For the HB .15 - something 7/8" ish?

NEW222 wrote:But I hear that once they are tuned and set, they will very rarely require any other tuning.

rsv1cox wrote:I can't find much on the net and I'm looking to run this thing.  I'm leaning toward the Top Flight 7/4 but I'm not married to it.  Brodak 5%N 29%C.  Not what I'm used to.  Clean, great compression, Pop.  Got that "good" feel. Only one I have seen with no head fins?

Peter Chinn wrote:[Note, please read previous paragraph on props used - GG] These figures suggest that, although the HP is intended to be a sport-type .15, it is not a low speed slogger and needs to be given its head to reach its full potential. [...]

A prop size that should be useful for most HB 15 installations is an 8x4 and we used a Cox 8x4 prop to check out and adjust the Perry Carb. The minimum idling speed obtained with this prop was 3,200 rpm and to achieve this, the idle disc was set in exactly the mid position.

Peter Chinn wrote:The maker's recommendations in regard to fuel include a one percent nitromethane content for breaking in and a five percent nitromethane content thereafter. The latter corresponds with our standard R/C engine test fuel and was therefore used in all our tests. However, if the user wishes to extract a little more power from the engine, HB also approve the use of a 12 percent blend.

Prop revolutions obtained in static tests on the HB 15, running on 5 percent nitro and with the muffler added, included:

9,500 rpm on a 9x4 Zinger maple;
10,400 on an 8.5x5 Zinger maple;
11,300 on an 8.5x4 Zinger maple;
12,500 on an 8x4 Robbe glassfiber-nylon;
12,600 on a 7x5 Zinger maple;
13,400 on a 7.5x4 Zinger maple;
13,600 on a Cox glassfiber-nylon; [8x4 indicated a couple paragraphs after - GG]
13,700 on a 7x5 Freedom glassfiber epoxy;
14,300 on a 7x4 Zinger maple; and
15,700 rpm on a 7.5x3.75 Bertels glassfiber-epoxy.

These figures suggest that, although the HB is intended to be a sport-type .15, it is not a low-speed slogger and needs to be given its head to reach its full potential. This was confirmed by the dynamometer tests which disclose an uncommonly flat torque curve, reaching a moderate peak at around 9,000 rpm but then falling off only very slightly over the next 5,000 rpm. When the figures were plotted it was found that the peak of the power curve, even with muffler installed, was realized at approximately 16,300 rpm, where a figure of just over 0.25 bhp was indicated.

rsv1cox wrote:I'm not kidding about that "good" feel.  I have cranked over hundreds of engines and know the difference.  I don't think that it ever has been run beyond the factory and it shows no evidence of ever being mounted.  Big change from the type of engine that I usually buy from this vendor.  Can't say as I mind the change.  

GallopingGhostler wrote:The Zingers tended to drop the rpms down more than the other makes mentioned, which makes me wonder if the Zingers were slightly wider bladed.

Although Chinn states 12% nitro approved, I would feel comfortable with 15%.