloid From , joined Dec 1969, posts, RR:
Reply 6, posted (9 years 1 week 4 days 6 hours ago) and read 4146 times:

Quoting Dougloid (Reply 5):
Quoting G4Doc2004 (Reply 4):
Not to correct Dougloid, but I think the N1 monopole is mounted on the accessory gearbox.

I believe that's the N2 monopole...the N1 monopole is accessible through the hubcap sized cover that you can see looking up the tailpipe....I remember shimming the N2 monopole one time.

I've referred this one up the chain of command...it's been a few years...if I am wrong I shall have a nice slice of crow thank you


User currently offlineAmtrosie From United States of America, joined Jan 2005, 274 posts, RR: 0
Reply 7, posted (9 years 1 week 4 days 3 hours ago) and read 4119 times:

I am checking with a buddy of mine who just changed one.

Quoting G4Doc2004 (Reply 4):
If I recall correctly, the N1 information is sent to the DEEC (digital electronic engine control) that in turn controls the fuel control solenoids. Hence the term "N1 DEECS".....the DEEC can be downloaded by a PC by an engine trend monitoring program called ECTM that Honeywell distributes. It is an excellent program that allows you to track every engine parameter, see exceedances, and also troubleshoot. I used it recently to track down a bad engine wiring harness....it had an intermittent short at the "A" solenoid

I am going to pass this along as well. He is pulling his hair out trying to figure out why his fuel computer keeps tripping and will not reset. I know he doesn't have the new DEEC's, because he is trying to finagle a set out of Honeywell right now.


User currently offlineG4doc2004 From United States of America, joined Feb 2004, 123 posts, RR: 0
Reply 8, posted (9 years 1 week 4 days 2 hours ago) and read 4116 times:

Amtrosie, If I recall, we got the ECTM software from our Honeywell Field Rep....
Have your buddy check the cannon plugs on the engine wiring harness at the "A" and "B" solenoids, at about the 3-o'clock position on the engine looking forward. That was where we had an intermittent short that was tripping our DEEC and we were getting the amber R COMPUTER annunciator on the glareshield panel....type of aircraft was a Lear 31A. From what our field rep told me, this is a common failure area for the harness. Our DEEC would reset, then we'd wiggle the harness just above those cannon plugs and the light on the glareshield would illuminate again. Then we'd download the DEEC and look at the data downloaded in time/fault format, and see the "A" and "B" solenoids failing. We swapped the solenoids over to the left engine and no fault at all, even when we wiggled the harness and ran it. It was our smoking gun, per se...... If you have trouble locating the ECTM program, contact me offline and I'll see if I can get you a copy....



"Failure to prepare is preparing to fail"--Benjamin Franklin
User currently offlineDougloid From , joined Dec 1969, posts, RR:
Reply 9, posted (9 years 1 week 8 hours ago) and read 4049 times:

Checked with my old crewchief back some 20 years ago when I worked in the motor shop....he still does.....I was correct.

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