Fixed Pitch Blade Fix..... - Page 24 - RC Groups
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Mar 20, 2006, 07:45 AM
Registered User
autoair's Avatar
Running the blades tight is the best bet, I honestly donít think blade damage is related to their tightness, itís the Kinetic Energy in the rotating mass that breaks things. For the loose blade scenario the first blade will impart its KE to whatever it hits and fold back until it hits the flybar paddle or head this will cause a reduction in shaft speed causing the second blade to rotate relative to the head until it hits the paddle/head at which point it will also impart its KE through the head to the impacted blade. There will be a tiny lag between the two events but the energy dissipated is the same as if the blades were tight.
Another major advantage of tight blades is when you get beyond the indoors hovering stage and fly outside in the wind and get blown upwards, you can reduce the head speed to reduce height without the blades moving and inducing the dreaded wobble.
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Mar 20, 2006, 09:22 AM
Registered User
Hi Autoair
Many thanks for the quick reply.It had not occurred to me to think of the kinetic energy in a blade strike.Just a couple of thoughts. Running through this thread, it seems that the blade springs are successful. For them to work, the blades must move freely enough for the springs to move the blades. The spring strength seems not great, so any resistance would render the springs useless.
Also, I have done a rough check on chordwise balance. On the standard blades, the c/g is fairly rearward anyway, so if the blades do self align on spool up,which I have yet to confirm, then they would align with the l/e forward which is desirable.
If there is sufficient mass in the blades for centrifugal force to align them, it can only be small, so again any resistance to blade rotation will prevent this from happening.
This is only a laymans thoughts, so I would welcome a more rigorous explanation.
Mar 20, 2006, 10:17 AM
Registered User
autoair's Avatar
Hi Border,
I have never used springs, I prefer to run the blades tight. If you are going to use springs then you're right, the blades should be loose. From what I remember of this thread the theory is that the springs hold the blades advanced at low rotor speeds until the centrifugal force is sufficient for them to self align.
Mar 20, 2006, 02:38 PM
dont play with rc anymore
micronut's Avatar
blades will align if not too tight or loose.
this can be a never ending battle which is how/why Geoffrey came up with the springs.

the thickness of the spring is not at all crucial.
I have made many sets of different thickness,and found that the tension is not so important as the advance.
you want the blade advanced about 15 degrees.

unfortunately,Geoffery has moved on to bigger and better things.
he may make a guest appearance once in a while,though
Mar 20, 2006, 06:22 PM
Who Says Penguins Can't Fly?
aeropenguin's Avatar
Looks like people have answered all your questions except about trimming the trailing edge. Adding TE weight does advance the blade forward and solve the problem. However, trimming the TE takes off the part of the blade that has the highest angle upward (angle of attack, or AoA), and it creates so much drag that it is a large part of the reason as to why the blade lags at all. So by trimming off the TE you get rid of the problem at the root. Not being a specialist, I cannot say whether or not this will add to the lift, because there is less lifting area and AoA, but this also increases the headspeed which adds to the lift. To add enough weight to the TE to make it solve the problem you would need a lot of weight (at least I did). I added a thick steel rod along the entire TE and anything less was not enough. This disrupted the aerodynamics of the blade and led to less lift, so I don't think this is the best solution. I have not tried cutting hte blades but it might work - it is irreversible however, so I am afraid to try it. By screwing the blades too tight, you will never have perfect alignment because you are locking it at a place which "looks about right". Also if you spool up fast or just nip the edge of something, it can slip back and lock into that position, making the wobble really bad. This is all just my experience. I am no physicist but I have gotten the aerohawk wobble free and have tried everything on this board.
Thanks, and I hope this can help you a bit!
P.S. Sorry about any typos, as I am at school with limited time.
Mar 20, 2006, 08:18 PM
The Great Santini
Santini's Avatar
Not sure if they'd fit that but the new gws blades are narrower from the midpoint out to the tip and they have higher headspeed, which may help you. You may want to look into these.
Mar 21, 2006, 11:17 PM
Who Says Penguins Can't Fly?
aeropenguin's Avatar
I see replacement blades everywhere but I am not sure which ones are those you suggest. Could you give a link to a pair? I might be interested, in case I bust mine up and am not ready for woodies yet.
Mar 21, 2006, 11:35 PM
The Great Santini
Santini's Avatar
I am using these, which I like:

Here they are the gray 2090s in action:
Mar 21, 2006, 11:55 PM
The Great Santini
Santini's Avatar
P.S. Loose blades, no springs... just balanced blades and a good set up.
Mar 22, 2006, 01:34 AM
Who Says Penguins Can't Fly?
aeropenguin's Avatar
Mar 22, 2006, 02:21 AM
Watts your motivation
roccobro's Avatar
But how do they work on an Aerohawk?

Mar 22, 2006, 03:39 AM
Registered User
Hi everybody
Many thanks to all for quick replies. Much food for thought,and conflicting opinions, but that is what forums are all about, isn,t it.
One thing I have found which may be of help. I recently broke my rotor head. I bought the OE Walkera replacement, but the one I received was totally different design to the original, and IMO poorer quality. In casting around for an alternative, I tried one from the E-sky ( Twister in UK, Honeybee in US )
Need to fit the centre hub as well, and a little work, but seems to be a better product alround. Main point is it uses a rubber o-ring between the stiffener and the blade. This means I can nip the blades up tight enough to stay in place, but gives enough resilience in the event of a blade strike.
Still a work in progress,but best results so far are as follows.
Line blades up by sighting from tip, and aligning both blade retaining bolts with trailing tip corner. Tighten blades as far as possible, remembering the thread is metal into plastic, so dont go crazy.
There is still a slight wobble on spool up, but this disappears as head speed increases,and is the smoothest I have had so far.
I am using GWS blades. They are identical in size to the originals, but seem to be better quality, and the light grey looks real cool. They are a direct replacement, no rework required.
Thanks for your thoughts. The GWS blades are cheap enough ( 3 pairs for £10, about $18 ) that not much is lost if you try trimming them. I think a higher head speed will improve things, so trimming the blades will help, as also will reducing the pitch slightly. Still working on that one.
I still have uprated motor, GWS 3in1, and D/D tail to fit. Anyone agree with me that experimenting is as much fun as flying?
Just an aside, on the GWS blades there is another pivot hole, about an inch outboard of the main one. Anybody know what this is for?

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