M

mlwynn

Well Known Member
Hi folks,

I finally decided I needed a constant speed prop on my RV 8. I have a James cowling, so there are some issues to fitting the new prop. In the mode of in for a penny, in for a pound, I bought the new Hartzell composite from Vans. The blades are quite wide and the hub is somewhat extended to (I assume) compensate for that. The prop itself is gorgeous--a real work of art. Now comes the fun of fitting it.

I have a 4" Saber extension with my fixed pitch prop. The guys at Saber opined that I would need a 2.25" extension with the new prop, but hadn't really seen the new Hartzell composite. With the Sam James cowl, the intakes are on the same line as the spinner plate. I have to extend the prop far enough forward so that at full coarse pitch, the blades have sufficient clearance from the intakes.

Two questions: does anyone know how far back the blades extend at full coarse pitch? If I knew that, I could calculate the correct prop extension length. The folks at Saber suggested making a 2.25" spacer from 3" PVC. Hold it over the flywheel and then rotate the prop blades back and measure the distance. The trick is, there is a really strong spring holding the blades in fine pitch. I cannot turn them with my hands and have been reluctant to make a lever to do so. The prop is really pretty and I am nervous about cracking or damaging the blade.
Question two: is it safe to take a couple of 3X1 boards, pad them excessively, and use them to lever the blades into coarse pitch. I have seen that described here but don't know if it is really okay on the composite prop.

Looking for any advice here.
 
Michael,
Use your air compressor and a rubber tipped nozzle to carefully apply air pressure to the port on the engine under the governor where the high pressure oil feeds in, to rotate the blades.
Bob
 
I have some posts about this exact combination. If you use the Hartzell spinner it extends farther back, then you can use a proper spacer to get clearance AND have a nice spinner gap.

I had a lot of discussion about the needed blade clearance to the cowl. I targeted for 1/2" based on experts and lately Scott (rvbuilder2002) says 1/8 is enough. Maybe that is ok since it only gets that pitch at full song.

You decide for your self, knowing the price of prop, but that seemed a bit small for me.

I used a 2.5" spacer as the bolts were cheaper.

For the sweep, I attached a plate to the governor pad and used an air pressure regulator to cycle the prop. The right side is closer based on engine twist in the mounts.

Let me know if you need some fuzzy pictures, the post has all the measurements from the back flange of the prop.

I found the post: http://www.vansairforce.com/community/showthread.php?t=103993 It has the dimensions you will need. Clearance is your choice.
 
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Back to fitting

Thanks for the reply, Bill.

I had read through the thread quoted below several times. The air pressure approach to moving the blades is definitely the most elegant, but requires the prop be mounted--which requires the extension be installed. The chief problem I am trying to solve is, what size prop extension to do I buy? I spoke with Saber and was told that if I order the wrong size, they probably will not take it back (gets scarred up in the install process). At the time of your original post, you were fitting the cowling to the prop. My cowling is installed and painted. I need to fit the extension to the cowling. What I am trying to accomplish is minimal modification of my nicely painted cowling. If necessary, I could bring the area around the spinner forward (if there is excessive gap) without too much trouble. Moving the whole cowling back would be a major PITA.

You said in your first post that the actual movement of the blade rearward is 1.15 inches. You stated that this number was calculated. It looks like you set up the air pressure approach to accomplish blade movement. Did your 1.15 calculation prove to be accurate? Given the shape of the blade, the distance moved will vary with the position on the cord--i.e. how far from the center. Was that measurement at the outside of the air intake? The last question is about your last sentence: "all the measurements are from the back flange of the prop". Since the intakes and cowl backplate (what ever you call the flat spot that the spinner sits in front of) are all essentially in a line, the real question becomes, what is the distance from the rear of the hub (flat part that mounts to the engine crank) to the rear edge of the propeller blade at coarse pitch at that cord that corresponds to the outside corner of the air intakes. That is a mouthful...
You said you used a 2.5" spinner. I assume you meant extension.

Thanks for the advice and taking the time to share your experience.


[Q
I found the post: http://www.vansairforce.com/community/showthread.php?t=103993
 
Michael,

These are the most accurate and latest numbers (from that thread):

Now for measurements. I have the standard prop hub, and using the mounting face as the datum, here are the axial dimensions:

to back of spinner - 1.60 inches.
to prop blade at fine pitch = 2.18"
to prop blade at coarse = 1.00"
This is at approximately 17" radius of the blade.

Mounting face is the flange contact plane. The back of the spinner is the Vans spinner. I can recheck some of those today if you need as I'll out of pocket for a week.

As I recall, (i can have poor recall) the Hartzell spinner is deeper, i.e. the back edge plane is closer to the flange plane. Using that spinner (if it is true) can avoid cowl modifications and still provide blade clearance by selection of the appropriate spacer. I did not dig into that as it was $$$ that I wanted to avoid.

My SJ cowl has the inlets, and area behind spinner, in the same plane. The closest point of the blade is ~17" from the center, the right outermost edge of the cooling air inlet. The intake air inlet is a non issue.

You could mount your prop to the 4" spacer and make measurements to be sure mine make sense, and to know exactly what your cowl fore/aft location yields for an appropriate spacer dimension. Thats is what I would do to double check everything. Just use my dimension above for the blade sweep delta. I am pretty sure of that. Checked it multiple times.
 
Prop Fitting Data

Hi Bill,

Great minds think alike. I tried to mount the prop to my 4" extension, but the prop has five recessed bolts and one not recessed. The four inch extension is set up for a fixed pitch and has six protrusions. I'm not sure what they are properly called. Hence, wouldn't fit.

I have the composite prop with the extended G hub -- PROP G2YR/N7605W-2X--as sold by Van's. Sounds like we may not have the same design. As I am sure others will find themselves in this same situation, I wanted to archive my results.

I went to the airport for measurements. I got about 16" from center to the outboard edge of the cooling vents. Similar to your 17". Hard to measure exactly with the prop on.

On to plan two:
I drilled six holes in one of my chapter 1000 workbenches. Placed the prop hub down and put nuts on the bottom of the bench to secure it. With the prop secure, I could twist the blades to full pitch and measure the movement. At sixteen inches outboard, I obtained the following measurements:

Height from table to blade in fine pitch (at rest) 3.2"
Height from table to blade in coarse pitch: 1.65"
Net movement was about 1.5 inches at 16 inches from center.

As the blade cord is wider farther out, I may want to repeat this at 17 inches.

Tomorrow, time permitting, I will fit the spinner. It is the polished Hartzell spinner required with this prop. There are some spacers involved that should permit me to move it in and out a little. I will probably pull my prop again and use the numbers obtained above to sort out the prop extension. More to follow
 
More Fitting Data

I removed the prop and measured from the flange, with a straight edge to the air intakes. The distance from the middle of the propeller to the outer edge of the air intakes is actually 15.25 on the left and 15.0" on the right.

The distance from the flange to the front of the intakes is 1.36 on the left and 1.42 on the right. The flange sits 0.5" proud of the 4" prop extension currently on the engine. By calculation, 4.5-1.36= 3.14 inches from the crankshaft to the front of the left intake.

Since the distance from the base of the propeller hub to the back of the propeller at full coarse pitch is 1.65, then the extension length is calculated thus:
De= distance (or length) of propeller extension
Dc= critical distance from crank to most forward cooling air intake
0.75" is how much clearance I would like between the intake and the propeller.
De=Dc+0.75-1.65
De=3.14+0.75-1.65
De=2.25"

Oddly enough, 2.25 is what Saber said I needed in the first place.

Calculating the gap between the cowl face at the spinner and the spinner:
With one washer in the spinner gap, it measures exactly 2" from the base of the propeller hub to the bottom of the spinner.
The cowl face is about 0.25" further forward than the cooling inlets.

De+2"=4.25 inches
Distance from the crankshaft to the cowling face is 3.40" The gap between the spinner and the cowl face becomes:
2.25+2.0-3.40=0.85"

The spinner has a certain degree of adjustment available. I will put it as far back as it goes and then see if I need to build up the cowling to look good. These calculations look right?

https://photos.google.com/search/_tra_/photo/AF1QipNz7v3jUufGquqMrrO6qxvELHB_-JhiACXgLVyP
 
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