What's needed to go from metal to wood prop?

[n6346m]

Re: What's needed to go from metal to wood prop?

I would attach some pictures, but I can't find the paperclip to add them to this post.
Looks like I figured it out.

[woodmw]

Re: What's needed to go from metal to wood prop?

The thought of swapping wood for metal just won't go away. I've been researching the idea on our forum as well as the dark side, i.e. J3Cub, Luscombe, Champ forums. There are quite the discussions on bolts, nuts, torque on both the prop to hub mounting bolts and the hub to crank. I did find a link to a paper by Robert Bristol, Sensenich engineer, about mounting a wood prop. It has the table that drude posted a number of years ago on this forum.

http://www.docstoc.com/docs/131816990/Installing-Wood-Propellers

There have also been some discussions concerning checking torque values periodically, due to humidity changes due to seasonal or location changes.

My question now is about the basics, nuts and bolts.

Correct length AN76 bolts don't seem to exist, at least not on the common suppliers websites. Wag lists AN6, Univair lists AN74 sets, Spruce has some short AN76, but says AN6 will be substituted. So I guess AN6 is the way one must go. Based on published Sensenich wood prob hub thickness, taper hub back plate thickness, crush plate thickness, and a washer (or two), AN6-43.

So:

What bolts are others using?
Head drilled?
Drilled shank with castle nut?
Undrilled shank with nylon stop nut?

How often are you checking torque? Each annual? Couple of years? Seasonal change? In Houston, we don't have those; just high humidity and higher humidity. Could be worse, could be New Orleans.

[waltermrich]

Re: What's needed to go from metal to wood prop?

When I use my Sensinich wood prop, The head s are drilled on the bolts just like a metal prop bolt, and the torque on the bolts is not very great I do not remember the value but it is in inch pounds. I never rechecked the bolts . But maybe should have.

[M Towsley]

Re: What's needed to go from metal to wood prop?

Not sure of the part number, but the heads on mine are drilled.

There is plenty of information on the Sensenich site regarding torque values depending upon what hardware you are using, when to do it and how to do it. You will have to re-torque an hour or two after initial installation, (I cannot remember but it is listed), and then seasonally. The wood will swell and shrink depending upon weather. There is more to having a wood prop but it just plain looks good.

[3Dreaming]

Re: What's needed to go from metal to wood prop?

Sounds like he has a prop hub instead of a flanged shaft. No drilled heads needed just drilled shanks for the hub installation. I always installed the bushings if the prop is counter bored for a flanged shaft. You will have to remove the hub from the engine to install the longer bolts needed for the wood prop.

[astjp2]

Re: What's needed to go from metal to wood prop?

The AN-6 has shorter threaded section than real prop bolts, I just order them from Sensenich. Tim

[3Dreaming]

Re: What's needed to go from metal to wood prop?

The AN-6 has shorter threaded section than real prop bolts, I just order them from Sensenich. Tim

With the hub for the taper shaft engine the real prop bolts will not do you any good.

[woodmw]

Re: What's needed to go from metal to wood prop?

I can now answer my own question.

Hardware:

Sensenich W72CK42 prop

6 - A437 Prop Bushings

2 - AN6-43 Bolts

4 - AN6-42 Bolts

AN960-616 Washers

AN960-616L Washers

6 - AN310-6 Castle Nuts

AN380-3-3 Cotter Pins

Continental hub crush plate

Information:

Sensenich torque specifications

Article on removing prop hub from taper crankshaft and special tools listed

Paper by Robert Bristol, Chief Design Engineer, Sensenich Corp, on amount to compress prop wood for correct torque

After cleaning and painting the prop hub and crush plate, I was ready to mount hub and prop together. I used the 2 AN6-43 bolts through the bracket for the skullcap spinner. Noting the problems reported here on our forum, how tight is right? Sensenich numbers for torque using AN6 bolts are 175-225 in-lbs. or 15-19 ft-lbs. Robert Bristol's paper calls for compressing the wood, after snugging the nuts, .006" per inch of prop thickness. For this prop/bolt combination, ½ turn. I think a source of error in this method is how tight is a snug. I chose to tighten the nuts, with a wrench, until some resistance was felt. I then torqued all bolts to 12 ft-lbs, then 15 ft-lbs, and finally to 16.5 ft-lbs. As I torqued the nuts, I noted the amount of turn, which resulted in just over ½ turn, but less than ¾ turn for each bolt. I estimate the prop wood was compressed .025" vs the .02" called for.

Now to remove the McCauley prop/hub. After removing the skullcap spinner and bracket, and the lock pin from the hub nut, I used a small cheater tube over the 5/8 bolt thru the hub nut to remove the whole prop/hub assembly. I did not need the special tool to jar loose the hub. But the spacer used to prevent the snap ring from collapsing is a must. I would recommend that the tab inserted into the snap ring space have a slight dovetail shape. This will tend to lock the tool in when removing hub.

While the prop and hub were removed, I chose to replace the front crankshaft oil seal. My old one had no fresh signs of leakage, but there was some old residual staining.

To torque the prop hub nut when installing the new prop, I used a large socket I have for the wheel bearing nuts on my 4x4 pickup. It is large enough to fit around the hub nut and has 6 flats rather than a round surface which made drilling easier. The hub nut was torqued to 190 ft-lbs.

[woodmw]

Re: What's needed to go from metal to wood prop?

Before removing the metal prop, I wanted to get some performance numbers to compare to the new Sensenich wood prop. The yellow tag from the prop shop states that the prop was twisted to cruise configuration. The hub is stamped 7444, which is between climb and cruise.

I flew a square box and recorded GPS ground speed. TAS is the average of the four legs. Some simple trig computes wind speed and direction, if you care. I have data from two different flights for the metal prop.

Since installing the wood prop, I have data from two more flights. One at 2000 RPM to compare to the metal prop, and one at 2150 to compare power settings.

Prop	Alt	RPM	OAT	IAS	North	East	South	West		TAS	Wind	W-dir
Metal	1800	2000		85	75	92	87	71		81.7	12.1	300
Metal	1800	2000	60	86	88	87	76	77		82.2	7.8	220
Wood	2000	2000	40	90	82	77	83	88		82.6	5.5	85
Wood	2300	2150	65	93	82	85	90	88		86.3	4.3	20

I also have a timed 1000' climb @ full throttle and 70 mph for the metal prop. 545 fpm from 2000' to 3000'. Data for the wood prop is in the future, but VSI shows that climb should be similar.

My interpretation of the data so far is that the metal prop is more of a climb than cruise configuration. It doesn't appear to be twisted even to a standard configuration. I have always felt the the plane was slower but climbed better than it should. The up side to all this is that the plane didn't drop any performance in going to the wood prop. It was slow before, but it's not any slower now.

I plan some more squares at different throttle settings. Probably 2300 and 1800 rpm.

[Guest]

Re: What's needed to go from metal to wood prop?

Hi Mike,

What were the specs on the metal prop? ie. make/model? diameter? pitch? I thought that I saw that info in your post but now cannot find it.

Dave

Never mind, sorry I see it now 7444. I use a 7049. 44 pitch seems shallow for cruise so I agree it seems like more of a climb prop.

How did your static rpms compare?

[woodmw]

Re: What's needed to go from metal to wood prop?

Static full throttle with the McCauley metal and Sensenich wood props were/are spot on. I was pleasantly surprised. Thought we would need to adjust.