Noah

Noah

Well Known Member
Planning a Hartzell CS Blended Airfoil Prop. Vans publishes two numbers (both for CS prop) regarding the correct thickness of a "prop simulator" for positioning and fitting the cowl. In the manual, they say build a spacer 2-1/4" long. In their "supplemental instructions" on their website titled "Simulating the Propeller for Fitting the Cowl" they say to make spacers 2-1/8" long (Both of these are for CS props). Which is correct?

Page 12-2 of the construction manual for the RV-7 (bottom of the page) says: "If the (CS) prop is not available, a spacer 2 1/4" thick, attached to the front of the crankshaft (be sure the starter ring gear is installed!) may be used to simulate it."

Here is Vans "Supplemental Instruction":
http://www.vansaircraft.com/pdf/Prop_Cowl.pdf

I called Vans and they were not concerned by this inconsistency in dimensions and said that there is significant variation between props and recommended buying a prop to get the right spacing. (Great answer guys:rolleyes:, why publish the option to use spacers if you don't recommend their use). I cannot believe that there is that much variation in thickness of CS prop hubs, but what do I know? I would expect that a type certified prop hub (which this is) would have thickness variation of +/- .005 to .010".

I don't really want to incur the expense right now, but more importantly, I don't want to wait 1 or 2 months (per Vans this AM) while I wait for my prop to arrive to get to work on fitting the cowl.

So, can anybody else who has installed a Hartzell BA prop recently and used a prop simulator weigh in on what is correct here??
 
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"With a table saw or chop saw, cut 6 pieces of the pipe that are
2?? in length if you are using a Sensenich or fixed pitch
propeller or 2 1/8? inch length if you plan to use a constant
speed propeller (square the ends!)"

Perhaps the instructions are not being read correctly.

I'd go with the 2 1/8" simulator. It says OR 2 1/8" if you plan to use a constant speed propeller. I know for sure the 2 1/4" spacer is correct for a fixed pitch prop.
 
You're missing the point

One of these documents says to use a 2-1/8" spacer for a CS prop, the other says to use a 2-1/4" spacer ALSO FOR A CS PROP. Both number can't be right.
 
PROPer fit

Noah said:
...Planning a Hartzell CS Blended Airfoil Prop..
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As you can see in the first photo, I installed the spacers as I interpreted the plans but in the back of my mind just could not shake a nagging sense of unease. Knowing how inconsistent and unreliable a simulation with spacers can be, in the end I decided I would remove all doubt and go with the real thing. Some builders luck out using spacers, others don't. I am inclined to believe that to achieve an optimum cowl fit when installing a constant speed propeller, it is probably best to just go ahead and hang that prop. Although some builders have reported undo difficulty and claim the propeller gets in the way when trimming and fitting the cowling halfs, I did not experience any such problem...and in the end got the exact fit I wanted. Would it have ended up the same way had I gone with the spacer trick instead? Who knows.

et9xyo.jpg
 
Rick, you're killing me! Did you ever measure your hub to determine its thickness and compare that number to the Vans number? Or does anybody have a new Hartzell BA prop hub handy who cam measure this with a caliper (i.e. to the nearest .001")

I know you're right, but I don't know what I'll do while I wait for the prop. I hate getting all geared up for a job only to find that you can't start on it for another 2 months. Maybe time to start the electrical design & panel.

So is that the consensus then, don't DARE fit the cowl without having the actual prop on hand?
 
Adding to that nagging feeling are the S-604 spacers depicted on drawing C4...
 
don't be impatient

get the prop first.. I did the spacer method and it ruined the look of the transition from cowl to spinner. I had it perfect then the actual prop was too close so I had to sand back the nose of the cowl. Get the prop and do it right the first time!
 
First off I respect everyone's suggestions. I can't imagine how frustrating it would be to have used a written measurement only to find out later it is wrong. All peices in hand would definatley prevent that.

But....

You spend 23,000 on an engine and 7,000 on a prop (actual prices may vary) and the proper spacing can't be determined ahead of time? Seems to me the manufactures would have that information within a couple thousandths. Not 1/16, 1/8, or 1/4. There should be no guessing.

Chances are I will have an engine long before I buy the prop and I definately don't want to wait to do the cowl.

Maybe we can get to the bottom of this.:eek:
 
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Is there a drawing?

I know this might be obvious and as such may add nothing to the discussion but I'll offer this anyway and risk being called out as an idiot.

Is there avaialable in any form an engineering drawing from Hartzell on the dimensions of the compact hub? I certain that Hartzell has a tolerance on this dimension and equally sure does it does not vary by 0.250".

Since I've never owned a CS prop I have no idea if any drawing comes with the manual or installatino documentation but I would hope that somewhere in the community there exists a PDF of trhe drawing that will solve this problem once an for all.

Lacking that, perhaps Hartzell would provide in an effort to support this not insignificant customer segment.
 
andrew phillips said:
get the prop first.. I did the spacer method and it ruined the look of the transition from cowl to spinner. I had it perfect then the actual prop was too close so I had to sand back the nose of the cowl. Get the prop and do it right the first time!
Click to expand...

Andrew, did you ever go back and measure your spacers and compare these to your prop hub thickness to determine the root cause of the problem? What length spacers did you use? What was your prop hub thickness? Which of Vans published numbers was correct?

With two numbers out there published by Vans, I submit that the reason some people "luck out" with their cowl fit using spacers while others have "bad luck" is that some are using the correct number, while others are not, no?

Guys, this isn't rocket science. Fabricating a precision spacer which maintains concentricity between the crank and the spinner backplate, as well as proper axial spacing between these two negates the need for a prop to fit the cowl. But you do need to have the right numbers!
 
I used 2 1/4" hardwood spacers..........

and I ended up having to remove the hinges from the back of the cowl because it was too tight. If you allow for sag and you should, I just think it is too tight. Reworked mine and it is fine now, but was a lot of trouble.
 
i went over to the local prop shop and asked if he had a red tagged back half of a hartzell compact. he pointed to a barrel full and said take your pick. mounted my spinner to it with hardware store bolts and the proper spacers and bingo proper spacing.
 
First off, thanks to everybody for their helpful suggestions. I ended up ordering the prop and received it today (not too bad a wait, thankfully)! For those who may be reading this in the future searching the archives, here is what you need to know if you are using the Hartzell HC-C2YR-1BFP/F7497 prop and Vans spinner, and want to wait to order your prop, but you still want to fit your cowl and do your baffles.

The spacer needs to be 2.125 inches, NOT THE 2.25 CALLED OUT IN THE BUILD MANUAL. If this number is used, the actual spinner position will be adjustable +/- .062 inches from this position by the use of washers.

The spinner backplate mounts to an aft facing machined face on the hub, which requires 4 fixed spacers (one for each of the 4 bolts) and also allows the use of adjusting washers. Two washers are allowed per bolt which have the effect of moving the spinner backplate aft toward the engine. The distance from the mounting face of the hub to the aft-facing mounting surface for the spinner plate is 2.500 inches. The required spacers are .250 inches, and one of the two permissible washers are .062 inches. The spinner backplate itself is .062 inches thick, so 2.500-0.250-0.062-0.062 = 2.125 inches. Again, removing the permissible washer or adding a second permissible washer has the effect of allowing +/- .062 of adjustment from the nominal 2.125 inch number.

I'll try to post a picture tomorrow to make this a little clearer.
 
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