SCEN Puma 3

[Nigel R]

Maiden flight today

No aileron or rudder trim needed. I did need a bootful of up trim - more on that below.

Flies big figures nice and smooth, and does lovely axial rolls (from what I can see so far) so thumbs up for that

Plus, it looks ace with gear up on a low pass.

At height, I could get it to go quite slow with some up held in, and a touch of power, without tip stall - which is nice.

So, a few teething troubles to sort out;

The engine is still not quite 100% - I've had trouble getting it to run consistently with nose up, it was leaning out something rotten to begin with. I swapped the needle for a second one and stuck some fuel tube over the neck to make sure it's sealed, and it is much better, but I didn't get it quite set right today - some drop off in vertical & upside down. Idle still needs a tickle to get a good reliable low idle and snappy transition.

I can't land. Which is annoying. This thing is kind of slippery, the landing strip was apparently one third of the usual size, the fence I had to approach over had doubled in height, and on top of that the idle wasn't set that low. At least those are my excuses for not dealing with the slight crosswind properly - *every* *damn* *flight* I stuck it in the long grass the far side of the strip (but right in front of me), twisted the nose wheel round, and after the third arrival, I noticed that I had also tugged an aileron loose (!) somehow.

Wing incidence is too low - somehow I've managed to sand in some negative incidence, which leads to a lot of up trim. And it was mighty hard to unstick on take off - I thought I was going to run out of runway, had to give full up to get it to lift off and go. Probably need to lengthen the nose leg an 1/8 if I can, too.

[Denis Watkins]

If you have an 11 x 6 in your box, try that

As the lack of low tickover maybe carrying you along preventing landing.

Retune top and bottom needle on the 11 x 6, and aim for 2200 - 2500 rpm tickover

[Nigel R]

I think I have an 11x6 available. Definitely worth a shot.

[Jonathan M]

Old thread I know Nigel, but enjoyable to re-read none the less!

 

Did you get the issues sorted - wing incidence, finer pitch prop, engine fettling, etc - and how's it been since?

[Nigel R]

Hi Jon

I did get a few of the issues ironed out before winter, but the next spring i was given a well sorted chilli wind, and I ended up retiring the puma.

 

[Creative RC]

Hi Nigel, 

 

Thanks for having posted this build.  I have the same SCEN Puma 3 Kit with the low mounted wing as well which I bought from a fellow in Florida as far back as 2016, maybe earlier.   

 

I will be referring to this thread when I do get to building it.  I will be converting the build to electric power and may very well put in electric retracts seeing that you were able to put in mechanical ones.  I see from the photos that you changed the appearance of the vertical stabilizer, will have to read further to see why you did so. 

 

Did you try flaperons to assist with slowing up the landings?  That helps with some of my planes. 

 

Did you add a spacer at the rear mount to deal with the negative incidence?  What positive incidence is needed on the plane?

 

Did I read correctly in your last that you lost the Puma due to a mishap?

 

Thanks for your reply. 

Edited November 7, 2022 by Creative RC

[Nigel R]

Hi Creative

 

In order...

Fin/rudder shape - no real reason I just fancied reshaping it.

Electric retracts would be loads easier, especially with electric motive power.

I never tried flaperons in the end - although I did get the idle sorted and landing speed ceased to be an issue.

I fixed the negative incidence with silicon sealant. I used some plastic from the covering film to stop the goop sticking to the wing. Just bolted it on with the TE about 1/8 away from the saddle, if I remember right.

Puma is still with me, but it now collects spiders in the loft space. I might resurrect it one day, who knows.

 

If I was building it again, I'd most likely stick with the unmodified low wing design and use a fixed gear install - it would make a nice all year hack in that config. A grass strip in winter and retracts don't mix so well.

[Creative RC]

 

A club-mate, Hugh, is building the SCEN Puma III for me and thought I would post some photos in this thread.  We plan to have it completed for a maiden flight in the spring of 2024.  It will be powered electric with the option of using a Power 32 or Power 46 motor as the X mount is the same size for either motor.  We will likely try it out with each motor before settling on a power setup.  The battery bay will accommodate battery sizes from 3300 3s to 5000 5s depending on the motor used.   It will have fixed gear.  The low wing will be built stock but with the lowest recommended dihedral, maybe less.  The top access hatch was made longer for ease of installing batteries.  A removable battery floor with support rails was built as with it being as close to the wing as possible.  Some additional reinforcing is being added where we think it is needed.  Of note for the fuselage the doubler along the wing saddle of the fuselage (to which the wing mounting blocks are glued on) was  lazer cut out of plywood as we thought balsa was too weak.  These are visible  in several of the photos below.  The cowl will be 3D printed as the one in the kit is flimsy and a better canopy from SIG will be used.  The wing construction is next.  His work is art and each time I visit his shop, I feel that I am attending RC plane building school, the only school I have ever found to be fun. 

 

 

Edited August 31, 2023 by Creative RC