OS MAX 35AX

[Pilot Ben 28]

Hi All I've got a 35 strapped to the front of my beloved cougar ATM, and all is going well which is surprising considering it's me, apart from the power I'm getting from it.

My last cougar had a 36 and ran an 11x3 prop and could prop hang at 1/2 throttle, and my current cougar also has an 11x3, but yet I'm prophanging at full throttle with no reserve power. I don't think the engine is too small as I've seen the 35 pull up quite a few funfly planes vertically yet mine won't really go vertical at all.

Any suggestions as to what prop to go to? I considered a 12 but I don't want to over prop it. What difference would going down to a 10 make? Should I increase the pitch?

http://www.osengines.com/engines-airplane/osmg0545/index.html

OS say an 11x6 or 12x6 but is that what I want for a funfly plane?

 

cheers,

B  

Edited October 2, 2017 by Pilot Ben

[Bravedan 106]

It's an imprecise process, getting a prop right.

Firstly, what fuel are you using?

[Pilot Ben 28]

I'm using Weston pro synth 2000 with 5% nitro 

Edited October 2, 2017 by Pilot Ben

[Bravedan 106]

Now, I'm certainly not experienced on OS, in fact I have spent a lot of time very actively avoiding them, as I consider them over rated and over priced.

However, MY Cougar 2000 with an Irvine 39 (THE fun-fly competition used by most of the "names" a few years ago), runs on an APC 11x5, so their smaller 35 on 11x6 or 12x6???  REALLY!!??

[Bravedan 106]

So, to summate, I think you need to try to generate a little more power and increase the pitch a little.

1. Use a higher nitro content, at least 10%. personally I would not try anything else till this done.

2. 11x3 is very low pitch, so when it is prop hanging it might not have the pitch "grip" to drive it out even if it does have the power (is it screaming or sagging, you don't say?). Once on the higher nitro content, try a 11x4 or 11x4.5

Fun Fly is much like indoor 3D, you need the ability to put lots of airflow over the surfaces when airspeed is near zero, so head for the largest diameter and lowest pitch the plane can cope with, consistent with it not losing grip in high alpha and of course prop hang. You are aiming for fast throttle reaction and lots of airflow from as low as possible in the rev range while not stifling the top end.

[Pilot Ben 28]

Right so me being an idiot what effect will raising the nitro content have as regards to the engine etc? Would I need to swap back for summer or can I use 10% alll year round? Would I use 10 for all my engines?

Thanks Dave

B  

[Bravedan 106]

Nitromethane is an Oxygen liberator, it makes the fuel element of the mix burn more efficiently, More bang, more thrust.

Now I'll jump to the last question, a few engines are abnormally nitro sensitive, There used to be all sorts of internet fights over Just Engines products suitability for example. MY personal view was that they were covering a potentially poor setup with a cautionary limit.

Generally 10% is not normally regarded as high or requiring special adjustment, but some engines do not like higher percentages than that. For example the TT Redline Helicopter engines I use (and highly regard) have an extra compression reducing gasket provided for "high" nitro use. Never used one, never needed it, never had an issue, even up to 30%!!

SO, to answer that last question, I can't!!!  ............ c'mon be reasonable, I have no idea what engines you have other than the 35AX nor would I necc be able to say with certainty how they would run even if I knew the model and make as not knowing age, previous use/abuse, whether they have suffered lean runs, what temp they run due airflow (cowled) etc, etc, etc!! 

Is Nitro weather dependent? No.   But.............. it makes an engine work harder to produce more power, and if that engine gets too hot, just like any other use, naturally it could be damaged.  No surprise there.

As an aside, a couple of years back I was given four early 70's Enya engines, and after bench testing (on 20%), contacted the donator, who's comment on me saying that they worked excellently idling perfectly from the first spin (I NEVER flick start!) was to reply that they were probably too scared to do anything else!!

 

[Lofty 5]

APC 12.25x3.75 is what I used on my OS 32 SX, with 10% to 30% Nitro!

I've had a few OS AX engines, and didn't think much of them vs SX / FX range! "Same can be said for the Alpha f/s range as well!"

 But having said that, the OS 75AX & Alpha F/S 56 were great!

The only problem now with using higher lvls of Nitro, is the cost!