sw74gls

Hi Guys I originally bought a PAW 55 Diesel Engine in a model FF from the BMFA nat's in august and it came ready to go including Master Airscrew 7x4 I had the prop off several times and noticed it was a nice tight fit, However I had a slight mishap and broke the prop in the process so I went and sourced a new Master Airscrew 7x4 only to find the centre was slightly larger?? So I then purchased one after another a Graupner Super 7x4, Yellow Kavan 7x4, APC 7x4, unbranded wood 7x4, and finally a unbranded plastic 7x4 prop all of which the same the centre is slightly too large?? Am I missing something here ? I would be grateful for you advice, Thanks again Simon.

controlliner

The prop would have had a bushing in it for the small dia. crank shaft thread.

ffkiwi

You can use a piece of suitable size fuel tubing as a prop bushing-or use some telescoping pieces of K&S tubing to make up a bushing. Of course if you have a lathe or access to one, then you can machine up a custom bushing from ally, brass, nylon or delrin. As regards props for the PAW 55- 7x4s work quite well for sport use-but if you want a bit more power you can use a 7x3 (the Master airscrew one is especially good on 0.5 diesels!) or a 6.5x2.9 APC....or to squeeze every bit of power out of it a 6x3 or 6x4 [it peaks at ca 12,500rpm-so there is no point in propping it to run faster].....note that it will get a bit 'snappy' to start on the smaller sizes...!

ChrisM
'ffkiwi'

sw74gls

Hi ffliwi I did what you said and used some small Dia Diesel Fuel Tubing and the prop fits perfect problem now solved, Thank You very much for your help and advice!!

ffkiwi

Often the simplest answers are the most useful....and this one works out on the flightline-where lathes and metal tubing can be a bit hard to find...!

'ffkiwi'

buzzard bait

Why all the 7x4s? I found a Rev-Up 7x3 was excellent on this engine. I believe APC still makes a 7x3. I thought a 7x4 was a little too much prop for it. Yes, it will swing it fine, but it makes more power with a little less load.

Jim

fiery

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buzzard bait

Yeah, depending on the type of plane, either 7x3 or 6x4. Turns out MA and APC both make 7x3s. You probably won't have a problem with the hole, certainly not with a 6x4.

ffkiwi

The MA 7x3 is a much better choice than the APC 7x3-the latter is a lot more load-and these wee ones do prefer to rev. There is also the narrow bladed 6.5 x3 Master which allows it to really turn up.......

ChrisM

buzzard bait

I think it's good to remember that the 55 is .033 cu. in., or 2/3rds of an .049. So even though diesels are famous for swinging larger props than glows, the props mentioned above, MA 7x3, Cox/MA 6x4, MA 6.5x3, are still large compared to what you'd use on a .033 glow. I use a 7x4 on my PAW 100; I think it's really too much for the 55, for most purposes. Jim