gas pressurized wing spar
That’s amazing. A sort of pre-stressing?
It’s not pre-stressing although that has been used on other aerospace structures to stabilize them, see Atlas missile.
The idea is that if the spar cracks, the internal
pressure will drop and with a gauge/light installed you will get a warning before failure. Famous Czech stuff, if you track such things. Some additional discussion in a previous thread here.
The Zlin design incorporated in later versions included a nitrogen reserve in the spar with a warning light if the nitrogen had escaped, indicating the need for the spar to be inspected. It also had a G meter event recording system, if there was an exceedance another warning light came on. Care needed to be taken to energise the event recorder after starting, as starting electrical surges could cause a spurious event warning.
The ‘modern’ 142/242 was a very honest aerobatic trainer, but not suitable for aerobatics beyond sport level (cambered wing, relatively under powered), although technically it could carry out all the advanced manoeuvres.
The competition box has a floor of 100 Metres AGL Unlimited and 200 Metres AGL Advanced, so it would require very skilful dexterity to jettison the canopy and successfully deploy a parachute. The USA requires a parachute in the regs, and some schools used them for UPRT in the UK, but a lot of operators/practitioners in the UK don’t use them.
I thought the ICBMs used fuel to keep the tube rigid enough to carry the weight above.
That’s correct, the skin of an otherwise unstable column structure is loaded outward via internal pressure. Since circumferential tension restrains it from going outward further, it is made stable. This saves weight versus adding structural stiffeners to the skin but does not make the structure stronger in the sense of reducing structural stresses.
(None of the above is in play with a Zlin main spar carry through structure, it is pressurized just to check for cracks and leaks)
In fact all large liquid fuel rockets need careful tank pressure control to ensure structural stability.
You don’t need to go all the way back to old Atlases: more recently a SpaceX Starship test article buckled under the weight of hundreds of tons of cryogenic fuel in the upper tank when the lower tank accidentally depressurized. This video explains it as well as the differences between old Atlases (unable to support their own weight even unfuelled) and Starship. Scroll to 01:00 to watch the demise of SN3
I still think it is amazing that Neil had the relative calm and instinct to fight for (and save) his live in such a clever and skilfull manner.
Silvaire wrote:
The idea is that if the spar cracks, the internal
pressure will drop and with a gauge/light installed you will get a warning before failure. Famous Czech stuff, if you track such things.
A similar system is also used in the main rotor of Russian Mi-8 helicopters: the blades have tubular spars pressurised to 0.25 barg, and if the pressure escapes, a red cap pops out near the blade hinge.
RobertL18C wrote:
The ‘modern’ 142/242 was a very honest aerobatic trainer, but not suitable for aerobatics beyond sport level (cambered wing, relatively under powered), although technically it could carry out all the advanced manoeuvres.
Yes, the unlimited aerobatic one is Zlin 50, which had its heyday in the world championships. Z142/242 can do most manoeuvres, but power-on spins and snap rolls are explicitly prohibited. Z242 also has an AEIO-360 engine, which has limitations on unusual attitudes, as opposed to the dry-sump AIO-360.
