Microlighters

Being new to the sport I have learnt so much by rebuilding my Raptor. Currently I am sorting a prop out for the trike and thought to post some results i got. We fitted a new shortblock and used the 72x50 prop that was on the plane. At the end of the breakin it was turning the prop at 6700 rpm. This prop however was very old and somehow the water that we used over the radiators caused the fibreglass cladding to seperate. Back to Piet to reburbish the prop. I have since tried different props and got the following results (QNH 1019):-

Type Pitch Static Cruise rpm@cruise - Consumption at Cruise
P Prop - 72x50 - 6700rpm - 52mph - 5150rpm - did not check
P Prop - 76x50 - 6450rpm - 52mph - 5070rpm - 8.4l/h
P Prop - 72x54 - 6500rpm - did not test fly
Warp - - 6400rpm - 52mph - 5400rpm - 12.7l/h

The static rpm numbers are accurate and confirmed but the flying numbers are spot reeadings.

Got the old prop back from Piet yesterday and what a job he has done. It looks brand new. He made it slightly thicker hoping to drop the static rpm. I did a static test and the motor still rev to 6640rpm with the 72x50 which is probably a little to high. The 76inch prop performs very well in climb, cruise and consumption but my concern is that the ground clearance becomes marginal. Any comments and advise will be appreciated.

Welcome to the world of propeller frustration.
Ideally what you're looking for will be about 6350/6400 rpm static and on take-off (climb out) it should unload to about 6500/6550.
That 76x50 looks like it can do the job for you but as you say, there may be a clearance issue.

I see you tested a Warp as well. That's good because you're able to set the blades at whatever static rpm you want. Now, if you like a 2 bladed P-Prop and you want it to perform like the Warp (rpm - wise) then get Piet to make you a prop to match the length and pitch of the Warp. How will you know what the pitch of the Warp equates to in a wooden 2 bladed P-Prop? Here's how:

a) You know the length of the Warp = 72"
b) Measure the pitch of the Warp blades AT THE TIP (important, at the tip) with the Warp protractor. Let's say for example it comes to 13.0 degrees
now
1) Determine prop circumference by C=diameter x Pi (3.14159)
eg: 72 x pi = 226.19
2) Multiply prop pitch in degrees by the constant .0175
13.0 x .0175 = 0.23
3) Multiply 0.23 times 226.19 to arrive at prop pitch in inches
0.23 x 226.19 = 52.02 (say 52)
So, a 72" Warp with 13 degrees pitch AT THE TIPS equates to a 72x 52 wooden, 2 bladed prop.
The P-Prop will probably have a wider chord than the Warp which will affect the characteristics. Just mention that to Piet and he'll make the necessary adjustments.

If all else fails, I suggest you try the 72x54 which has not been test flown yet. Nothing wrong with 6500 static and probably a little more in climb-out. Remember the 582 is rated at max 6800 rpm for 3 minutes continious. I bet you won't see that on climb-out so there's nothing to worry about.

What a great answer, thank you very much. I will also measure the Warp that I tested and deduce the pitch based on this calc. The Warp seemed to be less fuel efficient hence the preference for the P prop but let me check that angle first.

Thanks again

Pierre

I have the 72 x 54 prop and works like a charm. Static RPM of 4460rpm.

Cheers

pietmeyer wrote:I have the 72 x 54 prop and works like a charm. Static RPM of 4460rpm.

I'm surprised you can even get off the ground at that sort of rpm....
Finger problems?

pierrejacobs wrote:What a great answer, thank you very much. I will also measure the Warp that I tested and deduce the pitch based on this calc. The Warp seemed to be less fuel efficient hence the preference for the P prop but let me check that angle first.

Thanks again

Jis maar ek het jou mooi geleer
You can always trust the Duck to have a good answer! That's why he's my best buddy.....lol oh yes and he doesn't complain if we crash ........

Pierre....

Nee wat ou maat - too analytical for my liking. I fly with a Warp, get 18 to 22 l/h, the pig screams away quite comfortably at 6800 and tapping off to 6000, chugs along at 85mph. Life is good...

Jy luister na te veel mense met hulle dingetjies.... Duck's knowledge and insight does it for me and if you don't believe the old fart... go visit the master of props for serious insight. Pieter de Nekker will take you on a journey of chords & pitches that the majority never even knew existed!

Kom nou man... VLIEG 'n BIETJIE!

Please excuse my ignorance but what is static RPM?

Off topic Bayliner... your old baby is looking in excellent shape again. Louis has spent hours and hours getting her there. She sleeps in the hangar next to mine....

Will post a photo or two when I get her snapped...

Static RPM is when the aircraft is secured on the ground and engine is at full power....

Thanks John. My heart is still bleeding over DZY. Louis has sent me a couple of photos. He got such a bargain there but at least she is being well looked after. Maybe he will sell her back to me next year. Glenn.

Hi John

Pieter help my baie mooi maar met hierdie een het die nommers hom ook verbaas. I actually like the technical side and many people are teaching me as I go along, I see it as a part of the sport.

Moenie worry ek vlieg nou baie en geniet my eie airie. I have been flying every opportunity I get, weather permitting. Friday I got in a morning and afternoon flight and this morning again a lekker flight. Ek is nou amper klaar...

That's the spirit Pierre... you go boy!

Tell PietdeN I send my regards when you chat to him again.... he is a special ol' fart you see....