Introduction and Engines query

[Simon Lumsdon 1]

The Cougar is flying well (or i am improving), have increased throws to 50% and the FP40 is well suited to the model, starting to get my confidence and started to hoon it around on full power today In hind sight suspect issues were all flying related, c of g, throws and engine are all fine. Adding some circles to the top of the wing is a good shout, it does seem easy to get disorientated with this model, someone commented the purple doesnt help either, although that may also just be inexperience..

[kc]

Note that the original OS 40 FP benefits from a large diameter prop such as 11 x7 as it won't rev but does much the same revs on an 11 x 7 as on a 10 x 6 ( see engine tests of the time it was first sold) Later OS40FP had different piston and liner I think so it may not apply to them but worth a try.

So when you need more power try an 11 x7 - if the u/c gives enough clearance for the prop

[Martin Arnold 1]

"If I could find a four stroke to do it justice"

Several of us at my club have been running 4 stroke Cougars for years, powered by OS 52, Saito 50 and 56, the Saito powered ones are arguably the best as the Saitos have a sharper throttle response (most important on a Cougar) than the OS 52, there is not much difference in weight between the three they are all around 450gms with silencer.

Mine is the one with the Saito 56 on an APC 12.25 x 3.75 funfly prop, it is pulling 11900 rpm flat out (usually only used in the vertical) which makes for an impressive thrust to weight ratio. The plane is 3lb 10oz all up and those figures give 9lb 7oz static thrust !! With a top speed of 42 mph.

The point with a Cougar is not to let it fly too fast they are likely to self destruct with surface flutter if you over speed them, so I would keep away from props with too much pitch.

The thing I like the most about my set up is the instant knife sharp throttle response and grunt from the Saito, which most 2 stroke can't match also the 4stroke gives good engine braking to slow you down.

P.S.

I spend a lot of time setting up the motor for perfect transition and good idle as particularly on a Cougar the throttle is a primary control !!.... It will get you out of all sorts of trouble

 

Edited By Martin Arnold 1 on 30/09/2020 10:58:08

[Nigel R]

"The Cougar is flying well (or i am improving)"

Good stuff

"Later OS40FP had different piston and liner I think so it may not apply to them but worth a try."

I have two of the later version FPs.

Both will spin a 10x6 APC on any given day at around 11,500. I have seen near 12k for the odd peak from the (ever so slightly) stronger of the pair on the right day with all the moons in alignment etc etc. I recorded the 11x6 APC turning at a hair over 10,000. I use 5% Weston synth fuel and Model Technics warm plugs.

I would say the 10x6 is not ideally suited to the Cougar. A lower pitch would be better, say 11x4, which would provide more thrust at the low speeds the Cougar flies at.

[Simon Lumsdon 1]

Many thanks for the feedback on props which is interesting. The OS40FP runs well and is mostly reliable but cant be fully leaned out, never really comes on song which suggests a finer pitch prop might help? Throttle response is not amazing either so will try suggestion of 11x4 instead of 10x6

Have also moved c of g back a bit after mentioning rolls caused the nose to dive, which improved things. Starting to enjoy the model as i get more experience with it. Have now finished a Wot4 with os52fs which will be an interesting comparison, just need the weather to improve now!