New prop on jab 2200a engine

[bil438]

I flew my SII 25 minutes yesterday, first flight on the jab 60 X 42" prop.Here are the details.

I replaced the 54 X 48 prop on my Sonerai II , Jab 2200a powered, with a Jab 60 X 42. It turned 2600 rpm. Half an inch at a time I trimmed it down til I has 2800 static.i.e. 57"now
Yesterday I flew it for 25 min
Before I had been getting 120 -130 cruise. With the (now) 57 X 42 prop, it climbs out better than 900 fpm, but cruises at 110-115 mph. It was 70F/20C yesterday so I can't claim cool weather climb.
I had been getting say 400-500 fpm with the first prop.
So the rpm vs airspeeds are
2800 - static
2900 - takeoff roll
3000 - 80 mph BROC
3100 - 90-`100 cruise climb
3000 - cruise 115 mph
3200 - cruise 120 mph
3300 - full throttle cruise 125-130 mph.
I'd expected the 57 X 42 prop to give me better cruise but less climb. That's obviously wrong. For example the Takeoff roll is the same.

If you have been changing props and know this stuff well, then I'd like your opinion.

FWIW, the aircraft was constrained by ROC to just one seat used. 900 fpm may just change that.
Bill

[hans]

your 42 pitch vs. 48 theoretically is not improving cruise/top speeds. It should improve low speed & climb (as you have discovered), but only so if your prop diameter is small enough to allow the engine to rev up high enough to indeed produce the power it can. What's the operating point you want to optimize for? Cruise?

cheers
Hans

P.S. quite a few years ago I set up a Yahoo Propeller group. You might want to browse the files section for relevant information or ask members. Check out groups.yahoo.com/group/propeller/

[soneraifred]

Bill:
Hans is absolutely correct. The pitch number is directly related to the cruise speed. If you multiply the pitch number (which is in inches) by the rpm, which gives you inches per minute of forward motion if you were operating in a perfect fluid with no losses, and convert it to miles per hour, you'd find that a 42" pitch prop at 3000 rpm will provide a forward speed of 119 mph. 48" of pitch at 3000 rpm will provide 136 mph. Of course, efficiencies will lower the actual numbers.

[hans]

just to give you an actual data point from an airplane with a similar speed envelope using the same engine:

An IBIS canard with a Jabiru 2200 engine used a prop (manufactured by EVRA of France) with a diameter of 1.33m (52.4") and a pitch of 1.25m (49.2"). With this configuration it obtained 2980 RPM static and 3300 RPM full throttle in-flight @ 139 kts.

cheers
Hans

[juergen]

Hi Bill,
if you want, I will send you the Prop/Pitch calculation sheet by mail.
On this sheet, you see, the prop tips (60") are inside the supersonic speed and so all additional power goes not for forward, this power goes only for noise.
Send your mail address via PM to me and I will send it.
The sheet is similar to the old Yahoo sheet, but modified for more comfort.
with best regards
Juergen

[maddog]

Hi Juergen,
I have tried to respond twice with PM, and give you my e-mail, I'll try again...

mb

[maddog]

Sorry Juergen,
I did receive the spreadsheet, and thank you.
My bad...

mb