Helicopters C

[wx4caster]

We went with the 2017 FFM with a 2 x 2 config, but it was a total disaster. The copter was very unstable, and actually flew sideways instead of straight up (Memories/horrors of our Wright stuff days). It only stayed in the air for like 30 secs. Ugggh!! So, trying to save weight led to unstable and unusable copter.

Think we are gonna go with a 4 x 2 config, with a shorter stick to save some weight. An attempt at this led to the copter staying in the air for 60 secs.

I have 2 NEW questions.
On one of our flights the dime sized top disk fell off the copter as it bounced along the ceiling. (one of our best flights, btw). If I read the rules correctly, rule 5j states "flight stops when any PART of the helicopter touches the floor...". Would a "piece" falling off the copter constitute a PART hitting the ground?

As far as the single blade is concerned. Could you take one of the bottom double blades constructed with the 2017 FFM and just remove the mylar from one side, which eliminates its lifting surface and now makes it a counterweight, as one half of the blade only comes to a radius of 10.0 cm. How is the radius measured? Just the lifting side of the single blade?

[Unome]

I have 2 NEW questions.
On one of our flights the dime sized top disk fell off the copter as it bounced along the ceiling. (one of our best flights, btw). If I read the rules correctly, rule 5j states "flight stops when any PART of the helicopter touches the floor...". Would a "piece" falling off the copter constitute a PART hitting the ground?

As far as the single blade is concerned. Could you take one of the bottom double blades constructed with the 2017 FFM and just remove the mylar from one side, which eliminates its lifting surface and now makes it a counterweight, as one half of the blade only comes to a radius of 10.0 cm. How is the radius measured? Just the lifting side of the single blade?

1) Based on information from the 2011 and 2012 threads (unofficial opinions from jander and chalker7) this should end the flight.
2) Based on a statement from jander in 2014 where he stated his surprise that no one tried this, I would think it would be legal (subject to event supervisor proclivities as usual).

[jander14indoor]

2 by 2 is NOT inherently unstable. I wouldn't lead you down such a path (I might not answer your question fully, especially as I DON'T know everything, but I would not recommend something I know to be bad). I've seen a lot of these fly great.
Something else caused the instability. Could have been wrong cg, wrong relative pitches or motorstick bending.

And I stand by my previous unofficial opinions already quoted.

Radius is of the lifting surface for the one blade rotor. From axis to tip. Not any counterweight. Unofficially...

Jeff Anderson
Livonia, MI

[yew]

Very little effect until you get so short that you have trouble with the unwinding motor hitting the motor stick, or so long that you can't pack in as many winds.

Jeff Anderson
Livonia, MI

Ok, thanks!

[BuildingFriend]

For a heavier helicopter how would you increase the time spent falling down? The estimate (ideal) should be around 7 seconds a meter if I remember correctly. Falling from a 9 meter ceiling it takes only 20 seconds or less. Any suggestions?

[RJohnson]

For a heavier helicopter how would you increase the time spent falling down? The estimate (ideal) should be around 7 seconds a meter if I remember correctly. Falling from a 9 meter ceiling it takes only 20 seconds or less. Any suggestions?

The most effective way would be to make the helicopter lighter. However, as that generally requires rebuilding, you may want to try instead using slightly thicker rubber. This way, as your winds run out you have a little bit more torque to keep the rotors spinning.

Good luck!

[calgoddard]

I would like to give a different perspective on the importance of SO helicopter weight.

As in all engineering problems, achieving the optimal solution in the 2017 SO Helicopters event involves trade-offs. A helicopter which is lighter may fly longer, or it may not fly longer because it is not sufficiently stable. It also may need periodic repairs, resulting in weight gain over time, assuming it can be repaired. Using a shorter motor stick to save weight will usually impair stability in flight. Using a fixed disc instead of a rotating disc may save some weight but also may result in a helicopter that tracks across a flat ceiling and hangs up on a light fixture, prematurely ending the flight. Using single-bladed rotors, which are necessarily heavier due to the required size and configuration of their counter-weight arms, may be worth it due to the 25% bonus for each such rotor.

A well-trimmed lighter WS airplane (that meets the minimum legal weight) is always preferable to a well-trimmed heavier WS airplane in terms of competitiveness at an SO competition, assuming that the lighter WS airplane is sufficiently strong to hold its trim and not break in a collision. Even if you remove the single-bladed rotor bonus from consideration, a lighter rubber powered SO helicopter is not necessarily preferable to a heavier one. In the SO Helicopters event a stable flight, and the ability to avoid and/or recover (undamaged) from encounters with light fixtures and beams, is far more difficult to achieve and is much more important than in the WS event. This is because the no-touch flight strategy, which can be successfully employed in WS competitions with a high degree of reliability using a torque meter, will not be successful in the Helicopters event. You will not be able to win any competitive SO Helicopters event held in a typical high school or middle school gym unless your helicopter hits the ceiling and thereafter survives, i.e. it does not break, hang-up or crash.

Yes, all things being equal, the lighter of two SO helicopters will have the advantage. However, all things will not be equal as to two different rubber powered helicopter designs. Clearly, your helicopter must have a reasonable weight. A 2017 SO helicopter that is not entitled to any bonus and weighs 4+ grams is not likely to win a competition. However, a 2017 SO helicopter with a conventional design need not weigh 2.5 grams or very close to that minimum legal weight in order to win most SO Helicopters event competitions. Many other factors in addition to weight determine success in the SO helicopters event.

[jander14indoor]

I hear what you are saying, but we'll probably have to agree to disagree and let the student results prove one or the other right! A good thing I think.

I recognize all the tasks you mention, I just think you can meet most of them with clever design and still hit min weight. If a team can't they need to consider carefully how much benefit they get in solving the tasks you laid out vs the added weight.
Examples:
- I don't expect that doubling the number of rotor blades will offset a doubling in weight. It might offset say 25 or 50%. But that takes both analysis AND testing to demonstrate.
- Stability, I know that doesn't correlate to weight. 2X2 rotors can be as stable as 4X2. Motor sticks much shorter than the FF kit can be stable. I've seen and done it. No solution required the addition of weight. Rearranging weight, modifying aerodynamics, yes, but not addition of mass. Example, a perfectly good solution is to have both rotors at the top. One fixed to the motor stick, one free, with the bulk of the motor stick hanging down below both rotors. You can get away with a pretty short stick and I think its easier to solve the stiffness problem of stability. Makes it less important because you only need to worry about the bending in the stick between the two rotors and with both at the top can be a very short, stiff distance.
- Strength is harder. I have to admit, the carbon fiber rods for spars are hard to beat. But have you considered a CF leading edge with a good 5lb/ft3 density trailing edge? Some of that "special" balsa? The motor stick stiffness is also critical, but there are tricks to improve that with out adding weight. The FF model does that by adding bracing. Hollow tube or box sections can take that a step further.
- Free spinning disk. As discussed previously, its importance will depend on the site. And minimizing weight of either implementation is critical.

Added weight MUST pay for itself is my perspective. You need to fight every added part of a gram.

Oh, and making these tradeoffs, is one of the things that makes the flying events so valuable as an educational tool. Real life engineering.

Jeff Anderson
Livonia, MI

[BuildingFriend]

In increasing stability (as the 2/2 heli usually 50/50 on wright stuff or amazing flight times), would putting 1/16 by 1/16 wood on the motor stick increase stiffness and thus minimize the warping that occurs while attaching a taut rubber? We already have 3 nylon supports. Also, what is everyone's opinion of CF spars vs traditional wooden spars? I don't know the MIT scores (someone please update me!) but it seems national scores this year will be in the amazing 3 45 range which means there will be no time to trim and see if something goes wrong.

[Bazinga+]

In increasing stability (as the 2/2 heli usually 50/50 on wright stuff or amazing flight times), would putting 1/16 by 1/16 wood on the motor stick increase stiffness and thus minimize the warping that occurs while attaching a taut rubber? We already have 3 nylon supports. Also, what is everyone's opinion of CF spars vs traditional wooden spars? I don't know the MIT scores (someone please update me!) but it seems national scores this year will be in the amazing 3 45 range which means there will be no time to trim and see if something goes wrong.

You really think helicopters will reach 3:45 at nats??? Seems very unlikely considering current and past scores. I'm quite sure that the top MIT times were in the 1:50's or a little over 2:00 (went second or third to last time block and supervisor said that 1:50-something was the highest).