Dear John,

I checked the data on the classic after I answered your q in RAH, and tried
to find correct data on top speed SL on the Hatz?.
The Acrosport with 180 hp have a cruise of 123 mph (75%=135 HP) and then top
138 mph (152 sq.ft wing area (Cdo 0,0447)) Cdo= drag coefficient. related to
wing area.
The Hatz have 180 sq.ft so with the same Cdo it will make 114 MPH on 135 HP
And top at 119 MPH with 150 HP (correct me if I am wrong)
Normal cruise 65-75 % = 100-106 MPH

I worked on a prop on a Super Cub with an O-290 135 HP at 2600, they had an
Felix prop 72X54 / (very wide and thick) I planed it down to first 52" then
50" and reduced the width and got the RPM up I think 300 RPM, I think 48"
would have been even better. anyway, the Cub was making about 115 MPH with
this wood prop. the book said 125 with metal prop.
They later on bought an Sensenich wood 74X?? but did not get any better
result. They had an Sensenich metal 74X52 but it was to pity to repair,
that we tested on the ground only. It was some years ago so I don't remember
all figures.

So what about your Hatz?, first of all it is essential to have correct
numbers to calculate an propeller, what ever you are going to buy it or make
it your self, then you don't have to keep testing it over and over to get it
right. the figures on the Hatz Classic web say cruise 115 is it cruise or
top speed? = sales talk?
Most importend is that you can fly at climb speed with full throttle without
over revving, and if you want a good cruise fly at full throttle at
7500-8000 ft at redline
Is yours plane flying today? or do you know any builder that fly and can get
corrected (GPS) figures from him? Propeller?

Lets see what my program say; assuming 150 hp/2700 RPM and top speed 119
MPH,
Airplane



Hatz

Aspect Ratio =
5,92
74,00
D Climb P
45,05

Wing Span, b (feet)
25
25

Aspect Ratio =
6,47
74,00
D Stand. P
46,99

TOW (Lbs)

1700
1700

Aspect Ratio =
7,01
74,00
D Cruise P
48,92

Wing area S (sq.ft)
180
180,0

Aspect Ratio =
7,60
74,00
D Speed P
51,07

Body Interference

N








Engine



O-320




Initial Calculation


Rated HP @ Cruise (Design point)

150
100%
1,00
PSRU Ratio
74,21
D Climb P
45,06

Rated HP @ Max


150
1,00



72,92
D Stand. P
46,93

RPM @ Cruise (Design point)
2700
2700
2700
Engine-RPM
71,64
D Cruise P
48,80

RPM @ Max


2700




70,36
D Speed P
50,83

Design Speed, Cruise (MPH)
119
119,0
103,4
119,0
Max Speed




Camber Ratio (Thickness)

1,20








Aspect Ratio


6,00
0,78
872
Tip Speed
Output





It Says that an Standard prop is 74"X47" Climb is 45" and Cruise is 49"
You say it can't be right!
This Pitch is measured at the bottom of the airfoil at 75% of the radii, I
think Sensenich measure at the blades airfoils cord line.
I have had 2 Sensenich on my working table, one W72GK46 (Cub-C90) it
measured 42" at the bottom
and the above mentioned metal 74X52, it measured 50" at the bottom. the
metal is thinner then a wood so the different in the angle/pitch become
smaller on the metal.
So if we ad 4 inch an Sensenich become; W74X49, W74X51 or W74X53, Climb, Std
or Cruise (it is still same pitch at the bottom as my program say)
Then it is up to you to determined what you want your prop to do for you,
and what you want to do with the plane.
Is it an short soft grass strip, pick the climb prop, mostly cruising as you
say/longer runways, Cruise prop!
Aerobatics? Standard prop! (72" X 51-52"??)
High elevation airfield 4000+ ft MSL reduce the pitch with 2".

If you have correct numbers let me know.

Jan Carlsson
Aeronca Champion 7AC - A-65 (72"X42")
www.jcpropellerdesign.com


I have to decide between a climb prop and a cruise prop for my Hatz
biplane.
I am looking for a primer on propellor choice. For climb I was thinkng
Sensenich W74EM-54 and for climb Sensenich W74EM-58. Propellor experts
educate me please.

--
John "Ebby" Ebensperger
Hatz Classic s/n37
Camden, NY