2026 Speed Challenge - Telnar1236

[Houndpup Rc]

Figured out why my predictions were a bit faster than the plane - almost 20% of the drag on this design is coming from the motor can on the EDF. On one hand this is frustrating since it's hard to change, but on the other hand, it does show just how streamlined this design is.
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Unfortunately, my first though for a tail cone (mounted on struts) is only about 2% better than not having a tail cone at all, since the struts are quite draggy, but I think I may be able to improve that.
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Talk about science!😂😂👍

 

[telnar1236]

Beta files for the Rapier. There's a pretty extensive read me included with print settings, build tips, etc. I also included step files of the models I used for CFD for both ogival delta variant I decided not to go with and the Rapier itself since those could be good starting points if anyone wants to mess around with fitting different power systems or scaling the plane up or down. With a 6s setup this thing would be even more insane than it is now, but it currently isn't really set up to fit one.

 

[Houndpup Rc]

Beta files for the Rapier. There's a pretty extensive read me included with print settings, build tips, etc. I also included step files of the models I used for CFD for both ogival delta variant I decided not to go with and the Rapier itself since those could be good starting points if anyone wants to mess around with fitting different power systems or scaling the plane up or down. With a 6s setup this thing would be even more insane than it is now, but it currently isn't really set up to fit one.

Thanks!!

 

[telnar1236]

Did some more work on redesigning the thrust tube and adding a tail cone but unfortunately, I think this design is pretty much already very near its limits. Using a constant area nozzle and a tail cone, I should be able to get about another 3 mph out of the plane but I'm a bit worried this may overheat the motor.

I also looked at a more radical redesign of the whole airplane which attempted to wrap everything a bit more tightly, but even that would only give another 8 mph and it's a bit ugly, so I'm not going with it. Afterall, the primary reason to build an EDF is that it looks and sounds cool.

 

[telnar1236]

Got the EDF installed in the Sabre today

It goes in a 3-part housing that screws onto the back of the core fuselage but sticks into the tail fuselage for easy access

Since this design has an inrunner motor with the cooling through the motor in the opposite direction to the flow through the duct, it is much easier to design a good tail cone, since the tail cone should have a high pressure and can be fully optimized for pressure recovery. The EDF wires are also contained in an airfoiled fairing which should improve efficiency.

And for the Rapier, I've continued to look at ways to optimize it, which is where this crazy thing comes from. I'm not sure if I want to try and build it or fly it, but it should be a good 10-20 mph faster than the current design. However, landing speed goes up by another few mph and is already fairly high

It basically comes from making the Rapier pointier

And finally I came up with what I hope is a better tail cone for the 64mm EDF

By using a bunch of small holes in the low-pressure zone part of the tail cone I'm able to reduce the pressure inside the tail cone which should help the motor stay cool while still cutting down the drag from the blunt end of the motor can.

 

[Mr Man]

Got the EDF installed in the Sabre today
View attachment 258412 View attachment 258413
It goes in a 3-part housing that screws onto the back of the core fuselage but sticks into the tail fuselage for easy access
View attachment 258414
Since this design has an inrunner motor with the cooling through the motor in the opposite direction to the flow through the duct, it is much easier to design a good tail cone, since the tail cone should have a high pressure and can be fully optimized for pressure recovery. The EDF wires are also contained in an airfoiled fairing which should improve efficiency.
View attachment 258415
And for the Rapier, I've continued to look at ways to optimize it, which is where this crazy thing comes from. I'm not sure if I want to try and build it or fly it, but it should be a good 10-20 mph faster than the current design. However, landing speed goes up by another few mph and is already fairly high
View attachment 258416
It basically comes from making the Rapier pointier
View attachment 258417
View attachment 258418
And finally I came up with what I hope is a better tail cone for the 64mm EDF
View attachment 258419

By using a bunch of small holes in the low-pressure zone part of the tail cone I'm able to reduce the pressure inside the tail cone which should help the motor stay cool while still cutting down the drag from the blunt end of the motor can.
View attachment 258420

Wow, that thing looks insane... 😲

 

[dap35]

And the 64mm plane is done - and I actually flew it this morning (hence the slight grass stains on the left wing). And now it needs a name if anyone has suggestions - I kept the demon name when working on it, but I don't think it really fits with how graceful this plane looks.
View attachment 258352
Had one good flight and another attempted one that resulted in minor damage that has already been repaired. On the good flight, I asked someone to hand launch for me, and it wanted to roll left a bit but otherwise hand launches super easily. Thrust to weight is better than 1:1 so it climbs like a rocket with unlimited vertical and top speed is pretty good though I don't think I'm quite hitting 140. It slows down relatively well to land too, since it can come in high alpha like any other delta wing plane. Weirdly, despite the speed, this is not that hard to fly so long as you can keep track of it, and it would probably be super nice if made with LW-PLA instead of normal PLA and a lighter power system.

It's also probably the toughest plane I've ever built. On the second flight, I tried to hand launch myself and it also wanted to roll left, but I couldn't correct in time, and it hit the ground going 50 mph. The picture above is from this evening, post-crash. The nose cone was completely shattered so I reprinted that, but the only other damage was some minor and easily repaired cracking in the vertical stabilizer (it must have cartwheeled) and a bit of cracking in the motor wire channel which doubles as a landing skid. When it went in I was sure I'd be reprinting the whole thing, but it was only about 15 minutes of actual work from me to get it back in one piece and most of that was filling and sanding some dents in the vertical stabilizer that did not need to repaired to get it flight-worthy (the prints took about 5 hours combined, but I could leave the printers to do their thing). To avoid future crashes from bad hand launches I'm building a launch dolly so I can do ROG takeoffs and not have to worry about it.

I had the GPS onboard, but forgot to start it recording, so I don't know how fast it went and honestly can't really give an estimate beyond quite fast. I'm used to planes getting twitchy or otherwise weird as they get near their top speed and this one doesn't really do that, so it didn't feel that fast, but it gets small quick, and I did a low pass where it suddenly became obvious that this thing gets up and goes. Filming this thing will be pretty tough since it's so quick and fairly small (about average for a 64mm jet - 35" long with a 22" wingspan) but hopefully I can some speed measurements and a good video this long weekend if the weather lets me.

Have you thought of installing an Aura 5 for hand launch? Another option would be to use a stabilized rx and program in a launch mode (depending on what kind of gear you use).

 

[telnar1236]

Have you thought of installing an Aura 5 for hand launch? Another option would be to use a stabilized rx and program in a launch mode (depending on what kind of gear you use).

It's probably a good idea and it's something I am thinking of doing, but my big concern is the time spent tuning the gains. If I get something wrong enough, especially on pitch, the rapier is easily fast enough to tear itself into tiny little pieces so I'm keeping everything as simple as possible to minimize the number of things to go wrong.
I'll probably add one in eventually, but for now I'm also actively improving the design - I ripped v1 apart to add a tailcone to the EDF already - so a crash on takeoff is a pretty minor inconvenience since it prints so quick and is likely to be rebuilt at some point regardless

 

[dap35]

Even if you don't run the gyro for normal flight modes, a launch mode is pretty amazing. It is basically self-level mode with an offset . I run FrSky and have it set up to disengage once I take control and move either the elevators or ailerons. The Aura 5 does this very well without programming, but you do need to spend more effort to tweak the gains, etc.

 

[telnar1236]

Even if you don't run the gyro for normal flight modes, a launch mode is pretty amazing. It is basically self-level mode with an offset . I run FrSky and have it set up to disengage once I take control and move either the elevators or ailerons. The Aura 5 does this very well without programming, but you do need to spend more effort to tweak the gains, etc.

I have an Archer SR10+ that I might try that with - I think it's frsky. I have a TX16S so my receivers are a grab bag of whatever protocol is cheapest and most reliable that day - mostly flysky stuff. Feels a bit of a waste to put such a nice receiver in such a simple plane though

 

[dap35]

Yes, the Archer SR10+ can work as well. I haven't programmed an Edge or OpenTX system, but I suspect it is very doable. You basically need to set things up to put the RX in self level mode, then add an elevator mix to offset by 30-40% to set your ramp angle. The bigger trick is to get it to enable under the right conditions and then to dis-engage when you move the sticks. If you are interested, I can post how I do it for Ethos on my X20s

 

[Houndpup Rc]

It's probably a good idea and it's something I am thinking of doing, but my big concern is the time spent tuning the gains. If I get something wrong enough, especially on pitch, the rapier is easily fast enough to tear itself into tiny little pieces so I'm keeping everything as simple as possible to minimize the number of things to go wrong.
I'll probably add one in eventually, but for now I'm also actively improving the design - I ripped v1 apart to add a tailcone to the EDF already - so a crash on takeoff is a pretty minor inconvenience since it prints so quick and is likely to be rebuilt at some point regardless

I find ChatGPT is pretty good at predicting what gains will be needed, as long as you explain what your goals are, what speeds you expect to hit, what flight characteristics you want it to have, as well as pics of the plane and tell t what electronics you are running👍

 

[dap35]

I find ChatGPT is pretty good at predicting what gains will be needed, as long as you explain what your goals are, what speeds you expect to hit, what flight characteristics you want it to have, as well as pics of the plane and tell t what electronics you are running👍

Overall gains should be able to be mapped to an adjustable dial/slider on your TX and adjusted as required during flight.

 

[telnar1236]

Not 100% convinced still that I want to put a $60 receiver in an airframe where the remaining parts cost a total of about $80, but all good advice on how to get everything working - definitely gives me something to consider

 

[dap35]

Not 100% convinced still that I want to put a $60 receiver in an airframe where the remaining parts cost a total of about $80, but all good advice on how to get everything working - definitely gives me something to consider

Just think of your airframe as a big fluffy pillow around the RX They typically survive impact far better than the airframe. While you may only have $80 in parts/materials in the airframe, you also have time invested. The benefits of a small amount more in the RX can allow you to fly more than once when you make a trip to the airfield.

 

[telnar1236]

I thought the flap servo access was annoying, but the stabilator and rudder control linkage accesses take it to a whole other level

It feels like this section of the fuselage is as much access panel as it is fuselage. It needed to fit the normal 9g servo for the rudder as well as two 17g servos for the stabilators and be strong enough to support these servos against the forces associated with 150 mph flight. Hopefully it's good enough, but at the moment, the elevons are the part of the airframe I'm most worried about

It's also the last main fuselage section, so after this, all that remains between me and a maiden flight is the nose gear and the canopy.

 

[telnar1236]

Also, related to this, does anyone have experience with the strength of jb weld plastic bonder on ABS? I'm debating between that and normal CA glue to help fix the stabilators control horns in place and to prevent the stabilator from rotating on their pins. The glue is in red in the picture below

For the control horn, I plan to put a flat in the carbon fiber rod I'm using as a pin to keep it from rotating, but for the stabilator side of things, it's too long a section of the rod, so it will just be the glue holding it in place

 

[telnar1236]

And the fuselage of the Super Duper Sabre is done! Weight at this stage is 1640 grams which should give me a flying weight of about 2650 grams, about 150 grams over my original target

 

[telnar1236]

I find ChatGPT is pretty good at predicting what gains will be needed, as long as you explain what your goals are, what speeds you expect to hit, what flight characteristics you want it to have, as well as pics of the plane and tell t what electronics you are running👍

Just think of your airframe as a big fluffy pillow around the RX They typically survive impact far better than the airframe. While you may only have $80 in parts/materials in the airframe, you also have time invested. The benefits of a small amount more in the RX can allow you to fly more than once when you make a trip to the airfield.

Both of you were 100% right that a gyro is the way to go - night and day difference in hand launching

 

[telnar1236]

Flew the Rapier again today and it blew through its previous speed record by a whole 1 mph hitting 133 mph as its new best - but this time I got video for my first official speed run. I used a gyro for auto level during hand launching and you can see that the gains are way too high for this flight, but I did get them tuned in later on. You also get to see how dumb I look with a camera strapped to my head. Otherwise, not too much to say - plane go fast

Also, in case people find it interesting, the inside of the battery bay with the nose unscrewed - it's pretty tightly packed

And finally, in the beta release, I note that it should never be landed dead stick - that note can be considered outdated and dead stick landings are totally fine so long as you manage altitude and airspeed well