Viking 110 notice

[KeithO]

I have had people say that from a design point of view I should be running 7000rpm instead of 5800rpm because apparently the rev limiter just starts kicking in at 6800 in a descent. If one goes too crazy one would end up with something too heavy. The gyroscopic loads mainly influence the attachment point of the flywheel and the thickness of the web. Striving for a high rotational inertia is mainly a function of how much mass you pack into the rim under (and next to) the ring gear. The less mass in the rim, the thinner you can go with the web, to a point. One must at the very least be able to carry the ring gear.

The historical giubo that has been used in countless applications has been the 95mm pcd BMW part. The flywheel bolts are on a 63mm pcd which puts the attachment points of the giubo very close to the flywheel bolts. Because of the tender nature of the flex plate, the flywheel drive flange assembly was added which is made very strong. It and the giubo weighs 2.6lb. The flex plate with ring gear 3.5lb. But the weight of the giubo and drive flange is near the centerline thus not contributing any to damping the engine excitation.

The new coupling has an OD of 150mm 6" and bolt attachment PCD of 125mm. I like the fact that the attachment bolts are further away from the crankshaft itself and the web is going to be thick enough for the area to not be overstressed.

[charosenz]

Originally Posted by 12vaitor

I believe the flexplate/ring gear cracks are a sperate issue from the gearbox drive coupler failures. The flexplate is a stock Honda part with a starter ring gear welded to it. The welds are as good as any I have seen, they are uniform, and the plate shows no sign of warpage. There are no additional holes drilled.

The cracks appear to be limited to the 110 engines and not the 3-gear setup on the 130/150/190 engine which use the same part. Charlie Rosenzweig has the 3-gear version with the same flexplate/ring gear on his turbo 1.8L Honda, so it would be interesting to see if he has the same problem. If the cause is pitch/yaw induced bending it would affect every installation of this part.

So what is different about the 110 setup that could cause a bending vibration? The big difference is the bottom half of the flexplate is in the radiator airstream where it is subject to the prop pressure pulses. It may be the same phenomenon at work as cracked exhaust pipe-muffler joints because the pipe sticks out a bit too far from the cowling. The other engine installations use a horizontal radiator mounted under the footwells, vs the 45 deg angled 110's which is about 10" behind the prop. It could also be turbulent flow through all those holes are causing some resonance to occur.

Just one more thing to check during the CI.

John Salak
RV-12 N896HS

I just stumbled upon this post. I do not have a viking supplied flex plate. I made my own, by welding a ring gear on a flexplate. I do agree this is far from ideal, IMHO, but I did not see another option at the time I did this, which is probably more than 5 years ago now. I do have a 3 gear Viking supplied gearbox, But nothing else in my set up was supplied by Viking. I have inspected my flexplate carefully and I do not see any cracking. I also do not have any measurable end play in my GB input shaft.

[KeithO]

Charlie, did you unbolt it for the inspection and remove it from the crankshaft ? Because if you didn't you would not be able to see the cracks. The cracks are from the web being too thin for the gyroscopic load of the added ring gear that it was not designed for.

[charosenz]

Keith,

I have not. I have some significant non-aviation things going on now that I have to work on for a while. My flexplate is quite a bit different than the ones used on the 1.5L 110 set ups.

Charlie