Tecnam P2008 turbo

[SportPilot]

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[FastEddieB]

Eddie,

I looked up your citabria Accident. It seems the pilot tried to initiate a aerobatic loop from only 50 feet above the water. WOW!! The cause of accident is listed as acrobatics at to low an altitude that did not allow for recovery. They did mention being over gross as a possible contributing factor. It seems they were also concerned about the integrity of the wing attach point that broke. How old was the airplane?

With all due respect I don't see how this accident is comparable or relevant to what we are talking about here.

I mentioned it largely so some might see where overweight conditions can lead, and perhaps why my view on the subject is rather black and white.

I think it was a 1966 or 1967 model. So it was about 30 years old. It was in very good overall mechanical condition.

They did not think anything "broke", but that hardware was missing. Hardware that was there at the annual just a few hours prior. It was suspicious enough that it was turned over to Broward Homicide, but I never heard anything further.

As far as all the contributing causes, its the old "links in the chain" analogy. Possible that no item on that list would have resulted in a fatal all by itself. Put them all together and it spells tragedy.

[SportPilot]

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[drseti]

The 1,320 pound number was pulled out of thin air.

No, that is not the case. There are good, solid engineering and safety reasons for that limit. I will endeavor to explain them, but first, a bit of background:

My PhD (from University of California, Berkeley, arguably the world's second best engineering school) was in air transportation engineering. My research specialty for the past 36 years has been GA safety. I've done a lot of number crunching over that time-span. So, I think I'm qualified to address the safety implications of this spec.

Kinetic energy (a certain amount of which must be achieved for takeoff, and dissipated in landing) is a function of mass, and of velocity squared. In a takeoff or landing accident (the most frequent kind in LSAs), some fraction of that kinetic energy will be absorbed by the occupants of the aircraft. The higher the kinetic energy absorbed, the higher the likelihood of the human body sustaining fatal injuries. So, anything we can do to minimize kinetic energy will improve chances for survival.

From the basic equation KE = 1/2 m v^2, we can calculate that at 1320 pounds weight (600 kg of mass), at a stall speed of 45 knots (23.1 meters/sec -- the speed at which LSA takeoff or landing accidents are likely to occur), we have 160 kiloJoules of energy to dissipate. Let's arbitrarily say that the human occupants will experience half of that KE in deceleration - 80 kJ. Probably survivable with minor injuries.

Now, let's increase weight. KE will of course increase once due to the increase in m -- that's Strike One. But wait, there's more! Because stall speed increases with weight, KE goes up some more -- Strike Two. And, since KE varies with speed squared , it goes up again -- Strike Three!

Let's try plugging in some actual numbers. Load up your Tecnam to the European limit of 1600 pounds (727 kg). That 1.2 increase in load factor raises stall speed roughly 10%, to 50 kts. Plugging 50 kts (25.7 m/s) into our KE equation, we see that the kinetic energy to be dissipated in a takeoff or landing accident goes up 50%, to 240 kJ. In other words, the probability of fatalities goes up (roughly by the same 50%).

Perhaps you consider a 50% increase in fatalities negligible, but I do not. No, the weight limit was not arbitrary, it was established purely in the interest of accident survivability.

That said, I will be the first to say that FAA and ASTM have done a terrible job explaining the rationale behind their limits, which only perpetuates the perception that the LSA limits were pulled out of thin air. So, JetCat, I can't really blame you for your post...

[drseti]

Is it safe to fly a plane under the manufacturer's certified maximum weight?

I think you meant "Is it safe to fly a plane over the manufacturer's certified maximum weight?"

My answer is that it depends. If you are planning to run off the end of the runway, and you're concerned about survivability, I would say it's less safe than remaining within the required envelope. In such an accident, lighter is always safer than heavier (unless, of course, the extra weight was all due to the presence of airbags and crumple zones).

[3Dreaming]

Sure the same airframe and engine in Europe is certified to a higher max weight and the 'airplane can take it' but its not legal. Or safe.

Serious question. If the P2008 is certified with a higher max weight in Europe, and you bring that same exact plane to the US, wouldn't the plane be safe to the approved specs, just not legal?

Some food for thought. If the plane has been flying in Europe with the higher gross weight it could not be brought here and registered as a SLSA. The fact is if the airplane has been registered here or in a foreign country at a higher gross weight it can never be a light sport aircraft.

The fact that the model of aircraft has been tested to a higher weight should give an added level in the structure of the aircraft. However the simple fact remains that the SLSA version is only approved to 1320 pounds gross weight as a land airplane, and was never approved at a higher weight.

[Mark Gregor]

3Dreaming,

This is incorrect. The rule is individual aircraft specific. Not model specific.


Mark

[Mark Gregor]

Paul,

I do not doubt your math. But I am wondering if this has played out in real life.

For example we know the Cessna 150/2 fleet is fairly large and is close to the weight given in your example. They have been flying for a long time. I am not aware of any statistical increase in fatal accidents once this weight is reached.

Mark

[Cluemeister]

Perhaps you consider a 50% increase in fatalities negligible, but I do not.

If we are going to suggest that those of us on this side of the weight debate don't care about increased fatalities, let's take a look at hard numbers, not just math formulas.

I'm sure you'll agree that a plane and its likelihood to be involved in a fatal accident is much more than weight, as the 10 year FAA report shows. And looking at that data reveals a disparity with low versus high wing. But I am being dismissed out of hand for my data analysis.

Paul, I will respectfully steal your quote with my alteration.

Perhaps you consider a 900% greater death rate in the top four selling low wing LSA versus high wing LSA in a ten year period negligible, but I do not.

Perhaps you consider a 200% greater accident rate in the top four selling low wing LSA versus high wing LSA in a ten year period negligible, but I do not.

[Merlinspop]

Perhaps you consider a 900% greater death rate in the top four selling low wing LSA versus high wing LSA in a ten year period negligible, but I do not.

Perhaps you consider a 200% greater accident rate in the top four selling low wing LSA versus high wing LSA in a ten year period negligible, but I do not.

Then enjoy the heck out of your CT or P92 and don't look back! As I said in the other thread, it's all good.

For me, not having flown a large number of types, I can say that the couple hours or so flying a Carbon a Cub were the most pure fun I've had in an airplane. Were I in a position to buy one, I most certainly would. (A blue one). If I need to actually go anywhere in a hurry, the airlines seem to have figured that out well enough for me.

[drseti]

Mark, I haven't researched the 150/152 accident database, but I'm sure somebody has. The fields in the NTSB reports to study are phase of flight, and numbers of fatalities, injuries (serious), and injuries (minor). I contend that the heavier the aircraft (at the time of the accident, not max gross), the more serious the injuries likely to be sustained in TOL accidents. I leave it to my graduate students to do the research.

[drseti]

Cluemeister, I certainly do not consider the accident and fatality rates you cite to be negligible, and agree that the low wing / high wing question is a valid one, worthy of further study. Just remember that correlation does not necessarily equate to causality.

[SportPilot]

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[3Dreaming]

3Dreaming,

This is incorrect. The rule is individual aircraft specific. Not model specific.


Mark

Mark,

Approved is a synonym of certified. Since certification goes to the individual airplane I stand by my statement. Regardless of what gross weight other models of the airplane have been certified to, the SLSA version can not be certified at a higher gross weight and still be a SLSA.

[drseti]

Another potential issue with low wing planes I just thought about is the greater possibility of a wing tip touching the runway in a very strong crosswind.

Very valid. In fact, that happened to my first SportStar (before I owned it). The result was a non-structural scrape on the bottom of one of the wingtips. I could have repainted it, but chose not to, because it provided an opening for a lesson about when to slip and when to crab on final.

They are also more likely to hit a runway light or fence post, etc.

Also very valid. In fact, a couple of of the incidents I cited on the thread about the 10 year accident history were exactly of this type.

Personally, I don't have a preference. I have owned both and have lots of hours in both.

So have I, and for myself, I have no strong preference. For a primary trainer, a hidden advantage of low wing is that it exaggerates ground effect. This would be a negative in personal flying, because it makes the plane more likely to float just over the runway. In fact, for training, it forces the student to confront the importance of approaching with a stabilized airspeed (nailed to one particular value), so in that sense it's a benefit.