3
$\begingroup$

Been thinking of getting into the hobby of building ultralight helicopters, and would PVC tubing be a good choice to build the overall airframe?

$\endgroup$
1
  • 1
    $\begingroup$ Not only is the strength to weight ratio poor, PVC also has a rather low modulus, so the airframe will resonate at a multitude of frequencies. While tolerable in a glider, in a helicopter this is unwise. The resonance with all that is vibrating in a helicopter will shake the airframe apart before first flight. $\endgroup$ – Peter Kämpf Nov 25 '20 at 17:28
10
$\begingroup$

No. The strength to weight ratio of PVC is poor compared to aluminum and you would end up with a very heavy, albeit cheap, machine, and will be even worse when compared to carbon fibre tubing, which would be the optimal choice performance-wise. Extruded aluminum tubing would likely be the best choice cost wise. Forget about building a plumb-O-copter.

$\endgroup$
7
  • $\begingroup$ If you're talking about the sort of PVC tubing used for irrigation systems, not only is it not very strong, it's also quite flexible. Hold a 10-ft length (standard size in US hardware stores) in the middle, and it will deflect at least 6" on either end. $\endgroup$ – jamesqf Jul 10 '20 at 3:23
  • $\begingroup$ I think he has in mind Sched 40 or Sched 80 rigid plumbing pipe. $\endgroup$ – John K Jul 10 '20 at 11:55
  • $\begingroup$ If I'm not mistaken (I'm no expert), schedule 40 PVC is the white pipe commonly used for irrigation &c. $\endgroup$ – jamesqf Jul 11 '20 at 5:19
  • $\begingroup$ Sched 40 is the standard PVC for residential house plumbing, good for a 2 or 3 hundred psi burst. Schedule 80 is for higher pressure applications and has nearly double the wall thickness (smaller ID). $\endgroup$ – John K Jul 14 '20 at 20:00
  • $\begingroup$ Sure, but bursting strength is not really what's important in building airframes :-) $\endgroup$ – jamesqf Jul 15 '20 at 21:05
1
$\begingroup$

In my experience using PVC to build scale models, PVC doesn't make a good construction material:

  1. it's too flexible. PVC pipe will bend under its own weight.
  2. the glue typically used to join PVC is pretty weak, impact loads will break the bond.
$\endgroup$
1
$\begingroup$

PVC is no where near stiff enough for a given weight. And its strength to weight ratio is poor. The structural efficiency of air machines is absolutely critical otherwise you are building a machine that may not fly at all.

Plus, do a search for helicopter ground resonance, especially watch some youtube videos of helicopters destroying themselves.

$\endgroup$
2
  • $\begingroup$ Ground resonance only comes into play when the helicopter has a rough landing. With PVC tubing it will resonate so much that it will be shaken to pieces even before first flight. $\endgroup$ – Peter Kämpf Nov 25 '20 at 17:34
  • 1
    $\begingroup$ I'm pretty sure I have seen videos of ground resonance without a preceding landing of any sort 🤔 $\endgroup$ – Jpe61 Nov 25 '20 at 20:12
-3
$\begingroup$

PVC pipes are strong and flexible. 1 1/2" diameter pipe type SDR-26 is thinner-walled and weighs only .3 pounds per foot! That's three pounds per ten-foot length which only costs eight dollars each at Home Depot. PVC cement can form a solid integrated bond when applied thickly and left on for ten seconds to melt the surface before mating.
However, PVC is breakable when bent, so the airframe must have a lot of reinforcement braces to reduce the amount of bending of longer sections.
Strength-TEST.!! Test test, the strength of every section using sandbags. Get an EAA member to advise you on this.
Regarding self-bendability: I just tested a 10' length of 1 1/2" PVC type SDR-26 plastic pipe and when suspended it at center and each end drooped down 1/2" is all. I doubt that any ultralight designer would incorporate any unbraced pipe lengths longer than 2'.

$\endgroup$
1
  • 4
    $\begingroup$ I have removed your "signature" twice now. Please do not add it again or we'll have to consider you a spammer. $\endgroup$ – Federico Nov 25 '20 at 15:15

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.