Helicopters C

[Private Wang Fire]

Rules 3.b. and 3.f. (no pre-glued joints or pre-covered surfaces; any materials except boron filaments)

Can I use a plastic gearbox?

Yes but that'll kill your mass, might want to try a different solution (or somehow finesse a geared solution with very few gears that doesn't add too much mass, if you can do that congrats you are in some secret group that contains like maybe 3 teams from 2012).

[MGoGolf]

Sorry for the flurry of posts - I'm a newbie and seemingly behind the curve with no FF kits.

Does "fixed pitch rotor" mean the blades can't rotate relative to the rotor hub (i.e. like in a variable pitch propeller or collective pitch rotor, see https://en.wikipedia.org/wiki/Variable-pitch_propeller ), or that the whole rotor assembly can't rotate relative to the body of the helicopter, or both?

Thanks again to the community for any insight

[andrew lorino]

Sorry for the flurry of posts - I'm a newbie and seemingly behind the curve with no FF kits.

Does "fixed pitch rotor" mean the blades can't rotate relative to the rotor hub (i.e. like in a variable pitch propeller or collective pitch rotor, see https://en.wikipedia.org/wiki/Variable-pitch_propeller ), or that the whole rotor assembly can't rotate relative to the body of the helicopter, or both?

Thanks again to the community for any insight

I think it means that the pitch of the individual blades relative to their axis of rotation can't change, as they would on a variable pitch propeller. As far as I can tell, any rotor where the blades are securely fixed to the boss (middle part) would not violate this rule, as if the whole propeller were turned somehow the axis of rotation would change, not the blade pitch.

And for a gearbox, don't. The point of a gearbox is to change the torque/rpm ratio. It's much simpler to just change the torque by changing the thickness of rubber you are using than to add a gearbox.

[MGoGolf]

Sorry for the flurry of posts - I'm a newbie and seemingly behind the curve with no FF kits.

Does "fixed pitch rotor" mean the blades can't rotate relative to the rotor hub (i.e. like in a variable pitch propeller or collective pitch rotor, see https://en.wikipedia.org/wiki/Variable-pitch_propeller ), or that the whole rotor assembly can't rotate relative to the body of the helicopter, or both?

Thanks again to the community for any insight

I think it means that the pitch of the individual blades relative to their axis of rotation can't change, as they would on a variable pitch propeller. As far as I can tell, any rotor where the blades are securely fixed to the boss (middle part) would not violate this rule, as if the whole propeller were turned somehow the axis of rotation would change, not the blade pitch.

And for a gearbox, don't. The point of a gearbox is to change the torque/rpm ratio. It's much simpler to just change the torque by changing the thickness of rubber you are using than to add a gearbox.

Thanks! I was thinking of using a single motor to drive two props, and thus need to make a 90 deg. turn - hence bevel gears in a gearbox. Agree the weight and friction losses would make it unworkable.

[0ddrenaline]

I ran helicopters at the Portage invitational in Michigan on December 9. Some thoughts:
-The top 4 or 5 were comprised of Chinooks. Only one regular copter did better than a Chinook.
-Few people got the three minute bonus. Only one of the Chinooks got the three minute bonus, although I informed every team about the bonus. It seems that winding two motors during this time is difficult, although I believe people could have gone much faster if they were more urgent. I'll assume it's because we are early in the season.
-Every Chinook was the Freedom Flight model
-The top time, with the non-coaxial bonus and colored surface bonus, was close to 6 minutes. I believe they did not get the time bonus. The raw time was about 2:15

[bjt4888]

Oddrenaline,

Thanks very much for a nice job of officiating the Portage Invitational. The teams that finished 1st and 2nd were from a school that I coach. As I’m sure is the case with a number of the teams this early in the season, they are just beginning to explore the potential of the Freedom Flight kit. They were quite disappointed with 2:15, but they understand that it’s quite a challenge to have a best flight in the heat of competition.

Thanks again for volunteering in the interest of hands-on science,

Brian T.

[daydreamer0023]

I ran helicopters at the Portage invitational in Michigan on December 9. Some thoughts:
-The top 4 or 5 were comprised of Chinooks. Only one regular copter did better than a Chinook.
-Few people got the three minute bonus. Only one of the Chinooks got the three minute bonus, although I informed every team about the bonus. It seems that winding two motors during this time is difficult, although I believe people could have gone much faster if they were more urgent. I'll assume it's because we are early in the season.
-Every Chinook was the Freedom Flight model
-The top time, with the non-coaxial bonus and colored surface bonus, was close to 6 minutes. I believe they did not get the time bonus. The raw time was about 2:15

Do you remember where the general time range of the top couple (say top 5) of the chinooks were getting?

[SluffAndRuff]

2:15? Dang, that's pretty impressive.

My partner and I also built the FFM chinooks but mine broke frequently in testing, and hers broke on official flight #1. How do you prevent the breakages? Our motor sticks, the perpendicular thing - everything suffered badly and we didn't even test them much at all. We're planning to build the fixture thing described in the FFM instructions to help, though not sure if it is our method of loading the motors, or what.

[bjt4888]

SluffandRuff,

If your breakage issue is with the motor sticks, be sure to use a pretty fair bead of CA when attaching the 3k carbon tow to the motor sticks. As you run your finger along the tow, wiping the glue into the tow, a fair amount of the CA is removed moderating the weight gain from the CA. Use nitrile gloves and eye protection for this step.

Once the glue is dry and cured on the carbon tow (wait 24 hours) gently flex the motor sticks while looking at the tow at a shallow angle and with a good light shining on it. If there are loose spots where the tow is not attached you will see small buckling spots in the tow. Put a drop of CA above and below any buckling spots and flex gently again to get the CA under the tow. Set aside and allow to dry for hours after fixing each spot. This is a time consuming process as you can only really fix one buckling spot at a time since any additional flexing of the stick will disturb the drying glue.

If you are experiencing other types of breakage, describe in detail and I will see if I can help.

Brian T.

[daydreamer0023]

So I'm trying to color the mylar with sharpie before I put them on the rotors and they keep ripping. :/ Is there a better way to color the mylar so that it doesn't rip? :/ Thanks in advance!