Vibrating stabs are a big deal because they couple to the rest of the
airframe. Just think of riding a bicycle wiggling the front wheel
compared to not wiggling. Which is more efficient? The prop force
should be applied to making forward motion.
There is a lot of relative force causing this wiggle. Balancing is
the first step then setting pitch.
However even with correct pitch, camber of the blade changes lift and
may be causing your wobble. Many things can torque a different pitch
into a prop blade including plastic ones.
A way to check is to cut out camber templates. Mark different radii
on the prop and compare at those points on the blades. Stiff card
stock is a good material for templates. If the material is too thick,
like a sheet of balsa, you can't see the gap as well.
Making templates.
Mark radii - a point on the leading and trailing edge and number them.
Apply scotch tape to one blade. Make it a little less sticky by
putting it on your hand so it comes off easier.
Cut an approximate shape for the camber.
Apply a marking powder. I use graphite from my drafting pencil
sharpener but you can use anything. Be neat.
Touch the template to the prop. Cut off the parts that have the
powder on them until the whole template evenly picks up the powder.
I think you get the idea from here.
Most props made out of plastic will follow this template once you set
them up. It's a good set of gages to have.
If one prop is giving you fits use another. Sometimes you just know
know why one prop just doesn't work.
boz
--- In Indoor_Construction_at_yahoogroups.com, "Bill Gowen" <b.gowen@...>
wrote:
>
> If the blades are the same size but don't weigh the same then the
thickness must be different (not unusual). So thinning the heavy blade
shouldn't cause a problem if both blades wind up the same thickness.
The best answer to the pitch gauge problem is to get a better pitch
gauge! The one that Tim Goldstein sells works great.
>
> ----- Original Message -----
> From: calgoddard
> To: Indoor_Construction_at_yahoogroups.com
> Sent: Monday, October 29, 2007 8:00 PM
> Subject: [Indoor_Construction] Ikara Props
>
>
> Our team has trouble with the Ikara props in that they are
> usually unbalanced and therefore often make the stab of the plane
> shudder. We have purchased many Ikaras over the years and all but
> one or two were out of balance in terms of weight.
>
> If the team balances the Ikara props so that each blade weighs the
> same, that is not the end of the problem. If they snip off a slight
> amount of the tip of one blade, the blades have unequal areas and
> therefore they produce unequal thrust. If they sand one blade, it
> gets thinner and may flare more, giving unequal thrust. I assume
> that sanding is better in terms of achieving weight balance.
>
> Now the blades must also have the same pitch. We have two pitch
> gauges, but the blades of the Ikara are free to move a good amount
> when they are in the pitch gauges. All you are really doing is
> eyeballing each blade in terms of how it sits up against a 45 degree
> fence or reading degrees off a scale. How do you determine whether
> the pitch is identical for each blade given the relative lack of
> accuracy of these pitch gagues? Moreover, the pitch may only be
> identical at that radius, but not at all radii.
>
> Is this just hit or miss? Is the vibrating stab really not a big
> deal in terms of reducing flight times so our team is wasting time
> on this issue?
>
>
>
>
>
>
>
>
> [Non-text portions of this message have been removed]
>
Received on Tue Oct 30 2007 - 06:12:18 CET
This archive was generated by Yannick on Sat Dec 14 2019 - 19:13:45 CET