Patchen Explorer TSC-2

[joe yap]

Sleek, fast and aerobatic? Not really this time. In fact, it is the opposite.

Having decommissioned my previous Low winger and transferred of ownership of my Electric Cloud Kitten, I still have the same motor/ESC combo lying around. Not intending to impress people by doing wild stuff or tearing up the sky this time, I chose this stubby and cute looking semi-scale observation plane, that can scoot around low and slow for spectators and pilots to appreciate its lines.

A construction article is published in an RC magazine, but due to many deviations and customisations, I re-drew my own plans. The size is a little different and the nose section is completely built-up, instead of carving out from a foam block. A steerable nose gear assembly is installed with a suspension system.

I built this up these few weeks in the midst of my daughter and son falling sick, and now my wife's turn. So, instead of a full blown construction thread, I just whopped everything and dump them into this thread. As I did not have time to take any pictures in between the build, these are what I got so far and are the only pictures taken at this point.

[chiadennis]

You amazing you build this in the midst of your children and wife illness! This is really multi-tasking.

[joe yap]

I can only sneak out some time when the kids took thier naps. Have to do everything quietly though, or my building time will be shortened drastically.

[joe yap]

Busy week, but at least managed to do a little covering here and there. I covered the fuselage top and wings with white Monokote. The lower fuselage is Titanium and a strip of Teal. The windows are simulated with Oracover blue. This fat and stubby fuselage is actually quite cuddly.......

[Ghostfit]

Good job !!!

....kinda reminds me of our Skyvan SAR aircraft ages ago !

[joe yap]

Finally got the coverings and assembly done up. Just need radio installation now. The motor and the ESC is built into the pylon pod.

[fudge2k85]

Looks good, bro!

[joe yap]

Thanks, Fudge.

[joe yap]

Just maidened it just now, in between the raining periods.

The ground tracking is excellent. Taxis as straight as an arrow, which hardly veers off course. Initial radio check detected quite a lot of crap with power on, which is subsequently solved by relocating the receiver and re-routing its antenna.

With a successful radio ground check done, I did a little taxiing run before advancing the throttle. My usual practice is to couple the rudder to the aileron channels for slow flying planes, and this is no exception. It'll enhance slow speed yaw and roll response, coordinate turns and adverse yaw effects and minimises tip stalls. Better still, I'll have nose gear steering control even on aileron stick input.

This chub requires quite a fair bit of up elevator input than most models, in order to initaite the rotation. The main gear is not significantly far behind the CG, and should not be the culprit. It is some other design feature that causes this model to inherit this behaviour,not just on take-offs, bit also in flight. I'll explain this later. In flight, aerobatics look stupid, or rather the pilot's thumbs are dumb. Anyway, the model is still not fully fine tuned yet at this point to cancel or minimise some funny behaviours.

The ESC was programmed with motor brake, which is a mistake. In flight, when the throttle stick is retarded to cut, the sudden torque of motor brake will cause the model to roll to the left. I confirmed it after a few try and decided to advance the throttle trim a little to prevent motor brake in flight, or this may give me a heart attack during landings.

Slow flight is the forte of this model. At very low throttle, this chub can really crawl slowly across the sky before stalling. Even the stall is straight and level without dropping a wing, provided that the throttle is not abruptly advanced.

I wasn't quite sure about the landing approach and I thought I would just do a mock landing approach. With the throttle trim at flight idle, it came down so nicely and smoothly that made me wanted to commit to the landing. However, the glide path was so shallow that it passed me with still quite a fair bit of height. At that instant, I attaempted to abort and go-around by a decisive full-throttle. BIG MISTAKE! The model dived down immediately even with some gradual up elevator input, which is apparently not enough. The model's nose smacked to the ground a little before bouncing back into the air, bending the nose gear along the way. The second attempt is flawless as I fully cut the throttle at an altittude before letting it glide and settle down on the tarmac with minimum impact. In fact, it came down so smoothly that the bent-out-of-shape nose gear as no effect at all.

Luckily, the nose gear is made of very soft wire and I easily bent it back to shape before taxxing back. Now, all the funny behaviour can be traced to the pod mounted motor high above the wings and fuselage. Apparently, the rather high offset between the models models drag line and thrust line, tends to pitch the model's nose down with the throttle is advanced. When the airspeed and drag has reached equilibrium, the effect is gone, but any change in throttle settings will create the effect again. Also, the offset between the thrustline and the model's vertical CG creates a big torque moment, whenever the motor is stopped abruptly. Other than the pilot's input, there very little I can do to counter this inherit behaviour. Mixing elevator with throttle may not help much as the pitching effect is basically a function of airspeed, not the throttle setting.

In a nutshell, as long as the throttle inputs are kept smooth, the model will behave very well. Seeing it scooting low and slow is a treat to the eyes.

[edmond22]

Patchen Explorer TSC-2 maiden video

Hey Joe,

here you go!

[joe yap]

Thanks for the video,Ed.

[joe yap]

I did some re-thinking of how I felt about the funny pitch tendencies and realise that the pitch down moment with the throttle advanced may be the function of motor thrust, instead of airspeed afterall, due to the excessive moment arm. I flew it again on Sunday evening and noticed that the pitching tendency did not increase further while the model is accelerating at full throttle. it only happens with the throttle stick being moved, and not wit the changing of airspeed.


So Iwent ahead and mix some up elevator trim with the throttle function. I over mixed a little at first to make the effect more noticeable. I flew it today and the first flight revealed that the mixture is excessive. However, the effect is very similar to most high wing trainer that has insufficient down thrust, and I can still manage it with some elevator input. The landing came a little hard though. The reduce the mix for the second flight and it flew much better this time. It is now so much more comfortable that I did a few take-offs and landings to get accustomed to it.

However, there is still a little left roll tendencies if I shut down the throttle from time to time. It can be a little annoying during the finals but a few clicks on the throttle trim can further minimise this nuisance. Right now, I feel that this model wants to fly well, but the high pod mounted motor really does some undesirable things and needs to be tamed.