Floatplane engine falling off

[Rebel541]

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

[Linlei]

Jesse and Biggus thanks for your insight.

Jesse:
I used the formula for Kinetic Energy and chose the standard convention that upward acceleration was positive and downward acceleration was negative (with respect to the earth). The aircraft wasn't in free fall and I was only interested in what rate of descent would give the airplane enough Kinetic Energy to to exceed the negative load factor. Once the airplane hits the surface it is my understanding that an impact calculation is involved. Whether the result of that is a positive or negative outcome I can't say. If it were to be a positive "g" number it would have to be in the order of 1650 x 5.7 = 9405 lbs. That translates in to a descent of around 2100 feet per minute and is even less of a concern with respect to the Rebel air frame.

Biggus:
Here is the Wiki definition of load factor:

" In aeronautics, the load factor is the ratio of the lift of an aircraft to its weight ... and represents a global measure of the stress ("load") to which the structure of the aircraft is subjected: ".

Apparently it is a measure of the entire structure as engineers have to worry about all of the bits and pieces rather than just the wings. ( Lift is not solely obtained from the wings). I agree that during a normal landing the 1650 lbs is gradually transferred from the lifting surfaces to the landing gear, however, I believe that during a very hard landing, weight (force) is rapidly transferred through the entire structure. (There is a bending moment as you say on the motor mounts and on the wings and fuselage). In any case if the airplane weighed 1650 lbs in the air it will still weigh 1650 lbs on the ground (minus fuel burn). I believe that if I exceed the load factors of my airplane in the air or in contact with the surface the results will be similar.

I have to add that my calculations are estimates and I was trying to get a rough idea of how fast I would have to descend to cause the type of damage I saw on the video. I agree with Rick, if the pilot of the airplane in the video is on this list something other than speculation would be helpful.

Mike B.

[monty777er]

I agree with Rick. It is the weight of the concerned components and time of deceleration with resultant tension, compression and torsional loads.

I've got the N1H1 now so haven't the brain capacity to articulate. However as an aircraft accident investigator had to jump in.

Here's some research on light aircraft seats.
https://www.google.com/url?sa=t&source= ... NS3TZD4dZJ

I don't have my books at hand but the size of the crumple zone can make a difference in survivability.
Something has to give.

Assumptions on mode of failure can not be made without all the facts from a hands on investigation so I shall say no more.

[Linlei]

Thanks Monty,

I read the article. It was sobering to find that a free fall of 1.6 metes can produce a force of 10-14g's in that instance. I also found it interesting that they had a pelvis and femur of a small human female handy.

I agree wholeheartedly that "something has to give" and in crumple zones, tension and compression.

My original thoughts were that a load factor implies limits. The limits are designed into the airplane so it can perform it's mission. Part of an airplanes mission is landing, so limits apply to that phase as well. A pilot who exceeds any limit may or may not get away with it depending on the safety factors built in to the air frame. Both you and Rick have given a great description of what happens after the limits have been exceeded.

Here is a great link to an article on Load Factors:

https://www.flightliteracy.com/load-factors-part-one/

I think it says it better than I can.

Mike B.

[Brent Anderson]

Nothing positive about it, other than I'm going to take a good look at my rivets in that area!

[DirectFromTheFactory]

I watched the video and read some of the comments. One comment stated the aircraft had a larger engine installed and the factory told him not put it in. Another says it has a lyc 320 and the company accepts that. If the aircraft does have a 320 we have no problem with that.

The aircraft is clearly in a stall. I say this for three reasons. 1. When the aircraft clears the trees the elevator is up and yet the aircraft is still falling like a rock. 2. Just before the aircraft hits the water the nose dips down quickly. And 3. The angle of attack of the wings to the direction of flight obviously is exceeding the stalling angle of the airfoil.

The Rebel with out flaps will stall in the mid 40's. If conservatively we say the aircraft is descending at 40 mph at a descent angle of 30 degrees then the vertical descent rate is 20 mph or 29.3 ft/sec. Damage is inevitable.

The design vertical descent rates for landing of a light aircraft to meet Certification standards must be greater than 7 fps but need not be greater than 10 fps. The actual value for an aircraft is determined by its wing loading. For intermediate values the formula in feet per second is:
-------------0.25
V=4.4(W/S)

Where V=feet per second
W=gross weight of the aircraft (Rebel on Floats =1730 lbs)
S=wing area (Rebel 150 sq ft)

To certify the Rebel we would have to meet the maximum requirement of 8.1 ft per sec during a landing.

This aircraft exceeded a certified design rate by almost four times. As I said above damage was inevitable.
Some of the commentators have said they have landed aircraft a number of times harder than the aircraft in the Video. I find this highly unlikely.
A 10 fps descend rate upon landing is an extremely hard landing and very few normal aircraft would survive without some damage. At 29.3 fps I am amazed the damage was not greater.

Darryl

[Jenki]

Regarding the video ... what is the reason to make approach or touch & go without flaps down?
I can understand not full deflection (touch & go) but is there any reason for no flaps?
Thank you

[irishfield]

Thanks for chiming in Darryl! I threw out -3000 FPM and not far off your guesstimated calculated decent. Nothing is gonna save that, especially without suspension, other than correct flying.

..and Jenki, why no flaps? you'd have to as Rick Porteous about that. He's the only one with an answer!

[Ahewko]

I've heard some Rebels may have been built with a coated aluminum firewall instead of a stainless steel firewall. Is anyone aware if that was the case here?

[irishfield]

Being a 1993 completion it probably is an aluminum firewall and may or may not have been coated, but doubtful as BC's RAA inspectors at the time didn't snag said firewalls. It was an Ontario inspector that turned the wheel on that in about '94 to make Darryl start supplying stainless.

Regardless, firewall material would have ZERO effect on this failure / destruction.. . as we all know the engine is NOT attached to the firewall.

[Flying Indian]

Just a thought here , I m no expert on airframes, would a set of support bars coming from upper cage like the cessnas help out here with float equipped rebels ????? I know they are a pain to look around sometimes !!!

[irishfield]

I was looking for the picture Barry, and can't find it, but even V braced Cessna's loose the entire nose when you pancake them in like that!