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Advanced Technology Products Rotor Blades.

- Part Two -

As you may recall from last months Newsletter, Galtech Models Ltd. have kindly supplied me with a sample set of Advanced Technology Products Main rotors and Tail rotors for my Concept 30 SRX. Last month I described them as much as I could without actually flying the things (the weather was just plain disgusting!!)
To be pedantic, I oversimplified the description of the “rotatable hub insert” for the tail rotors. I said it “altered the chordwise C. of G.”. (I just quoted the instructions.....)

For the technical purists amongst us, it of course does no such thing. The chordwise C. of G. is dictated by the distribution of mass across the blade, something that we are not altering by rotating the hub. Similarly, the “center of effort” (C. of E.) of the blade is dictated by the aerodynamic shape of the blade, also something that we are not altering.
What we are altering is the pivot point at the root.
So, “what are the advantages of altering the pivot point ?” you may ask . Well, theoretically, not a lot as far as I can see.
Let me explain;
An aerofoil, or a rudder on a boat, has a chordwise (ie across its width) “center of effort” (C. of E.). This is the point (front to back, or leading edge to trailing edge) where the resultant forces (air or water) can be considered to apply.

If the C. of E. is ahead of the pivot point, ie further toward the leading edge than the pivot point, then the device (rudder of boat or aerofoil) will exhibit an “over center” action, it will try to continue to move (deflect) in the direction that you initially moved it. It is inherently unstable, and will try to go full one way or the other. It will not naturally stay at center.

If the C. of E. is at (in align with) the pivot point, then the device (aerofoil or rudder) is balanced, and will stay wherever you put it without any further input effort, even if that position is at some deflection from neutral (center).

If the C. of E. is behind the pivot point, ie nearer the trailing edge than the pivot point, then the device will try to undo the deflection you have instigated. Much like your car steering, if you let go the steering wheel your car will try to return to a straight line of travel.

So what does this have to do with ATP adjustable pivot point tail rotor hubs?

Well, assuming that your system has no slop in the linkages, and that your rudder servo is grunty enough to position the tail rotor at whatever position you have commanded, regardless of any forces that may be exerted back upon the servo, then the pivot point is kinda irrelevant?

OK, that’s the theory, now on to the flight tests.

The Review - Part Two.

(flying the blades)

The Main Rotor Blades :
Being lazy, I didn’t put any tracking tape on the blades. After a little guessing (adjust one blade, is it better or worse, adjust again, etc) perfect tracking was achieved within about 2 turns of one pitch linkage. The blades tracked very nicely and showed no tendancy to go out of track with pitch, or cyclic, or change in RPM. This shows that both blades react to loading in the same manner.

There’s not much I can say about the flying of these blades other than “they do damn fine”. The response to the cyclic is as positive and as ‘energetic’ as my glass blades. I suspect these blades may be more stable at hover, due to their C.of G. being further toward the tip, but my model is perhaps a bit ‘twitchy’ to test that properly. Top end speed of the model was equal to, if not slightly greater than, that which I had with the glass blades, but then the top speed of this model tends to vary a bit from day to day. (weather?) I have set up this model (Concept 30 SRX Hughes 500E) to be quite ‘responsive’, as I like to fly it as I have seen full size Hughes 500’s fly. (ie they don’t mess about) With the ATP blades, I was able to ‘hoon’ about with the same response and performance that my glass blades provided. Stall turns, ‘wing overs’, roll off the top of a half loop, vertical climbs, and flat steep turns at full throttle for example, all produced the response from the model that I expected.

There is no question that the ATP rotor blades responded superbly to my ‘hoonish’ flight tests. Although it doesn’t make much of a story, I have to say “nothing happened”. If I were blindfolded, (not that it would make much difference to my flying?) I would not be able to tell any difference between the ATP wood blades and the FunKey glass blades. (I did try everything I could think of, just to see if any difference would show up, but none did.)

Remember last month I said “I don’t know how they got the weights into the blade” ?
Well, now I do! As I suspected, the weights are added during the lamination process. Rene from Galtech chopped the end off one of these blades (not the one he sent me thankfully!) and sent me the result. It may not show up too clearly once this newsletter is photocopied, but there are two ‘beads’ of lead set in the leading edge, a very tidy way of putting weights in blades!

The Tail Rotor Blades :

Similar to my assessment of the main rotors, these blades do the job just fine. I intentionally kept my model settings (gyro, rudder channel, and RPM) constant, so that I could observe any performance difference. As far as I could tell, the model performed exactly the same with the ATP tail rotor blades as it did with the standard Kyosho tail rotors. The trim setting was the same, piroettes in either direction were at the same rate, and the model held the same heading whilst side on to the wind the same as before.
Now, while I admit that this model has the gyro set to ‘medium’, so the tail stays mostly where I put it, it is still reasonably responsive in the tail (about two piroettes per sec at full stick deflection), so I don’t think the gyro is ‘undoing’ too much rudder stick input.

I rotated the hub insert on the tail rotors to the ‘fast’ position, and did the same piroette tests, but could not tell any difference in performance, similarly with the hub inserts in the ‘slow’ position. In each case, the model performed piroettes and sideways crabbing just as it had done with the standard Kyosho tail rotors.

As you know, the effectiveness of an aerofoil is determined by how much air it can move for a given amount of deflection. (angle of attack) As altering the pivot point does not alter the amount of deflection, (that is determined by the angular movement of the blade grip) then I did not expect altering the hub insert to make any difference, and indeed that was the result observed in the air.

Conclusions:
Both the ATP main rotor blades and tail rotor blades do the job damn fine. The performance of the main rotor blades is by far the best that I have seen from any wooden blades, and even some glass blades. While the FunKey glass blades I have used as a comparison may be considered by some as not particularly ‘top line’ blades, I find their performance to be more than satisfactory, and hence I have no hesitation in recommending the ATP main rotors, as they perform identically to my $85 glass blades as far as I can tell, and yet cost only $39.

The finish on the main blades is superb, they are perfectly balanced and prepared for flight, and only require bolting onto the model.

The tail rotors work as equally as well as the standard Kyosho tail rotors without doubt, but I was unable, with my model anyway, to detect any performance enhancement over the Kyosho tail rotors. Neither could I tell any difference in performance of the tail rotors by rotating the hub insert, and I suspect from theory that none is possible, however I am happy to stand corrected.

My thanks to Galtech Models for providing these blades for evaluation.

Jeff Law