SonexBuilders.net

Hi all,
today on feb 14 www.kathrynsreport.com
follow up on an earlier accident.
carb ice?
possibly a corvair install with a MA3SPA carb?

WaiexN143NM
Michael

here is another link to the report....
.http://www.kathrynsreport.com/2019/02/s ... il-22.html
...
..
.
good day / rick

It's thankful that he wasn't injured, but the damage to the aircraft must be very painful to bear on its own.

On a side note, I noticed the report listed the following: "Certified Max Gross Wt.: 1250 lbs." For a B model, Sonex lists the gross weight with an Aerovee as 1100 lbs and with a Jabiru 3300 as 1150 lbs. I believe those gross weight limits were the same for the Legacy A model. Although there's no indication that had any bearing on the accident, it seems the builder he purchased it from took some liberty with that specification.

All builders are able to set limits per their own discretion. As you pointed out, nothing indicates this was relevant to this accident. So what are you trying to say?

GordonTurner wrote:All builders are able to set limits per their own discretion.

And at their own peril. No Sonex should be "certified" at 1250 lbs. It was not designed/stressed/tested for that. Whether a Sonex is capable of taking off and sustaining flight with such a weight is irrelevant. At 1250 lbs, running into turbulence or making a hard positive or negative G maneuver could cause the structure to fail. No matter what engine is on a Sonex, the specs call for a max aerobatic weight of 950 lbs. That's because the size of the engine has no bearing on the stresses imparted on an aircraft.

So someone "certifies" a Sonex at 1250 lbs. Now they sell it to someone who did not build the airplane and probably doesn't know all there is to know about it. They have now been set up with unrealistic expectations. He/she sees that it's "certified" for 1250 lbs and so they think they can load it up and fly off a 2,000' strip with trees at each end. Why not? It was built to carry 1250 lbs, right? He/she loads up the plane with gear and a friend for a cross country trip and runs into bad weather. Maybe a lot of unforecast turbulence, bouncing the plane around like a wet towel. But the plane can handle it, right? It was "certified" at 1250 lbs. He/she is flying along at gross weight and suddenly sees another aircraft on a collision course, so he/she banks hard and pulls back on the stick, pulling 4-5 G's. But it's OK, right, because it was "certified" at 1250 lbs.

If someone wants to "certify" their Sonex at 1250 lbs that's their business, as long as they fly solo at that weight. If they take passengers at that weight, or sell it to someone else some day at that "certified" weight then that's just negligence in my book.

This argument can go round and round. Fly smart, make your own decisions.

Gordon

Over Gross Weight

I agree with everything Mike Smith said.

To take the scenario one step further...….the "new uninformed owner" (not the builder) goes by the 1250 gross, but he's loading up the airplane to head to Airventure, Oshkosh and ends up 50 lbs. over the inflated 1250 gross...…..now he is at 1300 lbs (and probably at or past the aft cg limit)..... in and airplane that should be at 1150.

But he's not too worried because he figures he's only 50 lbs. over...….should be no problem.


This may not turn out well.......and it gives Sonex a "bad wrap".


Gordon......Hummel 2400......Onex

Over Gross...….continued

One thing I forgot to mention in my previous post...…….I live in Canada and a builder can NOT change the gross weight of the airplane he is building without "written documentation" from the designer/kit manufacturer approving the increased gross weight.

The builder would need John Monnett to issue that documentation to the builder and then that is submitted to Transport Canada for approval...…….which they may decline (at their discretion).

I suspect that John Monnett would ALSO decline.


When I sold my RV-6 twenty years ago......the new owner applied for an increased gross weight...from the standard 1600 lbs to 1700 lbs. He contacted Van's Aircraft for written documentation for the increase, Van's refused and that was the end of the story. It still flies today at the 1600 lb. limit.

Incidentally, the RV-7 has an "extruded factory spar" and the gross weight is now 1800 lbs., one of the big benifets of the RV-7 (among others).


Gordon.......Hummel 2400.....Onex

You guys have really missed the point here. This accident wasn't caused by the 1250 gross weight. He was flying solo, certainly under gross. How many Sonex have crashed because of an in-flight breakup caused by overstress due to a gross weight set above the 1150 factory recommendation? How many aircraft of any type have crashed recently because of overstress due to loading beyond gross weight? If you want to argue the performance issue, well there are a lot of situations you can be in where you are under 1150 lbs and still weigh too much for the runway length, DA, etc. I bet my 120HP Corvair, even if loaded to 1250 lbs(hypothetical as my gross is not set at 1250), needs less runway and would out climb an Aerovee powered Sonex at factory recommended gross anyhow. I'm neither recommending nor condemning a gross weight set above factory recommendations, we should all make our own decisions for our own reasons.

Now let's focus on the most probable cause of this accident, and arguably a much more dangerous situation. This was the textbook carb ice situation. Cool temperatures, moisture, low power settings in the traffic pattern. The pilot failed to apply carb heat until after the engine stopped. He then only applied partial carb heat to attempt a restart. Carb ice is dangerous guys. If using an MA3 type carb, as I suspect this Corvair powered Sonex was using, FULL carb heat should be used at ALL TIMES with reduced power settings. This is not something to forget or be lazy about. I use carb heat with reduced power settings even on the warmest, dryest day.

Here is a good article written on the dangers of carb ice, especially as applied to Corvairs: http://www.flycorvair.com/carbice.html