Brian Wilson 2 Posted February 24, 2015 Share Posted February 24, 2015 I was looking at the vacuum formed spinner/bases such as supplied by Traplett and my question is: how is the spinner and base attached to each other? Gluing would make a rather too permanent joint while if small screws were used they could pose a danger to eyes. The only spinner sI have previous experience with have a screw in the centre but this does not look like an option with the vacuum formed ones. Could someone enlighten me please? Quote Link to comment Share on other sites More sharing options...
jrman Posted February 24, 2015 Share Posted February 24, 2015 I certainly would never use a vacuum formed spinner for anything other than static display. Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted February 24, 2015 Share Posted February 24, 2015 Not wishing to be argumentative and I am not sure about the Traplet spinners, but all of my flying spinners are vac formed. I use at least a 1/4" aircraft plywood base, and use small screws around the periphery to retain the vac formed part. John Ranson also uses vac formed spinners, his are retained in the same way as an alloy spinner with a screw in the tip threading into an adaptor retaining the prop and back plate. The problem with vac formed spinners is that they don't like hi rpm, such as an ic engine would develop, so aside from the fact that you can't use a starter on the spinner as it isn't strong enough, it would fly apart at the sort of rpm that most ic's generate their power. However if you fly electric and are able to keep the rpm down then vacformed spinners are fine and for me have been perfectly safe. 60" Bistormer vac formed spinner 85" Chipmunk - vacformed spinner (first flew in 2009) 70" Hurricane vac formed spinner 66" Sea Fury vac formed spinner (this first flew in 2008) 72" Spitfire vac formed spinner The secret is to keep the rpm down, 6-7k rpm max Cheers Danny Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted February 25, 2015 Share Posted February 25, 2015 Danny's advice is essential in this I think, I've seen a couple of potentially dangerous failures of this sort, one with an electric motor but the rpm were probably too high, which is Danny's point. I think that the type of plastic used is a key issue here. Vacuum formed plastic spinners have been around for a while and I've used them safely but I think the ones I had were formed from ABS. (Pilot Models Spitfire 24/ Seafire 47, I still have it). The problem seems to exist with the type of plastic currently used, is it a PV type material? The issue of scale spinners is frequently a difficulty and the opportunity to vac mould them is really useful. Perhaps we need a bit more investigation into suitable plastics, then we could have complete confidence. Quote Link to comment Share on other sites More sharing options...
Dave Hopkin Posted February 25, 2015 Share Posted February 25, 2015 I think there would be various considerations... Thickness of the raw material - has to be enough meat to be structurally sound after being streched into the mould Internal un-relieved stresses contained in the material Focal points for fracture where the slot is cut out for the prop blades (either angled corners or stressed incuced by cutting/levering) Unbalanced through uneven moulding Unbalanced due to distortion when screwing to the base plate Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted February 25, 2015 Share Posted February 25, 2015 I think everything you say is right Dave, all of those things matter very much. The reason I mention the plastic though is that I think some of those being used now have a tendency to creep, or stretch under load and that is the precursor of a sudden catastrophic failure, they just burst and go in all directions. The ABS vac-forms never showed any tendency to do that, even though used at high rpm on an OS25. The last one I saw go on an electric multi left one shard of plastic embedded solidly in the fuselage, deep enough to still be there when the plane landed. If it went in your eye there's no doubt about what the consequences would be. There's no question, if you use one of those you have to do what Danny said and keep the revs low. He suggested 6,000/7,000 rpm max and clearly that is from his experience. Quote Link to comment Share on other sites More sharing options...
Brian Wilson 2 Posted February 25, 2015 Author Share Posted February 25, 2015 Thank you all for the input on this and I am now inclined to consider non scale aluminium Quote Link to comment Share on other sites More sharing options...
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