F-106.........ish

MacTuk777

Active member
Been playing around with a F-106 wing design for a few weeks now. From prior experience with my MiG 15 I know that flat plate wings seem to bleed energy badly in turns and that for me the KFm4 aerofoil worked best........but when I built a 29” KFm4 for the F-106 it just looked odd. Sooooo - I decided to try my hand at designing my first FT style Delta. To be fair, Zephyr1 and Ben Harber’s MiG21/A-4 wings were definitely my inspiration here, so a big thank you to them both!
What I ended up with is this
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Once the were joined together with 1/4” dihedral at the tips they formed a ridiculously strong wing that is very light. I designed in under-camber from the leading edge droops to the tips so I can test out slow speed and stall characteristics with and without the under-camber simply by adding a bottom plate with velcro. And also to help figure out how to do full scale droops with a flat bottom.
The original design was for a 29” F-106 powered by a 50mm 4S motor. Only problem is I can’t seem to crash my 50mm MiG no matter how hard I try😆. So I decided to slap a FMS 64MM 12 blade into a butcher block fuselage and make a flying testbed out of the wing.
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Please don’t judge the fuselage too harshly, my original design for the 50mm fuselage is very involved in order to get that area ruled shape, but since none of my drawings allowed for the size of the 64mm fan (and I’d already built the wing) I decided to just slap together a fuselage and get the wing in the air to test it out. I borrowed heavily from Flite Test concepts and anyone who built Ben’s AMAZING A-4 will recognize his intake design (this is not what the 50mm version will use, but it’s simple, light and very easy to build), basically I want to figure out if my design would fly well (it’s my first attempt at a Delta), the optimum CG range, how much reflex is needed for reliable hand launch, whether or not a scale vertical stab will work well at low Rn on a Delta planform, how much control throw is required, can the LE droops be extended to a scale length without getting broken off on landing - also, do they alter the flight characteristics at this scale, and if at 30oz AUW will the 650W of power (325W/lb power loading) be sufficient - because the 50mm version will be about 6oz lighter and puts out 580W............blah blah, you get the picture - Basically will my wing fly?
If the weather cooperates I’ll attempt a maiden today🤞. Standby for a crash (I mean flight) report, complete with pictures of the carnage😂
 

MacTuk777

Active member
Maiden flight successful!
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Was definitely nose heavy on first launch, so I landed and moved the battery back 1/2”. Second launch flew out of my hand level and accelerated away. 3mm reflex works well for cruise and 4 units of up trim (6mm reflex) gives a level launch with no drop. The 64mm fan has plenty of power even with the nose shaped like a barn door!
Maiden issues:
1) low rates 1” elevator, 3/4’ aileron with 40% expo - flys like a trainer. Ridiculously easy to fly at 60-70% throttle..........but you run out of elevator authority during the landing flare.
2) high rates 1.25” elevator, 1’ aileron with 40% expo - sportier flying, but still not enough elevator to achieve a proper touchdown attitude. Also, at full stick deflection the roll rate is frightening. The roll is completely axial with no altitude loss from level flight?!?!? After 6 complete rolls the jet was still in level flight and rapidly disappearing out of view . This is the first thing I’ve built that has perfectly axial roll characteristics........Is that normal for a delta?
3)slight directional instability at low speed. Tik-toc/Dutch Roll motion starts up on approach. Not bad, but definitely noticeable.
4) pronounced roll off during vertical maneuvers (loop/ Immelmann). Had 4 units of left trim for level - so I’m thinking I need to increase the throw on the left elevon a bit.

2nd flight. Upped the left elevon travel by 5%, added about 5% more foam to the tail, added a bit more nose, increased the high rate expo to 45% on roll.
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Results:
1) unwanted roll-off from vertical is definitely improved - but still there. Going to add another 3% to the left elevon travel and re-test.
2) still directionally unstable at low speed. Will add another 5% to the fin area and re-test.
3) upped the expo to 45% on roll axis at high rate. Roll is much less twitchy at speed. Will probably keep this for now.
4) increased elevator travel by 1/8”, but still need more authority at low speed. Will add another 1/8” travel and re-test.
overall this wing flys really well. It’s weird for me to say the maiden was almost relaxing and flight 2 was just pure fun! Definitely going to rebuild this one with the 50mm set-up and a more scale fuselage.

Next step will be to extend the droops by 1/8” at the tip which should make them almost scale and test some more..........eventually I’ll “box in” the under cambered sections and see if I get any speed increase and/or weird handling issues. Once I get the correct fin area and figure out the wingtips I’ll probably start working on V2.
 

varg

Build cheap, crash cheap
Very nice. I'm glad the CG calculator yielded a good result for you. How oversized is the stabilizer? Looks like a 15-20% extra area. My X31 had a very similar planform and construction and had serious roll axis instability at lower speeds, it also seemed to be tail heavy but I think the canards may have thrown the calculator results off despite my trying to take them into account. Version two will probably have a larger folded wing with cambered tips like yours instead of a reinforced KFM in addition to a larger stabilizer, when I get to it... Hopefully by the end of the year. Your successful build has given me renewed interest.
 

MacTuk777

Active member
Very nice. I'm glad the CG calculator yielded a good result for you. How oversized is the stabilizer? Looks like a 15-20% extra area. My X31 had a very similar planform and construction and had serious roll axis instability at lower speeds, it also seemed to be tail heavy but I think the canards may have thrown the calculator results off despite my trying to take them into account. Version two will probably have a larger folded wing with cambered tips like yours instead of a reinforced KFM in addition to a larger stabilizer, when I get to it... Hopefully by the end of the year. Your successful build has given me renewed interest.
Varg,
Love the X31! I built one a few years ago from Steve Shumates plans and flew it on a 50mm fan. It only flew once - it was tiny and got even tinier before I realized I’d lost orientation with it😱. Here’s a link to his plans, the CG is marked........It flew well at that CG but definitely had instability at slow speed. https://www.wattflyer.com/forums/attachment.php?attachmentid=49743&d=1198075904
I think a 64mm foamboard version with a bit more fin (or even a gyro on the rudder) would make a seriously cool parkjet - also the one I crashed had working canards and they worked a treat!
I increased the fin on the F-106 5% first and it seemed like it helped - maybe. The fin in the picture came out to be 12% larger than the original. I get home in about a week and hopefully I can get some more testing in.
Keep us posted on you X-31!!!
 

MacTuk777

Active member
Soooooo.........6 flights later.
First/second flight - the added travel to left elevon cured the roll-off from vertical. Loops are now as they should be😃. The added elevon travel in pitch fixed the lack of authority on landing and you can now hold a fairly realistic high alpha touchdown attitude. Still had some directional instability at high AoA.

Third flight - added even more fin area. ( 15-16% Over the original fin area). Oddly there was no improvement in low speed stability. I think 10-12% increase is the sweet spot. After watching it go gently waggling by in slow flight a couple of times I realized that at high AoA the wing is blanking the fin, not even sure if adding a rudder would help because the airflow over the tail is still reduced by the wing at those AOAs. Overall the 12% increase in fin really reduced the instability to a point where you really need to be watching for it to see it (unlike the maiden where you could see it rock back and firth on approach)

Fourth flight - added the droops. 1/8” at the tip tapering to 1/32” at the inboard end. Glued a popsicle stick along the joint on the back side for strength. They really make it look like the 106 wing. Cut the fin back to 12% increased area. Flew great. Adding the droops made no difference to the flight/stall characteristics. Nose drops straight ahead. Did have to add a click of left trim. But overall a non-event. Best of all - after a less than graceful landing on a rough patch of ground the droops were undamaged.

Fifth/sixth flights - added foam to wingtips to make them flat bottomed instead of under-cambered. Was expecting an increase in performance, maybe better roll rate and half expecting the stall to be a bit more pronounced.......... I was wrong on all counts😳!!! Best I can tell the flight performance didn’t change at all. After thinking about it for a while I think the fact that the droops extend below the flat bottom of the airfoil causes it to behave like an under-cambered wing because flat bottom or not - it is still kinda under-cambered because of the droop. Either way it looks cooler and flys the same😉

Here’s a shot of it before I added the droops. Next step is to make a removable nose cone and paint it.
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MacTuk777

Active member
Looks great, any updates?

Sadly yes..........It flew a total of 9 times, and was a joy to fly (unlike my MiG-211 which is giving me fits:ROFLMAO:). On flight 9 the cheap 4 channel receiver I was using brown’d out and I lost all control response. She slowly nosed over and and lawn-darted. Pitty - this was my first, and so far best flying delta design. On a bright note I was able to salvage everything but the receiver and recycle them into the MiG.
Moral of the story - don’t cheap out on no-name brand receivers:rolleyes:
 

quorneng

Master member
Lawn dart?
I suspect foam board does not work in quite the same way as a built up Depron structure.
My Fairy Delta 2, similar in concept to the F106, also lawn darted from a complete lack of control due to the shortcomings of DSM2 when visiting a very busy site!
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Note the complete destruction but it only goes back so far. An energy absorbing crumple?
After quite a few hours got it back to this.
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As the basic wing itself was not effected it still flies in exactly the same way, still on DSM2 but only at my 'lonely' site!
 
Lawn dart?
I suspect foam board does not work in quite the same way as a built up Depron structure.
My Fairy Delta 2, similar in concept to the F106, also lawn darted from a complete lack of control due to the shortcomings of DSM2 when visiting a very busy site!
View attachment 184626
Note the complete destruction but it only goes back so far. An energy absorbing crumple?
After quite a few hours got it back to this.
View attachment 184627
As the basic wing itself was not effected it still flies in exactly the same way, still on DSM2 but only at my 'lonely' site!
Wow - what a transformation! And your windshields look great.