Rubber

[illusionist]

So I tried a pitch of 1 inch vertical spacing, and 2.7 inches tip to tip. It still doesn't fly on 1/8!!!
The helicopter is 4.1 grams, and everything else seems fine. Maybe my rubber isn't actually 1/8 rubber.... It looks like it is 1/8 on a ruler. I can get about 1100 winds into it, so it acts like 1/8, excpet my helicopter doesn't even get 20 seconds with it. I know
I've asked this before, but what can I do? Thanks.

[mrsteven]

So I tried a pitch of 1 inch vertical spacing, and 2.7 inches tip to tip. It still doesn't fly on 1/8!!!
The helicopter is 4.1 grams, and everything else seems fine. Maybe my rubber isn't actually 1/8 rubber.... It looks like it is 1/8 on a ruler. I can get about 1100 winds into it, so it acts like 1/8, excpet my helicopter doesn't even get 20 seconds with it. I know
I've asked this before, but what can I do? Thanks.

Same thing I posted on another topic, it's probably not good rubber. The fact you can get that many winds means it has little or no elasticity. And b/c you're getting :20 it doesn't hold power. I wouldn't use them ever...

[lllazar]

So I tried a pitch of 1 inch vertical spacing, and 2.7 inches tip to tip. It still doesn't fly on 1/8!!!
The helicopter is 4.1 grams, and everything else seems fine. Maybe my rubber isn't actually 1/8 rubber.... It looks like it is 1/8 on a ruler. I can get about 1100 winds into it, so it acts like 1/8, excpet my helicopter doesn't even get 20 seconds with it. I know
I've asked this before, but what can I do? Thanks.

Hmm are u sure ur rotors are oriented properly? It just seems insane that it won't even fly....

O sorry i didn't read the part about 20 seconds. I think your rotors might not be spinning fast enough. Make sure u have the right rubber and that the bearings are low friction (beads, teflon washers, w/e)

[chia]

So I tried a pitch of 1 inch vertical spacing, and 2.7 inches tip to tip. It still doesn't fly on 1/8!!!
The helicopter is 4.1 grams, and everything else seems fine. Maybe my rubber isn't actually 1/8 rubber.... It looks like it is 1/8 on a ruler. I can get about 1100 winds into it, so it acts like 1/8, excpet my helicopter doesn't even get 20 seconds with it. I know
I've asked this before, but what can I do? Thanks.

Well... I actually think 1 inch vertical spacing and 2.7 tip to tip might still be a little too high. I build a helicopter with an almost identical pitch and it wouldn't fly (well, best flight was around 30 seconds) on 1/8 because it was turning too slowly, despite a good prop hanger, bearings, etc.

[jander14indoor]

Lets make sure we aren't confusing things here. Several folks have mentioned reducing pitch and then mentioned old and new rotor specs with vertical spacing AND tip width reduced. The net effect meant they actually didn't change pitch much!

example:

<SNIP>the rotors i originally made are 1 and 5/8ths inches verticle spacing and four inches tip to tip.
Figuiring i needed lower pitched, smaller rotors, i made new ones that are 1.25 verticle spacing and 3.5 inches tip to tip. these flew better than the first, but still only about twenty seconds. <SNIP>

Yes the pitch on the new rotor is lower, but NOT much. First prop is about 20 inch pitch, second is 18 inch. Only 10 percent lower. And in the process you reduced blade area, probably reducing lift.

So, pitch is a function of vertical seperation AND tip width (on our simple two spar triangular blades). Unless you are doing a proper desing of experiments array, you should only change one factor at a time, so if playing with pitch, reduce vertical spacing and leave tip width alone.

Jeff Anderson
Livonia, MI

[illusionist]

I feel so stupid for not realizing that sooner.... Thanks a lot Jeff! I'll try 3.5 inches tip to tip and 1 inch vs and go from there. Btw chia, you said that pitch didn't work for you. What did you do to make it work?

[chia]

Um... it still doesn't work not over 30-odd seconds, any rate. The only think that might help is a larger rubber size, which I don't have available/didn't want to buy, or more loops in the rubber, and either way I'm not sure the helicopter would be able to handle that much force.

[illusionist]

Okay, so I tried a really low pitch (.8 vertical spacing and 3.5 tip to tip) and with 1,000 winds on 1/8, it rises about 14 feet, and falls back. So clearly lift is the issue. From what I know, if the pitch is higher, it should get more lift. But, in order for flight with 1/8, I needed to use a pretty low pitch. When I tried 1 inch with 2.75, it is too high for the rubber to provide the sufficient amount of lift. So is my reasoning right? I need to use a low enough pitch so that the rotors will actually spin with the power of 1/8, yet provide lift. Does it all come down to finding the right pitch, or is there anything else?
Btw, I'm using 1/8 FAI Tan Super Sport rubber. My helicopter is 4.05 grams.
Thanks in advance. I know I've asked similar questions a few times before.

[chia]

That reasoning is pretty much right, to the extent of my knowledge and experience. You don't seem to be having stability issues, based on previous posts... so it looks like pitch is the main thing for you.

[chia]

We'll definitely be trying a winding stooge next year. I saw teams getting in 1100 winds (probably on 1/8) when we've barely been able to get 900.

Whoops, hadn't meant to double post.