While Hartzell data may indeed point to best speed at high rpm with their products, the same may not and does not appear to be true for MT products. At least 4 other people on this forum and other forums have stated from FLIGHT TESTING that lower rpms with their MTs results is higher cruise speeds despite obviously lower engine hp. MTs may be suffering a large drop in efficiency at higher mach numbers.

Hartzell data may not have any relation to MT performance. I'll wait for Jim's flight test data. Enough conjecture on this topic already.

You use the word efficiency but are not stating whether you are referring to prop efficiency or engine efficiency. For a given speed, high MAP and low rpm is more efficient since low MAP/high rpm has more pumping loss across the partial throttle plate. But that has nothing to do with prop efficiency. The statement I referred to is that the "drag" of a prop was higher at higher rpm, and that wasn't addressed in your posting. The only "drag" that a prop has that I know of is the parasite drag, and with the proper selection of airfoils and loading, the L/D can be 9:1-10:1, regardless of rpm. To iterate, prop efficiency is mainly tied to loading, tip shape and Mach, along with streamlined root sections. And with all this prop theory and advance ratios, thrust and power coefficients and whatever, how is it that these prop makers couldn't turn out a prop with 90% or more efficiency as I have? The one you show tops out at about 85%!

I obtained a power chart from Lycoming for my O-360 engine and used their RPM/MAP settings to obtain 65% power at each RPM.
I assumed their chart was correct, also. :-)

Regards,
Jim Ayers

hartzell prop application chart
 

george --

where did you get the quoted chart? i'm not questioning it's veracity, but i'm getting ready to order my prop, and i don't wanna screw it up. i'm installing a mattituck io-360 with forward facing sump, which is very close to the lycoming io-360-m1b, a 180 horse engine. according to the chart, i should use the 7497 instead of the 7496. but van's says the 180 horse should use the 7496 and the 200 hp the 7497. (see my confusion?)

i asked the hartzell sales dude at oshkosh, but he didn't know nothin'. he opened up a book that showed the 7497 as appropriate for the -m1a, but he didn't have a sheet on the m1b. i also can't find the chart on either van's or hartzell's site. so, where'd you get it?

thanks for answering.

Yep I can answer, but give Hartzell a call
 

John call Hartzell they are super nice and really can explain. The chart is new and from Hartzell. Had the same question. The 7497 is the newest blade and just was certified in the last few months, first of the year. That is why you may not have heard of it yet. The 7496 BA blade and came first, its great. The new BA 7497 blade has more metal in it, thicker to affect a change in its harmonics or ?tuning fork? characteristics. The good news, it has less or no restrictions, but it's a slightly heavier blade and performance might take a slight hit, due to increased blade thickness. The engineer told me the difference in top speed would be hard for most to detect he estimated, in the data "noise" or scatter as they say, meaning negligible. They have not done side-by-side testing, but when you add blade thickness you expect to affect performance. In this case its value added. We are splitting hairs. Weight? I forgot what he said, but it should not be significant to any one.

Van may not have the prop listed yet buy you should be able to order it, even if its not in their catalog yet. All props are drop shipped direct from hartzell any way. Its not like Van stocks them. I think the price should be the same. They use the same blank and just machine it differently I believe.

In my opinion you can't go wrong with either, they are BA Hartzell made for RV's. I'd probably go 7497 since weight is not an issue and a fraction of a MPH is not going to kill me. If I already had a 7496, I'd be happy with that. However I'm still rocking the old 7666 blade. I have plans for a BA prop.

All the best & you'll love your prop. G

Bill

I also have a high compression parellel valve 360 Lycoming that I had built a few months prior, and if I knew then what I know now I would have not went any higher than 8.7 to 1.

As far as i am aware Hartzell propellors has not tested blended airfoil propellors running high compression. Even though you will be within tolerable horsepower range your engine still could overstress the blades running those pistons. I am told it is harmonics and resonance (torsional vibration)that damage blades and cause blades to disappear from the nose of your aircraft not horsepower.

So what are we to do? Run MT because the wood/composite is less likely to be damaged by the effects of high compression because of its ability to dampen resonence. Or rip the cylinders back off of our 360's and through in those 8.7's and fly safe behind a Hartzel.

Like Bill; I also am looking for some advice or experience on this subject

Good question
 

That is true Hartzell has not tested higher compressions. I talked to the engineers and high compression may change the harmonic characteristics of the prop/engine combo, but the affect is not drastic. It makes a little more power but does not change the frequancy or pulse drastically like going from Mag to EI.

The affect of the electronic ignition (they only tested one brand BTW lightspeed) has a greater affect. However you're absolutly right, as you say its an unknown. Well actually its a partial unknown. The engineer I talked to said a bump in compression might expand or move critical RPMs up slightly higher.

Just stay out of the corner of the envelope. Look at the typical limits for other props. Its 2,700 rpm and at lower RPM's in the 2,250 rpm under range, especially with over MAP pressure. Keep it in the middle of the normal operating range 2,300-2,600 rpm and MAP approx square or under. That is wild freaking guessing on my part, but it comes from the conversation I had with Hartzell about this topic. Again I encourage you to call them. They did not express concern BUT the only way to know for sure is do flight test. None have been done and none planned as far as I know.

I think you are over stressing (pun intended). :rolleyes: 8.7:1 compression is very very mild and the affect will be limited. Stock is 8.5:1. If you get the better 7497 blade (better in that it's thicker, heavier and less susceptible to harmonic limits) and try not to fly at 2,700 rpm all day, all the time, you will be fine. Even the 7496 is fine in my opinion, but guaranteed unlimited fatigue life with out testing is not possible.

The older HC2YK/F7666 with the most restrictions with EI (or even with Mags) is good for I recall 8,000 hours. The new BA airfoil, specifically the newer of the new 7497 is designed for EI and well tested and understood. Criteria is unlimited fatigue life or hours. In fact the 7497 works on the IO360 angle valve with 8.7:1 compression. That is what it was designed for.

Are you also using electronic ignition. The affect of the compression alone from my understanding is not as drastic the change for adding EI. Call Hartzell engineering. They will be glad to help you. I have a feeling they will give you warm fuzzies, but not scientific absolute.

Now the guys going super radical high compression, different cam grinds, dual lightspeed's, cold sump, 4-into-1 exhaust are pushing the unknown scale much more. The last item, 4-into-1 is an unknown I thought about, which affects me. I realized Power Flow makes 4-into-1 exhaust for factory planes as an aftermarket STC. They claim higher hp. The FAA did not require a prop change. I don't think they check the prop harmonics. For some reason the EI makes the biggest change. Its not as much the greater power as much as the PULSE. Compression tends to possibly aggravate but not make big changes, with in limits.

Hope I calmed you down a little. :D I'm pretty conservative. I wouldn't hesitate to fly in you plane this year or 5 years from now. As long as you maintain the prop and engine and operate it properly, the prop will wear out from erosion well before fatigue is factor. Be sure to keep the prop free of nicks and gouges, grease the hub per hartzell's recommendation and fly regualarly. There are a lot of factors of safety and margins built into the prop and engine that make existing limits for the know configurations conservative. Also there are lots of guys with way more radical compressions and set ups flying with BA props. One of their props will fly off well before yours does. :eek:

long run
 

Hey George,
I see I started this post over two and a half years ago.

Does that beat the record for your longest running post.

Pete.

PS. I agree. Just because Hartzell hasn't tested High Comp pistons doesn't mean it's all going to fly apart. They just haven't checked.
P.

Which model M propeller?
 

Hi Peter,

Glad you could join back in on what you started.

What aircraft type and engine were you talking about?

What model Hartzell did your friend have?
And what model MT propeller did he try?

Regards,
Jim Ayers

RV8 Hartzell to MT
 

My mates aircraft is an RV-8 with Angle Valve.

I don't know the Model Number of the props, but it was a TWO bladed Hartzell (from a Mooney) to a THREE Bladed MT.

My RV7 with a TWO bladed MT seemed about 3KT slower than an identical engined RV7 with a Blended TWO bladed Hartzell, side by side on the Cruise at 7,000'.

The significant difference, to me after flying 160hrs, was that stone damage (Not many sealed strips in Australia) to the MT tore the Vinyl (?) sheathing on the Blades and dinted the Stainless LE strip. By comparasion, you can file a lot of damage out of an Aloominum prop.

MT prop. Lovely prop, but very delicate.

Pete.
PS. You should do a search on this forum under Props. THere has been a lot of good info, from people much more knowlegeable than me.

P.