Blades
Surprisingly little can be found on the web about the construction of scale helicopter blades. There are many possibilities to improve blade performance using the right materials, for instance see the paper of bruck and moore. It's not clear to what extend such techniques are actually used in scale helicopter blades. However, most scale heli blades I've seen from the inside (after a crash) looked pretty simple: an inner part consisting of hard foam, a layer of carbon or glass fibre around it and a metal wire in the leading edge.
So far I had 4 different blades, and here is some info about them.
Type details: thunder tiger, for raptor 30 (1999 model)
Length (hole to tip) 550mm, chord 50mm, Thickness 8mm.
Root: 12mm
Tip curve: ca 10mm
Weight: ca 100g
Type: semi-symmetric
Torsion strength: tordates quite quick, easily felt
Straightness of trailing edge: one looks perfectly straight, other has very light bend, less than what I can measure.
Off-balance: center of gravity 4mm, weight difference 2 heavy tracking tapes
Material: Leading edge looks like beukenhout, trailing edge is probably balsa. Finished with transparent shrink-wrap.
Finish quality: ok, shrinkwrap is melted together at blade tip.
Type details: (fits XCell30/40, JR Ergo 30/40, TSK Mystar40)
Length (hole to tip) 557mm including tip finish, chord 50mm, Thickness 8mm.
Root: 8mm
Tip curve: ca 2mm
Weight: specified at ca 100g
Type: symmetric
Torsion strength: Much stiffer than wooden stock blades, tordates only little bit, hardly to be felt.
Straightness of trailing edge: both perfectly straight.
Off-balance: center of gravity 0mm, weight difference 3 tapes
Material: Black, straight carbon fibre.
Finish quality: Good. No visible damage. tip has to be fitted by yourself and it not easy to do good. Small superficial scratches in surface. Slightly deeper lengthwise scratches at front side of leading edge. The white vinyl cover provided with the blades showed impossible to apply without air bubbles.
Notes: There seem to be problems with NHP blades: blade holes going oval, and damaging tips. For instance see this
RR thread
Type details: type 0330
Length (hole to tip) 605mm including tip finish, chord 56mm, Thickness 8mm.
Root: 12mm (up to 2004 this was 10mm)
Tip curve: ca 20mm
Weight: per package specified manually. mine are 135g to 145g. Newer ones seem lighter.
Type: symmetric
Torsion strength: Much stiffer than the NHP. Hardly any torsion can be felt.
Straightness of trailing edge: usually slight bent, less than 0.5mm in the middle.
Off-balance: average less than 1mm difference in center of gravity, and less than 0.1g weight difference.
Material: White coated woven carbon fibre.
Finish quality: Used to be good but dropped since end 2006.
Highly polished white cover. With most pairs the carbon mesh is slightly visible though.
Some blades have black spot at one tip, probably where balance weight was inserted.
Tips are very sharp, occasionally a tiny part of the point seems to be broken off right from the package (only 0.5 mm or so).
The first set (2002) had a dent of about 4 mm at a distance of 9cm from the blade holder, which seemed to have damaged
the carbon. Modelbouw Bloemendaal gave me another set when I returned this first set.
The swapped set had a blade root of 10mm. Carbon mesh was neatly laid down. The finish is a bit thin, lightly showing the mesh structure through. The balance was not perfect, I can't remember but it took a few tapes to get it perfect. Tips were slightly damaged.
Second set. In april 2004 I bought a new set of these blades. I noticed a few changes with my old blades from 2002.
To start with the improvements.
The weight balance is dead on straight from the box.
That is, down to the accuracy of my balancing stuff, which has an accuracy of at least 0.1g.
Also, the tips were undamaged on the new set. The rings to adjust the root thickness
to the blade holders have the right thickness, if I remember it right the first set came with spacers that
were way too thick to be useful. Finally, the white finish is smooth all over, no shade of
the underlying carbon fibre anymore.
The transparent window showing the carbon is now only on one side of the blades,
the old blades had such a window on both sides. One blade still has a slight bend, maybe 0.5mm, the other
one is straight.
Three small things are less good than in the old blades.
I was given the opportunity to view a few sets at Modelbouw Bloemendaal and saw these on all blades.
First, what I disliked most was that the carbon mesh looks is quite deformed, it is laid out less straight than in
the old blades. The pictures below try to show this.
| The old and 2006 carbon mesh lays neatly. | The 2004 mesh looks quite deformed: the meshes vary a lot in size, and are not square especially at the leading edge (left side). This causes the blurred impression in the photo. |
Second, Center of gravity is off 1.25 mm. This equals to 9 light cellotapes at the root to correct,
and another 9 at the center of the other blade to keep the balance right!!
Third, a few short carbon fibres apparently
got stuck in the finish or they have cats in the factory, see the picture.
Also there is a scratch at the blade root, I saw this on another set too.
| Carbon hair and scratch at blade root. |
Third set In june 2006. I hit the ground slightly with the tail rotor at the end of an auto, and
I needed a new pair of blades. The old ones cut the boom off with only a small dent as a result
in the blades, but just to be sure I replaced them.
Important change is that the blade root is now 12mm, it was 10mm up to now.
So no more spacers needed for the raptor!
Again balance is dead on straight from the box.
SAB again improved on a number of issues.
The main improvement is that the mesh is layed out clean again.
Now there are only one or two carbon wires in the white coating.
Finally, they got rid of the black spot (the balancing weight I presume)
at the tip of one blade, it's now all white finish on both blades.
There are a few other very slight differences. The white coat is very slightly thinner,
you can get a very slight hint of the carbon structure under the lacquer.
There are a few tiny issues that I see SAB can still improve on.
First, the blades are very slightly bent. Both blades are bent up about 1mm in the middle.
Both blades have the same bent, maybe SAB is sorting blades also on this characteristic?
Second, at the blade roots and the very tip one of the blades has a bit rough edge.
Looks like they grinded away just too little there.
Finally, there are some white speckles in the "carbon window" and
a small hard white grain sticking out at the bottom of one blade, like a grain of sand stuck in the final white coating.
Fourth set march 2007: another set of 0330's after the engine quit while inverted. I think the quality is a seriously down. Main issue that I have is holes in the blade. Figures below show two such holes. The first one appeared in the lacquer after the first flight, just hovering a bit and tuning for tracking. It looks like a damage in the mesh under the lacquer, because the lacquer is OK but just dropped down into a hole beneath it. After a few flights, two other, similar but smaller holes appeared on other places on the blade. There also is a dent-like round spot in the lacquer of about 4mm diameter, where one layer of coat is missing and looks like a crack in the lacquer. It has a tiny sharp grain inside as well. This looks like a problem with the lacquer itself. Mesh is slightly stretched at the leading edge. The mesh structure is lightly visible through the lacquer. Trailing edge is straight. Package indicates weight 135g. Balance not great, 0.1g off (6 cellotapes) and center of mass about 1mm off. Put 6 tapes at the very tip of the light blade, which is just too little to get the center of mass right. Finish is slightly dull at the tip of the blades, the black "weight insert" at the blade tip has returned. Still black hairs under the lacquer. The leading edge of one of the blades is a bit messy, you can see that they had to do quite some sanding to get the shape within specs, resulting in a non-straight break in the white finish.
| Hole in the lacquer. Looks like a problem in the carbon mesh underneath the lacquer. | March 2007: dent-like spot. |
I went back to Modelbouw Bloemendaal and they offered me to swap the set with another set from their stock. Unfortunately the other sets were even worse: one set had a large wart of white stuff (diameter of about 8mm) laying on one blade very near the tip. The other seemed to have a 2cm crack under the lacquer layer, in the chordwise direction, about halfway the blade. I will fill the hole in the blade that I have now...
Type details: Fun-Key CAT.# H 6001C
Length (hole to tip) 600mm, chord 55mm, Thickness 8mm.
Root: 12mm
Tip curve: ca 50mm
Weight: ca 147g according to seller webpage
Type: symmetric
Torsion strength: very stiff, just slightly less stiff than the SABs
Straightness of trailing edge: straight (less than what I can measure).
Off-balance: spot on: center of gravity <0.2mm, weight difference < 0.1g
Material: Transparently and yellow coated carbon fibre mesh.
Finish Quality: Highly polished finish. Few light traces of dust below the finish layer.