Mauleguy wrote:I am running a Hartzell compact hub, metal blades, 84" diameter. Blade stops are at 8 degrees and 38 degrees according to the prop shop. I have played with the set screw on the hub and seen take off RPM's at 2690 the way it was first set up. I screwed the set screw in 1 turn and that dropped it to 2580 on take off (I did not like it as well so I am back to 2690). I am going to set the governor to allow for higher RPM's (2800-2900) and see what difference this might make. Right now at 2690 it does not feel like it pulls as hard as my 90" fixed pitch did pitched at 33 (turning only 2450 static). I hope to get it where I am using the full 200 hp and it pulls really hard.

I think that makes sense. Here is my logic:

No matter how much pitch the constant speed takes out in order to achieve max RPM, it can't grow the prop longer, so no matter what you do, you are always stuck with the length and whatever pitch is needed to keep from over-rev.

I found this little airplane prop calculator to thought experiment: It's by no means accurate, but I think it makes the point. http://godolloairport.hu/calc/strc_eng/index.htm

If I put in this prop: 90x33 standard propellor CF .71 2580rpm 59F I get right at 179hp.

In order to get 200HP with an 84" prop with the same coefficient/temp/etc at 2690rpm I need a pitch of 42.5".

So even though the old engine is 20hp less, a 90x33 vs 84x42 is a huge difference. Static thrust is 1211 vs 710 and flying speed is 80 vs 108

I wonder if an 88" would split the difference... yea... an 88x35 with the same settings at 2700 gives more static thrust at 861 and flying speed of 90.

I have the same compact hub 84" Harzell for my project. I wish I would have gotten a 86, but on the flip side, I'm sure I'm willing to trade more low end for cruise then you are...

Can you just swap the blades?

akschu wrote:

Mauleguy wrote:I also have the VG's on the tail and a gap seal on the elevator. I had it up above stock position by 1" for the first flight and I ran out of up elevator on landing along with not enough nose up trim. I lowered it to stock and that helped some, I then lowered it 1" below stock and that help more. I still have to hold back stick pressure when empty fully trimmed nose up, if I throw 35 lbs. in my extended baggage that goes away. I am currently building a horizontal tail surface that is based on the N.A.C.A. 0012 airfoil to energize my tail. It should require a lot less trimming and lower stick pressures when slow. It will probably be several months before I complete them but I think this should be the cats meow.

Thanks for the information. BTW, I make some wood shims for the bearhawk guys that might make your tail upgrade faster. I just drew a NACA 0012 airfoil in cad with the same cord as the stock tail width, then subtracted out the existing stab leaving the upper and lower shims needed, then my friend cuts them on his laser cutter. You just sand them a little, glue them on, seal them up, then cover.

ribs.png

It's a quick way to get to where you are going, and not hard to make you a custom set.

Wow, not sure how much you charge, I wish I had known but I already have them ordered from a laser cutter in the shape I need for each station. I am doing it a little differently, your way may be better. I should have all the parts Monday.

I actually have pull tested the 90" and at sea level on a pretty much standard day, it pulled 905 (average of 3 pulls) at 2450 rpm which is all it will turn with a O-360 and 10.5 to 1 pistons.

Mauleguy wrote:
Wow, not sure how much you charge, I wish I had known but I already have them ordered from a laser cutter in the shape I need for each station. I am doing it a little differently, your way may be better. I should have all the parts Monday.

Not much, if you want to ping me about it shoot me an email at "schu"at"schu"dot"net"

Anyway, thanks for answering all of my questions, it's great to glean ideas from those that have gone before me....

akschu wrote:

Mauleguy wrote:I am running a Hartzell compact hub, metal blades, 84" diameter. Blade stops are at 8 degrees and 38 degrees according to the prop shop. I have played with the set screw on the hub and seen take off RPM's at 2690 the way it was first set up. I screwed the set screw in 1 turn and that dropped it to 2580 on take off (I did not like it as well so I am back to 2690). I am going to set the governor to allow for higher RPM's (2800-2900) and see what difference this might make. Right now at 2690 it does not feel like it pulls as hard as my 90" fixed pitch did pitched at 33 (turning only 2450 static). I hope to get it where I am using the full 200 hp and it pulls really hard.

I think that makes sense. Here is my logic:

No matter how much pitch the constant speed takes out in order to achieve max RPM, it can't grow the prop longer, so no matter what you do, you are always stuck with the length and whatever pitch is needed to keep from over-rev.

I found this little airplane prop calculator to thought experiment: It's by no means accurate, but I think it makes the point. http://godolloairport.hu/calc/strc_eng/index.htm

If I put in this prop: 90x33 standard propellor CF .71 2580rpm 59F I get right at 179hp.

In order to get 200HP with an 84" prop with the same coefficient/temp/etc at 2690rpm I need a pitch of 42.5".

So even though the old engine is 20hp less, a 90x33 vs 84x42 is a huge difference. Static thrust is 1211 vs 710 and flying speed is 80 vs 108

I wonder if an 88" would split the difference... yea... an 88x35 with the same settings at 2700 gives more static thrust at 861 and flying speed of 90.

I have the same compact hub 84" Harzell for my project. I wish I would have gotten a 86, but on the flip side, I'm sure I'm willing to trade more low end for cruise then you are...

Can you just swap the blades?

I played with the calculator a little and it does not seem very close to real world. I know because of all the time I had in the original Bushwacker that I had a cruise speed at 2500 rpm of 95 mph and I had a real world pull of 905 at 2450 rpm
I am pretty sure Lycoming rates the O-360 at 160 hp at 2400 rpm

The calculator gives 1092 pull 216 hp and 76.5 mph, Boy am I glad it was not right about speed! 76.5 mph would suck, I thought 95 sucked.

I have an 86" compact Hartzell experimental propeller for sale. I bought it and tried it on Bushwacker 8 or 9 years ago, it started off life 95" and pulled so hard it would slide my tires on asphalt at 2100 RPM (that is all I could turn it) but I did not had the HP to turn it up. I had it cut down to 90" thinking that I could turn that since I already was turning a fixed pitch 90. That did not work so I had it cut to 86", still had to much blade for the 0-360 Lycoming so I gave up on it and it has sat in my heated shop ever since. I almost tried it on the 200 Hp engine but decided that it was to much blade and had the 84" built up. It has never had oil pass through it so even though it was overhaul almost 10 years ago it is like the day I bought it. If you are interested email me. I think it is the perfect propeller for a O-540 Lycoming in a Bear Hawk or something like.