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Easy-Jet: By Malcolm Corbin |
It’s Sunday and as usual the weather is poor. I am sitting at the PC trying to start the words for my latest little toy and struggling!! The past year seems to have gone by so fast and I seem to have achieved even less than the year before! Possibly my age! All I have produced is this little twin and a modified copy of an original design plus an ARTF review for the mag. I keep trying to blame my apathy on the weather and foot & mouth. Easy cop-out but now the weather seems to be improving and all the flying sites look clear but I am still struggling.
The Easy Jet project hatched itself whilst on the Brian Harris trip to Dortmund last year. The hours wasted on the bus were taken up by much talk of the current batch of small electric models and the thought of many bargains to be had. Having flown a couple of the current batch of small electric models the rash statement of “ I reckon I could build a better flyer than that” was taken up by this eager band of dedicated modellers. Soon a viable idea (no beer consumed at this time)! For a small cheap electric toy had been conceived based on specific criteria. Not bad for a bus trip to Dortmund! My original idea was for a twin “Jet” like pusher with the motors at the rear. I am glad that this was to prove difficult, as mounting motors so close to the trailing edge of elevons does make some of these small models noisier than you might expect and the whole idea of this project was to produce a cheap QUIET model. With the motors out on pods the Easy Jet is very quiet. The two part pod system can either be glued in place or screwed in so that the motors can be removed for slope soaring.
Or just build a sloper if you fancy and put a receiver pack up front to balance. It will as I’ve tried. My first test flight was off the slope and I spent a good 20 minutes just sloping and that was with the motors and 3000nimh pack on board.
If you are going to purchase the cnc pack a lot of what is to follow will be redundant. I hope with all my models that I learn from previous mistakes and this model is no exception! Mini Jazz had blatant errors in the plan yet most of you seem to have built a good flier. Capiche was a better plan but the swap from wood pack to cnc pack proved more of a problem than first anticipated! I have tried this time to incorporate all aspects of the model in one go as apposed to a hotch potch of bits and pieces! The big difference is this is dedicated to electric! Or is it? Two OS 10 La motors on this model would be stunning! Alas my apathy has not led me to even try! A pity really as this would make the Easy Jet appeal to a wider audience. If anyone does go this route send me an e-mail please. malcolmcorbin@btinternet.com
The plan has had to be altered to fit the paper allowed by the printers. So the fuselage has been cut and the fuzz is chopped at the back. Not a problem if you have a cnc kit. If you don’t, take care to join these together carefully as a change in incidence here will not help the model fly well! Also the plan now has cut profiles dotted all over to help those who wish to build without the cnc bits.The down side to this is you only get one wing panel on the plan so take care to protect the plan and use the reverse side to produce the other panel or buy two copies of the mag J. I used WD 40 and lightly sprayed the plan when turned over and laid on top of a white piece of paper the plan was easy to read. I must admit that I built my model from the cnc pack!! So some areas of the plan may seem vague but most scratch build modellers are very good at adapting so I am not to concerned. The cnc pack uses very high quality wood from the old Balsa Craft factory now known as SLEC and is machined to a very high standard. To keep the costs as low as possible the pack only includes shaped pieces. This means items such as longerons and LE and TE stock, nose and tail blocks and wing sheeting have been omitted but the saving in labour (hours at the bench) on this pack is awesome. The motor mount plates and the marine ply pods are a work of art. Not me just a good computer attached to a router.
The fuzz is built upside down this gives a straight build line to make construction easier. You must appreciate at this time that cnc can only cut square edges in this application. So some adjustments will be necessary to achieve some of the angles. All the longerons should be added to the fuzz sides (Make left and right) and fit the formers in place. Dry check all is well and bond the formers in place. N.B. I used only blue and yellow Grip cyano for the whole model. Add the tailplane seat and the motor pod seat also the bottom cross grain sheeting (not in cnc pack) this will produce a good square straight basic fuzz. With a cnc pack and cyano this is little more than an hours work. Lift the fuzz from the plan and sand the top edge flat. If there is a tricky bit on this model this is it. Having cut the rear top decking out or slit from the cnc pack you must remove approx 2.5mm of material to create the angle necessary to achieve the angled join, do be sure to do left and right again. I deliberately over cut mine so that little or no glue was visible from the outside. This will always give a smoother join once sanded from the outside. The glue will take up any gaps from the inside. The same applies for the canopy. Having cut or sanded these angles the upper formers should be glued in place including the lock plate for the canopy. Add the rear decking using the angle at the front of the rear decking to get the best fit for F3a. Now sand the top edge flat to the formers and add the rear top deck. The nose and tail soft block should now be added and the whole lot given a real good sand to produce a soft yet angular fuzz. The canopy base should now be popped from the sheet and bevelled slightly. Add all formers and sheeting as per the fuzz and add the small locking tab. With the base of the canopy area pre flattened to fit slide in place and sand the fuzz and canopy as one unit rolling down onto the soft block nose cone to produce a sleek shape. The more time spent on this application will pay dividends in the finished model. That should have the basics done servo trays can be added at a later date depending on what method you adopt.
Easy! I can’t think of anything that could cause problems here. Pre cut the sheeting and add the spar. Do the same for the trailing edge. Glue the ribs in place and add the top spar. Fit all the sheer webs and the dummy LE add top sheeting and cap strips. Remove from plan and add lower cap strips. Sand dummy LE flat and glue LE edge and soft tip blocks and give the whole lot a good sanding. Do the same for the other panel. Cut the two tip jigs out and sand the root cord flat with its tip jig in place. I actually propped both the root and tip up so as my permagrit block covered the entire surface. Bring both panels together with there tip jigs in place and glue together. The next bit is a blend so measure the fuzz at the Le of the wing slot mark carefully on the wing and cut the front flat. I took mine back an extra 3mm and added a bit of scrap hard balsa, which I then rounded. To get the wing to slide in through the cut outs requires extreme accuracy so do make sure there are no lumps and bumps at this stage. Sand the join smooth and ease gently through a few dummy runs may be necessary. What ever you do “DO NOT FORCE”! With the wing in position make up the tail feathers and slide in place this bit is very easy so no notes here. Check all is square glue the wing in place. Or if you prefer leave until covered and then bond in place. Same goes for the tail feathers. I used a small piece of cloth to act as a dihedral brace ( a bit like a wing bandage) I added this once I had covered the fuzz and the wing was cyanoed in place. This makes it very easy to reinforce the wing join with odd bits of spare glass cloth from inside. You will now have to decide whether you will fit a rudder and one or two aileron servos.
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 My prototype plus my VERY powerfull Kontronic brushless model!! 2x 400\28 on2x 8x1300cp sanyo cells and 2xesp! 450 watts.Vertical performance. |
I used Mylar hinges, Profilm covering, a cnc pack, vac formed motor pods, a pair of very cheap Jamara 480 motors (flux rings removed) a good quality futura bec controller and mini servos, sticker set and last but not least a Sanyo 3000 nimh flight pack. Best performance achieved was with a 1,250 Sanyo sub c pack but duration was compromised.
I am using really low output Jamara 480,s with flux rings removed. The total current draw on 5.5” x 4.5” cam props was 27amps on eight cells even on seven cells I can hand launch the model on my own not bad to motors under ten pounds. If apathy were removed I would have tried the little permax 400,s or the slightly better power Robbe 400\35 wind motors with Gunther props also the speed 480 race Graupner motors would be good. I did try the very powerful Irvine cobalt’s but the current draw was huge (over 40amps) maybe a higher wind would have been better. Last but not least who’s going to try a pair of OS 10 la’s (Very light and fantastic power to weight ratio!)Um?
Installation is not difficult but requires care. I went for a single wing servo and made up a standard pair of torque rods to drive them. I also went for a rudder servo. The rudder servo has to drive the rudder at quite an angle and I would suggest you use closed loop and ball link fittings as the geometry is a little peculiar the steep rake (Looks like the rudder is being pulled up and down as well as left and right ). I have to admit to enjoying the rudder on this model. So I do think its worth the extra effort. The biggest point I can make here is choose a good speed controller and you MUST NOT run the aerial down the fuzz past the motors. Route the aerial down a wing panel and out through a tip.
The motor pods need to be sandwiched with 1\8” balsa and shaped to an airfoil. Position the pods in their slot and carefully align so as not to add any side thrust and mark the edge where the pods exit the fuzz top and bottom. Remove and add the 1\8” balsa to this point let the balsa over run the ply by a couple of mm to allow you to sand a concave to match the motor tube. The shape is not important and can just be rounded if you wish. The slot in the marine ply is to allow the motor wires out whilst keeping them hidden. Do use good quality wire here as losses in performance can be noticeable with cheap thin wire. I covered these prior to fitting in the fuzz and glued in place at the last minute and then cyanoed the nacelles on. The motor ring will need to rounded as the rear nacelle is a tight fit. The tube is made by cutting to pieces of thin ply one a couple of mm bigger cover one side with thin pva white glue and wrap around the motor can with the slightly bigger sheet outermost (further to go round) I wrapped a long piece of rubber band around the outside the more you add the tighter it pulls the ply to the motor can. Leave over night. (Safer than using cyano). I just cut the fully shaped air foiled pod section from the nacelle removed the inner circles to allow air through and when it fitted well I slid the front nacelle piece over the rear and fed the join with a little yellow Grip cyano.
The flying bit comes next month but do keep in mind that this models bare airframe weighs less than the nicad!!! So trim is very much dependant on a good C.G. If you find your model climbs under power I reckon the cg is to far forward you will also find a good push necessary when inverted with a forward CG. It will pay to make sure CG is correct for optimum performance.
The biggest loss of this type of model in flight is due to running out of power. Do not run the pack flat and expect the model to turn up wind when the bec cuts in because it won’t!! Always keep a good minute of power for landing.
I have just read last month drivel and as usual see great holes in my text! Best I can do is hope the “Ed” cheers Gizzard has managed to work out what the heck I was on about? (I’ve not seen the first part yet due to lead time on the mag) a few key areas probably need a little help so I shall start with these before we progress to the flying bit.
The nacelles are fitted by firstly cutting the cooling holes from all four-vac mouldings. Then cut an expanded shape of your pods section from the longer rear moulding. This should look like an extended airfoil shape. Slide the nacelle rear moulding onto the pod. If it fits well it should pull up tight to the rear motor disc. This will leave very little material at this point so be careful. If it does not fit whittle a little away at a time until the pod fits. This process should allow the front vac moulding to overlap the rear. All this can be done and dry tested. So when you are happy the front can be taped on or cyanoed in place or a little silicon will hold well.
Do make sure you route your aerial via the wing and NOT between the motors.
Do make sure your speed controller works properly and does not interfere with servo functions and has good range.This means a good range check MOTORS RUNNING. Buying the cheapest or lightest is not always a good idea and avoid indoor type receivers. I used a quality Shulze controller from West London models with a bec facility and a middle of the road dual conversion receiver, which is mounted right at the front. As a contrast my model is equipped with cheap low output motors, which give good duration if not top performance, but at least I get no glitches. With no dihedral brace do reinforce across the middle with light glass but do once the wing is in place otherwise the wing will not fit the cut-out. Avoid the temptation to use heavy epoxy bandages all you will achieve is an over weight model. The sheer use of a central aileron servo with light ply servo rails that go from fuzz side to fuzz side is acting as an external brace if you added another on top of the wing at the front above the spar and with a little cloth wrapped around the leading edge this will be more than sufficient and possibly the strongest part of the model.
I used a standard 3001 for the aileron mounted in the middle with torque rods but one in each panel say a MG80 or a Futaba 200 would be really good. I used a Futaba 200 on elevator and rudder also. I used closed loop for rudder and twin snakes for elevator.
Huge choice here but a good option would be a pair of Gunther props attached to a pair of permax 400 motors. Or a pair of race 480 motors with small cam speed props say 5.5”x 5” or 6”x3” Graupner greys. The great thing about a pair of 400 size motors is how cheap all the bits are. Two Gunther props cost a mere £2.00 ish and a pair of permax motors can be had for under £10.00 a bit different from buying a 17” x 8” apc for a YS 140L .
Just a quick note here. Attach a red and a black to each motor allow sufficient to bring into the fuzz and work on! Join both reds together and join to speed controller and join both blacks and join to speed controller. When you attach to nicad do for first time without props just as quick check if you are not sure. Then add props make sure props face FORWARDS running motors backwards. Try to avoid running on the bench too much. I know it hard to resist but it’s not that good for the motors J.
Almost as much choice here as the motors and props! I used many types in the early days and as mentioned. My best results were from a set of 8 x 1250 sub C nicad’s. The downside is duration. The new 1700 Sanyo (long ones) nicad cells would be better but I had none. I like the 3000 SANYO nimh C cells as these give the best balance between duration and power to weight. The good thing is the Easy Jet will fly on just about any combination so a 7-cell Sanyo 1700 C cell pack will work. So will almost any other combination.
Electric demands more discipline than I.C. power.
The biggest reason greater wing loadings. I have many good I.C. flyer mates who will insist in running their planes till the fuel runs out. Great I also love to land from height dead stick this shows good approach and forethought, plus a basic skill of the models sheer glide capabilities. Small aerobatic electric models however do NOT fall into this category!! The first few flights should be carried out with a mate on a watch with seconds hand and if possible fly as the only model up so as to hear the drop off in motor performance. You should be able to achieve an easy 6 minutes with power to spare say on 2,400 NiCad. I know of flights in excess of 10 minutes on 3000 nimh flat field without slope lift. I had a 40 minute flight on the models second outing in just 12 knots of slope lift fully loaded with cells and motors! This is just a start figure some of you will burn power faster than others. I have a timer, which is activated by my throttle set at 7 mins. The biggest no no is to allow the bec to cut in when you are not ready for it! Until you are used to the model I suggest at any skill level you land early or you will never get used to it. The classic is that last down wind fast pass and as you decide enough is enough the bec cuts in (Oh how I hate that) you try to bank and come back to the strip! Only problem is the 1lb of nicad sat in the middle of the plane that is now only driving servos wants to carry on down wind!!!! If you cant land straight down wind its. Good-bye mister Chips.
This really is part of (Most important bits!) But I think it should have its own little spot with this model. The swept wing design looks great and flies very well but the C.G is important. DO NOT think running a forward C.G. will be a safe option. Swept wings will feel nose heavy through the sticks more than a standard layout. Other side effects include height change under power. So if you find the model climbing at full power but neutral at half throttle and dropping on the glide it is bound to be a forward C.G. Unless of course you did not buy that cnc pack and stuck the plan together wrong? Joking aside please make an extra effort on the C.G. with this model, as it will affect many things. When its right landing is a pleasure with good elevator response when its forward you will end up tugging up on the stick. Forward C.G. will also make landing faster than they need be and turns will feel unstable.
Sorry to be so pedantic on this point but I see so many models slated of poor flying only to find out the owner thought he would be safe and run a C.G. 2” yes 2” in front of the stated! I have set the CG at a SAFE 115mm from the wing where it leaves the fuzz.
I think, and this has been backed up by an early beta test model built by the chairman of Jersey MAC Chris Munns and test flown by Pete Rondel that the optimum for slope and power is 120mm. Slope models with no motors or heavy nicad may just go back a tad more but this is due to a lower wing loading. I must just thank Chris and Pete for their input.
Flies really well the shape is absolutely great in the sky. All manoeuvres are crisp and easy to perform. Inverted is very good (with correct C.G). As are point rolls. Knife-edge is untested due to lack of power but this is not poor rudder but more lack of power. Come on you budding I.C blokes someone bolt a couple of OS 10 la motors on the front (URR I meant the middle!) and let me know? If you do I suggest you extend the arms a tad and beef them up a little. Slow roll performance is also good and stall turns are very accurate and easy to perform. Easy Jet looks fast but is in reality easy to fly and very stable. I have enjoyed this model very much and consider its shape to be my best so far.
With such a range of motors and nicad’s. Let alone an ever-growing range of top quality NiMH cells the twin 400 market can do little but grow. It has the same versatility as the single speed 600 models if anything more. Adapters etc are bountiful as are props. I have heard of many “Twin Jet” variants achieving more than the normal power output!! Some individuals, (nutters) even fitting brushless motors.
I (Yes) even know of a Twin Jet with two OS 10LA motors on it. Screams its nuts off. Flies like its on steroids. Can you imagine that same power and low weight with a RUDDER? Knife-edge city and a decent inverted performance. This model is easy to build and fly just obey the basic rules that I have mentioned and you will have hours of quiet flying fun. Ignore the time aspect of electric and you will have loads of BUILDING fun. I hope all this helps and as usual I look forward to input and any problems via my e-mail malcolmcorbin@btinternet.com
| Name: | Easy Jet |
| Weight: | including 3000 Sanyo nimh pack 3lbs or 1,344grams. |
| Span: | 40in |
| Construction: | Marine ply, light ply and balsa plus plastic vac form nacelles. |
| Length: | Approx 44” depends where you measure! |
| Covering: | Profilm. |
| Colours: | White, Pearl blue, fluorescent orange with black decal set. |
| Servos: | 1 x standard 2 x Futaba 200’s |
| Receiver: | dual con 8 channel standard |
| Speed controller: | Shulze 40 amp (bec) futura. |
| Motors test model: | Jamara 480 flux ring removed same as protech 480 Perkins motor. Mine now currently using two Graupner 480L reverse timed race motors on 10x 2,400 sanyo cells. VERY GOOD combi. |
| Props test model: | 5.5”x 5” Graupner speed. |
| Beta test model: | Chriss Munns 2 x Permax 400’s with Gunther props and 8x 2,400 nicad |
| CG: | 120mm final and best position both models. |