Helicopters C

[_deltaV]

What would be the best way to go about testing the thrust and efficiency of several different blade systems? So far all I've thought up of is testing them in front of a fan Wind Power style but i'm certain there's a better way. How would the motor setup described above work? Would it be a motor with a torque equivalent to a rubber motor lifting something or would RPM of the propellers be measured? Sorry just a little bit confused about the best way to go about testing this.

[Bazinga+]

What would be the best way to go about testing the thrust and efficiency of several different blade systems? So far all I've thought up of is testing them in front of a fan Wind Power style but i'm certain there's a better way. How would the motor setup described above work? Would it be a motor with a torque equivalent to a rubber motor lifting something or would RPM of the propellers be measured? Sorry just a little bit confused about the best way to go about testing this.

From experience, my opinion is that testing heli blades in front of a fan is not an accurate, nor very useful method for testing efficiency. The reason for this is that the optimal blade depends on the rotation speed of the blade, and also a fan in front of the blade does not model the air flow provided by the blade.
I think the best ways of testing the blade efficiency will require you to attach the blades to the heli body and wind up the rubber. This way you test with the right angular velocity at which the blades are meant to spin and also have lift coming from the blade rather than the reverse. A nice way of monitoring the lift (haven't tried this myself but read this method in a previous post and it seemed like a great idea) is to flip the helicopter over on a scale, zero it and then let it spin, pushing against the scale. Personally I prefer actually flying helicopters with each blade assembly since it accounts for all the factors, but this method takes more time since I need to make a ton of blades to get the right assembly.
I'm sure a motor rig could work, but it is quite difficult to implement it in a way where the motor accurately models the system. Particularly, as I mentioned, a lot of the air flow from the blade is not directed straight down so the fan would not be an accurate replication of the air flow from the blade.

[jander14indoor]

One of the things I love about Helicopters is the ability to static test and learn a lot. When the first version of the rules came out years back I built a dedicated copter to just that. To heavy to fly, but easy to mount on a scale for static testing. And you don't have to do it upside down on an electronic scale.

Here's what I did. I built a helicopter with the style of one blade attached to the motor stick and the other free to rotate from the motor stick. I had a motor stick arranged symetrically for the rubber to run down the center so the rotor and stick could spin balanced. I built a heavy base (so the helicopter WOULDN'T fly) to attach to the bottom of the stick, but with a bearing to allow it to spin freely. Blades were attached so I could easily change the pitch. I powered the system with a rubber band of consistent size for consistent torque. When ready to test, sit the base, helicopter and rubber on the scale and tare it to zero. Wind motor, attach to helicopter, attach helicopter to base sitting on the scale. Let it spin. Your scale should show negative values, that is the thrust. If you wind consistently, you should get consistent comparable results between rotors. Keep the rotors consistent and you can compare motors or torque vs thrust.

Result. I was specifically trying to determine if the pitch of two rotors closely spaced should be the same or not. Theory says two closely spaced props can generate more thrust than two widely spaced ones and first rotor should be at higher pitch than the second one. I was able to demonstrate the later, ran out of time to demonstrate the first one.

Some alternatives.
Use an electric motor of appropriate torque. Nice thing about this is you can control torque directly by controlling current if you have the motor characterized.
You can test one rotor at a time, or systems of rotors.
Some things to watch, you don't want the rotors to be too close to a surface on the outgoing side. You don't want to get ground effects mixed into your results as our copters don't fly that way.

Keep in mind, static testing is not flying. Its value is allowing you to test a lot of alternatives fast without worrying about flying space. But ultimately you have to confirm what you learned by flying!

Jeff Anderson
Livonia, MI

[_deltaV]

Thanks for the advice guys, I built a test rig similar to what Bazinga said. I glued my helicopter without the bottom rotor to a piece of carbon fiber set up so it couldn't twist, only lift, and set it on a scale that was zeroed. My results indicate that a higher length/width ratio increases the lift, but I've only tested with blades at a 30 degree angle.
I have another question that arose when I was actually flight testing. I'm using a 2 bladed free rotor at the top and 2 static blades at the bottom with a 25 cm. motor stick, and the motor stick consists of round discs at the top and bottom with 3 equally spaced lengths of balsa running between the discs. The problem I'm having is the helicopter seems to want to tip over and run into the ground. I've tried adding mass to the top, bottom, and putting a tail on to lower the center of gravity. Any idea what could be causing the instability?

[bernard]

Dave Zeigler's award-winning Helicopters kits are now available on his webpage: http://freedomflightmodels.com/paypal.htm.

Helicopters 2017.png

[Bazinga+]

Whoa... I am 'blown' away by his new design. The new blade shape is very interesting, and I think I know where he got the idea (optimal shape for blades is similar to that except more curvy). But regardless, I think all these changes from the traditional 2 blade, 2 stick, regular cambered rotor are not very beneficial. Of course I havent had a chance to test it out yet, so these are just theories and guesses, but from my experience the traditional design always comes through. I remember in the 2013-14 season a new kit was released with 3 blades on top along with some other interesting changes, but my impression was that the best helicopters at nationals ended up being the down-to-earth 2 bladed 2 stick design. Also something I found very odd was that the provided rubber is .094" and .085", which is quite thin for helicopter rubber(maybe because weight limit is lower light rubber can be used, but so far I have had best results with .125" and .116")

I know Ziegler spends a lot of time testing out various designs and optimizing and whatnot, but I cant help but think that even if a 'standard' design was optimal, Ziegler would probably still release something new just for the fun of trying something new and exciting or to encourage teams to buy the 'new' kits.

Does anyone else think this design may end up potentially throwing competitors off with the top helicopters being the classic model, or does it appear like the new blade design and 4-rotor assembly maybe be beneficial? Most people haven't received kits yet (which includes me, despite little faith in this new idea I look forward to trying this out) but maybe someone has tried something similar in the past.

New Heli:


classic blade:

[DoctaDave]

Whoa... I am 'blown' away by his new design. The new blade shape is very interesting, and I think I know where he got the idea (optimal shape for blades is similar to that except more curvy). But regardless, I think all these changes from the traditional 2 blade, 2 stick, regular cambered rotor are not very beneficial. Of course I havent had a chance to test it out yet, so these are just theories and guesses, but from my experience the traditional design always comes through. I remember in the 2013-14 season a new kit was released with 3 blades on top along with some other interesting changes, but my impression was that the best helicopters at nationals ended up being the down-to-earth 2 bladed 2 stick design. Also something I found very odd was that the provided rubber is .094" and .085", which is quite thin for helicopter rubber(maybe because weight limit is lower light rubber can be used, but so far I have had best results with .125" and .116")

I know Ziegler spends a lot of time testing out various designs and optimizing and whatnot, but I cant help but think that even if a 'standard' design was optimal, Ziegler would probably still release something new just for the fun of trying something new and exciting or to encourage teams to buy the 'new' kits.

Does anyone else think this design may end up potentially throwing competitors off with the top helicopters being the classic model, or does it appear like the new blade design and 4-rotor assembly maybe be beneficial? Most people haven't received kits yet (which includes me, despite little faith in this new idea I look forward to trying this out) but maybe someone has tried something similar in the past.

New Heli:


classic blade:

I believe the kit has the option to build 2, 3, or 4 bladed rotors so competitors can choose which setup to go with. As for the thin rubber, it is most likely due to the fact that the rotors are only 20cm in diameter this year, and the helicopters are very light as well.

[jander14indoor]

<SNIP>
I have another question that arose when I was actually flight testing. I'm using a 2 bladed free rotor at the top and 2 static blades at the bottom with a 25 cm. motor stick, and the motor stick consists of round discs at the top and bottom with 3 equally spaced lengths of balsa running between the discs. The problem I'm having is the helicopter seems to want to tip over and run into the ground. I've tried adding mass to the top, bottom, and putting a tail on to lower the center of gravity. Any idea what could be causing the instability?

When you say two 'static' blades, I assume you mean they are fixed to the motor stick, but you expect them to spin counter to the top 'free' rotor?
Couple of possible issues.
- Center of gravity of the system is way to high so the system isn't stable. Have to rebuild to fix that, paying particular attention to the weights of the rotors and the balance point of the motor stick.
- Center of aerodynamic effort is too low. The lower rotor is creating more thrust than the upper, possibly compounded by being through different center lines. Several possible fixes, you'll have to experiment to see which works best.
-- Increase the thrust of the upper rotor while reducing the thrust of the lower. More blades or area on upper. Relatively more pitch on upper.
-- Is your motor stick bending causing misalignment of the rotors? Stiffer motor stick. This has been a problem in prior years. At these light weights stiff motor sticks are problematic. You'll notice the new Freedom Flights design has a lot of bracing on the motor stick.

Good luck,
Jeff Anderson
Livonia, MI

[calgoddard]

World record holder Stan Buddenbohm is now selling an excellent kit for this event.

Details are given at https://www.amaglider.com/static/scioly ... t-2016.pdf

The well written and nicely illustrated instructions for Stan's MINI-PEARL helicopter kit are geared toward students with no prior building experience.

[HandsFreeCookieDunk]

World record holder Stan Buddenbohm is now selling an excellent kit for this event.

Details are given at https://www.amaglider.com/static/scioly ... t-2016.pdf

The well written and nicely illustrated instructions for Stan's MINI-PEARL helicopter kit are geared toward students with no prior building experience.

Am I correct in assuming that this kit comes with jigs? They are mentioned in the description, but not in the "included" section.
Anyway, I'll be interested to see how this more traditional design compares to the Freedom Flight Kit and its thin rubber.