What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

50-05, step 2, wrong nut?

MacPara

MacPara

Well Known Member
When installing the hardware to attach the throttle cable to the throttle arm, the instructions ask for the Rotax locknut (silver in color, blue locking insert) to be re-used. This nut should hold the VA-219 bolt which has a hole for the throttle cable to pass through.

IMG_0122.JPG


When I was trying to tighten this assembly, I noticed that the nut went on the bolt without hesitation - even when the locking feature was passed. Also, it appeared to be odd that the Rotax lock nut is a metric size while the head of the VA-219 needed an imperial size wrench.
My lock nut tightened a bit until it sheared off some threading and then would not go anywhere except off.
Closer examination showed that the VA-219 threading is indeed imperial size and the lock nut was definitely not.
I decided that an AN365-1032 locknut should be a perfect fit, given the dimensions of the VA-219.

IMG_0123.JPG


I searched the forum but could not find anybody else having this problem. Am I missing something? My 50-05 is revision 1 from 10/12/09 and has not been revised since.
 
I'll be interested in the answer to your question. While adjusting my throttle cable, I ran into trouble having the throttle arm not rotating freely about the bolt. Investigation revealed I had buggered the small shouldered bushing - it became deformed/ovalized when the nut was torqued. The nut gets quite a high torque - 35 in-lbs (MM pg 12-10) - it seemed very excessive when we applied it with a torque wrench - and then we had this bushing problem. (It was OK before we messed with it.)

I ordered new parts for both sides from Lockwood. While doing so, I noted in their Parts Catalog that they called out a Rotax bolt (screw) - P/N 241-847, which is indeed metric (and $15.59!). So, I ordered the bushing (called a graduated sleeve - which costs $15.20!), washer and nut from Lockwood, and the Bolt/screw VA-219 from Vans (which costs about $13.)

The total for 8 little parts - 2 each screw/bushing/washer, and nut came to $75 - which leads me to believe I am in the wrong business! It could be worse - the Rotax parts with a "C" after the P/N - meaning - Certified - cost roughly 40% more.

I thought it strange that Vans didn't use the Rotax screw, and instead substituted one of their own design, but since I haven't installed my new (expensive) hardware (I plan to probably go to the McFarlane vernier throttle system), I never checked the thread compatibility.

Thanks for bringing up this subject.

Bob Bogash
N737G
 
Some of the Rotax parts prices are nuts! At least some can be obtained from alternate suppliers. Their tools especially can be sourced elsewhere in some cases. For example CPS offers a gear case puller for a fraction of the Rotax price.
 
I was surprised at the cheap little`toolkit' that came with the Rotax, given the outrageous cost of the engine. I think my lawnmower had better quality tools.
 
That's it, I'm out'a here!

While building my -12, I've been lurking in the weeds listening and reading everything I can find about the ROTAX "experience" before committing to this marginal, horribly overpriced solution. I have to say that just reading this one thread alone is enough to turn me away.
For that...and many, many other reasons: EAB here I come!
 
Don't be too hasty. There is a reason most of the mainstream LSAs use Rotax. I agree the parts prices are ridiculous (I bought a 912 in 1998 for $8000 vs $18000 today). But they do seem to be durable, reliable and economical.
 
Not hasty...and not wasty

Thanks, man, but I've been following those clowns at Rotax for three years now. I'm out of there so hard it makes me grin. Started engineering various mods today and I'm having a great time for the first time since I started this tinkertoy project.
Free at last! Free at last!
 
While this thread has drifted into rants about the cost of Rotax parts (partly my fault), the original question has yet to be addressed - what's the deal with a metric nut on an English screw???

Perhaps Scott would like to chime in here.

Bob Bogash
N737G
 
With no response from VAF builders about this, I had asked Van's Builder Support and KenS just replied today that this issue had not come up before. They are looking into it ...
 
I replaced the Rotax nut with the appropriate sized mechanical locking nut....after the Rotax nut departed the throttle arm...in flight.:eek:
 
MacPara said:
With no response from VAF builders about this, I had asked Van's Builder Support and KenS just replied today that this issue had not come up before. They are looking into it ...
Click to expand...

I confirmed on my $75 spare parts that this is a case of an english threaded Vans screw with a metric threaded Rotax nut.

Have you heard back from Vans on the resolution to this situation???

Bob Bogash
N737G
 
NASA515 said:
I confirmed on my $75 spare parts that this is a case of an english threaded Vans screw with a metric threaded Rotax nut.

Have you heard back from Vans on the resolution to this situation???

Bob Bogash
N737G
Click to expand...
You would think that this is pretty obvious to figure out, Bob, but I haven't heard back from them since. In the meanwhile, I removed the plastic lined lock nuts and replaced them with the MS21042-3 mentioned above as this is a high-temp area.
I am still surprised that so few have replied to this thread and I am worried that many are flying with this incorrect nut on the bolt - but then maybe it was just too obvious of a mistake in the instructions and everybody just silently replaced the nut with the correct size...
 
NASA515 said:
While this thread has drifted into rants about the cost of Rotax parts (partly my fault), the original question has yet to be addressed - what's the deal with a metric nut on an English screw???

Perhaps Scott would like to chime in here.

Bob Bogash
N737G
Click to expand...

I've encountered this in sailplane and bicycle hardware. What I found is that there is a metric standard that is virtually indistinguishable from 10-32. Looking at RC forums, it looks like it's M5x0.8:

#10 nominal dia = 0.190" (yes, it's not 3/16" or 0.1875")
M5 nominal dia = 5mm = 0.197"

0.8 pitch = 0.8mm/thread = 0.0314"/thread or 31.75 tpi
32 tpi = 1/32"/thread = 0.03125"/thread or 32 tpi (tautology alert!)

So you can see that for looser holes and lower-tolerance hardware, it would be possible to interchange 10-32 and M5x0.8 screws to some degree. A 10-32 screw in an M5x0.8 nut will be a little loose, and an M5x0.8 screw in a 10-32 nut will be a little tight, but both combinations could probably be threaded together by someone who wasn't paying attention. I know I've done it myself.

Of course, one important issue here is that the tensile strength of the joint is an unknown. I imagine that the slight mismatches would result in sub-optimal joint geometry, and a commensurate reduction in maximum strength. I would also bet that a #10 screw in an M5 nut would have less than satisfactory engagement with friction locking features.

Thanks, Bob K.
 
MacPara said:
You would think that this is pretty obvious to figure out, Bob, but I haven't heard back from them since. In the meanwhile, I removed the plastic lined lock nuts and replaced them with the MS21042-3 mentioned above as this is a high-temp area.
I am still surprised that so few have replied to this thread and I am worried that many are flying with this incorrect nut on the bolt - but then maybe it was just too obvious of a mistake in the instructions and everybody just silently replaced the nut with the correct size...
Click to expand...

I can't explain why you haven't gotten a response from tech. support (if one had been promised), but I can tell you that the issue has been looked at by engineering.

The issue arose when an early production vendor change was made, switching to a different throttle control (McFarland). The cable diam. was larger and wouldn't work with the Rotax supplied bolt.

A mistake was made in specifying a new bolt but not also changing the nut.
The reason it hasn't been an issue after many RV-12 completions, is because our research has found that the actual dimensional differences and thread pitch difference between the supplied AN bolt and the original metric bolt are very small (thousandths of an inch). It is likely that the small number of builders that have noticed some interference, was because of manufacturing tolerances of each piece of hardware.

A change is being worked on, that will specify that an all metal lock nut, appropriate for the AN3 bolt, be used instead of the OEM one.
 
I think this whole stackup needs to be careffully reviewed by engineering. This is a critical piece of system.

As it stands now, we've got a Vans screw and three pieces of Rotax hardware. If a new locknut is specified, we'll have two english pieces specified by Vans - the screw and the nut - and two metric pieces specified by Rotax - the washer and the shouldered bushing (which sits in the Rotax throttle arm.)

What's a washer, you say? In my case, I think I buggered the expensive shouldered bushing because the washer was the wrong size. The washer is important!

Or, as Mel likes to say, "No! No! Not without a washer!"

Bob Bogash
N737G
 
You must log in or register to reply here.
Back
Top