Designs

[StampingKid]

As chord goes up, wing area goes up, lift goes up, flight speed goes down, drag goes down. But as chord goes up, drag goes up. Trick is to balance the two.

Jander, does drag go both up and down?

[jander14indoor]

The magnitude of the drag force vector goes up and down, direction is always opposed to the direction of motion.

When I said "balance the two" I meant to minimize the magnitude of drag by finding the sweet spot of large wing chord slowing flight speed.

Jeff Anderson
Livonia, MI

[danyalukin]

What do you think of the proportions of tailboom to motorstick in the freedom flight model of last year? I have a feeling the tailboom is too long...
What would be a good length of each? would that the morotstick needs to be at least 25-30cm to get the most of the rubber...and i would say same for tailboom... what do you think?

[smartkid222]

What do you think of the proportions of tailboom to motorstick in the freedom flight model of last year? I have a feeling the tailboom is too long...

i like the way you think. Thats true it did seem really long so i just cut off a few inches from the end because 1- it was really low density wood, very fragile and 2. it was tapered closer to the end so it was even more fragile. It was really easy to break so i just shortened it but about 2 inches.

[jander14indoor]

Can't say about the Freedom flights design from last year, but you actually need a long tail boom to get the dynamics right to fly on the tail as well as the wing. This will be especially true this year with no limit on tail chord. Big tails need large separation from the wing to work right. To look up theory and formulas behind this, search on tail volume.

Jeff Anderson
Livonia, MI

[danyalukin]

Big tails need large separation from the wing to work right. To look up theory and formulas behind this, search on tail volume.

Jeff Anderson
Livonia, MI

Most likely I'm wrong, but by the formula Tail Volume = (Tail Area/Wing Area) X ( Tail Arm/Wing Avg. Chord), one could see that the greater the area of the wing, the less the Tail Arm, that is, the distance from the LE of wing to LE of stab...
So bigger stabs must be closer to the wing...i would assume.

Please correct me...

My new plane:

Stab = 28 by 9
Wing = 40 by 12.5
Both are rectangular, not elliptical (yet!)

Using this table (which the Freedom flight model follewed, with 1.2 Tail Volume):

AMA gas models 1.0 to 2.0
Mulvihill rubber 1.5 to 2.2
Wakefield rubber 1.4 to 1.7
Indoor rubber duration 1.0 to 1.5
Hand launched glider .6 to 1.1
Full size 1913 Moraine-Saulnier, Type 'L' .16

I got that to get the 1.4 Tail Volume, the Tail Arm must be 35 cm... But i think thats reasonable, because pennyplanes, with Tail Area/Wing area proportions around .7-8, have a VERY short Tail Arm...

So, what do you think, makes sense?

[eta150]

There was clearly a superior kit last year, the Leading Edge (although it was a harder build). Does anyone know if they're having another model like that this year?

[blue cobra]

No offense is intended, but why do people use kits? It seems almost like "cheating" to me. Of course it's not an actual violation of the rules, but with my scratch built planes, I can say that I made it. I thought of everything that's on it, and cut and sanded the wood to build it. When I get great flights, it was my thought that produced it. With a kit, you're just using someone else's ideas and adding some glue.

[StampingKid]

People use kits because everything is in the box. Everybody doesnot have a hobby store nearby much less a store with ultralight balsa, props and rubber. Buying balsa one place online and props at another and getting rubber elsewhere you can spend more in shipping than anything else. And just because it is a kit doesnot mean it will fly any less or better. You still have to test and adjust to maximize its potential. And there's more to building a kit plane than adding glue. Building a good kit will also teach you more than just how to join part a to part b.

[andrewwski]

Kits are a good place to start if you've never built a plane before. They contain everything you need to get flying, and have instructions on how to build and fly.

Doesn't matter if you build from a kit or not, if you don't spend extensive time trimming and flying, you won't get good results.

I never cared for the idea of kits because it takes the design aspect away from it, but it seems the distribution in the positioning is pretty equally distributed among kit and non-kit. I've seen kits win, and custom planes win. I've seen custom planes terrible, and I've seen kits do terrible.

I built from a kit (Harlan's) one year. It was a nice kit, had thorough instructions, and did give me a few ideas that I hadn't been exposed to before. But there were a few things I didn't like about it too - I much preferred my custom planes (we had built custom the two prior years, but came in second to a kit both years). The kit would be a good starting point, but for us it was not ideal - we ended up making a custom plane anyway (and would have gotten first if the judges followed the rules...).