[Steve Holland Posts: 1580 Status: Offline]

I used 2.5mm on my frame except the two engine sections which were 3mm. If your galvanising you won't have future issues with corrosion and therefore slightly thinner sections can be used. It's true that larger dimensioned thin wall is stiffer than smaller thicker wall section.
Remember weight is the enemy, every kilo saved where its not required is a benefit to you.

[Ian Brooks Posts: 3550 Status: Offline]

In general when using v belts you can get away with lighter section materials, because the V belts will tolerate more deflection than toothed belts. Basically toothed belts require extreme rigidity or else they will jump off and/or break.

Obviously it's hard to say that any particular ection will be ok as the exact design will be important, but I can we no reason why 25x25 shouldn't work.

Ian

[Gaz Posts: 2344 Status: Offline Cruising around Cornwall WWW]

Not sure if it makes a difference but the TS3 uses a Ducted Fan & the Sev a Propellor, the differences in torsional loading & restricted space may require totally different approaches.


Of course as my wife will vouch for, I could be wrong... Again 

[Al Posts: 875 Status: Offline WWW]

The Sevtec design has proved very reliable and that is made entirely of 25mm square box.  My TS3 will only have 40hp at best going through it, so flexing should be minimal with correct bracing

[tomtilley Posts: 568 Status: Offline]

Hi Al  yes your right in thinking about the weight of frame work but you have to think of the reliability I will not like to be in the middle of nowhere with a broken frame work . Tom

[Gaz Posts: 2344 Status: Offline Cruising around Cornwall WWW]

My understanding is that a lighter weight (thinner wall) rectangular box section  is stiffer across the wider section than a thicker walled square box of  similar final weight. You would therefore have a stronger frame for the given weight of material by opting for a rectangular thin wall section over a thick wall square section. Having said that there comes a point where the wall is too thin and therefore too weak. There is a formula and no doubt john or Ian will point you to a calculator on the forum or Google somewhere.

[Al Posts: 875 Status: Offline WWW]

I'm thinking about how I'm going to fabricate the thrust frame & engine cradle for the TS3.  I'm using 3xV belts for the drive on a 2:1 ratio 6x5z blades in a 12 hub.  If my calcs are correct it should give me about 190 lbs thrust.


Most of the ts3's I've seen have used 50mm x 25mm box for the spreader bar from one side of the duct to the other.  I would rather use 25mm square throughout the frame to save on weight.   I'm thinking Sevtec only use 25mm box for their thrust frame, so will 25mm square 3mm thickness be up to the job, or am I better using 50 x 25 box throughout?


I want to order the steel ready for when the engine eventually arrives, so I can crack on with the build