Prop Hub Interference?

[NWade]

Michael - I agree. My problems seem to consistently stem from vendor-supplied parts. I feel for the Sonex/AeroConversions team. But I also am beginning to question their QC process and vendor-management. Its tough to do as a small business, but these are things that can have an impact on safety and brand reputation.. :(

I got a Dial Indicator and took several measurements today. I remain concerned about my Prop Hub. Here's an excerpt from my email to Sonex:
----------
I have performed additional measurements of the crankshaft and prop hub this morning and can confirm that while the crankshaft shows less than 0.001" of variance during a rotational test (see photos near the bottom of this album), the prop hub shows 13 thousandths variance in both major dimensions, throughout a 360 revolution. Here is a video of the measurements. Note that its tough to hold the camera and all parts properly in the recording; but I verified these measurements without the camera running. I also made sure that the crankshaft was pushed to the rear during all rotation tests, to ensure that run-out was not causing errors.

This is not a matter of the engine case being machined a bit offset or not enough; the prop hub is *clearly* not concentric to the crankshaft. A 13-thousandths error at the prop flange, multiplied out over the length of a Sonex propeller, is over 1/16" for each blade (assuming a 50" prop). That's over 1/8" of propeller track error due to the prop hub alone (leaving no tolerance left to deal with anything not perfect with the prop itself)!
----------

--Noel

[jeff0196]

Noel,

If you still have everything set up you could run through this experiment for more knowledge. On the face of the hub put a sharpie mark when the dial gets to 0 (the lowest reading). Then rotate to the 0.013" (Highest reading) and put a sharpie mark. Then do both of the 0.0065" readings with sharpie marks. If all sharpie marks are 90 degrees apart, then you know the hub is not bent and the face is fairly flat.

As far as the 0.013" on the OD of the flange, while it may not be desirable, it doesn't really show you where the propeller center is. The propeller on an AeroVee centers by the prop drive lugs, kind of like old car rims that centered by only the tapered nuts and were dubbed "lug centric". Basically all newer rims have a mating feature between the rim and the hub in the center that makes them "hub centric". Anyways, You would need to have a way of measuring where the prop drive bushings are in relation to the axis of rotation of the crank. If you can temporarily install something in the flange drive holes, you can measure the highest points on all six bushing holes radially and see what the difference between them is using your current set up. In addition, if I had to guess, the ID of the hub, where the bolt goes in has a different run out than the OD you measured in your video, or at least mine did.

If I remember correctly the Sensenich factory has a 1/32" limit to the elongation of the holes on the drive lugs-this really doesn't mean much to the hub itself, but is for thought.

Just some ideas,
-Jeff

[sonexsteve]

I concur with the vendor supplied parts comment, with some need to improve QC too.

I had great difficulty getting the rocker arms on my AeroVee (#0847) to move smoothly, after weeks of frustration and hair tearing I inspected each arm individually and found that 2 of them were bored waaay off centre, the thin edge width on one side being less than a third of the thick side opposite, and the bore diagonal across the arm so that the thick/thin walls swapped sides.

I've also had problems with QC on my fuel tank straps: 2 different sets of different vintages, the older ones very good for powder coating adhesion, the newer ones very poor with little or no adhesion over about 25% of each strap's surface area.

I've adopted a 'don't assume accuracy and finish of components' policy, inspecting all before use for dimensions etc.

Just my 1p's worth,

Steve Moody.

[NWade]

Just a quick update: The crankshaft (with prop hub) is being sent back to Sonex for evaluation and possible replacement.

While I am frustrated with the situation, I want to point out that Sonex has been reasonable to work with on these issues. This stuff is no fun for anyone involved, so I'm trying to balance my personal feelings with the fact that I've worked in a service/support role and know how it feels to be on the other side. Clear communications and solid data are key!

Take care and thanks again for the info and suggestions,

--Noel

[kevinh]

Thanks for the post Noel and the good quality comments in this thread.

[WaiexN143NM]

Hi noel,
Let us know what sonex says about the crank and hub. Yes, sonex has always been very helpful and responsive to inquiry, and parts problems. Maybe the wearhouse guys could do a final QC check , and any question defer to Mark S. For inspection. They get caught in the middle, your right, im sure they get fustrated too. Good luck and hopefully soon you'll have your engine together.

WaiexN143NM
Michael

[lgsievila]

If you still have everything set up you could run through this experiment for more knowledge. On the face of the hub put a sharpie mark when the dial gets to 0 (the lowest reading). Then rotate to the 0.013" (Highest reading) and put a sharpie mark. Then do both of the 0.0065" readings with sharpie marks. If all sharpie marks are 90 degrees apart, then you know the hub is not bent and the face is fairly flat.

Just a comment-you don't say anything about float when doing an axial reading on the hub. I believe to get a true reading you have to either push the hub back at each 90 degree reading or pull it forward at the beginning and at all subsequent readings. You need to know your total axial float anyway.

[markschaible]

Hello SonexBuilders.net,

Regarding prop hub concentricity, there have been a few cases of excessive prop hub runout found. As a percentage of total number of hubs produced, the number of instances of this issue have been very isolated. We are reviewing the machining and quality check processes for prop hubs with our machining supplier and our staff to help prevent future occurrences. If you have interference of the prop hub shaft with the nose of the crankcase and/or have observed runout at the face of the prop hub flange or excessive prop tracking issues, please contact our tech support email address with runout measurements and any other relevant data and we’ll take care of you.

It’s important to note that in some cases, it is the machining of the crank case nose that causes the interference, and removing some material from the nose of the crank case is the appropriate fix in those instances. Again, contact us with your runout measurements and we can properly diagnose the issue.

With regard to the post in this thread by DCASonex, the part concerned was actually our machined spinner/crushplate. The issue was not run-out of the part or the machining lathe chuck. This part is machined from a piece of round bar billet, and there are sometimes variations in the billet’s OD. The flaw reported by DCASonex was purely cosmetic in-nature and would have no effect on the balance of the rotating assembly.

As always, please feel free to contact us directly with your questions at the sources listed below.

Regards,
--
Mark Schaible
General Manager
Sonex Aircraft, LLC
phone: 920-231-8297
fax: 920-426-8333
http://www.SonexAircraft.com
http://www.AeroConversions.com

Sales Info: sales@sonexaircraft.com
Orders: orders@sonexaircraft.com
Accounting: accounting@sonexaircraft.com
Tech Support: tech@sonexaircraft.com

Build a Sonex Aircraft in Your School!
Check out the Sonex Education Initiative: http://education.sonexaircraft.com/

[SNX1508]

Got one of Sonex new hollowed out lighter weight prop hubs a while back .......
David A. Sonex TD, CAMit 3300

Anyone know the difference in weight between the original solid spinner and the newer hollowed out spinner? The Sonex web store says the new one is about 1/2 the weight of the original, but I would like to know how much weight I could take off with the new style (without having to remove my spinner to weight it). Yes, I have probably not given the proper attention to aircraft weight during the build and now want to trim off a few pounds !!

Any feedback greatly appreciated.
Thanks,

Terry L. Cooper
SNX #1508 Tail Wheel
AeroVee #0736
N296SX
Aircraft build took 2005 hours, and was completed in October 2016
http://www.mykitlog.com/SNX1508
FAA Inspected & Airworthiness Certificate issued 11/4/2016
Currently training in a Citabria for tail wheel experience, then onto a LSA for ASEL endorsement on my Sport Pilot cert.

[radfordc]

Yes, I have probably not given the proper attention to aircraft weight during the build and now want to trim off a few pounds !!

Any feedback greatly appreciated.

Garden salads and grilled chicken for a week and you're problem is solved!