Nc97 Posted August 27, 2009 Share Posted August 27, 2009 Please...Please...Correct me if I am wrong, I have been kicking myself about this for a while now: The ADH's RPM is that of the RGB, 1020RPM. It has to be, seeing that the Speed Sensing Control is an alternate mounting site for the Tach Generator, 1020RPM = 100% RPM. Why then, when setting the 94% switch on the Speed Sensing Contol, would we set it to activate between 3830RPM and 3930 RPM? Quote Link to comment Share on other sites More sharing options...
pjvr99 Posted August 27, 2009 Share Posted August 27, 2009 Because that is the speed of the pad via the particular reduction gearing, NOT the prop speed Quote Link to comment Share on other sites More sharing options...
NATOPS1 Posted August 27, 2009 Share Posted August 27, 2009 (edited) A BETTER way to display the information.... Each accessory Ratio to input rotor RPM at (13,820/ 100%) SSC----- .305 4215 SSV----- .3045 4208 OIL------ .2352 3250 FUEL CNT .2352 3250 FUEL PMP .2352 3250 EXT OIL .2352 3250 "Speed Sensing Control is an alternate mounting site for the Tach Generator" Never heard this one...) Edited August 27, 2009 by NATOPS1 Quote Link to comment Share on other sites More sharing options...
Nc97 Posted August 27, 2009 Author Share Posted August 27, 2009 Wow, you guys are good. Thanks a bunch! Quote Link to comment Share on other sites More sharing options...
Nc97 Posted August 27, 2009 Author Share Posted August 27, 2009 Hold on a minute. Seeing as I never had to swap the Tach Generator to the Speed Switch, how can it "translate" two different input RPMs (1020/4215) into 100% RPM? Quote Link to comment Share on other sites More sharing options...
NATOPS1 Posted August 27, 2009 Share Posted August 27, 2009 (edited) As stated I have never heard the SSC and the Tach Gen being interchangeable... Not sure what you are referring to..... (Physically not possible to swap the tach gen into the SSC spot) Edited August 27, 2009 by NATOPS1 Quote Link to comment Share on other sites More sharing options...
Nc97 Posted August 27, 2009 Author Share Posted August 27, 2009 I was am referring to the pad on the front side of the Speed Switch, which I was taught, was a third mounting pad for the tach generator. Quote Link to comment Share on other sites More sharing options...
Steve1300 Posted August 28, 2009 Share Posted August 28, 2009 The generator will fit on the face of the SSC,(not in place of) but it will not read 100% at 100%. The first problem you would find is that you would not be able to connect the wiring to the tach generator down there without a long pigtail to run from the current electrical connector location down to the SSC. I think that the story of the SSC mounting location falls in line with the Stag-Bar games of long ago. Since we do have two mounting locations for the tach generator on the back of the RGB, it would be difficult to imagine a time that I'd be forced to use the SSC and pigtail technique just to get an approximate RPM. Quote Link to comment Share on other sites More sharing options...
Nc97 Posted August 28, 2009 Author Share Posted August 28, 2009 Steve, I can't imagine a time when an approximate RPM would be useful at all. So we are in agreement, the Tach Generator could not read 100% given the higher drive RPM? Has anyone ever used the Tach Generator on the front side of the SSC, and is that what the pad on it was designed for? Quote Link to comment Share on other sites More sharing options...
NATOPS1 Posted August 28, 2009 Share Posted August 28, 2009 I have removed the "face" of the SSC and the generator will fit on the face of the SSC,(not in place of) but it will not read RPM at 100% at 13,820 (100%). The RGB Tach drive gear spins at 4195 @100% (13,820) SSC drive gear spins at 4215 @100% (13,820) So there you have it.....I'll see what I can find out about the use of the SSC/Tach gen pad..... Quote Link to comment Share on other sites More sharing options...
pjvr99 Posted August 28, 2009 Share Posted August 28, 2009 NATOPS1, if those numbers are correct you will have 0.5% overread installed on the speed switch - more than accurate enough to get you home. You also have the generator freq meter to cross reference. Correctly said, your biggest problem will be getting wires to it Quote Link to comment Share on other sites More sharing options...
FLYBOY773 Posted August 28, 2009 Share Posted August 28, 2009 Ok Guys , I have flown Herks with the Tach Gen on the SSC, We are flying one of our airplanes right now that has the Tech Gen mounted there its on # 2 Engine Acft Tail Number 92-3021. They put it there due to the pads on the gearbox are worn out . When you mount it there it has to be written up in the 781 A So you as an F.e Know where thereading is coming from. Archie Quote Link to comment Share on other sites More sharing options...
Steve1300 Posted August 29, 2009 Share Posted August 29, 2009 That is interesting. I can only wonder how both tach generator pads get "worn out" between overhauls, as I have not seen it happen before. I suppose then that you guys in Ohio carry extension pigtails on the airplanes in case you have to remount your tach generators on the SSC? I learn something new every week! That is what makes this forum such a good thing for me. Quote Link to comment Share on other sites More sharing options...
Lkuest Posted August 29, 2009 Share Posted August 29, 2009 We had one at Little Rock many years ago that had the tach gen mounted to the Speed Switch. It flew like that for a while until the commander made us change the motor---to clear up the K write-up. I can see one argument though; an engine decouple would be indicated differently, so the flight engineer might have a delayed response trying to figure out what was going on. There might also be a stigma against leaving a defective gearbox in service, even if everything else works. Quote Link to comment Share on other sites More sharing options...
GACFaja Posted August 30, 2009 Share Posted August 30, 2009 Steve, I can't imagine a time when an approximate RPM would be useful at all. So we are in agreement, the Tach Generator could not read 100% given the higher drive RPM? Has anyone ever used the Tach Generator on the front side of the SSC, and is that what the pad on it was designed for? I've only ever had to do that once, and we definitely had to splice in more wire to do it. I don't remember it affecting the indication any, though. Quote Link to comment Share on other sites More sharing options...
Steve1300 Posted August 30, 2009 Share Posted August 30, 2009 If you still have the round indicators with the tolerance of +/- 1%, it will not be as obvious. If you have digital RPM indicators, it will be noticable right away. That is a good point about the standards signals of trying to start a decoupled engine. It sure would make a difference,huh? Quote Link to comment Share on other sites More sharing options...
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