Are the FFM 26 Heli Trusses Necessary?

[sonicboom]

I wanted to ask if it's necessary to add the trusses and the thread to the FFM heli motor stick, or will just the carbon lamination without tapering the ends of the motor stick be strong enough? I didn't use the trusses for the 25 FFM heli motorstick last year since it made it harder to hold the helicopter when putting on the rubber motor but it was still strong enough to withstand a fully wound rubber motor.

[bjt4888]

Yes, the FFM lateral and dorsal trusses are important this year. The fuselage is quite thin and even with the carbon reinforcement the truss is needed.

Brian T

[sonicboom]

Ah ok, thanks for letting me know. I just added the trusses and now my motor stick weighs 1.28 grams without the front hooks added. Is that a decent weight or do you think it is slightly overweight?

[bjt4888]

Ah ok, thanks for letting me know. I just added the trusses and now my motor stick weighs 1.28 grams without the front hooks added. Is that a decent weight or do you think it is slightly overweight?

1.28 sounds fine. If you use good glue management for the rotors, you should be below 4 grams total. Especially be careful to use just one quick spray pass (accurately aimed) of the 3M77 for covering. If you haven’t used spray glue before, do a test spray off to the side of your rotor blade to be sure you know where the spray is going. Then hold the spray can 18” from the rotor, aimed to definitely get spray on all spars.

Keep asking questions as they come up!

Coach Brian

[sonicboom]

I just finished building the upper and lower rotors and covered them with mylar (I haven't added the red tube, piano wire, glass bead, and hook shaft yet). The upper rotor weighs 1.081g and the lower rotor weighs 0.625g and the motorstick now weighs 1.263g (without the hooks) and the total combined weight of what I have so far is 2.97g. Do you think what I have so far is a decent weight?

[bjt4888]

I just finished building the upper and lower rotors and covered them with mylar (I haven't added the red tube, piano wire, glass bead, and hook shaft yet). The upper rotor weighs 1.081g and the lower rotor weighs 0.625g and the motorstick now weighs 1.263g (without the hooks) and the total combined weight of what I have so far is 2.97g. Do you think what I have so far is a decent weight?

Sounds good. Shafts and red tubes can add 0.4-0.5g and bumper another .25g

[sonicboom]

I just finished building my helicopter, unfortunately I couldn't get under 4g and my heli now weighs 4.12g in total. What I tried to do was to find a way to get the ceiling bumper to not fall out when the helicopter is upside down, as, at least from reading the instructions, the bumper shaft is just meant to slide in the red tube and doesn't actually stay onto the upper rotor. So what I did was lengthen the .5mm carbon fiber rod to 1 3/16" and made the red shaft 1 1/16" and put the CF rod in just enough to have a little bit poking out of the end of the red tube. I then added a dot of thick CA glue to the end of the CF rod and sanded it so it was slightly smaller than the external diameter of the red tube but big enough to not let the CF rod slip out of the red tube. Then I added a thin wooden layer above the balsa "drum" part that connects the red tube to the upper rotor so that the dot of CA glue added to the end of the CF rod wouldn't grind against the music wire/added CA glue to stick the ceiling bumper. I think this probably added some weight to my helicopter. Do you think 0.12g abovt the 4g weight minimum is enough to lose 10 seconds of flight time?

[bjt4888]

0.12 grams overweight is not a big deal. This is 3% over and will result in about 3% lower flight times. So about 4 sec reduction from a 2:30 flight and about 6 sec from a 3:00 flight.

The top bumper retainer sounds like clever engineering.

Brian T

[Tom-TTom2015]

Hey Coaches-

Just an extension on this topic:

When we calculate the over-weight effect on flight time, should the rubber motor weight be considered as well? Such as if the rubber motor weight is 2.5gram, then the effect of 0.12g overweight will be 0.12/(4.12+2.5) =0.0181, or 1.8%?

Many thanks

[bjt4888]

Hey Coaches-

Just an extension on this topic:

When we calculate the over-weight effect on flight time, should the rubber motor weight be considered as well? Such as if the rubber motor weight is 2.5gram, then the effect of 0.12g overweight will be 0.12/(4.12+2.5) =0.0181, or 1.8%?

Many thanks

I’ve never factored in rubber weight. The linear relationship of flight duration to Heli weight would be based on keeping other variables (like rubber weight) constant. Good thinking though.

Brian T