I have loved the FT-Spitfire since it came out. Mine was made from Depron because at the time, I had no access to foam board. I literally flew it to death. The Depron finally gave out, sending the poor thing to her demise. I have always fancied the Hurricane over the Spitfire, so when replacement time came I thought, why not have a go at designing my own Hurricane?
I took David's FT-Spitfire plans and loaded them into a software application called QCAD. I found out about QCAD via a Flite Test article. I downloaded it and was very impressed with it. There is a free version (although paying $50.00 for the full version is money well spent), and it's available for Windows, Mac and Linux. I run Mac-OSX and Linux, so the ability to switch between operating systems is useful for me. At any rate, after scanning in the PDF files, I drew over the top of them to create DXF files for the FT-Spitfire. I then modified them until I had a Hurricane.
I admit it turned out to be trickier and more work than I first envisioned, but it was also a fantastic learning experience. I wanted my Hurricane to have similar flying qualities to the Spitfire, so I kept the wing area and the fuselage length roughly the same.
The Design Process
The centre section on the real Hurricane is much wider than the Spitfire so that meant a three piece wing instead of the FT-Spitfire's two piece wing. The shape of the wing caused me a bit of grief in calculating the angle between the lower wing edges and the leading edge. This was due to the taper on the outer wing leading edges.
Everything seemed to go smoothly, and suddenly I was printing and sticking together my plans. However when I started cutting foamboard, I found quite a few things I had missed and one by one these were all corrected with one exception. The Hurricane's wing has a wider chord than the Spitfire. I didn't want to widen the chord on my design because I was worried about allowing for that in the fuselage. The result was a wing which looked too skinny, so even before final construction I discarded the first wing and adjusted my wing design. For reasons I will explain shortly, I revisited the wing, widened it further and finally had a third wing that looked like a Hurricane wing.
Test Flying - Mis-Diagnosis and Modifications
During the first flight the model seemed to have a very mild Dutch Roll. I was intrigued by the fact that the original Hurricane also suffered from this. I applied the same cure they did which was to increase the vertical stabiliser area and add the under-fuselage strake. The next test flight went well...at first. For about thirty seconds, I thought I had cracked it but then I was banging the aileron sticks from one side to the other trying to keep the thing level. I deduced the problem was my skinny wing and so I went back and widened the wing. I had already scrapped the first attempt at the wing as not being correct. It just did not look like a Hurricane wing. So I built three wings and settled for the final wing.
It turned out that both of my theories were totally wrong. There were never any instability problems in the the model at all. I realised that the real culprit was a dirty aileron pot. After fitting the third and final wing I noticed that if you wiggled the aileron stick and then let go, the aileron servos would move up and down all by themselves! A quick spray of electrical contact cleaner into the offending pot and my problems were solved. Needless to say the next test flights were a happy joy in that it flew great. I don't regret building three wings because I think the final wing looks right while the other two are not quite there.
The above video is not the best in that the plane is too far away. I'll try again to get some better video footage and update this article when I do.
Here is another video filmed by my friend Shaun Atkins:
3D Printed Parts
I designed and printed a cockpit canopy, engine exhausts and a hatch cover for under the nose. The canopy is printed as a number of parts. The basic canopy is in two parts (front and rear), and the canopy frames are in 10 parts which can be printed, painted and then glued to the canopy.
My friend Shaun Atkins suggested copying Josh's idea for the Mini Scout to secure the power pod at the front of the fuselage. Hence I added some holes to the exhausts that I had found at Thingiverse and so now the power pod is held in place by two skewers running through the holes in the exhaust from one side to the other. I scaled it up from the original but I think I should have increased its size even more.
Finally the hatch cover simply reduces drag a bit. Hinging it at the front means I can simply tuck it under the foam at the other end which is why I Hinged it there. The drawback is, once installed, you cannot slide the powerpod out. I do not regard this as a big deal because, if I need to remove the powerpod I can remove the hatch by sliding a knife under the round supports on the outside and removing the barbeque skewer. By the way the outer supports are simply to spread the load across the foam and to provide a harder surface to pull against so that the holes in the fuselage do not widen with use.
I have a really poor 3D printer, so I tend to do things in parts that are likely to actually print successfully on my printer. What I am getting at is if I can print them, anyone can, so you should not have any issues if you go down this path. I will include a zip file containing the STL and sketchup files for all the parts down at the bottom of this article.
What if I Don't Have a 3D Printer?
No problem. A Flite Test contributer by the name of pintokitkat wrote an article where he had designed a Spitfire canopy which could be printed out, stuck together and then glued onto the plane. I took his canopy design and modified it for the Hurricane:
The exhausts could be done in foam or left off and the lower hatch could be done in posterboard, left off or using the same apporach as in the FT-Mustang.
I have really enjoyed the experience of designing, building and flying. I cannot recommend it enough. I have another design on the way and ideas for more.
The build is almost the same as the FT-Spitfire with minor differences, so the video below goes through these differences. If you are familar with the FT-Spitfire build and watch the video below then you should have no problems.
The fuselage is put together the same as the FT-Spitfire, its just that the parts have a different shape. There is one extra former to cater for the short straight section of turtle deck behind the cockpit. The only other difference is, if you are using the 3D printed cockpit then the second last former needs to be angled to match the angle on the rear edge of the printed cockpit. If using the paper version of the cockpit then it can be vertical.
The major difference here is we have three wing sections (left, right and centre) instead of simply left and right as with the FT-Spitfire. Each section is built the same.
The picture above shows the three components of the centre section: The wing surface, the spar and the trailing edge support. I creased the folds in the wing and cut the double bevel in the leading edge in exactly the same way as all the FT builds. The centre section spar will protrude from each side so that the outer wing spars can overlap them on the join. Each join being identical to the spar join in the FT-Spitfire.
Here we see the spar glued in place and the trailing edge support being glued on. One difference is that, with the FT-Spitfire, the trailing edge support was inset a little from the trailing edge of the lower wing surface. The Hurricane has them lined up level with the trailing edge of the lower wing surface.
In the above picture I have run glue across the leading edge and main spar, folded the wing over and held it until dry and then added the glue to the trailing edge and held it down until dry. It is really important to wait until the glue is absolutely dry at this stage in each of the three wing sections. It can seem dry and then open up at the trailing edge and when that happens it tends to ruin your day. I take Josh's advice here and I sing a jaunty tune (in my head so as not to upset people who do not appreciate my singing). I give it a good solid 5 minutes. It is about as much fun as watching grass grow but it only takes 5 minutes and it is worth the wait.
As you can see from the picture above we have the same three parts for each outer wing section (i.e. wing panel, spar and trailing edge support).
Each outer panel goes together in almost exactly the same way. One difference here is that, on the final wing, I tapered the spar so that it is full height towords the fuselage and 10mm at the tip. I did this under the mistaken impression that the high camber at the tips was causing turbulence. It wasn't so you can leave out the taper if you want. However the wing does look cooler with the taper and its not any more difficult.
Because the leading and trailing edges are angled inwards instead of being parallel, you need to be careful when holding the wing down to make sure you have the leading and trailing edges flat on the building surface. Its not really difficult just something to watch for and keep checking. Once again its jaunty tune time.
Next we have to join the three sections together.
The process is identical to that of the FT-Spitfire with two exceptions. Firstly we have to do it twice and secondly the dihedral each time is half of what it was for the FT-Spitfire. The planes have a wingtip support just like David included in his Spitfire except that it is 50mm high instead of 100mm.
We add glue to the spar join and top wing surface and hold the together until dry. Make sure you dry fit them first and trim as required to get a good fit before reaching for the glue gun.
Next run another bead of glue over the join and smear it flat with a piece of foam.
The next step is to run a bead of glue along the bottom the wing, smear it flat and then wrap some clear tape over the join.
Finally, to quote Josh, you repeat the process for the other side. The assembly of the wing to the fuselage and the tail feathers is identical to the FT-Spitfire. I installed the wing in the fuselage and then added the aileron servos. I fed some string with a weight on the end from the wing tip and out of the hole in the centre section and then tied the servo leads onto the string and pulled it through. One issue with the tapered wing spar is there is not enough room to slide the aileron servos inside the wing.
I used a hobby knife to slice out a section of the foam inside the wing so that it will fit. You could simply cut out a rectangular section out of the bottom wing surface but this way is neater.
That is all there is to it really. The next section provides links to the plans and print files.
Plans and Data
Finally here are the plans and 3D print files. They are all gzipped compressed files, but you should be able to uncompress them by double clicking on them after download. Happy building and flying.