Re: Floatplane engine falling off
Posted: Sun Dec 30, 2018 3:14 am
G'day Mike ....
The G rating refers to the main wings ability to withstand positive and negative loads ......... so your calculations of 1650 Lbs X various loads are not what at hand here re the engine breaking free .......
Once the plane "arrives" - the loads are on the floats and their support struts - as the wings are no longer involved .... and the 1650 Lbs that the WHOLE plane weighs is no longer in play either
Water is like concrete at high speeds and at high decent rates ... ( ever fallen off at high speed while water skiing ? .....
I have .... and you bounce - A LOT - before you slow down enough to "dig in" )
If you look at the clip - it's the top engine mount bolts OR the mount itself ( welds ) OR the brackets that the engine mount bolts locate in to that let go - and the engine swings downwards - pivoting on the bottom engine mount bolts
Once the plane hits the water ( or ground - re a hard landing .......... though - water is FAR LESS FORGIVING than an undercarriage and tyres are during a terrestrial landing ) - the wings have UNloaded their weight, courtesy of the landing gear now supporting the plane's mass in general ....
The things that now come in to play are things like the wing ( and tailplane ) attach points, the struts and each end of their attach points ...... and the engine - it's weight and IT'S attach points
With a Lycosaurus up front WITH a metal propeller - there's probably near as dammit 350Lbs - suspended on "an arm" / a lever if you like - that extends a few feet forward from the firewall - and that arm now wants to move DOWNWARDS - big time
A millisecond after arrival - the bottom two bolts of the engine mount are now in compression - not tension - as the kinetic energy transfers itself from a forward / pulling effect - to a downwards effect
The top two engine mount bolts alone, are what take ALLLLLLL the engine weight loads at this point in time ...
I don't have a ready reckonner for G forces - but my eyeball engineering, mechanical mind - figures that a 350lb weight - on a 3 ft arm ( the centre of mass of the engine and propeller FORWARD of the firewall ) coming down at around 20 FPS - exerts around 5,400Lbs of force on the engine mount welds, the two engine mount bolts, and/or the brackets that the bolts locate in to .....
I'm NOT a trained structural engineer - but I'm pretty sure the bolts would take that sort of load as they would cop half ( 2,700 Lbs ) each ..... my guess would be the welds on the mount letting go - OR the bolts pulling through the two upper support brackets / attach points ..... at the end of the day EVERTHING has it's limits - and something WILL give if those limits are exceeded
( I'd LOVE to know the exact numbers if anyone can interpolate the data for me ! )
I'll email my REG 35 design buddy - and he will be able to tell me ..... but I suspect he is away - holidaying O/S with his family at present ...
Does anyone actually KNOW the pilot ?!?!? .......... and has the full story on WHAT actually let go ???
Rick in Orrrstraylya
The G rating refers to the main wings ability to withstand positive and negative loads ......... so your calculations of 1650 Lbs X various loads are not what at hand here re the engine breaking free .......
Once the plane "arrives" - the loads are on the floats and their support struts - as the wings are no longer involved .... and the 1650 Lbs that the WHOLE plane weighs is no longer in play either
Water is like concrete at high speeds and at high decent rates ... ( ever fallen off at high speed while water skiing ? .....
I have .... and you bounce - A LOT - before you slow down enough to "dig in" )
If you look at the clip - it's the top engine mount bolts OR the mount itself ( welds ) OR the brackets that the engine mount bolts locate in to that let go - and the engine swings downwards - pivoting on the bottom engine mount bolts
Once the plane hits the water ( or ground - re a hard landing .......... though - water is FAR LESS FORGIVING than an undercarriage and tyres are during a terrestrial landing ) - the wings have UNloaded their weight, courtesy of the landing gear now supporting the plane's mass in general ....
The things that now come in to play are things like the wing ( and tailplane ) attach points, the struts and each end of their attach points ...... and the engine - it's weight and IT'S attach points
With a Lycosaurus up front WITH a metal propeller - there's probably near as dammit 350Lbs - suspended on "an arm" / a lever if you like - that extends a few feet forward from the firewall - and that arm now wants to move DOWNWARDS - big time
A millisecond after arrival - the bottom two bolts of the engine mount are now in compression - not tension - as the kinetic energy transfers itself from a forward / pulling effect - to a downwards effect
The top two engine mount bolts alone, are what take ALLLLLLL the engine weight loads at this point in time ...
I don't have a ready reckonner for G forces - but my eyeball engineering, mechanical mind - figures that a 350lb weight - on a 3 ft arm ( the centre of mass of the engine and propeller FORWARD of the firewall ) coming down at around 20 FPS - exerts around 5,400Lbs of force on the engine mount welds, the two engine mount bolts, and/or the brackets that the bolts locate in to .....
I'm NOT a trained structural engineer - but I'm pretty sure the bolts would take that sort of load as they would cop half ( 2,700 Lbs ) each ..... my guess would be the welds on the mount letting go - OR the bolts pulling through the two upper support brackets / attach points ..... at the end of the day EVERTHING has it's limits - and something WILL give if those limits are exceeded
( I'd LOVE to know the exact numbers if anyone can interpolate the data for me ! )
I'll email my REG 35 design buddy - and he will be able to tell me ..... but I suspect he is away - holidaying O/S with his family at present ...
Does anyone actually KNOW the pilot ?!?!? .......... and has the full story on WHAT actually let go ???
Rick in Orrrstraylya