So small prop diffrence between .70 & .91?
 

Hi
I have an OS .70-fs II and I plan to buy an OS .91-fs II and have done some research here on the forum regarding prop sizes.

It seem that many people favor the APC 13x6 for the .70 and the APC 14x6 for the .91, I thought it would be a bigger diffrence on the prop size for these engines?!?

I like the power of the APC's but they're too fragile and I'd prefer the Master Air Screw for general sportflying/bashing.
Should I order 13x6 for the .70 and 14x6 for the .91 or do I need bigger/smaller since it's MAS and not APC?

Any comments on the MAS "K-series" props?

RE: So small prop diffrence between .70 & .91?
 

My favorite props for a 70 and 90 (FS) are a Graupner 12 x 7 and a Graupner 13.5 x 8

If you're using a Master Air Screw, go with a 14x8

RE: So small prop diffrence between .70 & .91?
 

Should I understand your answer like this Minnflyer:
70-fs: APC 13x6 / MAS 13x8
91-fs: APC 14x6/ MAS 14x8


(I have a graupner 11x6 on my TT46-pro and it's dent and bruised but refuses to break even after numerous ground hits. It's great!
I put an APC on the 70-fs and broke it immediately after slightly touching the ground on landing. Great performance but not sturdy enough IMO.)

RE: So small prop diffrence between .70 & .91?
 

MS 15x6 for initial breakin. Had it in a GP Extra 300S. Went to APC 14x8. Big time difference. Vertually unlimited vertical.

RE: So small prop diffrence between .70 & .91?
 

IMO an 11x6 prop is a little big on a TT pro 46. Also if the prop is all dented up it may need to be replaced. First of all if it is out of balance it could damage the motor, second if it is dented up it could break it use... not a good thing.

Also, how is your prop setup. When the engine is not running where does compression start. The prop should be at about 2 o clock. I was breaking a bunch of props until someone told me to do this. Now I never break props.

RE: So small prop diffrence between .70 & .91?
 

Hello!
If you use the old gray Graupner props they are not particularly good...not compared to APC or the new black Graupner Cam-props.
11x6 is a good size for a 7,5cc engine (.46) but do not use Master A props... they together with the gray Graupner props are the worst props on the market as they are loud and don't pull as good as APC props.
As for a prop for a 15cc engine...well a 14x6 APC is a good prop/size but for a slowflying airplane a 15x4 or 15x6 APC could be used.

Regards!
Jan K
Sweden

RE: So small prop diffrence between .70 & .91?
 

It's the gray Graupner I have on the TT, It's ok because the plane is so light and the engine pulls it around just perfectly.
I have had many APC props and I know that they produce great power.
I guess APC and MAS is a tradeoff between durability and power, I choose durability as planes anyway tend to be overpowered for anything else than advanced aerobatics & 3D flying which I don't do anyhow.
After takeoff I usually fly around at half to 3/4 throttle and have little use for the extra thrust an APC would provide.

I think I'll order Master Air Screw K-series, 13x8 for my .70fs and 14.8 for my .91fs....Sound reasonable?

RE: So small prop diffrence between .70 & .91?
 

I'm sorry, but you guys can praise APC's all you want. Give me a grey Graupner anyday.

TEST 005, I would go with a 12 x7 MAS on a 70

RE: So small prop diffrence between .70 & .91?
 

MinnFlyer: 12x7 is not available from Tower, OK if I go 13x8 for the .70 and 14x8 for the .91? (All MAS K-series)

RE: So small prop diffrence between .70 & .91?
 

Minn to answer ur Q here are the prop sizes for both the 70 and 91 surpasses, i have 4 of each of these engines and run ONLY Gruptner or Master airscrews on them


70 == Gruptner 11/11 through 13/6 best overall prop == 12/8
Airscrew 12/6 through 14/6 best overall prop == 13/8 or 14/6

91 == Gruptner 12/11 through 14/7.5 best overall prop == 13/7.5 or 13/8
Airscrew 12/10 through 15/6 best overall prop == 13/8 or 14/6

P.S. those APC'S are junk! nick the tip,toss the prop away. I'll keep my Gruptners and Airscrews!!!!!

RE: So small prop diffrence between .70 & .91?
 

msry for typoe error best overall prop for the 70 in airscrew is the 12/8 or the 13/6

RE: So small prop diffrence between .70 & .91?
 

There you go Test, clip 1/2" off eash end of those 13" props and you'll have a 12x8

(Do a quick balance afterward)

RE: So small prop diffrence between .70 & .91?
 

This is so confusing because I get a bundle of diffrent answers.
I'll get 13x6, 13x8,14x6,14x8 and make up my own mind.

I thought there were some general rules/preferences, but everybody seem to have their own theory on prop-sizes..

One question though:abacro How can both the .70 & .91 have the same "best overall prop"??
It just doesn't make sence, then it's no reason why I should pay another $50 for the .91 if it swings the same prop as the .70??

RE: So small prop diffrence between .70 & .91?
 

Test, read his second post, he corrected the error