Zlin 526 Akrobat Was given a Zlin 526 Akrobat by a friend of mine which was in pretty poor condition due mainly to its great age, we estimate 28 to 30 years old based on a canopy modification from the original sliding canopy to a bubble type. This was introduced in a magazine advert in Radio Modeller from November 1980. As it has the original sliding type it must predate 1980. The fuselage was covered in nylon and the flying surfaces in Solarfilm. It has had a few engines fitted in its life. The guy my friend bought it off had a .91 (15cc) two stroke in it and my friend fitted a Super Tigre G23 (23cc - 1.40) and reckoned it was still underpowered! Judging by the engine cowling, which by now was more hole than cowling, I'd say it had had several more engines than that in its life! Would you believe that, back in the day, they used to fly them on .61's! I really liked the look of this model and was determined to make a nice job of it and had planned to re-cover it completely but, in respect of its great age (for a model), I decided to keep it as original as possible. As it turns out, I'm glad I did. As it's a fair sized model (86” wing span) I was looking forward to some big, lazy, relaxing aerobatics and so decided to fit an ASP 1.80 four stroke, which I had just taken out of my Funtana 90. This engine is very frugal and would sound terrific. Ahhh, the dreams we have! I could see it in my minds eye performing beautiful slow rolls covering a couple of fields and big slow motion avalanches and Chinese loops and gently rotating down in a perfect flat spin (that part turned out to be true but with one major flaw, as you'll see later!) and leaving a trail of smoke against an azure sky accompanied by that lovely slow revving four stroke sound! Boy, was I in for a shock! I decided to fit the engine first and immediately encountered several problems. First the engine box inside the cowl was over an inch too long to get the motor within the cowl. Second, if the engine were fitted inverted within the cowl the fuel tank position would be much too high and lead to flooding. There was no way to lower the tank further, so the only solution was to fit the engine sidewinder. I didn't mind this as inverted motors always seem to give problems with starting and cutting at idle etc. Third, with the motor sidewinder there was no way the cowl could be persuaded over the engine! This meant the cowl had to be split horizontally. Lots of work, still, it'd be worth it when it was done, eh? So, I chopped off the engine box to the required length and fitted a new firewall. I found a pair of glass filled engine mounts to replace the original heavy alloy ones, not realising at this point how important weight saving on the nose was to become. Then I discovered I couldn't fit a fuel tank because the tank bay was now an over an inch shorter! This meant I had to cut the centre out of F2 to get the 16oz tank in, but no big deal and was soon done with a hole cutter in an electric drill. With the motor and tank fitted it was time to fit the cowl, but first I had to get back to basics and fill all the ruddy great holes in it! This took a week of evenings to achieve but, somehow, I really enjoyed doing it. Maybe it's making something good out of rubbish that's the appeal, I don't know. It's lucky I kept all the broken, smashed, modified glass cowls I'd had over the years because I was able to find matching bits with similar contours to fit the various missing bits. Cutting the cowl horizontally wasn't as difficult as I'd imagined and even making the soft steel plates with soldered on 10 B.A. nuts was a piece of cake too, and soon the cowl was looking good. An afternoons work was all it took to get it cut out to fit over the engine. With the motor, tank, cowling, prop' and spinner test fitted I thought it about time to have a C.G. check. I didn't have any C.G. info' so had to work it out myself. With the model assembled I measured everything up and worked it out. Shock, horror! The C.G. was a mile ahead of where it needed to be! There was nothing I could do to reduce weight at the nose other than fit a plastic spinner so weight had to be added to the tail, groan! Later, I was mortified to find I had to balance three quarters of a pound of weight on the tail to get it to balance. This was bad news. Not least because of the added wing loading but also because of the dreaded pendulum effect when spinning. I'd already read in old mag's of people unable to recover from a spin when flying at competitions with this model, and they were using lightweight 90's. Oh dear! So somehow I had to reduce this blob of weight and spread it out a bit. One thing that occurred to me was how the hell my friend had managed to fly it as the G23 and my ASP are the same weight! The first thing was to fit a stronger steerable tail wheel using heavier wire. My friend had already modified it to have the elevator and rudder servo's mounted at the tail end to help balance his G23 so there was nothing I could do there except fit heavier M3 pushrods. I then cut a hatch halfway down the fuselage bottom and made a tray to fit the flight battery on - this helped a lot. At the end of everything I had to bolt 5 ounces of lead into the “V” at the tail end. Not too bad after all! Now it was time to paint and fit the gear. The nylon covered fuselage was pretty ropey but the application of a few well placed stickers and a coat of fuel proofer tarted it up a bit. The paint trim on the wings was rough but was soon touched up. All up weight 12lbs! Not bad. Time to fly! Now for it! Had to adjust the idle needle on the carb' as it was quite rich at idle. No prob's. Blowing a gale as usual but didn't mind as it shortens the take off and landing run! Into wind, give her some power and we're away. Airborne in about twenty feet and climbing well. Loops are fine, avalanches less so; there's a bit of heading change after the snap. Rolls okay, but once again there's a heading change. There are huge amounts of differential on the ailerons so this may be responsible. Stall turn, difficult to maintain a vertical up line, but okayish. Fly a little sequence but it's difficult to keep on the line. Needs some practice is all, I guess. Test the stall and find it can hang in there remarkably well. Some of this could be due to the high wind so am not confident enough to slow down that much on landing, consequently I overshoot by miles and go under the fence. Anyway, it sounds and looks the part, if only I could make it go where I want instead of where it wants. Good part is the motor is perfectly suited and provides plenty of power. Second flight. Time to test the spin. Bit nervous about this because of the tail weight issue and all the reports from the distant past. Decide I'll do it while the tank is full to give a more forward C.G., just in case. Climb to a good height. Throttle back and wait for the break. Full left rudder, full up elevator. She goes straight in and I release the sticks after one and a half turns and fly out. It seemed a bit keen to get into that! Climb back up, higher this time. I have a bad feeling about this. Throttle back, wait for the break, Full left rudder, full up elevator, full left aileron this time too. One turn okay, two turns and it's going flat, by three turns the spin is completely flat! The decent rate is very, very slow, the model looks like it's coming down on a piece of wire stretched vertically through the canopy. The rotation rate is slow and graceful and as flat as your hat. It really is beautiful to watch with the motor popping and sending out little blue smoke signals on its way round, I'm almost reluctant to recover and spoil the moment. However, the height is bleeding away so it's time. I centralise the controls, one turn, two turns, three turns and nothing! Okay, down elevator, gently at first but soon all of it, still nothing. Centralise again then opposite rudder, about half at first then quickly to full, still nothing. Rudder and elevator together then, but still no sign of recovery. Am starting to panic a bit now. Same again and opposite aileron too, again, nothing happens. Last chance so full down, full right rudder and about half throttle to get some airflow over the tail surfaces, and nothing continues to happen! I think, “That's it then, it's going in! I'm going to lose it!” Then I have a thought and begin pumping the throttle giving big bursts of power and hoping. I end up at full power but still it continues its beautiful rotation of death. So, having done everything I could think of and with the model now down to fifty feet I shut the throttle and let go of the sticks and prepare to watch the inevitable. The only good thing is that it will hit on the strip. As I stare, and after no more than two rotations after I let go of the sticks, the model suddenly gets its nose down and comes out all on its own. Phew! What a relief! I fly out and land with shaking hands wondering how it managed it. So here's the dilemma. Do I go out and spin it again and hope I find the secret of spin recovery before it hits the ground? Or do I fly it and (unthinkable this) never perform spins or snap manoeuvres again? Or do I never fly it again at all?   Well, if it's never going to be flown again it may as well be in the bin, so I am going to fly it, and spin it, but I'm going to give myself an edge. I'm going to remove that 5oz lump of lead in the tail and reduce the rudder movement, which is a little extreme to say the least, and pray that it solves the problem. Wish me luck. Now you see why I'm glad I didn't re-cover the whole model and turn it into a near museum piece. Because I'd be to afraid to crash it, that's why. As it is, it looks like a bit of a beaten up old harridan, so no great loss if it does go in. And if it doesn't and survives to fly another day, then I just may re-cover it at some time in the future and have a splendid and ancient model to play with. Good plan? G :-) FF-04-09-08

Virtually Free Aircraft! While going over the fleet in preparation for the new season I discovered that the fibreglass fuselage of my Little Toot biplane was crazed nearly everywhere and had several severe fractures developing in high stress areas. As those of you who have read the Toot articles will know, this bird is massively overweight anyway (like 35%!) and mostly because of the terrible chopped matt fibreglass fuselage. The thought of adding even more heavy resin to effect repairs didn't appeal, as the whole process would only begin again as soon as I flew her. So, what to do? I could sell her, I thought, but it's not really fair to pass on something you know will be falling to bits after a few flights, is it? So I decided to scrap her. At about this time I had occasion to empty out the loft, and it's lucky I did because, while temporarily storing old and broken models in the spare room, an unlikely pairing was formed. The Toot wings and the fuselage from an old own design .25 powered low wing 30's type monoplane fell together and gave me the spark of an idea. The monoplane was also overweight after a broken wing repair involving a 3/16 ply dihedral brace over a foot long and copious gobs of epoxy, so it too was effectively a scrapper. I weighed the fuselage and wings and made a few estimates for engine and gear etc and came up with an all up weight of 7.5 to 8 lbs, giving a wing loading of 16 to 17 ozs sq ft. Nice! It should be a fine flyer, and looking at it sitting on the bottom wing and with the top wing balancing on an old fuel tank, it looked really nice, real 1930's. Also having a major influence to meld these two airframes was the realisation that I had two old four stroke engines sitting idle, one a .65 and the other a .91 ASP, both of which have identical crankcases allowing either engine to fit the same mount, which could be useful. It's an unlikely pairing isn't it? The wings from a 23cc (1.40) powered aircraft and yet only a 4cc (.25) engine in the monoplane! In fact, the monoplane had a humble O.S. 26 four stroke before the wing repair made it too heavy! Well, I was quite excited about the whole thing now and couldn't wait to get on with it. So, once decided the first thing to do was hack out the tailplane and cabane from the Toot fuselage - not as easy as it may sound without destroying the parts I was trying to salvage! Damn fibreglass, I itched for days after that! The removal of the tail group from the monoplane was, by comparison, a piece of cake. The next task was to set the wing and tail incidence. The tail is set to 0 degrees parallel with the fuselage datum, so I needed ½ to 1 degree of positive incidence on the main wings. The wing seat for the lower wing had to be modified in any event because of the differing airfoil shapes. The monoplane had a NACA 2415 section and the Toot a NACA 2412. Both, conveniently, have a 10.25 inch chord. The bottom wing needed a little local reinforcement for the addition af a leading edge mounting dowel and once this was done I was able to drill the wing to line up with the original wing bolts mounts. A bit of shimming of the wing seat was required to achieve the correct incidence. Now I had something to measure from I could fit the cabane for the top wing. Ply patches were fitted inside the fuselage for the cabane to bolt to. The front cabane was drilled and positioned, then the rear was drilled. One hole each side was slotted so the whole cabane could be tilted to adjust the wing incidence. This is about as far as I've got at the moment. The tail off the Toot is too heavy, so I'll make a new one - no problem, as it's only balsa sheet. I can't foresee any problems ahead, and judging by the numbers it should be a sweet flying aircraft. The best bit though is the utilisation of two otherwise scrap airframes! Why not have a look in your own loft, garage, shed or whatever, and see if you have a free new aircraft waiting in the wings! Part 2 coming soon! G:-) FF-19-01-07

Hanger 9 27% Extra 260 The Hanger 9 Extra 260 is a nice IMAC/3D aeroplane at a good price. I bought mine because I had a Moki 1.80 doing nothing and some reports I'd read claimed the Extra could weigh as little as 12 lbs ready to go, which meant the 1.8 would be powerful enough for 3D work. Mine has come out at 13 lbs despite a couple of weight saving mod's, but I should add there's a 3600 mah sub C NiMH powering the radio in there to help achieve the correct (in my case, most rearward) C.G. As it turns out this gives me a nice option should I discover I need more power in that I can fit the more powerful Moki 2.10, with no modification whatever, and which weighs another 4 odd ounces, which I can trade off against a smaller, lighter battery for no increase in overall weight. This is good because often fitting a bigger engine causes an unacceptable increase in weight, which could compromise 3D ability. The kit comes well packaged and everything was present and in good condition - no damage. The hardware is of good quality and up to the job. Good quality ball links and Robart type hinges are supplied for the control surfaces, a carbon undercarriage, nice quality fibreglass cowl and spats, anodised wing and tail tubes, fuel tank, alloy engine mounts, wheels and a nice canopy. All in all a good package especially considering the price. There are many ways you can jump for model set-up. I opted for the light weight glow powered path, mainly, as I said, because I already had a Moki 1.80 doing nothing, but plenty of people are fitting 40 to 50cc petrol engines, but obviously the overall weight will escalate. 14 to 14.5 lbs should be possible with the likes of ZDZ40 to 50 or DA 50 engines. Once on this path, however, you have a lot of money floating around up there and users often opt for twin receivers and battery packs, often using Lipo's or Lion packs with regulators, and even opto isolators and so on. One British magazine's review model ended up at 17 lbs in this way, which I feel is way (weigh!?) too much for this size and area model, and while they may claim it performs beautifully anyone with an ounce of gumption would be very doubtful of this with wing loadings in the 35 ozs sq ft range. That kind of loading would more normally be seen on 33 - 40% models and is, in fact, a relatively light loading for models of that size.  Maybe, if your thing was IMAC  style flying you'd be happy, but, at that weight, 3D would be severely compromised. My 13 lbs example has a wing loading of 26.5 ozs sq ft, which is far more like it (in my opinion). Okay, so the set-up is this: Moki 1.80 with Bisson (BCM) Pitts style in cowl muffler and Cline pressure regulator, turning a 20x 6 Mejzlik carbon propeller. Futaba radio with a single high torque servo for each control surface. 9.5 Kg for ailerons and rudder and 8Kg for elevators with a 3001 on throttle. All servo's are supplied by heavy duty extensions and a heavy duty rx switch. After weighing the supplied engine mounts I decided to go my own way and use a homemade mount system I've used a few times with complete success. The supplied mounts weighed in at 6 ounces, my home made mount, including all nuts, bolts and washers, just 3 ounces. The backplate itself is 1/8” duralamin. The stand off bolts are 5mm with “T” nuts in the firewall. Another advantage of this system is that the motor is full adjustable for up/down/side thrust. The pix show the arrangement. I decided to use a Cline pressure regulator on the engine after years of battling the throttle when prop' hanging as the engine leans once the nose is pointing skyward.. I have high hopes for this, but, as with so many modelling “solutions”, it could all end in abject failure, we'll see! Its operation is as follows: Fuel is pressurised in the tank from the crankcase of the engine via a one way check valve. Tank pressure is from 2 to 12 lbs PSI. This forces fuel to the regulator, which is mounted very close to the carburettor inlet nipple. The carb “sucks” on the regulator diaphragm causing it to open the fuel valve in the regulator. It is a demand regulator, the more the carb “sucks” the more fuel the regulator passes. When the engine is stopped no fuel can pass. To sum up, it is a proportional fuel control system. (We hope!) In theory it shouldn't matter what attitude or “G” the model has put on it, everything should be fine. The engine should “see” no change in fuel head at all. (Oi! You at the back, stop laughing!) Some mod's have to be made to the fuel tank (see pic) to prevent the fuel lines blowing off. Everything went together well and no problems were encountered. Hanger 9 really does have its act together with these ARTF's. It really is just an assembly job that could be accomplished in a week of evenings. One modification I did make was to the air exit of the cowling. A few people have had cooling issues when using big glow engines and some have gone to petrol engines (which are usually fitted inverted with the cylinder hanging out in the breeze) to solve this. The exit area, as ever, should be about 3 to 1, i.e. 3 times the inlet area. This leaves a pretty big hole, which also slopes back to the firewall. Its effect is to leave a big chunk of flat firewall presented directly into the air stream. I felt this was probably deflecting air into the cowl area and preventing the smooth flow of air passing through from the inlet. So I decided to make an air deflector as per full size around the exit lip to solve the problem. It took a little work to get right - there are some weird angles in there - but eventually I got it fairly right. See pix. The only other modification I made was to cut out the plywood cockpit floor, which saved about 11/2 ounces. Weight was also saved by using an Irvine spinner. This type has a lightened alloy backplate and a plastic nose. This saved almost 4 ounces over the usual polished alloy spinner. Anyway, it's all ready to go and I may get out with it soon. It'll take some time to get the motor fully run in before I can give you an accurate flight report, the general feeling is about five gallons (ringed piston running on a hard chromed liner), so don't expect it till next spring. G:-) Spec's: Span:  78.25 ins Length:  71.25 ins Wing Area:  1134 sq ins Weight: 12 to 15.5 lbs Engines: 2 stroke 1.20 - 2.10 4 stroke 1.50 - 2.20 Gas 35 - 50cc FF-5-10-06

Extreme Flight Yak 55 SP-e The Extreme Flight Yak 55 SP-e is a small profile electric 3D ARTF with beautiful interlocking construction. You can buy one yourself here: http://www.freestyle-rc.com/ I chose it because I wanted a small but 3D capable introduction to electric flight. I had zilch knowledge of electric matters and so wanted a complete package with the motor and speed control already picked for me. I also wanted ARTF and 3D capability. My initial search for such a model was notable for its total confusion! Which motor for which model? Which speed control for which motor and motor type? What type of batteries are best for which type of motor? And so on. None of this was helped by the totally meaningless, to the newcomer at least, identification numbering systems of motors etc. However, it soon became obvious, even to a newbie like me, that Lithium Polymer batteries were the way to go. I was initially put off by the high cost of chargers but soon realised that some of the cheap 12v types were perfectly adequate. I use a Robbe Power Peak Lipoly 300. The search continued fruitlessly and confusingly and I was on the verge of giving up the whole idea when my Holy Grail appeared in the shape of a promo' video from Extreme Flight. It showed the lovely little aeroplane you see here, and it met all my criteria; small, 3D capable, ARTF and best of all it could be bought for a very attractive price with a geared brushless motor and speed control, better yet the amazing antics of the model shown in the promo' video used exactly those parts too, so I knew it would perform! The only parts for me to supply were radio gear and Lipo' batteries. The promo' video `plane used Hitec HS55 servo's and Thunder Power 1350 3 cell 11.1 volt Lipo', so that's what I bought too. Building, if that's the word, the model is quick and easy, there really isn't much to do at all. Fitting the control horns, push rod guides, radio gear, motor and speed control is about all there is to it. I fitted the Lipo' on Velcro so that it would be easy to swap them over during a flying session, and this works well. I haven't lost a Lipo' yet! Servo's are conventionally mounted and I fitted the receiver inside the wing with its own hatch, which also mounts the receiver switch. The aerial trails down the fuselage and behind as usual. I set all control surfaces for as much throw as I could get. The Hitec HS55 servo's are fast and accurate, unlike some of their bigger brethren. I also fitted an audible low voltage warning alarm which cost £12. This protects your Lipo's from low voltage damage. Flying the thing is fun, fun, fun! It's capable of just about anything and then some. I needed a little mixing for knife edge flight - about 6% up elevator correction for full rudder, mind you, I have a lot of travel on the rudder and to be honest, that amount isn't needed. I've managed to crash it quite badly on three occasions, once when trying to catch it from a hover, I caught the rudder with my hand as I made a grab for it and flipped it straight into the ground! The second time was due to losing synchronisation during low harrier rolls, and lastly, I flew it into my lower leg at high speed. Those of you who have flown this type of model will nod sagely and smile, while those who have not will think I'm an idiot… The damage in each case was to the nose only and was readily repaired. The model draws you into doing things you wouldn't ordinarily attempt, and therein lies its strength, because in attempting this stuff you're learning all the while. High alpha knife flight is one of its specialities and all the usual 3D moves are easily accomplished. Use plenty of expo' if you have extreme throws otherwise normal flight is pretty twitchy. On reduced throws it's a nice and safe model to fly and could be handled by anyone who's through the basic trainer stage. It can handle a good breeze and in fact can be a lot of fun when the wind is up. All in all a good and useful introduction to electric flight for the more advanced modeller looking for a first electric or someone on the early learning curve wanting to get into 3D flying. Yes, all the stories are true - what a delight it is to go flying without all the usual stuff you have to cart around. Also you can fly virtually anywhwere. There's very little noise and somehow, because of this, there seems to be less general stress. Electric is ideal for 3D flying as you're not having to fight the engine the whole time as it leans or stumbles depending on which way the nose is pointing and, of course, you don't have to worry about it suddenly going quiet! Throttle response compared to a glow motor is simply amazing. And when the day is done everything is clean and oil free too. G:-) Spec's: Span:  30.5 inches Length:  31.5 inches Wing Area:  320 sq ins AUW:  14 - 16 ounces Extreme Flight BL-20 brushless geared motor 15 Amp ESC 10x4.7 prop' HS-55 servo's Webra RX FF-20-6-06