Rotors

[illusionist]

Back to helical prop construction, is it "better" to build the outline on a helical block, or can I build the blade outline on a flat surface, then twist it into a helical shape?

[jander14indoor]

I don't know which is better, probably depends on your building biases, skills, and practices, but key is that the helical form stay when off the block. May also depend on what shape blade you are trying to build.

Jeff Anderson
Livonia, MI

[chalker7]

I don't know which is better, probably depends on your building biases, skills, and practices, but key is that the helical form stay when off the block. May also depend on what shape blade you are trying to build.

Jeff Anderson
Livonia, MI

Yeah, either way will probably work. It might be a little easier to build the blade flat on your board and then transfer it to the block, but you could have issues with cracking the outline if you are using too thick of wood. Also, Jeff pointed out the critical issue above, whatever will work as long as you have the helical shape on your final blade.

[illusionist]

I don't know which is better, probably depends on your building biases, skills, and practices, but key is that the helical form stay when off the block. May also depend on what shape blade you are trying to build.

Jeff Anderson
Livonia, MI

Yeah, either way will probably work. It might be a little easier to build the blade flat on your board and then transfer it to the block, but you could have issues with cracking the outline if you are using too thick of wood. Also, Jeff pointed out the critical issue above, whatever will work as long as you have the helical shape on your final blade.

How do you ensure that it stays? I plan on building it flat, wetting it, forming it to the helical block, then baking it while it's on the block. Any tips?

[chalker7]

How do you ensure that it stays? I plan on building it flat, wetting it, forming it to the helical block, then baking it while it's on the block. Any tips?

The key is actually gluing the ribs to the center spar. Their changing angle is what will bend the outline into position. Wetting/baking it will also help, but with any wet-forming like that, the final shape will always be a bit off from what you want. When you glue something, it's permanently fixed.

[illusionist]

How do you ensure that it stays? I plan on building it flat, wetting it, forming it to the helical block, then baking it while it's on the block. Any tips?

The key is actually gluing the ribs to the center spar. Their changing angle is what will bend the outline into position. Wetting/baking it will also help, but with any wet-forming like that, the final shape will always be a bit off from what you want. When you glue something, it's permanently fixed.

"Center spar"? I've never thought about having one... That makes sense, but won't it add some extra weight?

[chalker7]

How do you ensure that it stays? I plan on building it flat, wetting it, forming it to the helical block, then baking it while it's on the block. Any tips?

The key is actually gluing the ribs to the center spar. Their changing angle is what will bend the outline into position. Wetting/baking it will also help, but with any wet-forming like that, the final shape will always be a bit off from what you want. When you glue something, it's permanently fixed.

"Center spar"? I've never thought about having one... That makes sense, but won't it add some extra weight?

Yeah, somewhere awhile ago I posted a link to some articles that describe how to build helical props with a center spar. When you use one, it will be much larger than your outline (start with something like 1/8" square tapering down to 1/16" square for the center spar, and 1/32" for the outline). This way the center spar will take all of the lift stress while the outline will just hold the shape.

[illusionist]

Mr. Chalker, in the second link you posted, under the "Prop spars" section, it talks about splicing the spars. What does that mean?

[mrsteven]

In terms of rotors, although only one mans opinion, I much prefer NOT having elliptical (egg shaped) rotors. They're much more difficult to build and honestly I don't notice in my experience and watching dozens of people with them, that they help at all.
It seems that more 'experienced' teams try to do it and, with minor successes, they seem to cause havoc amongst them. Often times, I've seen them break and the team was left without a functioning helicopter at our state.

As such, last year I used a tweaked parlor helicopter type design as most people use. I'm very happy with its performance and its beaten every elliptical helicopter in any given competition last season.


Illusionist, in terms of splicing, that generally means cutting in half . . .

[chalker7]

Mr. Chalker, in the second link you posted, under the "Prop spars" section, it talks about splicing the spars. What does that mean?

Since you can only construct one blade at a time on a helical block, you will have to splice (connect) two blades together to make a full rotor.