Tommy Posted March 9, 2015 Report Posted March 9, 2015 On my recent commercial training, my instructor pointed out that my RPM doesn't go all the way to the red line on take off power (about 50rpm less) and suggested me to have my mechanic take a look at it? Was he right in saying that? And, if so, is it a simple fix? Thanks guys! Quote
FloridaMan Posted March 9, 2015 Report Posted March 9, 2015 I have seen tachs read low many times. There are a number of iPhone apps that supposedly work well that may help you get a better feel whether it's the tach or the prop. Also, parallax may make the needle appear offset from where it's actually reading. Quote
Bob_Belville Posted March 9, 2015 Report Posted March 9, 2015 I have an electronic tach with the 930 and my new prop governor had the prop maxing out too low. One full turn of the adjustment was worth 50-75 rpm (I forget which). If the tach is accurate you'll want to get it adjusted so that you have max HP available for take off when heavy/hot/high. Quote
orionflt Posted March 9, 2015 Report Posted March 9, 2015 it is not uncommon for the tach to read low, borrow an optical tachometer and check the true rpm of the prop. if it is truly reading low it can be adjusted up, if it is the tach, then I wouldn't worry too much about it unless it is jumping around of giving other indications of failure. the other possibility is the tach cable could need lubrication or replacement. Brian Quote
carusoam Posted March 9, 2015 Report Posted March 9, 2015 The tach and engine are designed to meet at redline at most conditions... Often... The tach gets tired. The governor needs adjustment. The prop needs OH. Our governors, when they fail, go to max rpm to produce max power... An example of how much power is lost by changing rpm... The O gains 10% hp by going from 2500 to 2700rpm. That 30hp is the difference of 400' of take-off run. Use your iPhone to determine if the prop is really being limited. Rpm app... Have your mechanic look at it to determine if it is an adjustment or some serious problem. Best regards, -a- Quote
Tommy Posted March 9, 2015 Author Report Posted March 9, 2015 Is it this app? Strobe light ~ tachometer to measure RPM and ... - Apple How does one safely measure the max RPM? Quote
carusoam Posted March 9, 2015 Report Posted March 9, 2015 That looks like it would work... But, look for an app that uses sound to determine rpm. They have been reported to work pretty well for all engines without being able to see the rotating parts... Best regards, -a- Quote
N601RX Posted March 9, 2015 Report Posted March 9, 2015 I've been using Engine RPM for a couple of years and found to always match my digital tach. I believe its $10. Quote
Vance Harral Posted March 9, 2015 Report Posted March 9, 2015 It might be the tach itself. But the nature of the max RPM adjustment screw for the prop governor is such that it does wear a little over time, and that wear can translate to a change in max RPM. At a point about 800 hours after prop governor overhaul, we found our max RPM to be about 50 off of the 2700 spec. Our mechanic made a small adjustment (half turn) to the set screw, and that fixed the issue. Quote
Tommy Posted March 10, 2015 Author Report Posted March 10, 2015 Great, I am taking a laser tachometer up next week and hopefully it's a simply one turn of adjustment screw! Quote
fantom Posted March 10, 2015 Report Posted March 10, 2015 Most likely NBD, but good that you'll check it. Hopefully your CFI isn't nitpicking your flying as much as he's doing on a less than 2% low tach reading. Quote
Bob_Belville Posted March 10, 2015 Report Posted March 10, 2015 Great, I am taking a laser tachometer up next week and hopefully it's a simply one turn of adjustment screw! I should have mentioned that since the governor is at the bottom rear of the engine, at least on my IO360A1A, the adjustment is kind of mean to get at. So it's a good idea to be pretty sure just how much the max rpm is off so your A&P only has to do it once. Quote
Tommy Posted March 10, 2015 Author Report Posted March 10, 2015 He is quite a competent instructor and it is indeed a good pick. I hope he is right and it's not just the tacho getting old. It means more take off power for me! Quote
Wesley brown Posted March 10, 2015 Report Posted March 10, 2015 I just downloaded a rpm app called GIRI. I haven't used it yet so I don't have any feedback. It works off sound. Quote
RobertGary1 Posted March 10, 2015 Report Posted March 10, 2015 Report back what you find. Its somewhat more likely that the tach is off than the governor. If the tach is off you can legally just placard it. -Robert Quote
Tommy Posted March 16, 2015 Author Report Posted March 16, 2015 Ok! I took an optical tachometer out flying today and it turns out that my tachometer was reasonably accurate (maybe under read by 25rpm). ie. the tach is showing 2625rpm, the optical tach is showing 2650rpm. Though anything below 2500rpm, both tachs read the same. So I asked my A&P to adjust the governor. After two full turns of the screw (I still can't believe how a tiny little screw can determine something as important as the max RPM!) - see attached - the max RPM is still 2650rpm. I just need to confirm that 1) we were adjusting the right screw (if not, I am changing my A&P!!) 2) it's anticlockwise turn to increase max RPM 3) 1 full turn = 25rpm 4) should I go back and make two more turns to get to 2700rpm? how much difference will 50rpm make? And any reason why it didn't change after two full turns on the screw? Should I look for something else (the prop knob and cable)? Thanks guys! Quote
Shadrach Posted March 16, 2015 Report Posted March 16, 2015 Make sure the linkage is not binding somewhere. If the governor never gets to the stop, it does not matter wher the stop is set. BTDT. Quote
N601RX Posted March 16, 2015 Report Posted March 16, 2015 It may be that the prop stop fine pitch bolt is set incorrectly and not letting the prop go to the fine pitch setting. Also some governors have 2 screw like the one in the picture. Look around on the other side and see if there is a second one. 1 Quote
Tommy Posted March 16, 2015 Author Report Posted March 16, 2015 I was reading this from another 2700rpm thread ""You first adjust the stop screw, then, adjust the rod end on the prop cable so the arm hits the stop screw full forward on the prop control. Make sure that the knob or lever has ever so slightly more travel than required to make the governor arm hit the stop. 1/2 turn on the rod end beyond what is required to make it hit the stop on the governor is about right. The cable shouldn't limit the travel on the RPM, the stop screw should."" One thing we didn't do is to adjust the rod end!! How do you adjust the rod end? Simply twisting the "metal ring" around it? Quote
jetdriven Posted March 16, 2015 Report Posted March 16, 2015 Take the rod end loose from the governor, loosen the jam nut and turn it. Quote
Tommy Posted March 16, 2015 Author Report Posted March 16, 2015 Take the rod end loose from the governor, loosen the jam nut and turn it. I think I need a video for this! Quote
kmyfm20s Posted March 16, 2015 Report Posted March 16, 2015 It may be that the prop stop fine pitch bolt is set incorrectly and not letting the prop go to the fine pitch setting. Also some governors have 2 screw like the one in the picture. Look around on the other side and see if there is a second one. This was the problem with my plane when I couldn't get the proper RPM with a new propeller/governor install. They fiddled with the governor for about 3 hours and several flights they then finally looked into the prop stop adjustment. Funny thing is when the Mx did the final run up it scared the S**t out of him because the plane was skipping forward forward even though he had the brakes on. Got to love 310 hp in a Mooney. 1 Quote
Shadrach Posted March 16, 2015 Report Posted March 16, 2015 I think I need a video for this! See illustration. While not a Mooney part, the principle is the same. Quote
Bob_Belville Posted March 16, 2015 Report Posted March 16, 2015 Be careful. Overspeed (10% or more) requires an engine teardown! Any overspeed is cause for corrective action and engine logbook entry. Lycoming Mandatory Service Bulletin # 369L. Quote
Shadrach Posted March 16, 2015 Report Posted March 16, 2015 Be careful. Overspeed (10% or more) requires an engine teardown! Any overspeed is cause for corrective action and engine logbook entry. Lycoming Mandatory Service Bulletin # 369L. I hate to be a cynic, but that SB looks like make work. I've not had any prop over speed events to my knowledge and it seems unlikely that I'd be ready to record the precise overage if it happened. Those of you with digitachs can pull the data. I do not think this SB is enforceable though it may be. What's interesting is that Lycoming has non-geared 360 varients that are certed for max continuous RPM of 3200, but one of ours would be subject to teardown at 2971RPM. I wonder how the hardware in the HIO360D1A differs in such a way as to let it run at 3200 continuous while ours require a tear down over 2970. Quote
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