WXB0015 airborne

[WilliamBatten]

Is your prop ground adjustable? Look for about 5200-5300 static. It’s not good for the engine to be overpitched.

Just curious - why do you say it is not good for the engine? What effect does it have on the engine if it is "overpitched"?

[Murray Parr]

Is your prop ground adjustable? Look for about 5200-5300 static. It’s not good for the engine to be overpitched.

Just curious - why do you say it is not good for the engine? What effect does it have on the engine if it is "overpitched"?

To some degree it can be managed by climbing shallower but over propped is similar to driving up a hill in too high a gear lugging the engine down (also producing less power). If other perameters are marginal, it could also lead to detination. My next test flight will have me climbing based on climb rate instead of speed and see what RPM it unloads too.

[sonex892.]

Is your prop ground adjustable? Look for about 5200-5300 static. It’s not good for the engine to be overpitched.

It is the fixed pitch 64" x 81 that Sonex/Sensenich were trying out earlier. I think they now sell 60" x 82 instead. I spoke with Sensenich and they said it could be trimmed but I am not sure who I could get in Australia to do that or where to find the info to do it myself.

Hi Murray.
Congratulations on the first flight.
Is the prop timber? Is it 2 blade? If it is timber there is no great skill involved in removing a bit from the diameter, just make each side symetrical measured from the centre. If your prop is glass covered I would avoid trying to reduce the pitch. With any alterations, balancing afterwards is the most crucial part.
I'm no professional prop maker, I have made 3 props over the years and my 3300 jab sonex has 570hrs on it and only flown with props I've made.
Steve

[roberto51it]

Is your prop ground adjustable? Look for about 5200-5300 static. It’s not good for the engine to be overpitched.

Just curious - why do you say it is not good for the engine? What effect does it have on the engine if it is "overpitched"?

I had a similar situation in my actual RANS S7, and was told by the ROTAX rappresentative’s mechanic that overpitching the engine, the crankshaft, being a press-assembled one (not a one-piece crankshaft) could move and get out of alignment with disastrous consequences…Just to be on the safe side, I diminished pitch as to have 5200rpm stationary as the manuals say…

Roberto from Italy
Kit #1433

[13brv3]

The problem with pitching for 5200-5300 static on a relatively fast plane is that it makes the prop considerably underpitched for cruise. A general rule of thumb from the Rotax Owners forum seems to be pitching for 5650 RPM at your normal cruise altitude, with full throttle. That's how I've got mine set up, and it only gives me about 5000 RPM in 90 mph climb. It's usually recommended to cruise from 5100-5300 from what I've read, with no issue at all running up to 5500 continuously. I'd definitely look to get that prop trimmed down if possible.

[WilliamBatten]

Is your prop ground adjustable? Look for about 5200-5300 static. It’s not good for the engine to be overpitched.

Just curious - why do you say it is not good for the engine? What effect does it have on the engine if it is "overpitched"?

I had a similar situation in my actual RANS S7, and was told by the ROTAX rappresentative’s mechanic that overpitching the engine, the crankshaft, being a press-assembled one (not a one-piece crankshaft) could move and get out of alignment with disastrous consequences…Just to be on the safe side, I diminished pitch as to have 5200rpm stationary as the manuals say…

Roberto from Italy
Kit #1433

OK - sounds like "over pitching is not good for the engine" is unique to the ROTAX engine. Thanks for the clarification.

[Murray Parr]

Is your prop ground adjustable? Look for about 5200-5300 static. It’s not good for the engine to be overpitched.

It is the fixed pitch 64" x 81 that Sonex/Sensenich were trying out earlier. I think they now sell 60" x 82 instead. I spoke with Sensenich and they said it could be trimmed but I am not sure who I could get in Australia to do that or where to find the info to do it myself.

Hi Murray.
Congratulations on the first flight.
Is the prop timber? Is it 2 blade? If it is timber there is no great skill involved in removing a bit from the diameter, just make each side symetrical measured from the centre. If your prop is glass covered I would avoid trying to reduce the pitch. With any alterations, balancing afterwards is the most crucial part.
I'm no professional prop maker, I have made 3 props over the years and my 3300 jab sonex has 570hrs on it and only flown with props I've made.
Steve

Thanks Steve and others who have chimed in.

Yest it is a composite covered wood prop so I should be able to trim it back probably to 60" diameter. Sensenich gave me some guidance on how much difference each 2" cut off should make, I will do some further testing before I make any changes though.

[Murray Parr]

Here is the Utube link of first flight.

https://youtu.be/wD0-G1jxmhc