My Thoughts on Fixed Pitch Blade Fixing (aka The Dreaded Wobble) - RC Groups
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Jan 16, 2005, 02:49 PM
Who Says Penguins Can't Fly?
aeropenguin's Avatar

My Thoughts on Fixed Pitch Blade Fixing (aka The Dreaded Wobble)

Hello everybody.
First I would like to say that I am very new with RC helis.
Second, I own a 100% stock aerohawk (new lipo is on the way though)
Third, I read the entire thread "Fixed Pitch Blade Fix..." and have my own solution which has worked better for me. It seems simpler and easer and perhaps is even safer.

The problem (as far as I understand it): In Fixed Pitch (FP) Helis, you cannot variate the AoA and thus the blades are set at a high angle. This results in very low headspeeds. When you combine this fact with the very low weight of the stock Aerohawk blades (which are very similar to the piccolo, and others I believe), you end up with blades that dont have enough centrifugal force to stay pointed outwards from the mast. Rather, they lag behind where they "should be". I think when the blades do this, they are called retreating (not sure).
In either case, this causes an incredibly unstable helicopter that vibrates very much, which we call the "Dreaded Wobble" (term copyright by G109 ).
All you have to do to fix this wobble is advance the blades forward of where they spin now. There are different ways of accomplishing this, such as...using rubber bands (but nobody likes to trust a heli with 'bands), using G109's awesome idea to use metal springs, or you can tighten the bolts. All of them work in theory.
I tried out the springs (made my own, results may have been better if ordered from G109), but they kept changing on me. It was hard to get the blades both advancing the same amount (this makes them parallel), and plus after impact the springs did a good job of soaking up the impact. However, it also softened up so now when spinning, one would flex more, and so they constantly needed reajustment. They also slipped sometimes and it just didn't seem like the best way to go.
That is what the FP Blade Fix thread goes over.

I decided that tightening the bolts would look neater and if they would hold the blades well, they would always stay in the perfectly aligned position and would never need tweaking. Only 2 problems:
1. The screws/bolts cannot keep them strong enough.
2. They would crack on impact.

So, here is my idea (Finally, I know... heh):
1. Loosten the bolts so the blades can travel.
2. Align them PERFECTLY.
3. Tighten the bolts as tight as you can
3. Spin up at a very low speed so that the blades dont budge
4. If the heli is COMPLETELY vibration free, then loosten the bolts a bit so the blades would be able to travel, but Don't let them.
5. Take thin CA, and put in a few small drops on the blade where the top piece that holds the blade meets (umm...) the blade. The thin CA will seep through the little crack and then add a bit more CA so there is a little peering out. of the crack. Let is sit for about 3 minutes so that the CA can fill the pores as best it can, then zap it with accelerator to make sure it it is all crystalized (CA dries with the absense of air).
Five steps, and you are Done!!!

The idea: the glue will hold the blade just as a very tight screw would, keeping it stationary under all the stresses of flight. This fixes the first problem with just tightening the bolts. But, as soon as the blades hit something, the CA will chip off of the plastic since there is little there, and the blade will fold back and absorb the damage, and not crack! So, after every blade collision, it just folds back and you have to take off the blade, scrape the dry CA with an exacto (or just a flat screwdriver), and repeat the five steps. It only takes 5 minutes max. I spent about the same time adjusting before each take-off with springs.

Very simple, Looks nice, and folds back, saving the couch or tree, and the blades as well. Only problem is that you cant fold the baldes for storage (unless you glue them on the field).

I know its a very simple idea, and there is very little I can take credit for, if it works for all of you. I know its unconventional to put glue there, but it works. It solves the wobble entirely and my aerohawk took off and hovered after only a few batteries of ground-training.

What do you guys think?
P.S. Sorry about writing so much heh. I was summarizing the FP Blade fix thread...
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Jan 16, 2005, 03:08 PM
It wasn't my fault!!
Headspin's Avatar
Not sure what you made your springs out of, but the ones I got from Geoff are still fine after months of abuse. They work great.

I guess we all do what is best for us, not sure I fancy putting CA on my blades.. at the rate I hit things it would cut my flying time by 75% chipping off old glue and resetting blades etc.

The springs do get out of shape but it takes 5 mins maybe once or twice a week to put things right again.

I have three Aerohawks (2 flying - 1 with seperates other with PHA-01) and a Skylark (PHA-01) and I find varying degrees of quality and succsess with the blades. Some weigh much more than others.. and the ones from Raidentech, although cheap.. seem to be WAY inferior and crack so easily. I have a set from there that just dont work.. the leading edge hes negative attack.. I'm thinking of slicing off 1/8" to see if that helps.

Anyway, getting a bit OT now.. so, I guess we all do whatever works best for us.


Jan 16, 2005, 03:10 PM
4-D traveller
glxy's Avatar
Interesting experiment. But why can't you trust the rubberbands? You can make rubberband wedges as bumpers as shown in this thread here which I reattach. In fact it's a far more safer and reliable method , adding no weight, and no potential hazard.

If you don't like rubber bumpers or metal wire blade springs, there is another effective method. Add tip weight at the trailing edge of the blades (tape will be do). Centrifugal force will align aned advance the blades in flight. After I cut my blades thin and add tip weight to move the CoG more towards the trailing edige, I have the blades quite loose and my heli flies silk smooth at any head speed. With blades advanced by the spring mechanics, the heli will shake until a certain head speed is reached, that is, until the blades are aligned.
Jan 16, 2005, 03:13 PM
Registered User
Lynxman's Avatar
Another way I think might work (and I have mentioned it before) is to drill a hole in the root of the trailing edge of the blade and mount a screw with some weights to help pull the blades forward using centrfugal force.

A flybarless heli doesn't wobble. Wobbling happens when the blade and flybar paddle come out of sync.
Jan 16, 2005, 04:33 PM
Registered User
i think your idea works, but not good for a beginner, as blade contact with another object is fairly consistent So you'd forever be stripping and caing the blades back.

The catch is that, as you get better, you would move to a set of wood blades or trim the blades or do something that gives you a higher headspeed. The headspeeds on these blades is enough to centre the blades and therefore eliminate wobble. (you can still get vibration, but that's another story ) Since i've been using wood blades, i haven't had a wobble issue since.
Jan 16, 2005, 04:57 PM
Blade Springs "Rock"
[QUOTE=glxy]In fact it's a far more safer and reliable method , adding no weight, and no potential hazard.[QUOTE]

ahh.........forgive me here kits contain the latest stainless steel blade bolts.....washers and springs that money can buy. There's no way the springs are leaving the rotorhead.....sorry. My captive washers make sure the spings are in total alignment and centered on the blade's the safiest possible solution.......there is...and stronger then any other method....I've spared no expense on safety here.......believe me.....You simply cannot sit there and say your stock blade bolts are stronger then mine......the kit is total stainless steel.....hardware......

Jan 16, 2005, 07:13 PM
Registered User
oh yeah, ca dries WITH air.

To be exact the moisture in the air cuases it to set.

An old trick from building lead miniatures and for other NON porous surfaces where CA can take a while to dry.

blow on it- the water vapour in your exhaled breath makes it set far more rapidly
Jan 16, 2005, 07:49 PM
Who Says Penguins Can't Fly?
aeropenguin's Avatar
Thanks for all the replies, guys!
I understand that GLUING a moving part together is completely against all basics, but it works for me.

Headspin, I have never ordered a "real" pair of springs from G109. If they are as sturdy as you say then perhaps it really is.......
I was hovering confidently with my second battery after my first attempts at blade advancement, so I learn fast. Anyway, the springs I made needed a lot of maintaining, and the glue in my fix holds them fine. I have hit objects before, and if it was a strong impact it stripped (thanks for the term ozzie, it fits better), and sometimes it hasn't, but nothing has broken....
It's also a much faster and cheaper way to do it. I am a freshman in highschool, so my budget is small. As soon as I squeeze all I can out of the aerohawk I'll either get a hornet or a helistar sub-micro; both run about $400 all together :/ . This also comes to... I think I will move onto another heli before I start upgrading this one, as it just wasn't made for flying capability, rather just a learning crash-proof platform. IMHO.
Galaxy (If you dont mind me calling you that), I also thought your idea was genious. I tried it as well, but the blades slipped back through the rubber. I was unable to put more folds in to make it tighter because I was unable to align the holes.... What I meant with not trusting rubber bands is when the rubber bands act as springs. The way you have it they are used as shocks or dempers.
Rapid, you may be right, but I have never found that to be true. glue dries fast when it is surrounded by objects pressed together, but if there is a bit that oozed out, it will take forever. I have, however found that blowing on it helps a tiny bit. I was almost positive that this is because water vapor settles on the CA and preventsthe air supply to it. My dad duggested putting a part under the faucet to act as an accelerator (just for fun, not practical) and it sorta worked. I have always thought this way and cannot remember whether somebody told me this or I just theorized it myself. Perhaps we can get another opinion on this?

Maybe the springs are a better choice - if ordered from G109 heh. Oh well, I think mine works for now, I am learning hovering and landings quickly. In either case, I owe my LIFE to G109 for bringing up a common issue that people have seemed to hide. I quite helis about a year ago because of this little problem. My dad asked me to help him take over my equipment (planes mostly) and after reading about helis I found I was not the only one. I might have never sparked the interest Thanks man.
Last edited by aeropenguin; Jan 16, 2005 at 07:53 PM. Reason: typos...
Jan 16, 2005, 09:26 PM
Blade Springs "Rock"
I'll quote myself.......

Originally Posted by Geoffrey109

If you don't belive me.....and are so cheap you won't buy a pair......I'll send you some for free.........just to prove you wrong.....

I'll stand by my word....and everyone here knows that........I don't have to prove myself anymore...
Jan 16, 2005, 10:51 PM
Who Says Penguins Can't Fly?
aeropenguin's Avatar
You are incredible. Check your email
Jan 17, 2005, 12:31 AM
Who Says Penguins Can't Fly?
aeropenguin's Avatar
BTW, I am wrong.
Quote from
Cyanoacrylate is an acrylic resin that cures (forms its strongest bond) almost instantly. The only trigger it requires is the hydroxyl ions in water, which is convenient since virtually any object you might wish to glue will have at least trace amounts of water on its surface.

Interesting. Then why do two pieces of dry balsa-wood cling together with no air. I doubt there is much moisture in the wood... Oh well.
Jan 17, 2005, 07:17 AM
4-D traveller
glxy's Avatar
aeropenguin. The rubber bumpers do act as blade springs as they keep the blades advanced, and better, prevent the blades from being too much advanced. To mount the rubber wedges, you have to slightly file the blade root, and push the blades hard to place and may need a helper.

Geoffrey. I have no doubt your metal wire springs are secure and safe, after being tested and used by so many. I'm just very strict with adding weight to the rotor head. A vey easy solution (weightless and costless) is there to work very well for the Aerohawk, why bother with doing it the hard way.
Jan 17, 2005, 08:00 AM
Its all fun
Tonystott's Avatar
Originally Posted by glxy
aeropenguin. The rubber bumpers do act as blade springs as they keep the blades advanced, and better, prevent the blades from being too much advanced. To mount the rubber wedges, you have to slightly file the blade root, and push the blades hard to place and may need a helper.

Geoffrey. I have no doubt your metal wire springs are secure and safe, after being tested and used by so many. I'm just very strict with adding weight to the rotor head. A vey easy solution (weightless and costless) is there to work very well for the Aerohawk, why bother with doing it the hard way.
What happens when the blade hits something? I assume the rubber band can take up some of the shock, but once it is fully compressed, doesn't all the force now come on either the part of the blade where it hits, or transfer to the rotor head?
Jan 17, 2005, 09:03 AM
4-D traveller
glxy's Avatar
You are so correct, Tony. The rubber band will absorb much of the shock. But if the hit is too voilent, some of the shock will have to be taken by the blade and the head.

On the 2-grip Aerohawk head, the rubber bumpers will also prevent the blades from cutting /cracking the hub.
Jan 17, 2005, 09:13 AM
Its all fun
Tonystott's Avatar
When I hit a blade on something, it flies back (first bending the spring) and finishes up sitting on the flybar paddle, so the obstacle only gives the blade a glancing blow. My (stock GWS Mini Dragonfly) blades have hit steel garage doors numerous times (at 4-5 feet altitude), and show no damage...

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