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deanfi

Cessna 180 inflight break up

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A reminder to know your aircraft. How many can nominate Va manoeuvring speed for their aircaft?. I had to look in the musketeer POH, Va 118kts so well above cruise. For the cessna 180 Va 106kts along way below cruise. 

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Certainly appears to be a turbulence induced airframe break-up.  The radar speed records showing a rapid speed build-up could be indicative of strong upwards airflow, with the pilot inputting forward controls to hold altitude - rather than 'going-with-the-flow' and allowing the aircraft to increase altitude.  The POH stated Va is 106 kts. However, because the aircraft was calculated to be 234 kg below MTOW, the 'real' Va would have been much less than 106. (my estimate is 96 kts).

 

So, given that there was a marked increase in speed from 83 up to 127 kts, (presumably due to pilot correction to maintain altitude?), the aircraft was well in excess of the real Va at the time.  This is a very real possibility when pilots are flying a reasonably fast cruise aircraft, but at a very low MTOW.  The very early model Cessna 210s were essentially a C182 airframe with retraction, and cruised up in the 130-140 KIAS range - all this with a (fully loaded) MTOW of 106-108 kts. There were some breakup events recorded with them - AFIK.

 

The aircraft had recently had some repair work in the stabilator and trim unit : but it's only speculation if this was influential.

 

What did surprise me was the large number of C180 accidents contained in Kathrynsreport. Didn't read them all, but several involved RLOC events, as you'd expect with challenging to fly taildraggers.

 

 

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 If you get caught in an updraft you may have to just go with it or  risk overspeed trying to maintain level.. Application of aileron and the resultant twisting of the wing in the 210 's is a factor with some wing failures. Higher speeds make high loads more likely at lower control deflections. Other speed limits are associated with structural flutter and not general airframe dynamic loading but the two can be combined. As  said "Know your Aeroplane". Nev

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I have mentioned VA and max structural cruise in various posts over the years. The max structural cruise of alot of the aircraft on the RAAus Register is very low compared to cruise speed. Common amongst the European designs operating here.

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Posted (edited)

Yeah ... an opportunity for us to do a bit of theory revision.

 

 

 

And, of course, it's not just an issue for the wee flying machines. This is part of an email discussion on the subject with an Airbus flying relative:

 

"Here is the Va chart for the A330. I imagine the caution note below was added after the AA587 crash. Fly by wire protects us every day in these aeroplanes, however in the sim when we degrade to Alternate or Direct law one must be very cognisant of those numbers.. as the Airbus becomes, well just a big SkyRanger Swift actually in those configurations.

You can see at 5000' any abrupt movement without normal law protections above 265 kts will probably bend the frame, at least! We are trained to stay off the rudders at all times in jet upset manoeuvres and of course swept back wings gives us a naturally stable platform. Having said that, I have encountered wake turbulence on the A320 that almost required an underwear change out, thus it's a very serious issue which requires proper distance and time separation and a situational awareness of the met environment around the airplane. Airmanship."

 

image.thumb.png.9eb9a1e29b2d371d50a758c2c77fd2f3.png

Edited by Garfly
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4 hours ago, djpacro said:

I didn't see that either video actually explained the correct definition of Va (although I skipped thru that long video so may have missed it but don't think so as I didn't hear some aspects of Va mentioned at all).

https://www.safepilots.org/documents/SAIB_Maneuvering_Speed.pdf

This is a very real subject for concern.

 

Va is the IAS at which full deflection of the most effective control, (usually elevators because of the leverage), which will cause the aircraft to stall, but beyond which structural damage or actual failure may occur.  The classic Vn diagrams illustrate this.

 

The manufacturer should have built the aircraft, and tested it, so that they can quote actual load factor limits, airspeed limits, and stalling speed guides to the purchaser via the POH. In the case of most RAAus non-aerobatic types, the Load Factor range is usually +3.8 and - 1.9,  with a Vs below 45KIAS.

 

The Va will always be less than Vno, (bottom of yellow arc/top of green) - beware if you mistakenly believe that in the green is ok in all conditions. It is calculated from the Vs, and so Va varies with the actual weight of the aircraft - the usual practice is to quote Va at MTOW. 

 

As a working example, I'll use our Brumby 610 24-8554.

 

Vs  @  600kg  =  44 KIAS    so Va = sq rt of LF 3.8  x  44  =  1.95  x 44  = 86 KIAS, or 14KIAS below Vno! (Brumby quote 88KIAS for the Vs of 44, but I have seen a Vs of 42 given = 82KIAS Va)

Vs  @  lower weights is lower than 44, (depends on test flying), but the calculated Va will always be lower than the Va as shown in the POH.  Some references vary Vs by actual MTOW/MTOW x Vs, although this would need to be determined for each aircraft.

 

The Va for full extended flap is based on the sq rt of 1.9, and happens to be the same as were the aircraft to be subject to -.1.9 LF in clean configuration. In other words - don't extend flap in rough air, and avoid inverted flight!

 

My RV9A is also quite a Va exercise. It is quoted as having a Va of about 109-112KIAS in the VANS references, but I can't make that number work.  My Vs at MTOW of 795 kg is 53KIAS, and using 3.8 LF  this calculates out to a Va = 103KIAS. As a precaution, I use 100KIAS as my absolute tops when things get a bit rough, and if it is seriously so: then I try for 80-85KIAS max. (keeping somewhere near midway Vs and Va).

 

Now, the question arises - why are manufacturers Va numbers higher than my calculations from the accepted formulae?  Could our Vs observations be in error due to the blurry stall characteristics of many RAA types? Is it an attempt by manufacturers to present their aircraft as 'tougher' and more 'capable' than competitors?  Cessnas are somewhat the same: I could never calculate a Va for any of my many aircraft over the years which was closer to theirs than 10 KIAS.

 

The next question is - why have there been so few in flight damage or break-up problems reported or attributed in accident reports over the years?  Could it be that the majority of owners don't risk flying as they are very much aware of their own skill limitations in turbulence, or they just don't fly in adverse weather full stop, or are our RAAus types actually a bit stronger than the +3.8 / -1.9 LF envelope?  I rather think that RAAus pilots do avoid really rough weather because there are so many RLOC accidents attributed to 'wind effects' that the lesson is clear to see.

 

happy days,

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52 minutes ago, poteroo said:

This is a very real subject for concern.

.....

My RV9A is also quite a Va exercise. It is quoted as having a Va of about 109-112KIAS in the VANS references, but I can't make that number work.  My Vs at MTOW of 795 kg is 53KIAS, and using 3.8 LF  this calculates out to a Va = 103K ....

Now, the question arises - why are manufacturers Va numbers higher than my calculations from the accepted formulae?  Could our Vs observations be in error due to the blurry stall characteristics of many RAA types? Is it an attempt by manufacturers to present their aircraft as 'tougher' and more 'capable' than competitors?  Cessnas are somewhat the same: I could never calculate a Va for any of my many aircraft over the years which was closer to theirs than 10 KIAS.

....

happy days,

1. Calculations must be done using CAS not IAS - that usually resolved most differences.

2. The flight envelope is determined at design stage, before the aeroplane has flown, based on estimated stall speed. The actual stall speed is often different than estimated and some manufacturers don’t bother revisiting the flight envelope! I can provide an example of this.

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4 hours ago, poteroo said:

The next question is - why have there been so few in flight damage or break-up problems reported or attributed in accident reports over the years?  

......

happy days,

I guess that many are saved by the 50% margin between limit load factor (where the structure may deform) and ultimate load factor (structural failure) - I know of quite a few. These generally don't appear in accident reports.

 

That Musketeer many years ago with buckled main spars and wing skins. Twisted steel tube truss, broken longerons, wing ribs broken etc on aerobatic airplanes.

 

Still too many Aero Commanders with catastrophic wing failures not to mention Cessna 210s and Tiger Moths.

 

https://www.flyingmag.com/technique/accidents/aerobatic-pilot-survives-extreme-failure

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7 minutes ago, Garfly said:

Let's give old Rod a go then ....

He still does not give the correct definition of Va.

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On 7 April 2019 at 5:01 PM, deanfi said:

Some people push down on the stabilator to swing the aircraft around , pretty stupid thing to do , 

 

https://www.bcaviation.ca/bcga-news/repositioning-a-cessna-aircraft-by-pushing-down-on-the-tail-an-expensive-lesson-learned

 

 

 

 

"There is no correct way to push down on the tail..."

It's not just the tail that is misused. Our aircraft are only just strong enough for flying; they're too flimsy for man-handling.

I've had an experienced airman lean on my wing LE as if it was a barstool.

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I remember a sad accident 7 years ago involving a Thorpe T18 that broke up inflight , wake turbulence may have been a factor , something to think about ,

 

I was watching a  A380 a few weeks ago with beautifully vortex contrails visible and it was amazing how quick they descended from 30, 0000 plus to around 5, 000 or so , hard to judge height accurately but it was a huge descent very rapidly.

 

Thorpe accident report

 

https://aviation-safety.net/wikibase/wiki.php?id=150966

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Posted (edited)
19 hours ago, djpacro said:

not to mention Cessna 210s

See:  ATSB  AO - 2017 -102

         Inflight Breakup of Cessna 210 VH-HWY near Darwin 23/10/2017

 

C210s move along quite fast, and are notably represented in accidents related to in-flight breakups.  With a Va of only 118KCAS, it is often the case that the 210 is flying 25-30 kts above this, and so needs to be significantly slowed if severe turbulence might be encountered. At lighter weight than MTOW, the Va is lower again.

 

210s are possibly more exposed to this type of airframe damage or failure than many other types because they have been a mainstay of the single engine charter industry for decades.  They fly more hours annually, and so encounter a range of weather, including some very dangerous wx in the tropics. They are more often an entry point into commercial aviation, and flown by relatively low experience pilots.  Ts avoidance may not yet be foremost in their thinking.

 

More info here:  AC 23 - 19A

Edited by poteroo
add last reference
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