Hartzell Trailblazer Question

[spinningwrench]

I am talking to Hartzell's technical staff about using the Trailblazer with my Lycoming O-360 on my Patrol project. I am planning on using two E-Mags for ignition. According to Hartzell the Trailblazer prop is not approved on an O-360 with dual E-mags because it has not been tested. It is not disapproved for any particular reason either. Is anyone running this combination of engine & prop. I suppose I could fall back to a single mag and one E-Mag like on a certified engine but that would be looking backwards.

[Nev]

That’s a question that I never thought to ask either, but I’ve got an IO540 and dual EMags. I guess this is where the “experimental” in experimental category kicks in.

[svyolo]

I would call that a disclaimer, like Mcdonalds warning about hot coffee being spilled on your nether regions. They are correct in putting that out there, but composite props have much less problems with torsional vibrations that metal props. Metal props are extremely prone to it, and after a few accidents they will put limitations on them with certain engine/prop/counterweight/airframe combinations.

Composite props dampen vibrations naturally. Electronic ignition can change (depending on the timing) the power pulse and that is user definable, so no way for Hartzell or MT to test every combination.

[spinningwrench]

Well that’s interesting. I know torsional vibration is difficult to detect without instrumentation but your comments about composite props makes sense.

[Rollie]

It's also only certified for engines up to something like 9:1 compression. I'm running 10:1 compression and dual P-mags. Over 300 hours and no issues so far. I asked the same questions before I ordered my Trailblazer and they guy I talked to at Hartzell said it simply means it hasn't been tested in these configurations so you would be truly experimental. I also set my prop governor for a max rpm of 2770, by my rough math that has the tip speeds just under mach. Time will tell but as smoothly as the thing runs I don't expect any issues with the prop.

[zkelley2]

My prop manual is pretty explicit about 2700rpm limit and % overspeeds and what is required if that happens. Lycoming is on their engines to. How did you come up with 2770?

[spinningwrench]

Thanks Rollie. Just found out American Champion runs them with single electronic ignition. I believe I’ll give it a go.

[whee]

I'd be very confident you would have no issues with dual p-mags. The potential issue is a sharper power pulse from the better ignition of electronic ignition.

I would call that a disclaimer, like Mcdonalds warning about hot coffee being spilled on your nether regions. They are correct in putting that out there, but composite props have much less problems with torsional vibrations that metal props. Metal props are extremely prone to it, and after a few accidents they will put limitations on them with certain engine/prop/counterweight/airframe combinations.

Composite props dampen vibrations naturally. Electronic ignition can change (depending on the timing) the power pulse and that is user definable, so no way for Hartzell or MT to test every combination.

I agree that the warning is just a disclaimer that they have not tested in and therefore cannot approve it. It has been a long time but I recall that composites do have resonant frequencies but they can be altered through different layup methods. MT props are wood with a composite covering which is why they don't have harmonics. Hollow or foam core composite props can have resonance issues. I recall two brands of experimental composite prop brands that had cracking/failure issues that were attributed to harmonics. Also, some of the big bore 4 cylinder Lycoming clone engines had issues with braking blades on props except the MT due to their massive power pulses.

Sorry TLDR. Hollow or foam core composite props may or may not naturally dampen vibrations. MT props do dampen vibrations because they have a wood core; it is the wood doing the work.

[zkelley2]

I am talking to Hartzell's technical staff about using the Trailblazer with my Lycoming O-360 on my Patrol project. I am planning on using two E-Mags for ignition. According to Hartzell the Trailblazer prop is not approved on an O-360 with dual E-mags because it has not been tested. It is not disapproved for any particular reason either. Is anyone running this combination of engine & prop. I suppose I could fall back to a single mag and one E-Mag like on a certified engine but that would be looking backwards.

They will never test it on dual electronic ignition, because you can't certify dual. So there's no point in them doing that test.

[Bcone1381]

I wonder if Mags are ok because the spark event is somewhat random..... which might mess with resonance that a precise spark event could induce.

[spinningwrench]

So many advantages to a modern ignition. Spark advance, such a novel concept. I’m building the engine to take automotive plugs. One could afford to toss the old plugs at annual. Just put some aviation fine wire plugs in my Citabria at $55 a plug.

[zkelley2]

I toss them every annual. I can buy 12 iridium plugs for the cost of a single fine wire.