2026 Speed Challenge - Gadeirus

[telnar1236]

*I wish I got a video of it😂😂😂

Still one of my favorite still shots I've ever gotten from one of my designs

 

[telnar1236]

Nice. For best top speed, a prop spinner and fairings on that square firewall that blend into the fuselage. That'll cut drag to a minimum, and as speed increases, drag is your biggest enemy.

Well, next to poor flying skills. 😆

Poor flying skills are consistently my problem. Yeah, a spinner is a pretty big deal for top speed

 

[Gadeirus]

Nice. For best top speed, a prop spinner and fairings on that square firewall that blend into the fuselage. That'll cut drag to a minimum, and as speed increases, drag is your biggest enemy.

Well, next to poor flying skills. 😆

Spinner is very well something I may add. I've designed, printed, and used them on several other airplanes, though have to be careful with vibration

Thanks for the buzzard models link! I've been wanting to make some slowflyers for the backyard, behind work, etc. so this comes in handy

 

[Gadeirus]

Ok, I finally got a moment to maiden Mercury, it didn't go so well XD

I wasn't particularly in love with the wing design and I felt like it was going to give me issues, and sure enough the plane behaved in a peculiar fashion and my CG was too far aft to boot. I'm not upset about the crash at all as it will motivate me to finish up some other designs I've got in the works. It didn't cost much, but I hope I didn't trash my brand new motor, that would be a little annoying.

 

[telnar1236]

Ok, I finally got a moment to maiden Mercury, it didn't go so well XD

I wasn't particularly in love with the wing design and I felt like it was going to give me issues, and sure enough the plane behaved in a peculiar fashion and my CG was too far aft to boot. I'm not upset about the crash at all as it will motivate me to finish up some other designs I've got in the works. It didn't cost much, but I hope I didn't trash my brand new motor, that would be a little annoying.

Looked tail heavy like you said, but didn't look too bad otherwise. Good job keeping it in the air as long as you did. What was the weirdness you experienced with the wing?

 

[RickHunter]

Ok, I finally got a moment to maiden Mercury, it didn't go so well XD

I wasn't particularly in love with the wing design and I felt like it was going to give me issues, and sure enough the plane behaved in a peculiar fashion and my CG was too far aft to boot. I'm not upset about the crash at all as it will motivate me to finish up some other designs I've got in the works. It didn't cost much, but I hope I didn't trash my brand new motor, that would be a little annoying.

Been there done that. Gonna hopefully maiden the Sharknado on Sunday. Which is just a bigger version of the mercury...........think I'm gonna move the CG a bit more forward.

 

[Gadeirus]

Looked tail heavy like you said, but didn't look too bad otherwise. Good job keeping it in the air as long as you did. What was the weirdness you experienced with the wing?

Well, it's a tapered wing with constant thickness, so the effective airfoil section thickness continuously increases as you move from root to tip, which is almost the opposite of what you'd really want. I wouldn't be surprised if this could lead to nasty tip stall issues.

This is an inherent issue when trying to build a thin wing with DTFB.

I may actually try one of these funny KFm airfoils next, either with a constant-chord wing sort of what the Quickie 500 pylon racers use, or with something with a swept back leading edge. I'd love to have a bit of dihedral as it makes planes easier to fly, but dihedral makes it more complicated to build a stiff wing. If I keep it flat, I can run a continuous CF tube the length of the span.

 

[telnar1236]

Well, it's a tapered wing with constant thickness, so the effective airfoil section thickness continuously increases as you move from root to tip, which is almost the opposite of what you'd really want. I wouldn't be surprised if this could lead to nasty tip stall issues.

This is an inherent issue when trying to build a thin wing with DTFB.

I may actually try one of these funny KFm airfoils next, either with a constant-chord wing sort of what the Quickie 500 pylon racers use, or with something with a swept back leading edge. I'd love to have a bit of dihedral as it makes planes easier to fly, but dihedral makes it more complicated to build a stiff wing. If I keep it flat, I can run a continuous CF tube the length of the span.

Not so great in terms of drag, but a lot of the times it helps resist tip stalls. With a flat bottom airfoil, you're effectively increasing camber without increasing angle of attack which tends to help make an airfoil more stall resistant, especially if you can also increase the radius of the leading edge. A constant chord wing is an easy fix as well, though you don't get the potential benefits of that increased stall resistance. KF step airfoils are awful in terms of drag - they're a good easy solution to building something quick but the instant you introduce that step you get crazy turbulence and flow separation.

Yeah, building spars for wings with dihedral is a huge pain. Aluminum square tubing can be a good option since you can get it pretty cheap at a lot of hardware stores and it's easy to bend, but it's both heavier and weaker than carbon fiber.

 

[Gadeirus]

KF step airfoils are awful in terms of drag - they're a good easy solution to building something quick but the instant you introduce that step you get crazy turbulence and flow separation.

See, that's what I keep reading, too, and that's partially why I've never built one like that. Not that "low drag" and DTFB really go hand-in-hand to begin with, but some attempt at drag reduction certainly can't hurt. I have a pretty serious love-hate relationship with this foamboard stuff.