It's been over a year since I (Colin Paddon) and Kevin Beale first posted details of our home built and designed 3.8m composite F5J glider, PROGLIDE. This update brings us up to date with the project.
It’s all very well designing and building your own competition plane but its not worth a lot if it turns out to be lacking in performance compared to the professionally manufactured gliders that it will be flying against. There seems to be a general misconception that home built F5J competition gliders are in some way inferior to the professional commercial offerings in terms of their flying performance. Straight away lets dispel this myth. The prototype PROGLIDE in its first full year of competition use won three UK F5J league competitions and finished 2nd in the 2016 National UK F5J league with an overall score of 99.06%. Myth dispelled.
The only downside of designing and producing your own composite F5J plane is the time and effort it takes to do. If we paid ourselves 50p per hour for all the time we have put into this project we still wouldn’t be able to afford to buy them! It’s a complete labour of love in every way but the sense of achievement makes it all worthwhile. A quick look at the web gallery that accompanies this article will give you some idea of the time and effort that has gone into achieving our original goal which was that it must be economical to build, use techniques that anyone with reasonable building skills can learn/do and most importantly have as good a flight performance as the commercial offerings. Achieving the 100% perfect finish compared to the hollow moulded professionally produced planes was not a high priority. We were only interested in its flight performance and were happy to accept a good finish as opposed to a perfect one.
During the development period we worked in parallel on different areas of design/construction. For example I decided that I wanted to be able to split the fuselage in half for ease of air transport which meant that the elevator and rudder servo’s were both enclosed within the tailplane mount pod with the boom being secured to the Fuselage Pod spigot by two carbon tubes that could be removed and the boom slid off. Ditto the fin/rudder assembly. Kevin worked on optimising his layout with the servos under the wing at first followed later by the elevator servo in the tailplane pod and the rudder servo under the wing. For his Fin/Rudder he went along a similar route that the Nan Xplorers use. Finding easy to do home build solutions to problems took time, effort and testing.
One of the things that several people asked us about was how we made the wing joiners. In the end it was so simple that I wondered why I hadn’t thought of it before. Buy yourself from HobbyKing a protruded 10x10mm square section carbon rod which comes with a 8mm dia hole all the way through it. Cut into required joiner lengths and angle the two inner end faces to the required angle. Roll up 40mm of unicarbon tows to achieve a tight fit inside the hole, wet out fully with epoxy and slide it half way into one half of the joiner and then the other. Put balsa caps down the hole so that it just very slightly compresses the central wet unicarbon and keeps them centrally located within the length of the joiner and then clamp into required position and allow to set. Result, pair of carbon joiners that weigh 23g total. The plane would be destroyed before the wing joiners broke. This technique wouldn’t be strong enough for F3J planes but more than adequate for our lesser stressed F5J models. Quick, cheap and foolproof with the ability to create any angle of joiners you require. Kevin went a different route by using straight solid round carbon rod which allowed him in our normal wing section to get the required dihedral tip angle he wanted.
All this problem solving sounds as if it was a PITA, and at times it felt that way, but in reality we both enjoyed finding home build solutions to these challenges.
The first two Proglide’s produced used cheap fibreglass cloth on the flying surfaces which enabled us to learn the required composite skills knowing that when it goes wrong (it will BTW!) that it hadn’t cost the earth in materials. However, the aim was always to eventually use Carboline which is a fantastic cloth but it’s not without good reason that it’s called “Black Gold”, its very expensive but gives a strength to weight ratio that is unbeatable for our purpose.
The early fibreglass skinned versions of PROGLIDE achieved RTF weights of between 1450-1580g, ie still reasonably light for a full house 3.8m electric plane. With each new plane we tried different lay-up’s, build techniques and incorporated various detail design changes along the way. Lots of time was expended in producing test pieces during this period to prove the viability of what we were doing. We had failures along the way on pieces that we felt sure would work well but turned out not to be of the standard we were seeking. Amongst the various failures though we managed to have some light bulb moments which were always welcomed! One such moment came when we started to investigate how to achieve repeatable 100% success with shaped inflation bladders in the moulding of the fuselage pod in order to minimise the weight. After quite a few failures it turned out that a fine tipped soldering iron and Recycled black rubbish bags (yes really) worked brilliantly. The variable air pressure for this task was handled by a £50 EBay airbrush compressor which had a small air reservoir tank. After trying various layups, like most of the professional manufacturers, we have now settled on using all carbon for the fuse pods.
Another light bulb moment came in regard to hinging the flying surfaces. At first we used silicon hinges which did work but were relatively heavy and difficult to get perfect every time. We later moved to using Diamond tape for the hinge along with Microfibre tape on the inner faces of the foam. (Microfibre tape sticks like the proverbial to raw pink foam). This resulted in strong, lightweight quick to apply, field serviceable (if required) hinges that were very free in their movement. They have turned out to be every bit as good as silicon hinges and in many respects far better.
After building a few Proglides we felt confident enough to move onto using Carboline. We also decided at this point that we would again take advantage of having two of us involved. Kevin’s first Carboline PROGLIDE was to use our normal wing section whilst mine was going to use one of the new F5J Syner ultra-thin wing sections. We had hoped to use a friend’s CNC foam cutter for this new prototype wing but unfortunately he moved house just at the wrong time and we all know how much time they take up to get sorted out. So, yet more wing /spar templates to make! Using such a thin wing section on a 3.8m wing brought with it a host of new structural problems to overcome and additionally neither of us was totally convinced that these Ultra-Thin wing sections were the right way to go for F5J.
Kevin progressed quickly on his first Carboline build as we now knew exactly how and what to do. He made no attempt to get this plane down to be a super lightweight and used standard sized servo’s with a heavy motor/ESC/battery in the fit out. Even so the finished RTF weight came in at just under 1440g. He estimated that had he used lightweight equipment the finished RTF weight would have been easily under 1300g. The project was moving in the right direction. After flying it Kevin liked his PROGLIDE so much that he immediately decided to press on and make a full on lightweight Carboline version. This ultra lightweight PROGLIDE, which he seemed to put together in record time, came in at 1280g. It fly’s superbly.
Meanwhile, it took me a while to iron out the new structural issues raised when building a 3.8m solid core ultra-lightweight thin section wing. Eventually though we were ready to proceed with the build. Did it go smoothly, of course not! Due to a stupid error on my part during the bagging up of the centre panel, I managed to ruin the entire panel. It was an expensive and time consuming mistake to make. After the required amount of San Miguel I decided to build a new centre section straight away. I took this “opportunity” to try a different approach with the spar structure. The rest of the build thankfully went without a hitch. The plane RTF came in at 1245g using lightweight radio gear, 1000mah 3S Hv Lipo and a 85g direct drive motor. All that was needed now was to test fly it to see if it performed as well as we hoped it would. Following several test flying sessions we can report that its flight performance has exceeded all expectations. All preconceived negative thoughts on whether ultra-thin wing sections would work well for F5J have been dispelled.
In light of the successful flight testing of the first thin wing PROGLIDE we have decided to build a heavier windy weather version using the same thin wing section. In the meantime the Carboline Ultra light just tested can be ballasted to 1550g AUW which hopefully will be capable of handling a decent amount of wind (yet to be tested). But as we all know, here in the UK there’s times when you just need a heavy plane.
For those that are interested in weights here they are.
|Part||Finished Weight||With Gear Installed Weight|
|Carbon Fuse Pod||89g||135g|
|Boom & Tailplane Mount||35g||55g|
|Left Wing Tip||128g||150g|
|Right Wing Tip||130g||152g|
|Other installed equipment||78g|
|Total AU RTF Weight||1245g|
In terms of airframe material costs, the fibreglass skinned versions come in at around £100-£130 and Carboline versions at £200-£250. Labour cost….well let’s not go there! Overall, somewhat cheaper for an equivalent commercially produced 3.8m F5J model at this kind of weight!
So what next? We are confident that we can further reduce the overall weight with minor detail changes, improved lay-ups etc, but recognise that we are getting close to what can realistically be achieved in this regard with home building.
A picture really does say a thousand words, so if you are interested in seeing how the PROGLIDE is constructed, the photo web gallery that accompanies this write up shows all. If you have any specific questions about the plane or its construction please feel free to ask on this thread.
Colin Paddon/Kevin Beale