For those of you that do not know me, I work as a mechanical engineer, and I have spent the bulk of my post graduate 15 year engineering career in manufacturing and assembly. Most of these years were spent in an automotive manufacturing and assembly setting. I am currently working in aerospace assembly and manufacturing. Much of my personal thinking is rooted in manufacturing methodology including Six Sigma and Lean Manufacturing. Basically, this means that I believe that the “real” solution to any difficult problem is to find the real “root cause”.
One of my favorite techniques that can be used to dissect complex problems or find real customer requirements is a technique called the “5 Whys”. Here is a short explanation of the “5 Why’s” from Wikipedia:
“The 5 Whys is a question-asking method used to explore the cause/effect relationships underlying a particular problem. Ultimately, the goal of applying the 5 Whys method is to determine a root cause of a defect or problem.
The following example demonstrates the basic process:
* My car will not start. (the problem)
1. Why? – The battery is dead. (first why)
2. Why? – The alternator is not functioning. (second why)
3. Why? – The alternator belt has broken. (third why)
4. Why? – The alternator belt was well beyond its useful service life and has never been replaced. (fourth why)
5. Why? – I have not been maintaining my car according to the recommended service schedule. (fifth why, root cause)
The questioning for this example could be taken further to a sixth, seventh, or even greater level. This would be legitimate, as the “five” in 5 Whys is not gospel; rather, it is postulated that five iterations of asking why is generally sufficient to get to a root cause. The real key is to encourage the troubleshooter to avoid assumptions and logic traps and instead to trace the chain of causality in direct increments from the effect through any layers of abstraction to a root cause that still has some connection to the original problem.
The technique was originally developed by Sakichi Toyoda and was later used within Toyota Motor Corporation during the evolution of their manufacturing methodologies. It is a critical component of problem solving training delivered as part of the induction into the Toyota Production System. The architect of the Toyota Production System, Taiichi Ohno, described the “5 Whys” method as “… the basis of Toyota’s scientific approach … by repeating why five times, the nature of the problem as well as its solution becomes clear.”
After years of being faced with complex problems, processes, and designs, my brain is literally hard wired to use the “5 Whys” to examine just about anything. (Writer’s Note: Keep in mind that saying “why?” “why?” “why?” over and over can get you slapped in my face if you are talking to your wife about “why” you need to do the dishes, but I still do it on occasion). Many times this simple exercise can be quite illuminating. It is very typical that if this exercise is applied to common tasks, much of what we do every single really makes no sense or has no explanation as to “why” we do it all. Much of what we do every day is only done because “we have always done it that way”.
As a logic exercise, I would like to apply this technique to the idea of pull testing. If I were having a discussion about pull testing with a fellow stunt flier you might hear something like this:
“We need pull testing for stunt planes.”
1. Why? – The controls need to be tested to be safe
2. Why? – So the plane will not fly away and hit a spectator
3. Why? – So we do not get sued
4. Why? – Because people suing due to fly away stunt planes is a real problem.
5. Why? – Airplane control failure was a common problem before we instituted pull testing, and pull testing fixed the problem.
Nearly always, this discussion seems to go exactly the same way. The gist of the argument is that we need to pull test because we want to be “safe” so we do not “get sued” leading to a “great financial calamity” resulting in the “end our hobby/club/flying site as we know it” (which is an interestingly the inevitable conclusion to many discussions in stunt). Keep in mind the above responses would be perfectly reasonable if #4 and #5 were true in the slightest (which are not). This would be a good analysis of presumed safety requirements if you could compare pull testing, to say, seatbelts in cars. One could easily show that there was ample evidence that people were dying in car accidents in large numbers before seat belts. It was obvious that steps needed to be taken to improve the mortality rate of automobile drivers and passengers. Even if seat belts made no difference the issue was so prevalent that something needed to be tried to improve automobile passenger’s odds of surviving a car crash.
I am in no way saying that safety checks are not needed for model airplane flying. They are needed. REASONABLE AND LOGICAL safety checks and safety measures are always needed. We all need to be safe every single day, in every single way we can, when we are flying our model airplanes. For example, I think there is plenty of evidence to show that mandatory electric engine starters and remote needle valves for gas engines would be effective (although unpopular) safety measures because we DO HAVE a problem with people sticking their fingers in propellers on an ongoing basis. In fact, this happens all the time, and safety articles are constantly written about this safety issue (see the previous issue of CLW). Many times these incidents with propellers have catastrophic results including permanent injury and expense, so it would make perfect sense if someone were to make a rule to reduce the ongoing problem (see seat belts above).
However, I do not think there is any real evidence to show that testing control line model aircraft controls to nearly catastrophic levels on an ongoing basis solves anything.
As a result of this assertion, I am here to ask these questions:
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What does a pull test accomplish?
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What ongoing safety problem does a pull test remedy?
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Have we ever had an in flight control failure/causing injury safety problem?
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What was safety record for in flight control failures BEFORE pull testing?
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Are other types of model aircraft outside of control line subjecting their control systems to near catastrophic load testing before flight?
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Have these pull tests CREATED failures and safety issues where none would have existed before?
#1- What does a pull test accomplish? From what I understand (and I admit total knowledge of this subject is sketchy at best among the control line community) pull tests seek to test the control system of an airplane at loads that approach loads that are equal to “fly away-catch” levels. In other words, the pull test seeks to simulate loads that would be achieved at the handle if the airplane were to fly away in high winds and then be caught in an attempt to recover. This would result in a very high instantaneous force load. While this explanation is reaching, there really is no other explanation to the force loads required by the current AMA and FAI pull tests. They certainly do not reflect anything approaching flight loads.
The pull test requirement of 10G force load adopted by the FAI (to be adopted by the AMA in 2009) certainly does not reflect in-flight loads. For example, it would take a flight speed in the range of 100 MPH to achieve 10G’s of line tension for an average weight .60 sized stunt plane. That would equate to a 4 lbs stunt plane flying on 70’ lines flying right at a 3 second lap time to reach 10G’s. Uh…yah. That happens a lot.
2008 Pull Test and Line Size Requirements
2009 Pull Test and Line Size Requirements
For another logic experiment, I will examine my own pull test requirements and what they mean to the loads on the pilot. I personally fly .60-.76 sized engines for the most part. For the 2008 pull test requirement this equates to a pull test force of 45 lbs. Now I ask you…how many people at your last contest could even LIFT 45 lbs with their flying arm? If I brought a 45 lbs barbell to the next contest, how many people would you suppose could do one single pull up rep, much less pick it up and hold it for any time at all (7 minutes)? What do you think that number would be? 10%? 20%? If I were to throw a 45 lbs barbell up in the air, how many people could you catch it in one hand as in the case of the “fly away-catch”? Do you suppose if you had a “fly away-catch” you would be able to keep hold of the handle?
#2- What ongoing safety problem does a pull test remedy? This is a big one. As in the example of the propeller injuries mentioned before, what ongoing safety problem are we fixing? Are stunt plane “fly aways” an ongoing problem like propeller injuries? I would guess that I have seen a dozen or more serious propeller injuries in the 20 years I have been doing this hobby. There seems to be one a year in my region. Personally, my hands are full of scars. Also, I can honestly say I have NEVER seen a stunt plane “fly away” that has lead to an injury. In fact, I only know of one instance where the airplane even attempted to fly away and that was when Doug Moon let go of the handle when he hit a bird with the lines when flying his Saito 56 Furias in practice. The handle caught on the handle safety thong and went straight into the asphalt.
#3- Have we ever had an in flight control failure leading to personal injury safety problem? While some people might argue that we do not have a safety problem BECAUSE we pull test. In response to that I would simply ask what percentage of all stunt flying is done without pull testing? 95% to 99%? The truth is that for every hour of practice and sport flying we have a micro fraction of that hour of competition flying. Many competitors practice hundreds of flights for every flight they perform in competition. Again, all of this practice is done without any real safety issues to speak of. This in-flight control failure that these pull tests seek to prevent have certainly never been an ongoing safety issue outside of competition. In fact, it is nearly unheard of. In other words, we have no pull tests for practice and sport flying, yet we have no rash of safety issues for sport and practice flying. Hmmmmm…interesting.
#4- What was safety record for in flight control failures BEFORE pull testing? Does the common guy even know the answer to this question? I am not sure there are a lot of people that could tell you when we started pull testing control systems and why we did it. I guess that “fly aways” could be considered a very serious problem for a mono line speed planes (although these events require nets around the circle), and maybe there was a trickle over to stunt, which has no real safety threat.
#5- Are other types of model aircraft outside of control line subjecting their control systems to near catastrophic load testing before flight? Now, this one makes me chuckle (I hope you think it is funny too). If I were to go to the local RC field and walk up to the local RC model aircraft competitor and proceed to tell him that I was going to require that all of his control servos be load tested to 5X or 10X in-flight loads every time they flew a flight they would hit me in the mouth. Seriously!!! No one outside of control line is required to load test the controls of their aircraft. In fact, I think you would find that the entire concept would be considered ridiculous in the rest of the modeling world. Can you imagine walking up to a RC helicopter aerobatics pilot at a contest holding a big torque wrench and cranking a big test load into the rotor system? I can tell you if you do that, you might want to run! Fast!
In fact, RC Pattern Aerobatics competitors are simply required to sign a safety declaration to compete. From the AMA Rulebook for RC Aerobatics: “Safety Declaration: At all sanctioned contests, each contestant shall sign an AMA Flight Safety Declaration (perhaps as part of an entry form), attesting to the fact that he/she has previously and is now capable of confidently performing the maneuvers comprising his competitive event. Furthermore, the contestant shall also similarly declare that any and all aircraft he/she uses in said competition have been test flown at least to the extent that they have performed the same competitive maneuvers and are therefore qualified to be flown in the contest and in the presence of fellow contestants, contest officials, and all others who may be in the flight area during the competition period.”
#6- Have these pull tests CREATED failures and safety issues where none would have existed before? I am going to answer this one for myself. The answer is “Yes”. In my relatively short career I remember (at least) three planes that failed in flight shortly after experiencing pull test problems (including issues with the pull test equipment itself). So, in these cases the pull test caused the in-flight failure where none existed before. Many times pull tests can create internal control failures or issues that escape the pilot’s attention until they actually try to fly the plane and the plane crashes. I also have to wonder how many planes that exploded in air failed due to stress encountered during the pull test.
Lastly, I do know that pull tests have served to damage a lot of perfectly safe model aircraft. I am pretty sure I know of at least half a dozen model planes ruined or severely damaged by a pull test in my district recent years. I admit I have never had a failure at a pull test, lest you think I have an axe to grind, so these are not my planes.
Maybe the next time someone tells you that you need to pull test 10G’s on your hand built, hand finished, one of a kind model plane that you have 100 hours of sweat and blood into building, with another 20 hours of trimming (not to mention a hefty pile of pocket change) maybe you should stop and ask this question:
“Why”? Maybe even ask it 5 times, even if to yourself… Some other questions you might ask are: What would happen if we cut the pull test requirement in half? To a third? Anything? What if we eliminated these pull tests and changed to a waiver or a visual inspection like our RC brethren? What risk would we be taking? Are the testing requirements that we use today based on anything logical? Are we causing more problems than we are fixing?
As my friend Bill Wilson says, “It seems stupid to test a $5 set of lines with a $10,000 airplane”. So, Bill you owe me one…
