Lift Fan installation

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pelford
Posts: 1
Joined: January 14th, 2013, 10:32 pm

Lift Fan installation

Post by pelford »

I am rebuilding an older sev. The craft came with most of the bits including the lift fan assembled to the pulley. The lift fan seemed to work fine with good inflation but after ten minutes the bolts holding the fan to the pulley broke. I replace dthese with new grade 8 bolts. It was a pain getting the hub off. A couple of the b;lades were damaged with small chips but nothing major. The first try after reassembly it inflated and then 4 of the six blades shattered. I dont see anywhere they may have been hitting.

When I assembled I put the hub on the sahaft as far as the center bolt would tighten it on. Is there supposed to be a spacer or washer above the hub so it does not go further up the shaft? It may have been a case of just old brittle parts but if anyone couild share pictures or a procedure on installing the hub I would appreciate the help

The craft is a 14' Vanguard originally bult in 1996 I have a 22 horse Briggs as the engine
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jchovernut
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Joined: September 11th, 2011, 8:14 pm
Location: Longwood, FL
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Re: Lift Fan installation

Post by jchovernut »

Hi Peter,
There should have been a "stack-o-nuts" spacer between the fan hub and the thrust pulley. Those are what determine the spacing of the fan from the prop driveR pulley...a stack on each mounting bolt. They're kind of a pain to mess with, and if you want something simple, Bryan has a machined & drilled HDPE spacer you can use instead of all the nuts. The nuts are just like the ones used to space the prop off of the prop driveN pulley. The spacing should allow the fan hub to pilot onto the engine shaft; they're what limits fan hub travel up the shaft. The crank center bolt/washer is there to keep the whole mess from being 'float tested' if the hub mounting bolts fail. It's a fail-safe retention device...use locktite!!

I haven't heard of a SEV lift fan exploding. I've seen plenty of Multi-Wing thrust fans explode on the SCAT-type hovers. You may have fractured the blades somehow during the previous failure, and they let go during the next run-up. The situation may have been exacerbated if there were chunks out of blades setting up an imbalance resulting in vibration.

I've been rebuilding a mid-90's Vanguard, too, for the last few years. It all started with just an engine swap....well, it turned out to be a complete "frame-off" restoration project after discovering wood rot in the skirt strips, delamination on the hull (poor builder fiberglassing techniques), etc. Finally on the up-swing of things and hope to get it operational sometime soon. I really want it flying for the Central Florida Cruise on Loughman Lake just East of Orlando coming up the 1st weekend of April.

Cheers,
John Carter
John Carter
SEVs: Vanguard, FanTastic, Prospector, Explorer
Others: StarCruiser, UH-18P, RX2000
http://www.hovernut.com
highlandhovercraft
Posts: 152
Joined: February 14th, 2012, 3:51 am

Re: Lift Fan installation

Post by highlandhovercraft »

Maybe the fan blades had become brittle with age and UV degradation. Sev fans are not usually spinning anywhere near the fan blade limit
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bphillip2
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Joined: February 2nd, 2012, 10:29 pm
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Re: Lift Fan installation

Post by bphillip2 »

If assembled correctly the bolts breaking should not cause fan damage. The bolt can break if the assembly is loose and the engine hammers on them. I have never used high grade bolts for this. Do you have 6 bolts?
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