Sensenich GA prop on RV-6 PIREP

Well I got the prop installed and a couple hours flown on it today. Here's my first report on it... more to come later.

I also took pictures of the install, and will post them to this thread later.

First impressions... it's smooth, really smooth. The enormous P-factor and tendency for the plane to want to suddenly side-step to the left upon leaving the ground that the wood prop had, seems to be gone or vastly diminished. It needs much less right rudder on takeoff now.

I started with the #4 pitch pin and it looks like I need to bump it up to the #5 pin tomorrow. I got almost 2400 static rpm, and did my high-speed tests at 8500MSL, which was 10500 density altitude since we were at +2000 feet on the ground this afternoon. I was able to hit 199-200MPH TAS at 2700rpm at that altitude which means that it's pitched a bit too shallow with the #4 pin. Acceleration and climb on takeoff was notably improved over the old Aymar-Demuth wood prop. The plane felt more positively under control and in the air immediately after lift-off too, instead of the wallowing feeling the wood prop gave me until I built up a bit more airspeed.

This prop "feels" more like a metal prop than a wood prop. It also slows down in the pattern much more readily when I throttle back too.

So far I'm liking it a lot. It also looks fantastic on my plane.

More to come later.... gotta run for now.

Ok, changed to the #5 pitch pin setting and the airplane is even happier now. Got just a hair under 2300 static RPM and the acceleration on takeoff feels really good (it still ain't no CS prop with that throw-you-back-in-the-seat feel however). Climb is good, and once leveled off at 7500 MSL (DA 8000-8500) I was just able to hit 2700 rpm at WOT and mixture peaked at "full rental power". True airspeed crept up to 197-198 mph in level flight... I kept wanting to see an even 200, maybe I did, maybe I'm just being optimistic but anyway, this prop at this pitch is at least 3, maybe 4 mph faster than the old wood prop under similar conditions... probably because it can spin the full 2700 rpm at ~8000 density altitude. Flew another 2.5 hours today and the phrase "turbine smooth" comes to mind. I'm sure a proper balance job would probably make it better, but it definitely feels smoother than my old wood prop felt.

This is the pitch setting I'll use when I take it to Oshkosh on Thursday, I think it'll do well with the #5... the #4 was just pitched a little too shallow for overall flying but I still want to try the #6 pitch setting someday, and at the other end of the spectrum... the #3 setting... but those are for some other day.

PS: I tried to get my photos of the install to upload to Picasa, but something went wrong and they vanished after uploading them. :-/ I may have to try a different photo sharing website.

This is pretty interesting. How hard is it to change the pitch? Is it something you could do away from home base or is it pretty involved?

ChiefPilot said:

This is pretty interesting. How hard is it to change the pitch? Is it something you could do away from home base or is it pretty involved?

Click to expand...

It takes about the same amount of time to take the spinner off and re-install it as it does to loosen the prop bolts, set the pitch using the machined stainless steel pitch pins , and re-torque the bolts. Once you've got the procedure down, it's probably about a 15-20 minute task. All you need is a good Philips screwdriver and a 3/8 drive torque wrench with a good quality 5/8" six-point socket to set the 45 ft-lbs torque on the bolts. I spent a lot of time meticulously bringing the torque up starting at 20 ft-lbs and increasing 5 ft-lbs at a time until I hit 45 ft-lbs (540 inch-lbs) for the 7/16" bolts. It's probably a good idea to check the blades' runout after torquing down... I set a portable carpenter's workbench next to the blade, put a mark on the bench with a Sharpie marker on the bench where the blade tip just barely touched the bench at about the 5-o'clock position then carefully rotated the prop around to check the other blade without moving the aircraft, and both blades always lined up perfectly against the mark for me.

I'm still a bit concerned about how many times you can re-use the NordLock lockwashers. They feel like a really positive lock when brand new, but once you remove them for the first time, they make a really loud clicking sound, but seemed to torque back up just fine... but there's definitely some amount of wear happening to their ridges when you do that.
I'll probably buy a supply of spares to keep on hand for the future just because the comfort factor of using fresh lockwashers is going to be worth the cost for my peace of mind.

From: http://witorque.com/wp-content/uploads/2012/08/nordlockboltsecuringsystem.pdf

"Reusability
Since sliding always occurs between
the Nord-Lock® washers and the head
of the bolt/nut when tightening, and
between the cam faces of the washers
when untightening, the friction will
not increase under the nut/bolt as with
other serrated fasteners. In combination
with 8.8 bolt/nut Nord-Lock® can be
reused up to 5 times if the washers are
lubricated before re-assembly.
On high-grade and stainless steel bolt/
nut it is not recommended to reuse
Nord-Lock®."

I'd guess that they can't be that expensive that you wouldn't want to afford changing them each time. The other thing that comes to mind is that I suspect once you've played with different pitches, that you'll settle on one and not change it after that anyway... So maybe going through a few sets of washers while tweaking will just be a teething pain.

The Nordlocks used (size = NL12SP, part# = 1531) are about $2 each when purchased individually, or you can get a package of 8 for $15 from Zoro Tools. The inner diameter hole of these Nordlocks is actually the size for a metric M12 bolt, which makes it a little large for a 7/16" prop bolt, but they they needed a washer with 1.0" outside diameter and Nordlock does not make one with the large outer diameter and an inner hole for 7/16 bolts.

With the awful noise they make when you loosen them, it's gotta be wearing down the inside locking cam ramps pretty good, so I'd hesitate to reuse them more than once... for a grand total of 2 uses, and the advice to not use them at all on "high grade" bolts (e.g.. prop bolts) is probably a good idea.

I've re-used mine exactly once, since I only had the set that came with the prop, but will definitely buy a supply of them to keep on hand for the next time I wish to change the pitch.

There are also two small Nordlocks used for the two #10 screws that hold the front spinner bulkhead to the prop hub, but since those slip on the carbon fiber bulkhead instead of the cam ramps when you loosen them, they can probably be re-used infinitely. Next time I remove those, I'm probably going to get a couple of #10 screws with drilled heads and safety wire them together instead of relying solely on those two Nordlocks.

Finally got the Picasa photo album fixed so the photo sharing works
https://picasaweb.google.com/103492993411711088784/Prop?authuser=0&feat=directlink

Crack found in old Aymar-Demuth prop


Unboxed the new prop and spinner





...continued next post...

Installing spacer, rear spinner bulkhead and back half of hub


Blades inserted and front half of hub added


Setting pitch of blades


Checking blade tracking against a Sharpie mark on a portable workbench. Both blades lined up exactly the same...


Front spinner bulkhead is held in place with only two #10 screws


The finished installation!

Thanks for this Neal, I hope to order my prop in the spring.

One question if I may, I mounted my cowling using the stock Vans's spinner backing plate. This plate has flanges that are 9/16" deep, so the forward face of my cowling is about 11/16" rearward of the prop mounting surface.

In your pictures the spinner backing plate looks to be deeper in this area, looks like I may have to rework the cowl or order a custom propeller extension. I have a 4" extension that I used to do the cowl work with the idea that I would order a Sabre extension when the time came. Don't think a custom length is a deal stopper, but I'm curious.

Can you tell me how deep the flange is on the backing plate?


Thanks, Terry.

Originally, my plane was equipped with the 2.25" prop spacer and a stock Van's 13" spinner assembly. The builder of this plane made the spinner to cowl gap very tight... maybe 1/16-1/8" max. It made removal of the cowl quite a pain, and he typically removed the prop before each time he removed the cowl halves. I was able to remove the cowl with the prop on, by using a piece of thin cardboard as a protective shim to keep from scratching the spinner rear bulkhead against the cowl, but it was still a pain. The new spinner's rear bulkhead is actually a bit more shallow than the Van's spinner backplare so I think you'll be OK with your current measurements. This now gives me a bigger... about 3/16" to 1/4" gap, so now it's pretty easy to remove the cowl with the prop installed. If your plane will be using a 4" prop spacer instead, then yes you'll need to get the Saber 4"spacer and bolt kit and delete the stock 2.25" spacer and prop bolts from your Sensenich GA prop order.

The flange on the carbon fiber backplate may look bigger than the stock Van's aluminum backplate, but the carbon fiber backplate had a bevelled shape which brings everything forward enough of the crankshaft spacer mating surface which negates the deeper flange.

Here's a side view of my spinner-to-cowl gap with the new prop

Thanks Neal, she looks great. Please keep us posted as you gain experience with the prop.


Terry.

Does the GA prop have the same 2600rpm limitation of the metal prop, and is it approved for aerobatics?

Snowflake said:

Does the GA prop have the same 2700rpm limitation of the metal prop, and is it approved for aerobatics?

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The metal prop has a 2600 rpm limit. The composite GA prop does show to have a 2700 rpm limit in the installation manual, equal to a typical Lycoming O-320 redline of 2700 rpm, and the manual is silent on aerobatic ops, so I guess they're not prohibited. The Instructions for Continued Airworthiness also says that if you run the prop for longer than 2 minutes at greater than 10% above max rpm (the example says 2870 rpm, which is a math error, because 2700 x 1.1 = 2970) then you must perform the "Inspection After Suspected Impact".

Here's a link to the manual: http://www.sensenich.com/files/docu...te_2_Blade_Lycoming_2G0_Series_1373393617.pdf

So, all in all... the 2700 rpm limit is nowhere near as bad as the 2600 rpm limit on the metal prop, which is there for known harmonics/resonance problems.

Good to know. I've been heading toward 2600 a couple of times on a downline and wondered about that. Never made sense to me that the fixed prop for the O-360 doesn't have an RPM limitation, but the one for the O-320 does, and it's right where you're likely to hit it.

Snowflake said:

Never made sense to me that the fixed prop for the O-360 doesn't have an RPM limitation, but the one for the O-320 does, and it's right where you're likely to hit it.

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Yeah, the 2600 rpm limit on the O-320 props really hits right at an rpm level that is optimum for the engine to produce power too, that's what kept me from buying one. The 360 engine and Sensenich metal prop for that engine has a completely different set of harmonics, and the engineers at Sensenich really know their math and physics about this kind of stuff, so I trust their expertise. They've also gathered a lot of knowledge with carbon fiber prop blades in airboat applications and I think they've hit a home run with the GA prop for O-320 engines. At Oshkosh I asked them about the O-360 and the guy there said they're working on a GA prop for the O-360 so if they get the vibration and harmonics stuff figured out, there will probably be one of these props available some day for that engine too.

Is that 2600 rpm limit with full power? How about over 2600 going down hill when the engine is not producing power or very little and the harmonics would not be there or at very reduced levels?

Norman CYYJ said:

Is that 2600 rpm limit with full power? How about over 2600 going down hill when the engine is not producing power or very little and the harmonics would not be there or at very reduced levels?

Click to expand...

I'm pretty sure it's 2600 rpm, period.

It's 2600 at any power setting.

Yes, 2600rpm limit for the metal O-320 prop at any power setting - because of torsional vibration issues. Advice from Sensenich is to not exceed the limit under any circumstance.

Pete

Neal;
I installed the SENSENICH GA prop with 13" spinner. Now for the weight & Balance...I looked for the weight on the installation guide....I don't see it anywhere. I didn't think to weigh it before installing.
Do you know how much it weighs?

I weighed my old prop, spinner, bulkheads, crush plate, and all hardware by piling it up on top of a bathroom scale.

Then I did the same with all the new prop components before installing it.

That gave me an exact difference of old vs new with all related components, bits and pieces included for each.

The new prop and all its related components weighed exactly 3 lbs more than my old wood prop and all its related components. I can't remember off the top of my head what the new prop's total was... I've got the numbers written down in my W&B paperwork with the airplane logbooks, I'll stop by the hangar tonight after work to get the numbers and post here when I get home.

Total installed weight of the new prop, spinner, spacer and all related hardware was just shy of 25 lbs. Mine has the 7/16" prop bolts.