'G' Limits - Wings or Engine??
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'G' Limits - Wings or Engine??
Hey
Quick question for everyone...
If the 'g' limits of a single engine piston aircratf (C152) are exceeded, what will fall off first? The wings or the engine?
There's a beer on it, so lets get this sorted..
Cheers, HSVROX
Quick question for everyone...
If the 'g' limits of a single engine piston aircratf (C152) are exceeded, what will fall off first? The wings or the engine?
There's a beer on it, so lets get this sorted..
Cheers, HSVROX
With a beer as prize this is indeed a serious contest so I'd like to clarify the rules:
an Aerobat or not?
positive or negative g limits?
rolling g limits?
flaps up or down?
limit or ultimate "g" limits? i.e. fatigue damage or static overload considerations?
an Aerobat or not?
positive or negative g limits?
rolling g limits?
flaps up or down?
limit or ultimate "g" limits? i.e. fatigue damage or static overload considerations?
Not an engineer so I’m no expert, but I remember some test pilot in the US about 10 – 15 years ago pushing a Partinavia to its limit in front of an air show crowd with his wife doing the commentary. The poor sole parted both wings from the airframe just outboard of the engine nacelles. Both engines seemed to be intact and running until impact in a 45° nose down attitude, wings level and his wife in hysterics. 
Safety First!
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The engine!
You have to take into account the weight at which the aircraft is being operated.
If the aeroplane is stressed to take 6'G', for example at a MAUW of 2000lbs, then the wings are designed to take 12,000lbs of force, and the engine mounts the weight of your 1,000lbs engine (6,000lbs). If on the other hand you fly at half that weight and you take the aeroplane (stupidly) to 12'G' then your wings will still only be producing 12,000lbs of force so wont be as likely to fail structurally. The engine mounts on the other hand, have double the designed maximum load factor on them (12,000lbs as opposed to the original 6,000lbs limit) and will no doubt fail in some horrific manner.
My money's on the engine.
Cheers,
Kerms
If the aeroplane is stressed to take 6'G', for example at a MAUW of 2000lbs, then the wings are designed to take 12,000lbs of force, and the engine mounts the weight of your 1,000lbs engine (6,000lbs). If on the other hand you fly at half that weight and you take the aeroplane (stupidly) to 12'G' then your wings will still only be producing 12,000lbs of force so wont be as likely to fail structurally. The engine mounts on the other hand, have double the designed maximum load factor on them (12,000lbs as opposed to the original 6,000lbs limit) and will no doubt fail in some horrific manner.
My money's on the engine.
Cheers,
Kerms
Good point, Kermit.
It is not an Aerobat but we know it has the same engine mount as an Aerobat so it is good for at least 6 g limit at any weight. (I've seen a bent engine mount from a hard landing though.) The rest of the airframe is good for at least 4.4 g limit at 1600 lb.
It is not an Aerobat but we know it has the same engine mount as an Aerobat so it is good for at least 6 g limit at any weight. (I've seen a bent engine mount from a hard landing though.) The rest of the airframe is good for at least 4.4 g limit at 1600 lb.
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Ultimate Design Strength.
The aircraft designer starts with a target design strength for a particular weight.
All of the strengths should be consistent. If any structure is too strong then it will be too heavy. If any structure is too weak then this is a design fault and the most likely source of failure.
A wing or engine doesn't fall off. The wings or the engine mounts fail under excessive load.
For safety the ultimate design strength is usually 50% greater than maximum specified for normal operations.
A 3g aircraft should break at 4.5g or a 9g fighter should break at 13.5g.
But beware of the rolling pull out! An up going wing will be loaded up much more than what you feel or what the g meter registers in the fuselage.
Beers all round!
The aircraft designer starts with a target design strength for a particular weight.
All of the strengths should be consistent. If any structure is too strong then it will be too heavy. If any structure is too weak then this is a design fault and the most likely source of failure.
A wing or engine doesn't fall off. The wings or the engine mounts fail under excessive load.
For safety the ultimate design strength is usually 50% greater than maximum specified for normal operations.
A 3g aircraft should break at 4.5g or a 9g fighter should break at 13.5g.
But beware of the rolling pull out! An up going wing will be loaded up much more than what you feel or what the g meter registers in the fuselage.
Beers all round!
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You might notice most if not all normal category aircraft have a g limit of 3.8g. Its a regulatory requirement. Some are designed to take more than this, but you only know for sure up to 3.8. Nothing will break off until 150% of this limit at the earliest.
in a C152.....
my beer is on the engine.
Can any engineers out there tell me the loading factor for the"jesus bolts"?
The mount may bend so that you could have a really intereting lesson of EofC and for the first time in a C152 apply power and the nose pitches down
But i wonder if a jesus bolt would fail before the mount...
any takers?
my beer is on the engine.
Can any engineers out there tell me the loading factor for the"jesus bolts"?
The mount may bend so that you could have a really intereting lesson of EofC and for the first time in a C152 apply power and the nose pitches down
But i wonder if a jesus bolt would fail before the mount...
any takers?
very true. Just check any C152's that are continually flown overweight.. .generally the ones with long range tanks used in training
now give that tail spar a shake
you'll be shocked by the sound ... crack crack
now give that tail spar a shake
you'll be shocked by the sound ... crack crack
