In-flight spar failure the tale of my broken tail

[l_reason]

I’m new to the forum and thought some of you would be interested in the experience I had. You are the first to read what I wrote when got home while enjoying a “few” stiff rum & cokes the day the rear main attach spar broke on my 1947 Luscombe while airborne.

"September 1, 2005

Today is a day that as long as I live I will never forget.

I was out flying my 1947 Luscombe 8E, shooting aerial photos for work near Ridgetown, Ontario, when for some unknown reason my airplane started yawing side to side without any control inputs from me. This was not something that I have ever had a plane do to me before. I started “playing” with the rudder pedals, they felt unstable and over reactive. It was very difficult to maintain control of the uncontrollable side to side motions and I was only able to get some control back by holding a lot of pressure on both rudder pedals. It was at this point that it became apparent to me that this was not something I wanted to be trying to fix while flying at 100 mph, in a plane that was nearly sixty years old.

I immediately started looking for a suitable field to land in, while at the same time making a distress radio call to London Flight Service, to which I got no response! There were many fields below me, all of which were full of 6 foot tall corn, nothing I wanted to attempt a landing in. I used my GPS and located the Highgate airfield just less then 5 nautical miles north of where I was and after struggling through a turn towards the airfield I initiated contact with another aircraft in the area who relayed my distress call to Flight Service. As I got sight of the airfield my elevator controls started to be affected by what ever was going wrong in the tail section, I was no longer able to hold the nose in a steady position. With constant pitching up and down, right and left, I attempted to make a slight left hand turn to do a straight in approach to the North facing runway. She would have no part of this so I started a turn to the right in order to come all the way around and line up with the runway. The runway was nothing short of perfectly ideal, strait into a 10 knot wind, 100 feet wide and way longer than I would ever need. Once I was on short final and had the engine at idle I realized I was doing more then 100 mph and was only 100 feet from the ground! I immediately pulled the carb heat on, and turned one magneto off in attempt to slow the engine. I was flying a plane that had no flaps, and no useful rudder to help me slow down with a slip. Remarkably the landing was uneventful. Once on the ground I made one last radio call to the aircraft relaying the messages “I’m safely on the ground”. I then took a deep breath followed by a huge sigh of relief.

Once the initial drama of making an emergency landing was over, I had to get my disabled airplane off the runway and figure out what the hell went wrong. A quick inspection of the tail section I found that the vertical fin and rudder assembly was loose and able to lean freely from side to side about 18 inches. I removed the damaged inspection covers and discovered the whole assembly was being held on by only two rivets at the front and the lower most rudder hinge bolt at the rear. I suspect that they both only had a minute or two of stress left before they would have given way as well. Had this of been the case it would have left me with no longitudinal control, a situation that I am not so sure I would be here to describe.

After investigation of my aircraft by my mechanic and the Transport Canada Safety Board, it was determined that the rear fin attachment spar had cracked and failed, thus causing the fin to move and break the fin other mounts. The rudder and elevator were also bent from these unusual fin movements.

Lucky… I think so!

Patrick"

What it looked like:http://i14.photobucket.com/albums/a334/l_reason/IMG_0072.jpg http://i14.photobucket.com/albums/a334/l_reason/IMG_0077.jpg http://i14.photobucket.com/albums/a334/l_reason/IMG_0111.jpg

[LondonJ]

What a lucky escape. Well done for getting it down!

[shortstripper]

Some tail! eeerrrmmm tale :\

SS

[mazzy1026]

Jesus, good job on getting down safely - the adrenalin must have been in it's pints. something which you will never forget.

Maz

[l_reason]

It was rather odd, the thoughts going through my head when I was trying to figure out what the hell was causing the ludicrous handling. I remember thinking “well if the rudder is not going to work I’ll use the doors to steer and hold the stick with my knees” some how things just seem to work out if you keep your cool and keep thinking of options. That is not the first thing I have had go wrong in a plane and I’m sure it won’t be the last.
Patrick

[Milt]

I_reason

How lucky can you be!!

You have joined a very exclusive club. We should give it a name such as "The Broken Spar Club" or "Oblivian Escapees".

Fortunately there are very few of us and most eligibles didn't make it.

The three surviving foundation members could well be self, another pilot and a flight test engineer. We were the crew of a prototype Valiant which suffered a broken wing main spar. Overloaded alternative structure managed to hold the wing in place until landing when the increased dihedral cancelled out.

There used to be another member who recognised he had a broken wing when doing some aerobatics. Stayed inverted until very short final when he rolled out to a floppy touch down. Having survived that his number came up later when he was knocked down from his bicycle by a wayward car.

How many others are there out there who have survived to join our exclusive club?

[Mike Cross]

As a fellow Luscombe pilot I'm interested in more detail of the failure itself.

I think there's three AD's relating to the fin attachment bracket and damage to the spar due to overtorquing the attachment bolts.

Has conclusion been reached as to what caused your failure?

(Congratulations on the successful outcome by the way :ok:)

Mike

[l_reason]

Milt
I am thankful that I am able to become a member of this exclusive aviation club. (Okay now only one other club I want to join ALT 5280’ ;)) It first hit me as to how fortunate I am when the Transport Canada investigator said, “In my 25 years at this job I’ve seen a few structural failures but have never had the opportunity to ask the pilot any questions, never mind inspect an intact aircraft”

Transport Canada has not come out with a report as of yet and I don’t think I’ll be seeing it for a few more months. From what was said to me about the failure it looks like a crack initiated at a rivet hole witch was not visible if the fin was installed on the plane. My standard “wiggling” of the fin during my morning walk around did not show any amount of flex or play as I remember. One of the main reasons I got the Luscombe was because of its strength and maneuverability. Witch I needed to do low level aerial photography.
Patrick

[spekesoftly]

There used to be another member who recognised he had a broken wing when doing some aerobatics. Stayed inverted until very short final when he rolled out to a floppy touch down. Having survived that his number came up later when he was knocked down from his bicycle by a wayward car.

Sounds remarkably like Neil Williams's incredible escape, apart from the bit about the bike. Neil, I believe, was tragically killed on a ferry flight.

[Milt]

spekesoftly

Thanks for the correction re the bicycle.

Do you have any further details on the remarkable inverted recovery. Memory twinges are causing me to think that there may be two similar recoveries.

I_reason Go you halves in a BIG lottery ticket.!!

[mazzy1026]

By the way - welcome to Pprune :ok:

I seem to recall a thread about 2 years ago entitled "When you almost became another statistic" - it was good reading, as you could learn from people experiences. Perhaps a re-incarnation of this (searching for it was unsuccessful).

Maz ;)

[l_reason]

http://i14.photobucket.com/albums/a334/l_reason/IMG_0109.jpg

This is the part that broke, the rear fin attach spar. It broke due to stress when inspected closely by a Transport Canada metallurgist. The cause was a crack that initiated at a rivet hole witch did have signs that it had been cracked for some time but the part was not corroded in the least. What made it break on that flight I’ll never know but I’m thankful I was alone & in the area I was in. A few theories of how it was originally cracked are: someone pushed on the fin the wrong way when moving the AC, it could have been hit with some jet-blast when it was tied down (my old parking place was rather vulnerable). Myself I think it broke because its 58 years old and I fly the hell out of it doing hard turns (30-60 degree) and constant side slipping at 100mph. For the purpose of getting great photos. I work by my self shooting aerial photos of farms & rural homes(flying and holding a 2.5lb camera). I push this little plane really hard because faster I work the more money I make. Most days I’ll take around 400 photos over 3-4 hours of flying. Out of the 400 pictures I’d circle the property about ¼ of the time searching for the best angle. I put 200 hours on the Luscombe since May 05, most of witch was shooting photos. One more side note I do have the aircraft looked at every 30-40 hours when the oil is changed.

PT

[Biggles Flies Undone]

There's a report of Neil William's amazing escape here. (http://www.aerobatics.org.uk/repeats/zlin_wing_failure.htm)

[Genghis the Engineer]

Myself I think it broke because its 58 years old and I fly the hell out of it doing hard turns (30-60 degree) and constant side slipping at 100mph

I believe that the Luscombe 8E has a manoeuvre speed of 85mph, so a full rudder sideslip at 100mph will take you to about 8% below the ultimate design load on the fin and rudder - WHEN IT WAS NEW. So, even without quite using full rudder, that'd probably do it, yes.

G

[l_reason]

Genghis if the Luscombe 8E has a manoeuvring speed of 85mph & I’m almost always under gross weight, Va would be lower still. I just looked over all TEN pages of the “Owner’s Handbook” and was unable to find any such information….. (85mph) what I did find was Vne 145mph, Vno 48-112mph & stall 48mph all speeds are T.I.A.S. If you have a reliable source for more information regarding my aircraft I would be grateful for any help you could provide.
Thanks
PT

[Genghis the Engineer]

Firstly I'm not a Luscombe expert, what I do have is some expertise on the art and science of airworthiness - which I teach at a couple of universities.

Anyhow, the definitive limitations data on the 8E are in FAA Type Certificate Data Sheet No. A-694 (http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/8d006abbddeb78428525673c004dd3f3/$FILE/a-694.pdf), however this doesn't show either a stall or a manoeuvre speed.

I confess that I got the manoeuvre speed from an unapproved checklist for an 8A online (http://www.popularaviation.com/docs/Luscombe_Checklist_Sheet.pdf), however if we look at this again.

- Your stall speed is 48mph, we'll assume (as is generally the case for an aircraft of this type) that there's little difference between CAS and IAS.

- It'll have been certified in the normal category to an early version of FAR-23. This will have used a maximum g value of 3.8

- The manoeuvre speed is therefore defined as the stall speed times the square root of the g limit. So that's 48 * (3.8^0.5) = 93.5 mph - okay, a little higher than I said (and this is at MAUW).

- As you say, at lower weights, the manoeuvre speed reduces. However for present purpose this doesn't matter. The reason for this is that Va at MAUW is used for determining the strength requirements for the fin and rudder (amongst other things).

- The requirement then and now is that the "limit" (maximum load expected in service) equates to the worse of full instantaneous rudder deflection at Va or 1/3 deflection at Vne. You can assume that the load goes with the square of airspeed.

- So, if you apply full rudder at 100mph, the fin and rudder will see loads of about (100/93.5)^2 = 1.14 times the limit load. In other words, it's seeing 14% above what it was designed to take.

- It is likely that a 1.5 safety factor was applied between limit and ultimate (although some companies use 1.4 I think this is unlikely for the Luscombe). So, 1.14/1.5 = 0.76, you are actually 24% under the load at which the structure was designed to fail when it was new.


But realistically, as you've said, the aeroplane is old and couldn't possibly be expected to be as strong as it was at manufacture - due to work hardening, internal corrosion, the odd small dent and so-on. So, to be honest by routinely sideslipping above Va you are taking the fin every time to within a small (but uncertain) margin of the failure load.

The result was probably a rapidly growing fatigue crack at some point which, I'd guess, is the likely reason for your fin failure. (And from what I can see, appears consistent with your most recently posted photo).

G

[l_reason]

Thank you very much for the detailed explanation Genghis!! I will be getting my self a copy of the type certificate for my plane and look forward to learning more about my bird. Considering that I’ve seen checklists with more information then the POH I have.
As for the repairs that were done to the tail of my Luscombe We were able to order “factory new” fin & rudder, only a few of the old parts had to be used: ruder horn, light and inspection covers. I do spend a lot of time in my plane and this incident has played with the confidence I have for all aircraft. I am sure my wariness will subside in time. I do believe that if I land up as a fatality in a TSB report. The reason will be MY error or my lack of skill & knowledge to deal with a standard emergency.

Two days after the tail on my plane broke I rented a C-150 from a local flight school to get some work done. 2.3 hours into the flight I had a partial engine failure: power loss, extreme vibration and some awful noises. First thought when that happened was sh*t this will be easy. I limped it back to the airport (5nm) without even a distress call and returned it to the flight school.

Genghis thanks again for your insight
PT

[DubTrub]

Patrick:
There's quite a good Luscombe support network on the internet here (http://lists.topica.com/lists/luscombe/) .

[Genghis the Engineer]

I-reason, always a pleasure. For some perverse reason, I actually enjoy this stuff!

G

[chandlers dad]

IR,

What ever happened with this? Did TC come out with a report?

I live just North of where the new Luscombe assoc has their offices and sure is good to see people keeping the old airplanes alive. Mine has fabric on it and turns 60 years old this fall.

CD

[18greens]

Fascinating thread.

I do recall my TigerMoth instructors getting upset at sideslips above 70 or 80 mph (I can't remember the exact figure) because of the stress it put on the tail post. A tale like this makes you take it all very seriously.

Well done for getting it down.

I was also amazed to hear the Neil Williams story is almost 40 years old. The tale is recounted all the time as if it happened yesterday.