Microlighters

Windlass 503,Aquilla 1 15sqm wing, flying from sea level. It is currently swinging a 2 blade 72 X50 wooden prop,which seems huge. What size/ pitch should I be looking for ?

What is your static RPM? i.e. if you put the nose of the trike against the side of a hangar and rev it full? Should be between 6250 and 6400

If it is then the prop is fine If not then look at a lower pitch like a 46. But check the Static RPM first.

What gearbox do you have?

Hi Morph Will have to come back to you with the static RPM after the weekend. It is an E-box ,the prop just seems huge for the hp

kiwilad wrote:Hi Morph Will have to come back to you with the static RPM after the weekend. It is an E-box ,the prop just seems huge for the hp

On the E-box the prop would seem huge, because you are probably used to a 1:2.58 B-box prop, and they are smaller, because the prop is running faster than on your E-box. Should be perfect. Check the static though, just for peace of mind.

regards,

Thanks guys, will check the static first thing Saturday and post what I find

Morph wrote:If it is then the prop is fine If not then look at a lower pitch like a 46.

Hey Morph, you're slipping.........you need to clarify.
If the revs are too high, then increase the pitch to something more than 50 and if the revs are too low, then decrease the pitch to something like 48 or 46.

Kiwilad, a 72" prop on a E box with 3.47:1 ratio is usually correct, so you're right, it does seem huge.

Duck Rogers wrote:Hey Morph, you're slipping.........you need to clarify.

You're right, I assumed that if anything a 50 pitch would be overpitched and thus the static rpm would be lower. Therefore again I assumed a reduction in Pitch would then be needed to bring it up.

As Duck said. If the Static is too high, Above 6500, then increase the pitch.

Just remember that all the gearboxes came in different reduction drives. You can get an e-box in a 4:1 and 3.47:1 and 3:1 and 2.62:1.
SO if you have a 3.47:1 your prop sounds OK-ish but maybe a bit too much pitch as morphs says. If it is a 4:1 you might find it's actually too little and will need either a bigger prop or even more pitch. So you can't just say e-box - you have to specify ratio as well.

Or you could use a "ploegskaar" and not worry about the pitch at all.

Ok , Static tested it today,reached 6050 rpm,I guess you have to allow a bit of innacuracy in the rev display,so I guess it must be about right.It still looks like a mighty big hunk of wood to be spinning though

kiwilad

6050 rpm static is too low. Size of prop sounds fine, but you need a finer pitched prop to get the static rpm up a bit.

kiwilad wrote:Ok , Static tested it today,reached 6050 rpm,I guess you have to allow a bit of innacuracy in the rev display,so I guess it must be about right.It still looks like a mighty big hunk of wood to be spinning though

I would double check that rpm with a handheld optical tachometer just to verify. Handheld tacho is an optical type instrument and works by holding it in front of the moving prop. Digital readout will display a number which is then multiplied by the gear ratio of the box and the result is the real engine rpm.

If that 6050 is the real rpm then I would suggest that it's too low. You have 2 options: 1) Reduce the 50 pitch of the prop to 48 or reduce the length of the prop itself to say, 70 or 68 inches(this is the "not-so-good" option) In theory, you want to spin the longest prop possible.

If you need further help we'll have to know the reduction ratio of the box. Usually stamped on the side of the gearbox, but be careful, the actual gears may have been changed inside the box. Confirm with the previous owner.

Also, you can try and fly it as is with that low rpm, being at sea level or close to it anyway, will give you enough oomph to fly comfortably but it will be far more efficient once the prop is sorted out.

Do you know the gearbox ratio?

Hi,

I used a 70 / 45 Prop on my 503, with C-box (3.47:1) and got 6450 to 6600 rpm static.

Ok ,the E-box is 1 :3.47 according to the stamp on the box.Also nothing in the logbook to suggest that any gearing has been changed.So do you think I should be looking at a finer pitch prop. It would be nice to have a little more ground clearance from the prop tip

Finer pitch won't give you more ground clearance, only less length will. Finer pitch will be much more effective though, based on what you've posted