Helicopters C

[Bazinga+]

I would say Wright Stuff is a bit more involved than Helicopters in terms of the complexity that can be reached in the trim. Wright stuff involves finding an optimum pitch for the propeller just like in Helicopters, but there are also things to consider such as flight attitude, circle diameter, intentional torque-rolling, flaring props, etc., where helicopters really only need to fly up and down. In Wright Stuff, you need to match the propeller to your rubber but also find the optimum torque to launch at for a specific ceiling height, but in helicopters you can pretty much launch at whatever torque your copter is designed to handle. It doesn't matter a whole lot if it goes into the ceiling (in fact that's what we want). The only major trim variable that I can think of off the top of my head in helicopters that isn't present in Wright Stuff is that in this class you get unlimited rubber, where it is usually limited in Wright Stuff.

I am not quite sure what you mean by two and three part helicopter, but I assume you mean something like a chinook? where each rotor has its own axis of rotation? Might need some clarification before I can comment on that.

But I think I would have to overall agree with calgoddard on this one. I would say a large majority of the performance of the helicopter is going to come from just matching the rubber to the rotors and winding well. Even if you keep the rotor pitch the same as the stock freedom flight kit, but match the rubber very well, you will be very successful, and things like rotors scraping the ceiling vs. not scraping will have very little impact on the overall flight time comparatively.

But of course this is not including the bonus, which I think will be a huge challenge to get the full 75% increase in time as that introduces many more variables and engineering challenges to overcome, but it does not seem impossible either.

By the two or 3 part helicopter I meant that the bottom/top blade could be attached or separate from the body. What I meant by the contrast between helicopters and wright stuff was that Wright stuff was a lot more about calibration than building (like you pointed out circle diameter, starting torque etc.). I also agree that there definitely will be successful helicopters that use the provided kit's materials + pitch, and rubber combination will play the major role with that. But the best helicopters will surely capitalize on the other factors to try to reach the time cap. Just as an example, for the last few years of helicopters being an event the best times have been around 2:45-3:00. Helicopters is inspired, or at least incredibly similar to other independent competitions for rubber helicopters with the same dimensions, and the winning times for those are often in the 4 minute, sometimes 5 minute ranges. This is because they have many years of experience and don't have other events to worry about, and often go as far as to use carbon fiber bodies or hollow balsa bodies and have incredible knowledge of rubber winding, able to squeeze 10-15 extra winds on a 1:15 winder than the most experienced helicopter/wright stuff competitors. Overall I would encourage manipulating factors other than just the rubber length.

@Bazinga how many chromosomes you got?

42069 chromosomes. 42068 if you don't count my helicopters national medal as a chromosome.

[Unome]

By the two or 3 part helicopter I meant that the bottom/top blade could be attached or separate from the body. What I meant by the contrast between helicopters and wright stuff was that Wright stuff was a lot more about calibration than building (like you pointed out circle diameter, starting torque etc.). I also agree that there definitely will be successful helicopters that use the provided kit's materials + pitch, and rubber combination will play the major role with that. But the best helicopters will surely capitalize on the other factors to try to reach the time cap. Just as an example, for the last few years of helicopters being an event the best times have been around 2:45-3:00. Helicopters is inspired, or at least incredibly similar to other independent competitions for rubber helicopters with the same dimensions, and the winning times for those are often in the 4 minute, sometimes 5 minute ranges. This is because they have many years of experience and don't have other events to worry about, and often go as far as to use carbon fiber bodies or hollow balsa bodies and have incredible knowledge of rubber winding, able to squeeze 10-15 extra winds on a 1:15 winder than the most experienced helicopter/wright stuff competitors. Overall I would encourage manipulating factors other than just the rubber length.

@Bazinga how many chromosomes you got?

42069 chromosomes. 42068 if you don't count my helicopters national medal as a chromosome.

+1 almost as good of a comeback as mod trolling. You all right if I tweet this?

[Bazinga+]

@Bazinga how many chromosomes you got?

42069 chromosomes. 42068 if you don't count my helicopters national medal as a chromosome.

+1 almost as good of a comeback as mod trolling. You all right if I tweet this?

Go ahead.

[calgoddard]

Bazinga+

Thank you for your October 11, 2016 reply.

All of the things you mentioned fall within my broad description of "well built helicopters that use optimum rotor-rubber combinations."

"Well built" includes a good design and optimum materials. That term is not limited to, for example, excellent craftsmanship in assembling the 2017 FFM helicopter kit.

"Optimum rotor-rubber combinations" includes proper winding. That term is not limited to, for example, a particular rubber motor (length and weight) for the particular rotors (P/D and chord) of the helicopter in a static condition. It clearly contemplates the dynamic conditions of how the rubber motor is wound, as indicated by max turns put into the motor, minimal turns remaining on landing, and max time aloft.

In your post you stated "Helicopters is not like write stuff where you really just have to make a well built plane and find the perfect pitch for your ceiling height." I beg to differ.

There are other very significant factors involved in achieving success in the Wright Stuff event, besides those falling within the scope of those you recited. For example: 1) proper trimming of the plane; and 2) winding to max torque and backing off to the proper launch torque that will achieve a no-touch flight, are two of them. The gold medal winners in very competitive Wright Stuff competitions rarely, if ever, re-pitched their Ikara props. They typically took the easier option of altering the width (and therefore the length) of their rubber motors which they made very close to the max weight allowed under the rules.

[andrew lorino]

How would a rotor with many high aspect ratio blades compare efficiency wise to a rotor with fewer, lower aspect ratio blades?

[jander14indoor]

Excellent question. Not sure there is much data available to provide a clear answer.

You have two efficiencies competing with each other and going in opposite directions. And efficiency is only one factor you need to consider.
In general, as aspect ratio for a lifting surface increases (long skinny wing/blade) efficiency increases.
In general, as you add blades to a propeller/rotor system, efficiency decreases.
The problem is, the rate those move in opposite directions is affected by the system you are designing for and neither is linear. You can get away with moderately low aspect ratio without large efficiency hits, but at some point it starts getting larger faster. Same for number of blades. Not a lot of loss from one to two, more to three, even more to 4 and so on. And its the combination that you care about for system efficiency.

And frankly, that's why we have the bonus is to get you to THINK about such things and experiment with alternatives.

So, instead of me saying "I don't know" with a lot of words (see above), let me try to suggest how you can go about testing that.

I'd suggest you set up some sort of bench testing where you can measure thrust with rotors you can build to the rules and power equivalent to the rubber available. You might want to use an electric motor for consistency, but set to the torques available from a rubber motor.

Then build and test some rotors with controlled variation across the parameters (aspect ratio, blade count) of interest. Try to do it in an organized way, look into design of experiments for how to do that correctly and efficiently.

When you build your rotors, don't worry about weight, but repeatable building.

The blades for rotors testing one, two, three, four, more blade and efficiency should all be the same for all the rotors. Yes the weight will vary, but you are not trying to fly here, just measure thrust. Which you can separate from weight.

Similarly for aspect ratio, the blade count shouldn't change, the blade curve shouldn't change, the blade area shouldn't change, JUST the aspect ratio. Hmmm, with fixed diameter you may have to change the blade area, but you should try to factor that out...

And so on.

Jeff Anderson
Livonia, MI

[Bazinga+]

Adding to what Jeff said, an option to find the optimal aspect ratio efficiently is to build and test 2 blades on opposite sides of the spectrum, one much wider than the other, and see which works better. Then make one in the middle and see how that compares to the previous ones. Continuing this process for a bit will close in on the optimal aspect ratio. Make sure you use the same type and length rubber for all blades though, to preserve consistency with data.

[andrew lorino]

Thanks for the in depth answer. Another question: Disregarding the practicality, feasibility, or functionality; in your opinion, would 3D printing rotor blades violate rules 3b or 3h?

[Unome]

Thanks for the in depth answer. Another question: Disregarding the practicality, feasibility, or functionality; in your opinion, would 3D printing rotor blades violate rules 3b or 3h?

Based on my limited knowledge of Helicopters: so long as you designed the rotor, it seems like it wouldn't have pre-glued joints or pre-covered surfaces (since you "programmed" the machine to put down the glue and wing covers) and you have designed and constructed the rotors (with the aid of tools).

Obviously, your point about practicality is far more important

[jander14indoor]

As usual, not official.

3D printed blades would be problematic from a rules point of view, I'd expect some ES to be OK, and some not. Primarily because you'd have to convince them you, the student, designed the shape, programmed the printer, and then printed it.

From a practicality point of view, I suspect the state of the art in printers available to SO students wouldn't make a propeller of sufficient strength AND lightness at the same time. I certainly could be wrong, but...

Now where it would be useful and legal would be in making JIGS and FIXTURES to make helicopters. The only way to make reliably repeatable devices in the flying events is with good jigs and fixtures. When I'm building I typically spend a large amount of time and thought on how to jig up what I'm building. And I have to trade off flexibility with ease of use. Much of the skill and accuracy to build a plane or helicopter actually comes from making good jigs.

If I had a 3D printer, I could design a jig or fixture in CAD and then just have the printer spit it out. Some of the kits I've seen recently I found more valuable for the clever laser cut fixtures that the plane design or material. Leaving me more time to select good balsa and build carefully. And more importantly, more time to FLY.

Jeff Anderson
Livonia, MI