Composite rotorblades

[rotorblades]

Hi,

I am taking on a project to build composite rotor blades by following instructions
outlined in the file attached.

http://www.tervis.fidisk.vi/jt-5/Drawings/JT-59.pdf

My understanding is that it is 3 step process.
1. Make 1 meter long piece shell from NACA profile.

2. Join 7 meter long shells by inserting epoxy glass and foam and 7 meter long lead rod.

3. Finally place the 70mm by 100 aluminium at one end. Wrap both pieces in carbon fibre fabric and seal them using resin infusion vacuum process.

This document is very old can you please confirm that if I am missing something
And what is the recommended resins one should use.

Thanks

 

[RPstress]

Can't access URL from link. Found it by googling for jt-59.pdf inurl:tervis . It seems to be

http://www.tervis.fidisk.fi/jt-5/Drawings/JT-59.pdf

? (It's .fi/ not .vi/ .)

I can't see any mention of the blade length. Note 2. implies that maybe it's 3 m long plus a bit more at the root ("sand or cut the foam core to shape in a jig in three one meter pieces"). That sounds like a better blade length for an autogyro than seven meters...

It makes no mention of joining the three one meter pieces of foam together. I would add some resin between their ends.

'shell' usually means the outer skin, which should be the full length of the blade, not made in sections (a chordwise joint in such a skin would be a major weakness). So, the glass cloth needs to be the full three meters long (as does the big mass of rovings (not 'rowings') in the nose and the little bit of them in the tail). I'm not sure why the foam is in one meter pieces. It should be possible to get it in three meter lengths. Getting cloth at 45° in a three meter length may not be practical (suppliers do weave it at 45° to the cloth roll direction but it's more usually supplied at 0 and 90° to the roll direction. If you only have 0/90° cloth make an overlap joint in the 45 plies about 75 mm long (rolls of glass will be at least a meter wide so a 45° ply could be about 1.4 m long). However, it should be possible to get a roll of each ply direction (at an extra cost, or course).

The foam core density is not mentioned. I think it should be about 5 lb/cu ft (about 80 kg/m³) or maybe 8 lb/cu.ft (130 kg/m³). But, Jukka Tervamäki may have made it lighter. He really ought to say somewhere. The foam is a PVC or a PU according to text on section A-A.

I'm not too sure about solubility of PU in common resins. Note 11 says the resin is epoxy. It looks like a low temperature cure (well, 70°C isn't that low, but it's probably intended to be a RT cure and 70° makes sure that it goes off quickly). A combination such as Araldite AY.103 (25 parts by weight) and AV.144-2 (75 parts by weight) resins with HY.951 hardener (7.5 parts by weight) would work but there may well be cheaper options. Make sure you check for solubility of the foam in the resins and hardener. Ask the manufacturer of the foam for guidance.

The microballoons mentioned in note 10. could be glass or phenolic. Something like 3M type K20 would work. Quantity should be something like 10 parts by weight (that's quite a lot and gives a sizeable decrease in density).

You should probably aim for the rovings to be jammed in with an equal volume of resin (resin should probably be about 35% by weight of the total resin plus glass weight). The same goes for the resin infiltrated into the skins.

I'm not too sure of the statement below the fiber directions plan view that "Unidirectional rowing is wound around the blade root aluminium block". I think it maybe means that some of the rovings should be twice the blade length and wrap around the block in the way pointed to by the note. Along with the note at the far left to "Mold root studs to fit the aluminium blade root block for roving layup" maybe it makes some sort of sense. I assume there's more information on the root fitting somewhere. It should probably be something like 6061T6.

The lead rods look quite heavy. Only one of them is full length. The other looks like about 50 or so mm long. The procedure to balance the blades must be addressed somewhere. You will need to be quite careful to have the two blades (I assume there are just two) the same weight and also to have the cg in a very similar spanwise position.

 

[rotorblades]

Thank you very much for the detailed response.
The full diamter of the rotor blades is 7m so each blade is 3.4m and the aluminium block is 100 mm. Thank you for clarifying roving rather than rowing, I can Google and get more info on it. Sorry for mistypo on url link.
It does say make 3 meter lengths, I have got the female moulds done of NACA profile, it is difficult to get even 1m lengths if you want to get cnc'ed.So I got .5 m length which will be glued together. You are also correct in that the second rod is 50 mm. This is to stop the blades curving up. The full length rod is the way to join the 3.4m long three and a bit pieces and the glass fiberglass cloth of course. The root blocks I made from aluminium
Once again thank you.

 

[blakmax]

If you are bonding the aluminium, I suggest you look at my postings on surface preparation prior to bonding.

Regards

Blakmax