FAI-F1D
Free Flight Indoorist
Ok gents, I'm about to go down a rabbit hole. After doing a fair bit of research, it looks like the Folkerts Sk.4 is the best choice for how I want to approach the air race.
17" Sk.4 built by fellow FAC'er George Bredehoft
I somewhat idolized this plane over the years. It's a somewhat obscure model in my disciplines, and I never encountered one in my time in Flying Aces Club mass launch events. For my own work I got most of my contest successes with a Chambermaid, which is a very smooth flying design when built as a rubber powered model. I always wanted to try the Sk-4, and now I finally have the chance, albeit in a completely different context, so here goes!
The Sk.4 was built as a replacement for the Sk.3 after its fatal crash and incorporated a larger engine, different wing structure, and a new tail design. It was initially plagued with flutter problems, but these were resolved. Unfortunately the engine broke a valve during a qualifying run and the fatal crash ended the Folkerts series of air racers.
This model will be built from foamboard, but I'm taking a different approach from the norm. If it's gonna be scale, it's gonna actually be scale. As such, wherever foam can't make the scale cut, something else goes in there. I'll tweak the fuselage cross sections for ease of construction, but scale outlines will largely prevail from nose to tail. I know there's a bonus for retractable landing gear, but I'm not going there. The gear aren't going to be present, and besides, a small (34" span) racer has no business attempting a landing on scale gear. That's a recipe for disaster.
Because of humidity concerns and because I like the lifespans of my models to be measured in decades, all the paper will be stripped off and replaced with light glass cloth. I'm keeping the design in a format where regular foamboard with paper can be used, though, so others not comfortable with this technique can still attempt the design.
One word of warning: this is not a simple model, nor is it a slow one. It there's a question as to whether you can built it the way it's presented, then you need to be looking at something else. This is a challenging build and it will be very fast and very unforgiving. Don't take excessive risks with your safety or your wallet.
On to the build...
It's got sweet lines:
If you can't tell, this is going to be a pretty curvy fuselage. A pain in the neck to draft, but worth it in the end.
The wings will borrow heavily from nerdnic's beveled outline methods, but with a few tricks of my own. A rather beefy carbon spar will enter the mix. Servos will be buried in the wing, and I'll probably go with either heavily streamlined linkages or a top drive setup if appropriate doublers can be put into the aileron faces. One diversion from scale is that I've linked the flaps and ailerons to go full span. More control=better, plus I can put the servos farther inboard and so reduce roll inertia and flutter tendencies.
I think this wing should actually be a very easy build compared with the rest of the plane. Tail surfaces, same way. Cut them from DTFB, peel off the paper, sand to shape, add carbon spars, and glass it. Done. And we're going rudderless just to avoid an extra failure model that provides no benefit at speed.
17" Sk.4 built by fellow FAC'er George Bredehoft
I somewhat idolized this plane over the years. It's a somewhat obscure model in my disciplines, and I never encountered one in my time in Flying Aces Club mass launch events. For my own work I got most of my contest successes with a Chambermaid, which is a very smooth flying design when built as a rubber powered model. I always wanted to try the Sk-4, and now I finally have the chance, albeit in a completely different context, so here goes!
The Sk.4 was built as a replacement for the Sk.3 after its fatal crash and incorporated a larger engine, different wing structure, and a new tail design. It was initially plagued with flutter problems, but these were resolved. Unfortunately the engine broke a valve during a qualifying run and the fatal crash ended the Folkerts series of air racers.
This model will be built from foamboard, but I'm taking a different approach from the norm. If it's gonna be scale, it's gonna actually be scale. As such, wherever foam can't make the scale cut, something else goes in there. I'll tweak the fuselage cross sections for ease of construction, but scale outlines will largely prevail from nose to tail. I know there's a bonus for retractable landing gear, but I'm not going there. The gear aren't going to be present, and besides, a small (34" span) racer has no business attempting a landing on scale gear. That's a recipe for disaster.
Because of humidity concerns and because I like the lifespans of my models to be measured in decades, all the paper will be stripped off and replaced with light glass cloth. I'm keeping the design in a format where regular foamboard with paper can be used, though, so others not comfortable with this technique can still attempt the design.
One word of warning: this is not a simple model, nor is it a slow one. It there's a question as to whether you can built it the way it's presented, then you need to be looking at something else. This is a challenging build and it will be very fast and very unforgiving. Don't take excessive risks with your safety or your wallet.
On to the build...
It's got sweet lines:
If you can't tell, this is going to be a pretty curvy fuselage. A pain in the neck to draft, but worth it in the end.
The wings will borrow heavily from nerdnic's beveled outline methods, but with a few tricks of my own. A rather beefy carbon spar will enter the mix. Servos will be buried in the wing, and I'll probably go with either heavily streamlined linkages or a top drive setup if appropriate doublers can be put into the aileron faces. One diversion from scale is that I've linked the flaps and ailerons to go full span. More control=better, plus I can put the servos farther inboard and so reduce roll inertia and flutter tendencies.
I think this wing should actually be a very easy build compared with the rest of the plane. Tail surfaces, same way. Cut them from DTFB, peel off the paper, sand to shape, add carbon spars, and glass it. Done. And we're going rudderless just to avoid an extra failure model that provides no benefit at speed.