Capacitor powered profile scale - Tom Crompton
As promised, a few lines on indoor flying with capacitor power aeros. I first started flying with this form of power about 25 plus years ago in the days when we had no micro/rc and the thought of flying f/f with electric power was almost a dream. Along came a little kit called strangely enough the capacitor plane(I think they were sold by SAM's at the time).I was fascinated and bought two, not that I was interested in the model, a simple stick type, but what possibilities were on the table. Upon their arrival the power train went into a profile scale (rubber power) Tiger Moth. Yes it flew!. Duration was quite short ,only about 20 seconds ,but oh so consistent. Great fun, and convinced me that electric f/f was practical indoors. The power source was a 3.3F super capacitor(note we are talking Farads, not normal capacitor talk, micro or pico farads (mf,pf).Working ,as I have all my working life in telecommunications, thoughts turned to trying to source capacitors of greater size. The Farnells catalogue was always floating around and a quick scour of the pages revealed 5F and 10F super capacitors were available. Needless to say some were ordered and duly installed in my faithful Tiger Moth. This of course boosted the duration to almost double using the 10F capacitor. And so I flew this and my Ord-Hulm profile scale models for a couple of seasons.
Slowly other developments ,like the use of 50 ma NiCad's and infra red radio took over and that two capacitor models were retired to my workshop shelf.
A recent article in Aeromodeller for a capacitor powered (outdoor model) reawakened interest ,especially as the capacitors the chap was using appeared smaller than I had previously used(physical size).,so a quick search on the net and I had a couple of the new 10f capacitors. I also noticed that they had 25F and50F capacitors also ,so I bought a couple to try. I dusted off the old Tiger and Ord-Hume and re-equipped them with the new gizmos. The models were fairly rotten by this time having spent all these years on the shelf. So after refurb and repair there was more repair than model, so neither was a lightweight. I put a 25f capacitor and a KP00 (standard gearing and prop) into the Tiger and a 10F capacitor and direct drive KP00 into the Ord-Hume. Took them down to the clubroom for trials. The Tiger ,on the setup described is totally impractical as an indoor model. It took off (ROG) like a rocket and hit the centre of our clubroom ceiling(50ft!),hit the beams several times came down and climbed up again...so this combo 25F and KP00 geared is for outdoors (and I would suggest if anyone tries this combo to obtain running shoes first, as there is the power of a small diesel (Bambi,K Hawk, Kalper) available here.The Ord -Hume is the practical one for indoor. Several nice circling laps of the clubroom .So this would seem a good place to start .I suggest limiting the power to a 10f capacitor. Use a KP 00 as it is is cheap and plentiful to start with. I have tried several different geared pager motors and they were lacking in go. Now the practicalities! 10F super capacitors available from Maplins for less than £2.00 apiece (If anyone struggles to get one let me Know and I,ll try to pick up a couple for the October meeting).
KP 00 motors ..well just pick up the phone and ask Derek Knight at KP Aero, again won't break the bank! Charging setup...nothing expensive or technical. I use three D size rechargeable batteries (mine purchased at Maplins along with a Plastic holder and a couple of leads attached to a press stud gizmo that we are all familiar with),nothing more needed just attach your leads to the capacitor ( + to+ ,-to -) and put in what you want. It doesn't seem like you can overcharge, as they will only charge up to a max then no more ..a bit like pouring water into a cup, it will only hold what will fill it; and I've not managed to break one yet!
The power curve of these capacitors is very much like that of a rubber motor. Lots of go at the beginning ,cruise and decend. ROG,s are possible without too much worry. Iíve tried electronic gismos on the 25f capacitor to see if it can be used effectively indoors, but no success so far, so lets stick to 10f for now. Geared motor needs a coarse pitch prop to get the best from it whilst direct drive motor is the opposite. Prop choice seems to be the area to play with for best results.I,ve also tried coupling capacitors together to get different values and whilst there is some improvement ,its all swallowed up by having to carry the additional weight. I found it advisable to use ply reinforcement around the nose .Helps keep the motor where you set it so helps consistent trim. Plans...I've used this idea for years((Iíll bet a few others have also!).If you can't find the plan of a model you like ,try thumbing through old Aeromodellers or Model Aircraft mags. When found ,blow it up on the copier, discard everything except the outline. Add your own structure / rigging angles etc. and there you are ,profile scale without trying too hard!
CLARIFICATION OF RULES FOR CAPACITOR POWERED PROFILE SCALE
Power...1 x 10 farad super capacitor or as proscribed by Contest Director
Motor /prop....any you want
Model...profile SCALE (not easyB/Duration type) max 16 inch wingspan. If of an obscure type, a picture or 3 view to authenticate needed.
Best flight wins. Any number of attempts, ROG or hand launch. In the event of a tie ROG gets the win.
So lots of fun experimenting ,little cost .