ArcherIIDriver

Pictures are worth a thousand words, so I'll try to keep the "wordiness" down to a minimum (at least initially). Before everyone starts claiming that the prop-nut/jam-nut weren't tight...yes they were (using standard legnth box-end wrench...not a cresent or any other "short cut" method). They were even double & triple checked prior to this run. Front bolt was also tight...used the "tight as you can with only two fingers" method as described on TT's website, + a little more for good measure.

Equipment: Saito 125a, TT-2502-B-W spinner, TT-0825-A adapter, APC 16x6 prop (balanced)

Conditions: Test stand, finishing the break-in on the new motor (approx 1 gal total through engine), very low vibration, 1,800 rpm idle, 8,500 rpm wide open, varying speed throughout this 15 minute run. No backfire that I ever heard/noticed from approx 3 ft away, engine never gave any indication that it, or the spinner/prop was unhappy. Only discovered this upon shut-down.

What do y'all think? Anybody ever experienced this yourself?

I have e-mailed True-Turn to get their take on it as well.

ArcherIIDriver

A couple more pics...

blw

My Feedback: (3)

My 1.25 backfires so softly, you barely notice it. You really have to be paying close attention to even hear it at all. It doesn't throw props, but loosens like yours appears to have. I doubt I would hear mine 3 feet away.

ArcherIIDriver

Wow...less than 20 minutes and TT has responded to my e-mail...discussing my particular incident & not just a boiler-plate response. Very impressive service! They seem to be quite sure that the damage was caused by a small backfire, which loosened the prop just enough. Even though I never heard/felt a backfire...I know that it is possible. They claim to have seen this many times in the past, and feel that their product(s) did their job & held up better than most others would have. Unfortunately (for me) I tend to beleive them, and will just have to order a new thrust washer from Saito & a new spinner from TT...back out the needles (high & low) and try it again.

Feel free to repond with any experiences y'all have had similar to this & what you did to prevent it from happening again.

rcdude7

My Feedback: (264)

The threaded end of the crankshaft may have bottomed out in the spinner adapter. Even though the adapter was tight, clamping force on the spinner backplate and prop were not sufficent to keep the whole assy from spinning.

Did you take any measurements to determine that the threads were not bottoming out in the adapter?

ArcherIIDriver

Yes, actually I did measure for clearance. It is close, but absolutely not bottoming out. Now, the front bolt is another story...had to cut that one almost in half to get it to fully seat.

ArcherIIDriver

blw, could you expand on your backfires? Are we talking only at start-up, only @ low rpm, @ all speeds, etc.? 3ft away was the furthest I stood. Most of the time my hand was on the test-stand actuating the throttle. My statement of 3 ft was only a rough guess.

Thanks for the replys.

onewasp

Frankly it really boils down to "what was not tight enough i.e. holding properly" as a backfire is the obvious cause.

No criticism intended-----simply has to be!

ArcherIIDriver

Agreed. Something has to give, and I guess I would rather it be a thrust washer and spinner than some internal engine parts.

Hobbsy

My Feedback: (102)

PiperDriver huh, cool, I can say with all honesty that a Saito is not rthe only engine that can do that to a spinner backplate, my Fox .74 converted to Diesel and turning a Graupner 12x8 three blade at 9,000 rpm has done it to more than one. I just kept on using it the way it was.

ArcherIIDriver

Yeah, but with the $$$ of 100LL these days [X(], I'm not doing too much Piper driving[]

This was my 1st experience w/ an aluminum spinner in 15+ years of RC. Until now, I've always been too cheap...er...I mean..."price conscious" to spring for the good stuff.

I've already ordered a new thrust washer (drive flange) from Horizon and a new TT spinner from the LHS...just contemplating what I can do to reduce the occurances of backfires/kickbacks in the future.

Jezmo

My Saito 91 did it when it was too lean. (Before converting to spark ignition/gasoline) It would backfire and loosen the prop much like the pics. Most of the time it was obvious as it would die but there were a few times it kept running and I was lucky enough to hear a weird noise, stop it, and the prop would be loose. Each time it was just a little too lean. It still has a tru-turn on it as a gasser.

rainedave

My Feedback: (1)

I have been weening myself off of APC props because they tend to slip more often than wooden props and because I'm simply getting too much scar tissue on my "flipping" fingers. I can't hurt to try some wooden 16x6's.

David

ArcherIIDriver

Good point, rainedave. I use wood on most of my sport planes, and actually prefer wood...with the full understanding that they are less efficient than the APC design (at least the Zinger props that I typically use). Any suggestions for a good, high efficiency wooden prop in 16x6 or 16.5x5?

BTW, a good, thick leather glove goes a long way towards saving the 'ol "stick wigglers"

Iflyglow

My Feedback: (79)

Archer,
I have been pinning my spinner plates to the drive washer for many years. I learned this from a guy in my club who flew in Pattern competition for over 30 years. He was doing way back in the day with piped .60's all the way through current flying today. I myself do this on YS's, MAGNUMS and SAITO'S. Trying to tighten an aluminum knurled drive washer to a piece of smooth aluminum to me is not capable of transfering the load safely. (Went to school for Engineering)
(1 st step) I mark on the spinner back plate were I want the pin to be located in the prop driver.
(2 nd step) I then drill the spinner back plate with a Number Bit (decimal size) one size smaller than the pin (3/32 Hardened dowel pin) on the drill press.
(3 rd step) I now mount the spinner back plate on the engine and take the same drill bit and transfer the mark to the drive washer( do not try to free hand drill the hole).
(4 step) I remove the drive washer and drill it to the depth I want (usually about .125) on the drill press.
(5 step) I take the drive washer and drill it two number bits larger than the pin (couple thousandths larger).
(6 step) Press the pin in with "RED" Loctite.

WAHLA, I have never had the problem since. If it has to slip for some reason, it now has to slip were the prop meets the backplate, and not aluminum on aluminum.

I copy the spinner backplates from one to another, by inserting a piece of 3/8 stock (The hole size of a TT spinner backplate, no adapter) to stack two and transfer the hole. All of my spinners have the same exact hole, and all will fit any engine I own. I have 3 done now that are waiting for homes.

I have attached a couple pic's

ArcherIIDriver

MotorMan, thanks for the step-by-step and pics! Very interesting. I have heard of this being done, but never actually seen it. I'm no engineer, but I would think that adding a pin in that fashion would throw the crank out of balance...am I wrong??? Or do you somehow compensate for the additional mass through prop (un)balancing or some other means?

While I am unlikley to go that route, personally...I am very interested in your take on the balance issue.

Also, just as an ironic side note - both Tru-Turn and Horizon specifically advised me earlier today to never pin the back plate to the thrust washer...and I never even brought it up.

Upnet

My Feedback: (8)

Mine has done the same thing. But using a ball peen hammer and a vice.....you can get that spinner close...then put it on and make the final adjustment as you tighten the 10-32 bolt on the nose of the spinner. Wonder if Xoar makes a 16-6 prop?

LeeHop

Motorman -

Trying to tighten an aluminum knurled drive washer to a piece of smooth aluminum is galling!

liquid_TR

Xoar, MenZ, JXF, etc.. these are all high performance high efficiency wood prop mfgs.

I use their 15x6, 16x6 and 17x6 sizes exclusively.

ZAGNUT

My Feedback: (1)

i've used the pin trick many times on all sizes of engines but usually use two pins. can't see what's wrong with it as all you're doing is making the drive hub and spinner backplate into a single unit just like you can find on many high performance engines. horizon and TT are just covering their butts.

on big gassers i would even leave the pins protruding so that they would engage the prop as well.



dave

Iflyglow

My Feedback: (79)

I allways align the pin so that it is centered on the counter weight. You can never balance a single cylinder enough (counter weight is to small). If your engine has a woodroof key, you have to be more carefull as to were you locate the pin. Collet drives are the easiest but require a puller to remove (rotate the crank untill the pin is centered on the counter weight, IE counter weight and pin at the bottom and piston at Top dead center). The pin is also so close to the rotating axis that I have never noticed any problems at all.

The Super Tiger 2000, 2500, 3000 and 3250 had a cast drive washer that had two cast points on it.

TT and Horizon are also in the business to sell parts, and are worried about people doing '"HACK JOB" things that could compromise the integrity of there product.

You can use a Battery terminal puller, or a puller like the the one I have attached a link too.

You can continue to do it without and maybe have quite a few expensive lessons, or maybe luck out. I know how well it works, so I do not even think of doing it with out it. I have even seen it done with a piece of 1/16 music wire. You could also do it with two pins, but you would then need an indexing talble to make sure the holes are really inline, or your back plate will only fit in one position. IF the engine still has to slip for some unseen reason it can by spinning on the knurled surface of the spinner, but it will not wreck your drive washer at the same time.

http://www.centralhobbies.com/tools/tool1.html

Iflyglow

My Feedback: (79)

It is not galling it is scary, but the first time it slips it will be galling, and that is expensive.

ArcherIIDriver

Good point about the ST coming from the factory w/ the pin/spike. Both companies (TT & HH) cited valve train damage in the case of a abackfire/kickback as their reason for not pinning. I have to side with your (MotorMan's) original post stating that slippage can still occur, only now it would be @ the prop-to-backplate surface.

I do not understand how a knurled surface (thrust washer) mating to a smooth surface of the same material/hardness (backplate) can make a solid connection. [sm=confused.gif]When asked, TT stated that "It's incorrect to knurl the aft side of a spinner backplate when running a motor with a knurled drive hub as this would lessen surface contact and increase potential of the parts running out of square or untrue. In addition, you would never want to run drive pins, nor any type of locking pins in the thrust washer as this would do great damage to the valve train of the motor upon backfire."

Now, I do not personally agree with TT's "lessens surface area" argument...actually, I think that a smooth backblate would only be contacting the peaks of the knurles, resulting in the lowest possible surface area contact.

All of this feedback is great! I truely enjoy hearing/reading everyones take. Keep it coming!

NM2K

My Feedback: (14)

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I managed to remove the tip of my left forefinger and left thumb by going into an APC's rotating arc from the rear while the engine (HP .49VT) was at idle.

Yeah, hard to picture, I know.

Who would think that the back of an APC prop, spinning in the normal direction, would be capable of such damage? To be fair, I haven't tried it with other brands of prop, so I'm not nailing APC with any unusual behavior.

However, it did teach me that if one is going to use a sawhorse to hold the engine test stand, one must ensure that the sawhorse cannot move fore and aft when power is applied and then reduced to the engine. Be sure to put some kind of braces on the sawhorse to kill the fore and aft movement. Take my word for it, losing your finger and thumb tips hurts just as bad from either side of the prop.


Ed Cregger

Iflyglow

My Feedback: (79)

Archer,
What is the difference if the prop slips on the drive washer, or on the spinner back plate. The only difference is that you might be only buying the Replacement cone from TT, not the entire spinner, and drive washer from Horizon. You see, this is a win win situation for both TT and Horizon to recommend that you do not pin the assembly. In one way I can understand, and that being they do not want people doing something they have no idea how to do safely. Can you imagin some of the pic's that you would see.[X(][X(]

But like I said, I have never had a problem since. And I pin my friends engines too.