AndysAtCoffs

Forgive me father have I sinned? Its been many days since I made my lastlast NES post and I was a tad over exuberant. Never mind enthused Cappy...lets get back to my confessions...... This may take a while......

determine if the afore mentioned 50cal could be used as a "Duct Off" control.... Turdy quickly realised that the 50cal patented "Duct off!!!" was a single use control, requiring you to be 100% certain that youd never need "Duct On" ever again.....and even then you needed to be a good shot....... If you were merely an average shot then it became more of a MOA off control, as previously described. If you were a bad shot then it was simpler to list it simply as an "Off Control" cause the list of things a 50 cal could turn off was extensive.... After Turdys extensive testing Captain was heard to mention that Turdy was capable of turning things off at a much faster rate that he was of Turning them on.... and that in most cases the off device was now r@@ted..... "Meanwhile after a 13 second radio delay the C130 Captain yelled that maybe the 50 cal was his only hope of preventing an incursion into uncleared space.... with some trepidation Turdy turned the 50 cal towards teh C130, noted that the 8-mile tattoo would need an update if he was successful and....

someone working on a duct stimulator. Duct stimulation in the natural MOA was entirely the purview of the MOA, but when it came to mustering a MOA with no external duct control seemed less than ideal... Captain was heard to say that if the MOA couldn't be reliably forced, through an enhanced control to emit flames from its orifice then the difference between a slow land speed record and flight seemed an impossible chasm!!! So soon it came to pass that an enhanced control that could "turn on" the duct operation was found and quickly applied with liberal use of the aptly named duct tape........ but as can be seen above in captains C130 photo where the crew, had gear down due to their expectation that they should be at circuit height and turning final shortly, but in fact as the photo shows that were about to pierce the atmosphere/space boundary found themselves needing duct tape to stop the smelly stuff from floating around the cockpit as they rapidly flicked page to page in their "C130 Crap has happened" (C130CHHM) manual to determine what the best way to return to atmosphere was for a c130 that inadvertently found itself in desperate need of a a duct off control...... The captain of the C130 was heard to ask, does Bernoulli even apply is space?? and at teh same time introduced a boot full of right rudder, so that the skid marks left weren't only in the underwear of said crew.... Meanwhile Turdy...who was heard sniggering...duct off to......

I agree with you Nev....smoothness introduced through a dynamic balance is just that and nothing more, smoothness contributes to ongoing wellness but if something was unwell to begin with then your simply masking it until the next degradation occurs....and it will

the other issue with an extension shaft is that generally, in the ones I've seen, there are 2 flat plates that are bolted together with the engine/gearbox output flange with 6-8 bolts around the circumference, and the prop at the other end. They are supposed to be made so that the plate on the engine end, and the other are at a perfect 90 degrees to the shaft (and so perfectly in parallel to each other so that when everything is bolted up and you look for run out by spinning the gearbox/engine and measure at the haft as far away from the engine/gearbox as possible you don't see any/very little which means the surface was at that exact 90 angle all around. If there is any introduced runout because of a manufacturing defect or the uneven bolt tensions have pulled the shaft away from its center position then no matter how good the static balance the shaft at speed will introduce a vibration because its center of mass is no longer in line with the output shaft of the gearbox/engine. If the runout cant be Zero'd with bolt tension variations/adjustments, then a dynamic balance can help counter the vibration but to me that's a bit lipstick on a pig..... swap out the pig.... At least thats what Id do....YMMV

Not at all...I was poking fun at Turbo....not you...

I reckon CASA would love that, at least their enforcement and legal sections👮‍♀️!!!!..... Not sure that Turbo would silly enough to do that in a public forum 🤣 Nor me!!! for that matter Sorry!!! back to seriousness now!

Nev, The Accelerometers included with these balancers are sensitive devices but in my experience work best when you are at or near to intended operating speeds. a tiny (barely evident) vibration at slow rotational speeds uncorrected can become teeth rattling at higher speeds. An accelerometer, that is fit for purpose, has no issues sensing "Teeth rattling" but may well struggle with slow and barely evident vibes at low speed. In my limited prop balancing experience, you want to dynamically balance at the speeds your going to have your props spend most of their time at. Also while defining job realities... A dynamic balance can imho absolutely fix vibration at any one speed...it may, however despite being smooth as silk at that one speed be a complete disaster at another speed if you haven't first statically balanced. So when you intend to dynamically balance always statically balance first. Manuals on prop balancers cover this in detail...usually Andy

Oh yeah should have added that there are some practical limitations as to how you would balance such a config. The accelerometer has to sense at the point where the extension is bolted to the gearbox/direct drive shaft and then at the opposite end of the shaft either at the front of the prop, or if it was a direct drive engine at the rear of the engine. If there is a reduction gearbox involved then the rear of the engine is not a viable measurement point. In such a case you may be better removing the extension and prop and balancing on a purpose built balancing rig..... that'll be cheap to create and be done in an afternoon....not!! Also worth noting that you need to do dynamic balances at the rotational speed you intend for the device to work at....so a balancing rig will likely need the same input power as your engine is capable of producing but be direct drive and not through a gearbox...at least not where the accelerometer measurements are taken.... alternatively balance the prop extension on its own using a 2 plane balance at the cruise RPM you want and the prop separately and hope that mating them together maintains the extension shaft balance. Ive done lots of 2 plane balances over the years, so much so that we provided balancing to other users of big rotating devices....There's defiantly science involved...lots...and to many mechanics and owners of machines it was all simply magic!!!! one day a machine might take 2 hours to balance...teh next day a similar machine might take a day and a half...... why??? magic!!!

Hey Guys...Ive been off site for a long time.....but reading this thread I feel I can add to it in a hopefully positive way. For a number of years Ive worked for a local contracting company that manages tree mulchers, those huge beasts that have a 1200Hp cummins KTA Diesel engine and a rotating drum with big teeth that would happily get rid of the average human in about 1.1Seconds. Anyway, interesting thing is that those really big heavy drums with teeth all over them when they spin need to be balanced.... Any guesses as to what we use to balance them.... Yep a smart avioinics PB-4 prop balancer...the major difference is that the test weight can be up to 1Kg in weight......don't recall needing that much test weight on a prop but. I guess if your way out of balance....... And the other major difference is that a drum is not really like a prop in that a prop is really considered to be a spinning disk which is in one plane.... A drum is just a really long shaft which is balanced as a 2 plane balance where weight added to one end obviously affects that end but also affects the other and vice versa. The smart avionics PB3 and PB4 balancer has a module added to it to allow 2 plane balancing. Why is this all relevant here.... well you guys have been talking about extensions being used and props sitting on the end of teh extension. IMHO that turns a 1 plane balance using any prop balancer into a job that requires a 2 plane balancer. Is it possible to balance out all vibrations in a 2 plane shape with a 1 plane balance...Nope not at all possible!!!! I know cause I worked with the SmartAvionics guys to test the 2 plane balancing module which had never been used before. Up until I did that I tried for days to balance a drum with a single plane balancer. I could get one end perfect but the other end never could be perfected until we changed over to 2 plane. So I'm guessing that you may solve the vibration issues if you balance the prop and the extension shaft using a 2 plane balancing method. This will result in correction weights being added to the prop and the end of the shaft that connects to teh engine. I don't know that as fact that this will solve it but it may be worth looking into.... Here's the manual from SmartAvionics that talks about the PB4-Balancer. Have a look at pages 57 through 61 especially teh diagrams showing situations where a 2 plane balance is required and see if in your mind it fits the scenario described? https://smartavionics.co.uk/pb4/pb4_ui_manual.pdf Regards Andy