FYI: New SB 18-07-05 on RV-12 Sensenich Props

[joedallas]

Sorry for the confusion

I posted the photos that Bob Lindell sent me with his permission.

This page is posted to help notify builders of the seriousness of SB 18-07-05

I added a few notes to the page

http://joesrv12.com/Builder%20Lo..._Bullitens.htm

Joe Dallas

[Hotscam]

We inspected the hubs of both our RV12?s and found no cracks, but a very time consuming job to set the correct pitch again to get the specified rpm value at WOT.
As we are not keen at all to do this every 50 hours we ordered new design hub plates at Sensenich.
They charge $ 195 per unit. 😡

[Piper J3]

Originally Posted by Hotscam

We inspected the hubs of both our RV12?s and found no cracks, but a very time consuming job to set the correct pitch again to get the specified rpm value at WOT.
As we are not keen at all to do this every 50 hours we ordered new design hub plates at Sensenich.
They charge $ 195 per unit. 😡

You replaced just the front plate or entire hub? I believe the hub is machined as a matched assembly with matching serial numbers...

[Hotscam]

They asked for the serial numbers of the hubs and quoted all the parts required including fasteners, so I may assume it is correct.
I will pick them up at Oskosh so will see what we get

[Hotscam]

I re-read their mail and it clearly says top half and fasteners

[DonFromTX]

That must be a change. When I upgraded mine a year or so ago, I had to buy the entire hub and send my blades to them for whatever they done.

Originally Posted by Hotscam

I re-read their mail and it clearly says top half and fasteners

[rvbuilder2002]

Originally Posted by Hotscam

We inspected the hubs of both our RV12?s and found no cracks, but a very time consuming job to set the correct pitch again to get the specified rpm value at WOT.
As we are not keen at all to do this every 50 hours we ordered new design hub plates at Sensenich.
They charge $ 195 per unit. 😡

Assuming you were happy with performance before removing the propeller, returning to a specific pitch/performance value is a rather simple process.
If the set pitch value is recorded in the log book or you measure it before removing the propeller.
As long as you have that number, getting setting back to that pitch will give you the same performance you had before.

[Hotscam]

Thats what I did but the plane needs to be exactly level and the angle tends to change a little when you tighten the bolts.
I took the spark plugs out to move the prop without disturbing the level of the plane.
After two iterations I got it within 100 rpm of the original WOT rpm.
It took me 4 hours for two 12?s

[Piper J3]

Originally Posted by Hotscam

Thats what I did but the plane needs to be exactly level

Not so… Refer to Page 07 of Section 47 Construction Drawings. The plane does not need to be level at all and can even change angle between measurements.

The prop pitch angle is relative to the canopy longeron regardless of aircraft level. Each time the prop is moved recheck the digital level on the longeron before measuring the blade pitch. If the aircraft “level” has been disturbed while moving the prop simply re-zero the digital level on the canopy longeron before continuing to measure blade pitch.

It is not necessary to remove spark plugs or even upper cowling.

Tools required include a good quality bubble level and two wooden spacer blocks to level prop hub. Mark blocks L-R, forward and top-side so they are placed same exact position on hub each time. Likewise, mark bubble level so it is not “reversed” for each use.

I use Vans sheet metal TOOL-00002 Prop Pitch Bracket and same Craftsman Multifunction Digital Torpedo Level # 48295 as shown in construction drawings. For each measurement of blade pitch first place digital level on longeron and verify zero and re-zero if necessary. Next place the magnetic base of the digital level on the Prop Pitch Bracket (PPB) and finally place digital level/PPB onto the prop. Use gentle finger pressure to seat the PPB against the front edge of the prop.

I have not found tightening of the front prop hub to influence final blade angle. I snug only outer bolts and leave center bolts loose while adjusting blade pitch. When one blade pitch is correct, snug outer bolts even further before setting second blade.

Total time for above procedure is approximately 30 minutes and will attain relative pitch between both blades to within 0.1° angle.

[joedallas]

SPI

0.10 dg Resolution Digital Combination Protractor and Inclinometer

SPI Tronic Price $243.97


0.10 dg Resolution Digital Combination Protractor and Inclinometer
Accuracy (Degrees) 0.1 (Level 10 ); 0.1 (Plumb 10 ); 0.2 (Maximum Error)

.1 Degree = 6 minute arc . 2 Degree = 12 Minute arc


With four moves of level and the built in error of .2 in the level how is this possible ?

Keeping the aircraft level makes this more possible ?

MY view


Joe Dallas

Originally Posted by Piper J3

Not so… Refer to Page 07 of Section 47 Construction Drawings. The plane does not need to be level at all and can even change angle between measurements.

The prop pitch angle is relative to the canopy longeron regardless of aircraft level. Each time the prop is moved recheck the digital level on the longeron before measuring the blade pitch. If the aircraft “level” has been disturbed while moving the prop simply re-zero the digital level on the canopy longeron before continuing to measure blade pitch.

It is not necessary to remove spark plugs or even upper cowling.

Tools required include a good quality bubble level and two wooden spacer blocks to level prop hub. Mark blocks L-R, forward and top-side so they are placed same exact position on hub each time. Likewise, mark bubble level so it is not “reversed” for each use.

I use Vans sheet metal TOOL-00002 Prop Pitch Bracket and same Craftsman Multifunction Digital Torpedo Level # 48295 as shown in construction drawings. For each measurement of blade pitch first place digital level on longeron and verify zero and re-zero if necessary. Next place the magnetic base of the digital level on the Prop Pitch Bracket (PPB) and finally place digital level/PPB onto the prop. Use gentle finger pressure to seat the PPB against the front edge of the prop.

I have not found tightening of the front prop hub to influence final blade angle. I snug only outer bolts and leave center bolts loose while adjusting blade pitch. When one blade pitch is correct, snug outer bolts even further before setting second blade.

Total time for above procedure is approximately 30 minutes and will attain relative pitch between both blades to within 0.1° angle.