Houndpup Rc
Legendary member
Aw man, that's too bad!
2025 Speed Challenge - Telnar1236
- Thread starter telnar1236
- Start date
Proptastic
Active member
Could you reshape it with a heat gun? If not then print it again. I can't guess how fast it could be, but it's definitely innovative. Nice work.
telnar1236
Elite member
Already reprinted and ready to go again, and with some minor improvements - the nice thing about this thing's size is that it's less than 48 hours of printing for the whole thing. The big questions now are mostly if the weather cooperates tomorrow and of course if this thing actually flies.
I've never had good luck with heat guns (or hair dryers as the cheap equivalent). The problem tends to be that the skin starts to sink into the space between the infill since it's only one layer.
Houndpup Rc
Legendary member
Nice!!! Great job man!
telnar1236
Elite member
It's a bit of a mixed bag to report from the first flight. Starting with the bad, I won't have any good speed runs in time for the competition, so if it does end up doing well, it will have to be an honorable mention. My first guess for aileron throws was far too high and this plane is already on the edge of my piloting skills (I'm a fairly mediocre pilot) so I ended up crashing shortly after launch. If you want to have any chance of seeing the plane for more than about a second, you need to turn the resolution to 1080p and full screen the video.
Now on to the good - it flies, hand launching is a non-event and significantly easier than even my modular trainer jet because of the ridiculous thrust to weight ratio, and it seems like it will be FAST. I never got it out of launch mode which has 10 degrees up elevator and was struggling with roll the whole time while also climbing, and I still hit 75 mph in the first 15 seconds of the flight.
And now back to the bad - the bungee launcher I designed was almost comically bad and significantly worse than just hand launching. At least the damage was minor and I could glue it back together for the flight in the video.
And now back to the bad - the bungee launcher I designed was almost comically bad and significantly worse than just hand launching. At least the damage was minor and I could glue it back together for the flight in the video.
telnar1236
Elite member
I think my next step in this project will be to reprint the plane fully in ABS. This will both save a bit of weight and mean and I can safely keep it in my car to fly after work. Now that I don't have the time limit, I also want to improve the hatch so you don't need to undo 6 screws every time you need to open it and do a couple of other quality of life things I neglected in the rush to try and get it built.
Brian B
Elite member
Awesome project. Keep working at it. Just don't leave it in the car to long!
Houndpup Rc
Legendary member
That's too bad! Though be all means keep trying! (I am still going to keep trying to pass @Mr Man and break the foamboard record!)
telnar1236
Elite member
I got the airframe reprinted for the third time with some refinements. The only visible change from v1 is that the elevons now have an additional hinge point (this was in the v2 in the "flight" video as well). The airframe is also fully ABS now which is why the elevons are now red since I didn't have blue ABS on hand, so I should be able to leave it in my car safely.
I haven't redesigned the hatch yet, since I figure if I just crash it again, there's not much reason to waste the time on that, but the geometry of the fuselage now allows for a redesigned hatch, so I won't have to build a whole new v4 if it works.
I haven't redesigned the hatch yet, since I figure if I just crash it again, there's not much reason to waste the time on that, but the geometry of the fuselage now allows for a redesigned hatch, so I won't have to build a whole new v4 if it works.
Houndpup Rc
Legendary member
Sweet! What model EDF do you have in there?
telnar1236
Elite member
Powerfun 4s 50mm fan. So far as I know, it's the highest thrust 50mm fan out there you can get for reasonably cheap, so long as you set up the nozzle carefully, but on the flip side it is very sensitive to the inlet and nozzle design and can be quite bad if set up wrong. If I get this working well and it's fairly fast, I might put their 3s fan in there instead since I know from experience you can run it on 4s, at least for a bit, and the power is a bit crazy.
Houndpup Rc
Legendary member
Nice! I have the 64mm Powerfun version! Maybe if this flies you should submit it as a resource with the vid!
Mr Man
Mr SPEED!
Yeah, that’d be cool!
I REALLY love the looks of this!
telnar1236
Elite member
I may end up just posting the STLs to this thread if it ends up working but submitting it as a resource isn't out of the question. In the interest of time, I didn't really focus on the build process, so it's not all that great to put together. It's not awful, just because of how small it is, but pretty much every part requires at least some post processing as it stands right now, and there's a lot of fiddly gluing stuff together that all has to be done in a specific order or you have to reprint the whole thing.
telnar1236
Elite member
I've unfortunately come to the conclusion that the combination of this plane and me as a pilot just won't really work. It's too small and too fast for me to manage. I've gotten it up to 126 mph, but at that point it's a tiny dot that I can't really keep track of and I lost control and crashed pretty quickly. I think it could go faster, but not with me at the controls. Launching it is also a bit of a lottery - it's about a 50-50 chance on if it gets airborne or smashes into the ground. Ultimately, because I designed it so fast, and especially because it's so small to make the print time as short as possible, I think I compromised it's flyability for the sake of speed.
I still want to go faster however, and I like the basic design, so think I'm going to split this into two longer term projects.
One will be a boundary layer ingesting wing designed to use a 64mm fan instead of the 50mm fan in this design. It will be designed for flight time more than speed in an effort to keep the stall speed more reasonable and because I want to get more of sense of how this kind of design flies without it being a dot I can't see most of the time. The wingspan is 1200mm vs. the 500mm wingspan of the original speed plane. It uses the MH 45 flying wing airfoil which also makes the wing more efficient than that of the original plane, although it's so much bigger that it still won't go anywhere near as fast.
The other design will be meant to go fast. It's much more conventional and uses 2 of the 50mm EDF units instead of the single one I used in the original. This gives it enough power to carry a larger wing and more importantly, retracts, which will make launching a lot simpler. I'm currently still working on optimizing it to reduce drag, but this is the current design. My current prediction is 140-160 mph for the top speed, but I'm hoping to maybe get a bit faster still.
At the heart of this design is a new airfoil I designed to get the performance I'm looking for. It's a laminar flow airfoil designed for Reynolds numbers between 300,000 and 1,500,000 and the XFoil and CFD predictions have it outperforming even the amazing MH27 and MH 16 pylon racer airfoils, especially at lower Reynolds numbers. It is substantially more efficient than the original NACA airfoil I selected for the smaller flying wing which allows a thicker larger wing (to fit gear) and a lower stall speed without a significant penalty in terms of top speed.
As a comparison with the MH 27 airfoil, here are some plots of the performance. The MH 27 airfoil is in pink, and my airfoil in dark blue. You can see the difference between the two is not all that substantial. My airfoil has less about 15% less drag at a Reynolds number of 1,500,000, and at lower angles of attack at the cost of a smaller drag bucket. This increases to 30% less drag at a Reynolds number of 300,000 Since I'm not pylon racing, I don't really need to worry about higher drag above a 4g turn, since I won't really be turning that hard at high speeds anyways. XFoil didn't converge for my airfoil at higher AOAs, but from CFD, the max lift coefficient is almost exactly the same. The pitching moment is also very comparable which means I'm not adding back in trim drag.
I still want to go faster however, and I like the basic design, so think I'm going to split this into two longer term projects.
One will be a boundary layer ingesting wing designed to use a 64mm fan instead of the 50mm fan in this design. It will be designed for flight time more than speed in an effort to keep the stall speed more reasonable and because I want to get more of sense of how this kind of design flies without it being a dot I can't see most of the time. The wingspan is 1200mm vs. the 500mm wingspan of the original speed plane. It uses the MH 45 flying wing airfoil which also makes the wing more efficient than that of the original plane, although it's so much bigger that it still won't go anywhere near as fast.
The other design will be meant to go fast. It's much more conventional and uses 2 of the 50mm EDF units instead of the single one I used in the original. This gives it enough power to carry a larger wing and more importantly, retracts, which will make launching a lot simpler. I'm currently still working on optimizing it to reduce drag, but this is the current design. My current prediction is 140-160 mph for the top speed, but I'm hoping to maybe get a bit faster still.
At the heart of this design is a new airfoil I designed to get the performance I'm looking for. It's a laminar flow airfoil designed for Reynolds numbers between 300,000 and 1,500,000 and the XFoil and CFD predictions have it outperforming even the amazing MH27 and MH 16 pylon racer airfoils, especially at lower Reynolds numbers. It is substantially more efficient than the original NACA airfoil I selected for the smaller flying wing which allows a thicker larger wing (to fit gear) and a lower stall speed without a significant penalty in terms of top speed.
As a comparison with the MH 27 airfoil, here are some plots of the performance. The MH 27 airfoil is in pink, and my airfoil in dark blue. You can see the difference between the two is not all that substantial. My airfoil has less about 15% less drag at a Reynolds number of 1,500,000, and at lower angles of attack at the cost of a smaller drag bucket. This increases to 30% less drag at a Reynolds number of 300,000 Since I'm not pylon racing, I don't really need to worry about higher drag above a 4g turn, since I won't really be turning that hard at high speeds anyways. XFoil didn't converge for my airfoil at higher AOAs, but from CFD, the max lift coefficient is almost exactly the same. The pitching moment is also very comparable which means I'm not adding back in trim drag.
Houndpup Rc
Legendary member
Yeah, I know! Flying these planes are NO JOKE!
Houndpup Rc
Legendary member
That's how it was for me with the Radjet....@Mr Man gets it right every time!😲😂
Houndpup Rc
Legendary member
Sounds really cool! BTW do you think it would fly with a 64mm if scaled up? (I am hoping to get my own 3D printer this fall...)
telnar1236
Elite member
Hand launching is definitely a difficult skill for these faster planes
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