wing strength

[Blue on Top]

57 minutes ago, M20Doc said:

The tail section is held on with two double shear fittings.

Clarence

... and the actuator (the weakest link ... that takes pitching moment of the horizontal (and drag of the vertical).  I have been told that the design is fail-safe in that if the actuator physically fails.  The two upper bolts, the hinge and the geometry will allow the airplane to be flown home with just the elevator.  I would estimate for a flap up (gear down still  ) landing. 

[cliffy]

On 8/10/2021 at 8:35 AM, A64Pilot said:

Yes, but I believe the tail bolts are in shear and the engine mounting tension, shear loading is much, much stronger than tension.

The Wings on a U-21 which is a Beech Queen Air are held on by three bolts, two for lifting up. and only one for neg G’s, they are in tension as well.

Many helicopter rotor systems are held on by one nut.

‘Just silly observations.

Unless I’m mistaken but Va has nothing to do when something will break, it’s simply when a full, rapid control movement will exceed Certified G limits.

Even G limits really don’t necessarily have anything to do when something will break, Normal category aircraft are if memory serves are Certified to +3.8 and -1.52, doesn’t mean anything happens at those G numbers, just that the aircraft can handle Ultimate load, which again by memory is 1.5 times that amount without failing, it is allowed to bend or deform at ultimate, just not break, for three seconds anyway.

‘Some aircraft are much stronger than min required, some just barely meet the requirement, but ALL meet it. Most are I’d say well exceed it as it’s real hard to design to barely pass, it’s much easier to design to be much stronger so that if your off a little, you still pass, redesigning is expensive, costs weight though.

What is not accounted for, at least I’m sure what isn’t accounted for in CAR3 aircraft is aging and fatigue,so it’s prudent for a manufacturer to well exceed min requirements for new parts so that when they accumulate thousands of fatigue cycles and decades of aging, that they are still strong enough.

Want to bump Va to a higher number? It’s simple just turn control authority down to min required, Va will go up as control authority goes down.

Of course you can’t do that will all types of aircraft, some require more maneuverability than others.

 

I seem to remember that Boeing designed a wing (787) and when put to the ultimate test (failure point) it failed to meet its design spec" by 1  1/2%  (a first for Boeing and the composite spar was a first for Boeing!). Designed to "just make" parameters? 

Our 2 tail hinge bolts are also "close tolerance" bolts and not just normal AN bolts so their design parameters are held to tighter limits that I feel contributes to better sear loading strength control and surface "wobble" control through tighter tolerances. If you find a horizontal stabilizer that exceeds the "wiggle" tolerance in the book one might assume that standard AN bolts were misused to attach the tail allowing a loose fit. This I have seen. Just changing back to close tolerance bolts solved the issue.

[Blue on Top]

3 hours ago, cliffy said:

I seem to remember that Boeing designed a wing (787) and when put to the ultimate test (failure point) it failed to meet its design spec" by 1  1/2%  (a first for Boeing and the composite spar was a first for Boeing!). Designed to "just make" parameters? 

That is the ultimate in design (lightest design to meet the regulations).  This is possible with composites as layer by layer can be added/subtracted.  Metal on the other hand only comes in specific thicknesses.  Going from one thickness to the next will add lots of margin ... and some weight.  

A good example is bolts in the flight control systems.  An AN3 will handle all the loads really well.  A pilot is not going to double shear an AN3 bolt ... even with the mechanical advantage of the system.  BUT, a mechanic can (and has on many, many occasions) over-torqued (stripped) the nut.  Today, we will not design a flight control system with anything smaller than an AN4 bolt.

Remember the 50% margin is to allow for: corrosion, mis-install, fatigue, tolerances, etc.

[EricJ]

9 hours ago, cliffy said:

I seem to remember that Boeing designed a wing (787) and when put to the ultimate test (failure point) it failed to meet its design spec" by 1  1/2%  (a first for Boeing and the composite spar was a first for Boeing!). Designed to "just make" parameters? 

Back before the Boeing management paradigm shift where making profit was prioritized over making good airplanes and HQ moved away and isolated itself geographically from the factory, they routinely exceeded design goals.   They weren't required to test to failure but it was sort of an engineering tradition to do so.   I remember this particular event because I was working on some of the digital comm boxes for the 777 at Honeywell at the time.   The raw vids got circulated around.

I think missing the spec by any amount back then would have been considered a failure of sorts.   Times change.

 

[Alan Fox]

On 8/29/2020 at 4:47 PM, carusoam said:

Speaking of reenactment...

Many an MSer stood on the wings of M20E #1 a couple of years ago, prior to it being parted out...

It really demonstrated how many people can stand on a wing that is 50 years old...

Still has nothing to do with how well a real plane survives the awesome forces of a pilot losing control of his plane...

 

1) Airplane manufacturers test things up to a certain limit.... (of their choosing)

2) They publish those limits with a margin of safety in the POH...

3) When flown within the limits of the POH... the plane is nearly guaranteed to be reusable for the next flight...

4) The edges of performance get a bit fuzzy, and can change with age, cleanliness, and the weather...

5) it is highly recommended to stay within the limits of the POH...

6) when exceeding the limitations set in the POH, you become known as a test pilot...

7) Good test pilots know the limitations of their machines, and their own skills, and have a fitting plan B, when plan A falls apart...

 

It wasn’t my fault... the DIVE caused my over spending.... 

-a-

 

It was I think 17 of us , and I was sitting on the roof.. 

[Igor_U]

1 hour ago, EricJ said:

Back before the Boeing management paradigm shift where making profit was prioritized ....

I think missing the spec by any amount back then would have been considered a failure of sorts.   Times change.

 

While post before yours is referring to 787 "failed" to meet the test, I believe that was actually 777-9 couple of years ago (With a number of problems 787 had, I can't recall any issues with failing the ultimate load test). Test is really not "pass or fail" but it resulted at, what I remember, fuselage crack due to wing bending at 148-149%. Relatively minor redesign a modification followed and it was shown by calculation that is good. No test is needed.

This is really a normal situation in test as design with modern tools is optimized as much as possible with minimal margins to achieve a  lowest possible weigh, max payload and performance for the customer. In commercial air transport airplane you just can't sell a plane that is not optimized like you can in business aviation or military (different requirements, number of cycles and maintenance cost)  as the airlines would loose money and would shop on the other side of pond.

it's a very competitive business.

 

 

[Blue on Top]

Business jets are no different ... nor are our Mooney aircraft.  Lack of useful load hurts the M20s, too.  Taking a passenger out of a business jet would limit sales ... just like adding one helped the CJ2 a lot!

The Citation X wing nor horizontal stabilizer has been tested to failure.  The coke bottle portion of the fuselage fails first ... beyond 150% of design load.

Knowing how much margin one has for future gross weight increases is priceless!

[Raymond J1]

1 hour ago, Igor_U said:

While post before yours is referring to 787 "failed" to meet the test, I believe that was actually 777-9 couple of years ago (With a number of problems 787 had, I can't recall any issues with failing the ultimate load test). Test is really not "pass or fail" but it resulted at, what I remember, fuselage crack due to wing bending at 148-149%. Relatively minor redesign a modification followed and it was shown by calculation that is good. No test is needed.

This is really a normal situation in test as design with modern tools is optimized as much as possible with minimal margins to achieve a  lowest possible weigh, max payload and performance for the customer. In commercial air transport airplane you just can't sell a plane that is not optimized like you can in business aviation or military (different requirements, number of cycles and maintenance cost)  as the airlines would loose money and would shop on the other side of pond.

it's a very competitive business.

 

 

On the other side of the pond they say and do the same thing... They give a name: "Neo wing" (long-range machine).

[Raymond J1]

29 minutes ago, Blue on Top said:

Business jets are no different ... nor are our Mooney aircraft.  Lack of useful load hurts the M20s, too.  Taking a passenger out of a business jet would limit sales ... just like adding one helped the CJ2 a lot!

The Citation X wing nor horizontal stabilizer has been tested to failure.  The coke bottle portion of the fuselage fails first ... beyond 150% of design load.

Knowing how much margin one has for future gross weight increases is priceless!

In France it is colloquially said: "The shallot race", because one moves away from the virtuous circle of (technical) progress. There was an interesting initiative in our manufacturer "Robin", that of keeping the MTOW and increasing the payload by reducing the empty mass. On the "DR" range, they replaced the Lycoming O235 with a Rotax: Weight gain of 30 Kg and reduced fuel consumption (6 Gal/h vs 10,5). Today, the 135 hp DR 400 Rotax 915 is the performance equivalent of the Lycoming-powered DR 400-160 (hp). Everything goes through an STC, so we can transform the old cells. In fact, it is as if we were riding on an M20C limited to 3 places the same engine.

Edited August 13, 2021 by Raymond J

[Igor_U]

19 hours ago, Blue on Top said:

Business jets are no different ... nor are our Mooney aircraft.  Lack of useful load hurts the M20s, too.  Taking a passenger out of a business jet would limit sales ... just like adding one helped the CJ2 a lot!

 

I disagree to the point. Business jets have normally less seats that there's room in a fuselage (feature of comfort), sofas, luxurious interiors that are very heavy, stone countertops and then there's Gulfstream with large windows cutting through the frames with is structurally very inefficient... all features of comfort and something their owners want...

Airbus and Boeing would just prefer to remove all those together (they are looking at it, seriously) as it cost money and weight. Not to mention that business jets are mostly hangar queens and their cycles numbers are much lower then airliners...

 

19 hours ago, Raymond J said:

On the other side of the pond they say and do the same thing... They give a name: "Neo wing" (long-range machine).

I don't follow. Isn't it a NEO New engine option?

[Raymond J1]

12 hours ago, Igor_U said:

I disagree to the point. Business jets have normally less seats that there's room in a fuselage (feature of comfort), sofas, luxurious interiors that are very heavy, stone countertops and then there's Gulfstream with large windows cutting through the frames with is structurally very inefficient... all features of comfort and something their owners want...

Airbus and Boeing would just prefer to remove all those together (they are looking at it, seriously) as it cost money and weight. Not to mention that business jets are mostly hangar queens and their cycles numbers are much lower then airliners...

 

I don't follow. Isn't it a NEO New engine option?

New engines and new wings (with differents wingtips, tanks (long range) and mod structure).

[A64Pilot]

Weight reductions and fuel cost to airlines is phenomenal. What we would consider irrelevant adds up to being significant.

‘For example I’ve read that the weigh of everyone carrying cell phones cost SouthWest 1.2 mil in fuel per year.

https://www.traveller.com.au/airline-weight-reduction-to-save-fuel-the-crazy-ways-airlines-save-weight-on-planes-h14vlh

They would kill for a 1% fuel savings,I’ve even heard of proposals of aircraft being tugged to the departure end of the runway.

[Will.iam]

On 11/6/2020 at 7:36 PM, N201MKTurbo said:

My ex airplane partner was from Minot and knew the Pietsch’s 

He said the the senior Pietsch (I forget his name) did all those dive tests. 
 

He would dive them at full power and do whatever he could to make them go as fast as possible.

That is some serious coronas but what was his plan B? I. E. When he went for high speed dive test and a wing did breakup or tail separated was he just SOL? Was he planning on trying to bail out of a now tumbling aircraft that may or may not have  incapacitating high G forces to open his parachute? 

[ArtVandelay]

Weight reductions and fuel cost to airlines is phenomenal. What we would consider irrelevant adds up to being significant.
‘For example I’ve read that the weigh of everyone carrying cell phones cost SouthWest 1.2 mil in fuel per year.
https://www.traveller.com.au/airline-weight-reduction-to-save-fuel-the-crazy-ways-airlines-save-weight-on-planes-h14vlh
They would kill for a 1% fuel savings,I’ve even heard of proposals of aircraft being tugged to the departure end of the runway.

I think they should just charge by weight….that would get peoples attention.

[Blue on Top]

On 8/13/2021 at 4:04 PM, Igor_U said:

I disagree to the point. Business jets have normally less seats that there's room in a fuselage (feature of comfort), sofas, luxurious interiors that are very heavy, ...

Full fuel payload in a small business jet is often the crew plus 2 or 3 passengers.  It is not like removing 100+ passengers and luggage from a 737 and calling it a "business" jet.

[cliffy]

And at the airlines they use "Standard Weights" for pax and THAT is a joke

On a weight limited T/O I'll bet $500 that they are all over by 1 or 2 tons!

Been there done that - staring at the red and white checker boards at the end of 31 R at Midway as we gathered speed  to clear the blast fence in the summer in a -200 737

Let's put a truckers scale at the end of the taxiway at the hold point and see what we really weigh :-)

[PT20J]

I flew cruise boat tourists out to the Misty Fjords from Ketchikan for a couple of seasons in float Beavers. Customer Service agents didn't weigh them -- they just asked for their weights. Don't know how many times I had 300 pounders show on the manifest at a petite 220. One nice thing about a floatplane is that you can eyeball W&B by looking at how far the aft end of the floats sink. And we had as much "runway" as we needed and didn't fly much above sea level.

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