Scioly.org

HAS ANYONE THOUGHT ABOUT A CHINOCK DESIGN?

WOLFPACK

WOLFPACK wrote:HAS ANYONE THOUGHT ABOUT A CHINOCK DESIGN?

WOLFPACK

Okay, first of all, please turn your caps lock off if you want people to actually take you seriously.

Now to your question. Yes, many people have. If you scroll through the last few pages, you'll find references to chinook style. So that answers your question. Now if you want to know something more specific, or have a specific question about a certain design aspect, we'd love to help you with it.

WOLFPACK wrote:HAS ANYONE THOUGHT ABOUT A CHINOCK DESIGN?

WOLFPACK

There are various designs already floating around. Some people are thinking of basically connecting two helicopters with two different motors, but obviously matching thrust is an issue. You could also try building a transmission system or something using gears connected to the motor shafts to make the two rotors rotate side-by-side. Of course, with any of these designs, the biggest challenge is keeping weight down, which is why some people are opting instead to do a "normal" design and maximize time with that.

Anybody have any idea if when building a Chinook do you need to have two of the flat balsa wood discs that they mention in 3a of the rules? Speaking of the wood disk, does anybody have any idea what they mean by "time stops if it dislodges"?

Kordo wrote:Anybody have any idea if when building a Chinook do you need to have two of the flat balsa wood discs that they mention in 3a of the rules? Speaking of the wood disk, does anybody have any idea what they mean by "time stops if it dislodges"?

It means that if the wood disk comes off then they stop timing you and whatever your time is so far is the time of your run. For example, if it falls off at time 1 min but it keeps flying for another minute, your time is 1 min not 2.

thedoctor wrote:

Kordo wrote:Anybody have any idea if when building a Chinook do you need to have two of the flat balsa wood discs that they mention in 3a of the rules? Speaking of the wood disk, does anybody have any idea what they mean by "time stops if it dislodges"?

It means that if the wood disk comes off then they stop timing you and whatever your time is so far is the time of your run. For example, if it falls off at time 1 min but it keeps flying for another minute, your time is 1 min not 2.

I really don't understand that rule. I mean, there's no point since you can attach it pretty firmly... Chalker(7), can you explain the origin/purpose of that?

illusionist wrote:

thedoctor wrote:

Kordo wrote:Anybody have any idea if when building a Chinook do you need to have two of the flat balsa wood discs that they mention in 3a of the rules? Speaking of the wood disk, does anybody have any idea what they mean by "time stops if it dislodges"?

It means that if the wood disk comes off then they stop timing you and whatever your time is so far is the time of your run. For example, if it falls off at time 1 min but it keeps flying for another minute, your time is 1 min not 2.

I really don't understand that rule. I mean, there's no point since you can attach it pretty firmly... Chalker(7), can you explain the origin/purpose of that?

Last year at least one (possibly multiple) team(s) was attempting to extend their flight times by utilizing a thin music wire standoff at the top of the helicopter instead of the standard wooden poker. This wire at the top would stick into soft ceilings like a pin and the extra friction held the helicopter up longer, sometimes much much longer (there were rumors of over 5 minutes being achieved this way. So, with both that in mind and as a general safety control (we have seen multiple helicopters flip over and become accelerating drills towards the ground), we decided to require the upper most part of the helicopter be blunt. Since we can't just say "blunt," because every requirement has to be measurable (what is "blunt" to one supervisor might not be to another), we settled on the disc, which is easily measurable.

As for the falling off requirement, we just wanted to reinforce the other rule written in 4.j. The disc at the top of the helicopter is in a vulnerable position where it can easily be knocked off, so we wanted to make sure teams (and supervisors) knew it would be treated like any other component of the helicopter. Plus, if we said time continues after it falls off, I could see teams taking advantage of that scenario by building very heavy discs that intentionally fall off and effectively lowering the flying weight of helicopter below the minimum.

That makes sense, thanks for the explanation.

Has anyone considered a design with wider rotors, with the purpose of pushing down (or up) more air?

Rotor blade chord (technical term for width) is one of the parameters you can tune to match your rubber and maximize lift efficiency, increasing flight duration.

Just like a wing, theoretically a larger chord blade can rotate slower to move the SAME amount of air (expressed as mass flow rate, that doesn't change, you have to move enough air to hold the copter up, neither more nor less. You get the same upward force by accelerating a lot of air a little, or a little air a lot) as a narrow chord blade. Slower means more efficient (less drag by square of velocity), all other things equal. Of course, all things are NOT equal. Wider blades eventually have a significantly higher coefficient of drag than narrower blades. Trick is to balance the two. Theoretically you can come close mathematically. Pretty advanced math. Practically, probably faster to test a range of blade chords and see which works best.

Note, related to chord length is overall blade shape, see also previous discussions on this board on Larrabee shaped props vs triangle.

Jeff Anderson
Livonia, MI