Posts: 6736
Joined: 12/7/2001 From: Andover,
MN, USA Status: offline
This is APC's suggestion:
Racing Props
8.75 N,W and 8.8 series 40 Pylon props Maximum RPM=225,000/Prop diameter (inches)
Also, from APC"s site (and there is a lot more)
Ideally, a product can be designed with credible knowledge of the environment (loads acting on the product) and capabilities of the product to withstand that environment (not fail). There is nothing ideal about designing a model airplane propeller because some major components of propeller loads are very uncertain. The principle load components acting on a propeller are:
Centrifugal (from circular motion causing radial load) Thrust/drag (from lift and drag acting on blade sections) Torsional acceleration ( from engine combustion and/or pre-ignition) Vibration (from resonant frequencies or forced excitation) Another potential source of loading is aero elastic tip flutter. This may be caused by self exciting aerodynamic loads at a resonant frequency.
Posts: 754
Joined: 1/3/2005 From: mather,
CA, USA Status: online
Ok, I cut down a 8.8 X 9.25 to 8.5 diameter and it still broke. So I put on a 8.75 X 9.25W (bottom prop) and it broke too. Yet a 8.8 X 9.0, 8.75 X 9.5 NN or 8.8X 9.75 will not break. I’m almost positive I heard the props tips let go near the bottom of a shallow dive so it’s not a change of direction that triggers the event. It must be harmonics + RPM that causes it to happen. The 9.25 pitch was the fastest prop……before it self trims. The fastest prop that stays intact is the 8.8 X 9.75. I’m waiting on some 8.8 X 9.5 to try.
The used OS 46 VX DF engine now has 2 gallons that I have put though it, this doesn’t take long when 8oz lasts only 2½ minutes at WOT . The engine still has some pinch at the top with the glow plug out and cool. It’s not a finicky engine, starts, idles and runs great. I lost some glow plugs due to vibration/foaming (ya-think? ) so ran out of OS# 8 and found that K&B 1L’s and Fox standard /long’s worked just as well and within one or two clicks of the #8. My YS 45 is very picky, it wants OS #8 and won’t run for beans on a Fox standard /long.
The real good news is, I think I have the hand launches down real good on this heavy, torquie clipped wing devil. I’ll wait for no wind condition launches to confirm it.
_____________________________
When in doubt, give it full power. The smaller pieces fit easier in the bag! Revver Bro #201
Posts: 754
Joined: 1/3/2005 From: mather,
CA, USA Status: online
I can’t quite tell what your prop shaft looks like, but normally you use a short shaft adapter (Tru Turn part number TT-0141-A) for props. Ream out the prop to fit the adapter’s OD. On the back side (engine side) of the prop's hub (APC), there is a .375 diameter counter bore, this is your true center pilot diameter for your reamer. You should pre-drill the hole .020"to .040" smaller than the reamer first. Stone/grind the lead/hook off the drill flutes just a touch to zero so the drill won’t grab or dig in. To keep the hole strait this should be done in a drill press or mill using a VICE, NOT YOUR HANDS. I like to finnish it off by reaming a clearance diameter about +.010" half way through from the front. Practice on those broken props I know you have hanging on your wall They do sell little stepped hand reamers, but half the time they tend to run too far off center for high speed apps and take too long to do. Balance when done.
This is only safe to do to large hub props like APC pylon(D-1) or carbon.
Good luck.
< Message edited by freakingfast -- 5/29/2008 7:16:17 AM >
_____________________________
When in doubt, give it full power. The smaller pieces fit easier in the bag! Revver Bro #201
Posts: 754
Joined: 1/3/2005 From: mather,
CA, USA Status: online
It looks like it uses a split cone/collet drive and this needs to have a fan or prop tightened before the prop driver will clamp to the crankshaft. I don’t know if it’s an easily doable prop drive. That extension sure hangs out there to clear the carb, I wonder if you need it? And you may not need a short shaft adaptor if you can do without the extension.
< Message edited by freakingfast -- 5/30/2008 4:38:37 AM >
_____________________________
When in doubt, give it full power. The smaller pieces fit easier in the bag! Revver Bro #201
Posts: 4455
Joined: 10/18/2002 From: Rome,
NY, USA Status: online
IIRC the prop should just barely clear the carb without the extension ( gonna haveta check one of mine just out of curiosity ) and FF is right about the collet, all ya gotta do it put a prop on it and tighten the nut and you'll be able to turn it over.
If not, just get a longer stud and use the extension. The prop stud is your standard 1/4 x 28 so you can get an all threaded 1/4 x 28 bolt and just cut it to whatever length you want/need.
< Message edited by proptop -- 5/30/2008 9:28:22 AM >
_____________________________
It's bad luck to be superstitious... Revver Bro #77
Posts: 754
Joined: 1/3/2005 From: mather,
CA, USA Status: online
Discovered more power! In a glow plug of all things. I was using mainly using OS #8’s, K&B 1-L and Fox standard Longs. The Fox worked once the engine had been running but otherwise they are too cold blooded. The K&B seemed to be a tad better than the others, so I sent for some, and while I was at it, I got some K&B HP longs P.N.7300 (good for ducted fans and 30% or more). I tried the HPs and got a surprise in the air, much more unload with the 8.8X 9.75! The new speed is harder to control; the roll axis is twitchier. I’m already at 100% expo so I may need to drop the rates a bit. The new plug was wanting it richer by a quarter turn so my flight time is less. When the timer goes off at 2 ½ minutes, land! No cool down laps.
The bad news Now this prop is throwing tips in a dive after about 10 flights with the new plug. I used a cut down prop 8.5X9.75 with about the same speed and so far so good.
The news gets worse Thrown tips, imbalance and subsequent lean outs took it’s toll on the main bearing. Two of the balls started fretting (flaking) and small pieces knocked out glow plug element, mercifully killing the engine. The top of the piston and the bottom of the cylinder head button look like they were sand blasted. There was very little scoring and the compression is sti
Printable Version
All Forums >> RC Airplanes >> Extreme Speed Prop Planes >> RE: 8.8X9.75 @ 19,300+ ! 
RE: 8.8X9.75 @ 19,300+ ! - 
...a superior power is trying to tell you THAT is the diameter you should be using.....
) so ran out of OS# 8 and found that K&B 1L’s and Fox standard /long’s worked just as well and within one or two clicks of the #8. My 
