Helicopters C

[Krypton]

Our helicopter appears to fly alright, but it always lands with more than half of the rubberband's winds remaining. Does anyone know why this may possibly be and what could be done so that the helicopter makes use of all of its winds?

Either you need to shorten the length of ur motor or increase the thickness of it.

[aldragon]

How did you guys reach 200 winds? Hearing that number is insane. I've been using .094" thickness and I've been going 100 winds with a 15:1 winder, giving me a time of at least 1:30 (being beaten up, my best time been 1:45 - did not hit the ground and was in better condition). I'm trying to increase my flight to 2 minutes but I'm not sure how much longer I should make my rubber band. I tried using .085" thickness instead with 105 winds and got a much shorter time. I need to test for hours to figure a somewhat better optimization and my competition is in a week so I don't have a lot of time. Any help is appreciated!

[Bazinga+]

Just wondering, which has given you better times: stationary top and rotating bottom or both rotating?

In my experience stationary bottom and rotating top has worked best for me, but realistically there's virtually no difference. Because of the balance of forces both rotors will end up going at the same angular velocity whether one is stationary or not as long as both rotors are built to the same specs. The biggest difference is the extra weight required to make the bottom rotor rotate (adds about .05-.07+ grams to make it rotating because of the extra length of piano wire and the tube).

I wanted to switch over to both rotating because I was under the impression that the body would then count for the bonus if you attached a small rotor on it, but now i'm a bit unsure about that.

The official clarification on that is very unclear about the bonus as is the description in the rules. The clarification states that a legal lifting surface is defined as something that "must contribute lift to the overall flying assembly. An easy way to demonstrate that would be to demonstrate flying it with and without the surface, if the surface is not present then the flight would be significantly different."

Fuzzy words like 'significantly' low key trigger me, especially in this case where 'significantly different' has such a broad interpretation. So if I attached a small (~5cm) single rotor to my center body is that enough for the bonus? Or does the body have to have a net torque applied to it? If it needs a net torque to be applied then how is it possible to get 3 single bladed bonuses with just one rubber band? smh.

[Krypton]

Just wondering, which has given you better times: stationary top and rotating bottom or both rotating?

I wanted to switch over to both rotating because I was under the impression that the body would then count for the bonus if you attached a small rotor on it, but now i'm a bit unsure about that.

.

The single bladed rotor has to be freely moving from the motor stick :/ Having a blade attached to the motor stick would not satisfy the bonus.

[bernard]

Just wondering, which has given you better times: stationary top and rotating bottom or both rotating?

I wanted to switch over to both rotating because I was under the impression that the body would then count for the bonus if you attached a small rotor on it, but now i'm a bit unsure about that.

.

The single bladed rotor has to be freely moving from the motor stick :/ Having a blade attached to the motor stick would not satisfy the bonus.

What rule makes you say the blade and motor stick cannot be rigidly connected?

[maxxxxx]

Just wondering, which has given you better times: stationary top and rotating bottom or both rotating?

I wanted to switch over to both rotating because I was under the impression that the body would then count for the bonus if you attached a small rotor on it, but now i'm a bit unsure about that.

.

The single bladed rotor has to be freely moving from the motor stick :/ Having a blade attached to the motor stick would not satisfy the bonus.

I saw a helicopter at an invite last week that had a blade attached to the motor stick and it was scored as the bonus.

[bernard]

I wanted to switch over to both rotating because I was under the impression that the body would then count for the bonus if you attached a small rotor on it, but now i'm a bit unsure about that.

.

The single bladed rotor has to be freely moving from the motor stick :/ Having a blade attached to the motor stick would not satisfy the bonus.

I saw a helicopter at an invite last week that had a blade attached to the motor stick and it was scored as the bonus.

Rule 3.f. describes blades that are rigidly connected (i.e. no degrees of freedom for one blade relative to the other). A blade attached to a motor stick does not necessarily violate this rule.

[calgoddard]

maxxxxx -

A helicopter could have one two-bladed rotor rotatably mounted on a bearing at the upper end of the motor stick, and one single-bladed rotor rigidly connected to the lower end of the motor stick.

As long as the blade of the single-bladed rotor had a correctly oriented pitch opposite to that of the blades of the two-bladed rotor, each rotor would provide lift based on the torque of a wound rubber motor. That rubber motor would have to be connected between a hook on the shaft of the upper rotor and a hook connected to the motor stick near its lower end.

The helicopter configuration described above would be entitled to receive the 25% bonus in Rule 5.a, provided all other provisions of the rules were satisfied. This is not the only helicopter configuration that would be eligible to receive that bonus, but just an example.

Based on a previous answer to an FAQ in a prior season of this event, in order to be entitled to the 25% bonus the single-bladed rotor must be rotatable independent of any other rotor and it must be driven by the rubber band so that it actively generates lift, i.e. it cannot passively rotate due to airflow generated by other rotors.

This is not an official source for rules interpretation.

[kaziscioly]

Does the twisting of o-rings influence the performance of the rubber motor during flight? I've noticed that sometimes at higher winds the o-ring begins to twist itself around the hook.

[jander14indoor]

<SNIP>Because of the balance of forces both rotors will end up going at the same angular velocity whether one is stationary or not. <SNIP>.

Not necessarily. Both rotors have the same torque applied, whether they spin at the same angular velocity depends on having the same aerodynamic drag. Unlikely, but should be close if both rotors are carefully built to same aerodynamic spec.
One way to improve stability is to NOT have them built to same spec. For example, you may want to play with the pitch or blade count so the top rotor provides more lift than the bottom. This will help keep the helicopter from flipping over. In this case the two rotors will absorb the same torque, but not spin at the same rate.
An extreme case is the Wright Bat style helicopter. One top rotor and then large vertical sails on the motor stick that just produce drag reducing the rotating speed of the stick and forcing the top rotor to spin fast.

Jeff Anderson
Livonia, MI