I was given a stunter without a motor that originally had an OS 45FSR in it .  Went thru my stock of motors and nothing matched
the mounting bolts. Then a friend offerred me an OS 46FS that was set up by Tom Muggelton and it fits the plane well . What are the differences in these motors in how they run .
      Bill

  Thanks Pete  for the info  and yes your right the .46 is an SF not FS . I was given an "Arabesque" stunter and it's in great shape  but
 nothing I had would match the bolt pattern .  The .46 SF fits but had to open the cowl a bit . Anyway I have been told that the Muggelton .46 SF likes to run in a fast four stroke and produces Lot's of torque . Looks to be a good combo !
    Bill

Thanks for the straight info Randy. That 11x4 prop I mentioned on the FSR may very well have been a 12x4. At any rate, I remember it running fast but delivering a good stunt run.  

   Sounds like I need to get some 12" props with a low pitch  .
   Thanks guys ,
                      Bill

     Today I was able to get a couple of flights with my Arabesque powered by
 a borrowed OS .46 SF . Like I said this motor was modified by Tom Muggelton . One of
the mods he did was a button head , the changes seemed to have made the motor like to run
 at a lower RPM. First flight with a Thunder Tiger 11 x 4.5 launch RPM was 9200 and the 51 ounce
Arabesque was turning roughly 5 second laps . Motor was producing lots of power and breaking into
 a two stroke when the nose was lifted  . Second flight turned into a run away , traced when I got
 back home to an air leak in the tank . Need to do more testing but I am impressed
so far by the motor plane combo .
              Bill

Inddedie , young Bob hunt started the FSR trend , FSR .40 , with a 11 x 6 EW THREE BLADE to ' tame ' it .
A coustom prop. dunno about the pitch. The " E.W. " ( extra wide ) series of  props appeared as if say two
inches over cut and reshaped.
Yatsenko props have ' a bit ' of blade area . too .

Hawker ' Sea fury ' used 5-blade prop to get enough BLADE AREA to absorb HORSE POWER on take-off, without
the torque reaction of the massive 4-blade, of a manadgeable degree , at least .NOTE ; it is the " Blade Area "
used to absorb "the Power ", of course their pitch is variable, set FINE for Takeoff at Max. H.P. / r.p.m.s to
drag several tonne of 'stores' of deck , without the aeroplane rolling around the propellor , ON acceleration .
Though with the Catapult its thrown clear and past the ' critical effect ' area; where the tourque reaction from
ACCELERATION  would be unmanadgeable AT full Throttle . Ordinarlly on an airfield the throttle is PROGRESSIVELY
increased , and not 'at the stop' untill the aircraft is airbourne and ' clean ' (gear and flaps up).
Lancasters ( multi engine ) throttles were advanced assymetrically to hold aircraft straight .
This ' digression ' illustrates that theres one or two forces at work , relateing to model A/C .

11 x 6 E.W.s sorta work on a G-51 , TWO 11 x 5 Zingers get about the blade area of a yatsenko ,12 x 5 ?? .

Some were trying 13 in on the .40s , the Dia of a ST 60 prop , with a bit less pitch .Wide props not Tooth pick's.

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Other ' boogie ' was speed up with engine heat. Often a few ducts / tubes were fitted directed at Crankcase.

Was stated Revs would increase as temp came up on ground, A few laps after release the cooling had taken effect and rpm's dropped to that set.

Someone stated recently FP runaway is Temp related, maybe a peculiarity of Schneurles ?

Note; info garnered armchair potatoe mode, generally. I have a FSRS .40 , Feed Pipe Bore Dia  was ' an issue ' with this. (was caught out with undersize thick wall 1/8 pipe,
leaning out @ 1/2 cirle hight.) Otherwise good steady speed run even in semi gale conditions, 12 x 5 min. prop was minimum to stop revs ' bounceing and holding  ' .
Have the 13 x 5  Zinger I used with back of tips rounded , (full L.E. length ) .

Or in short, as Randy says ; put a bit of propellor on it , please .

Just checked, current prop I'm using on that engine is an APC 12x4. Turns it with ease at a pretty high RPM. 

   Pete  my .46 SF  does not like high RPM's , tested on the ground it's turning a  TT 11x4.5 at 9200 RPMs .
The original owner of the motor ran it a 4 stroke mode with an 11x4 . My guess is that Tom Muggelton
modified so it runs a very strong 4 stroke mode . Still plan to do more prop testing .
                          Bill

I have an OS 45 with a stamped F.  The cast circle under the exhaust only has room for the 45F.  Is this the same as the OS 45 FSR or other?  It is a plenty strong engine.

Surging in the .46SF can often be traced to the trick looking but hard to seal stock 90 degree spray bar assembly. Very prone to air leaks unless major effort is made to tighten it up. A PA or ST NVA will cure that issue. Can't do anything 'bout the weight though.