accident sonex N610DJ

[N190YX]

Reading this thread to this point I would like to offer two thoughts:
1. Remember Bob Hoover's adage, "fly the airplane as far into the crash as you can" and what this means is if you loose control of the airplane (stall, spin, etc.) while still in the air you become a passenger with likely much worse results. You cannot defy the laws of physics and extend a glide by pulling back and stalling, you must instead gently turn to the best of what may be no very good options.
2. Pre stall buffet in low wing airplanes is generally caused by disturbed air from the wing hitting the horizontal tail surfaces. In Vee Tail (and Y Tail) airplanes (Waiex and Bonanza) much of the tail surfaces are above this disturbed air, so not so much (if any in some configurations) pre stall buffet is experienced in these airplanes. For example, my conventional tail Debonair gives a tremendous buffet and shake prior to an actual stall, while the same airplane (Bonanza) with the Vee Tail gives very little pre-stall buffet.

[Rynoth]

Does this mean that the Sonex design does not provide an inherent stall buffet to warn of impending stalls?

2. Pre stall buffet in low wing airplanes is generally caused by disturbed air from the wing hitting the horizontal tail surfaces. In Vee Tail (and Y Tail) airplanes (Waiex and Bonanza) much of the tail surfaces are above this disturbed air, so not so much (if any in some configurations) pre stall buffet is experienced in these airplanes.

Inserting my personal experience here... I have a Waiex and the buffet is very pronounced. I've practiced power on/off and accelerated/turning flaps up/down stalls. The cues (buffeting, noise) are definitely there before the stall breaks.

https://youtu.be/7aVS91ogf1c

[GraemeSmith]

it would necessitate that nearly every flight would be a practice flight and that's not a realistic expectation.

I respectfully differ.

EVERY flight - you should be trying to better the last time you flew. Better at staying on altitude and heading, Thinking through "what if" at take off. Practice to fly better than your current rating and to the standards of the next rating. On the limit of a glide to the airport and if the pattern is quiet - simulate engine out and see if you CAN do it. Aim to spot land EVERY time (doesn't mean you will do it - but try). After landing - go do two more to sort out why you didn't hit the spot the first time - it doesn't take long. If there is a split between runways and either could be used - obviously you take the more head to wind one. Now for your other two landings - take the less favored one and get your crosswind game up - if it doesn't work out - go-around and go back to the other runway. On a longish leg - cover up the GPS answer and map read to see where you are. Anytime you think - "I really need to practice...." and don't - change your outlook and DO!

And you can still meet up with your friends for breakfast as planned (or whatever else you were doing that day).

YMMV :-)

[fastj22]

I have had an engine out during climb out. About 500 ft AGL turning to crosswind at 100mph due to a Rotec carb issue. I had a LRI (Lift Reserve Indicator). I immediately flew the LRI to return to the airport. I came up short and landed about 100 yards into a frozen field short of the runway. But I didn't spin it in. I flew the LRI. It was a bumpy landing, trashed my wheel pants and bent my gear. I think the LRI saved my butt. This was before I got my glider rating. I still fly the LRI close to the ground. Had I not had the LRI, I probably would have tried to extend it and spun in.

Now that I have 100 hours in gliders, dead sticks become your normal flight. Waiex just have a real aggressive glide slope. No need for spoilers. But in the glider we know approach speeds, don't go below, be very careful of keeping it coordinated in the turns, no skids, inside rudder is death. If you come in fast in a glider you will bounce and float and all the other glider pilots will mock you. In a Sonex, you come in fast, you stick the landing and roll to the taxi way.

[sonex1374]

[snip]... my suggestion of utilizing an audible AoA, which provides a warning considerably above stall speed ... [snip]

Art and I both fly with Dynon Skyview systems, and the way the Skyview does AoA warning is with an colored bar-graph displayed on the screen as well as an audible warning to your headset. The audible warning is a beeping that gets faster as the AoA gets higher, until the beeping becomes a continuous tone at the stalling AoA. I've come to really like this approach.

Early on I asked Dynon to give us the option of installing a remote display head that we could mount on the glareshield like some of the competitors use in their AoA systems. I reasoned that getting it into the pilot's line of sight would make it easier to reference and more useful. I still think this may be the case if you want to fly a specific AoA for approach, as training your eyes to go right to the on-screen bar-graph can be tricky. However, I'm now firmly convinced that the audible beeping is superior as a "stall warning" to any visual display. The beeping has a way of grabbing your attention and letting you know in no uncertain terms that you're getting close to the stall, and the rate of beeps gives you finer understanding of exactly where you are AoA-wise (like the position of the needle on an LRI gauge).

After several years of experience I can say share my conclusions. Multiple separate and redundant paths for information is a good thing. Whether it's a Dynon AoA tone, or an analogue LRI gauge, something that *supplements* all the other information is a good thing, and adds additional margin to our flying. However, as always, we benefit from regular practice on perceiving these discrete stimulus - airspeed indication, stick back-pressure, pitch attitude over the nose, sound of the wind rushing by the canopy, aerodynamic buffet/shudder, and discrete AoA indication/warning. The key thing is to train yourself to be "tuned-in" to what's happening. I practice this regularly, and even though I make it a point to pay attention I truly enjoy having the Dynon audible AoA feature. It's a wonderful addition to your bag of tricks, and I highly recommend it.

Jeff

[JCollinet]

Just my two cents based on a serious problem my aerovee had when I first acquired it...and one I KNOW others have had. First several flights in my second hand Onex (090) I had multiple engine shut downs shortly after landing due to vapor issues. A couple while taxiing back to the hangar or from the pumps, but one immediately after landing right on the runway. Not cool. (Literally)

I pulled the airplane from service and started seriously scrutinizing the location of the fuel system relative to the exhaust and the amount of airflow under the cowl. The stock exhaust runs WAY too close to the fuel system (absurdly close in my aircraft) and there is simply not enough airflow I under the cowling to cool things at low speed. Consequently when slowing down in the pattern the airflow drops even more, the temps go up, and the fuel vaporizes.

My solution was to chop the exhaust and move it to a completely different location, far from the fuel system. I wrapped the fuel system with ceramic mat and foil. I opened up the lower cowling to allow airflow. The problem is solved. 98 degree weather no vaporization ever. Hot starts just fine. Hasn’t even thought about shutting down.

Before those mods I was terrified I was going to end my life on short final.

I posted videos of all this on YouTube. https://youtu.be/187jbCLdEoQ

[9GT]

Just my two cents based on a serious problem my aerovee had when I first acquired it...and one I KNOW others have had. First several flights in my second hand Onex (090) I had multiple engine shut downs shortly after landing due to vapor issues. A couple while taxiing back to the hangar or from the pumps, but one immediately after landing right on the runway. Not cool. (Literally)

I pulled the airplane from service and started seriously scrutinizing the location of the fuel system relative to the exhaust and the amount of airflow under the cowl. The stock exhaust runs WAY too close to the fuel system (absurdly close in my aircraft) and there is simply not enough airflow I under the cowling to cool things at low speed. Consequently when slowing down in the pattern the airflow drops even more, the temps go up, and the fuel vaporizes.

My solution was to chop the exhaust and move it to a completely different location, far from the fuel system. I wrapped the fuel system with ceramic mat and foil. I opened up the lower cowling to allow airflow. The problem is solved. 98 degree weather no vaporization ever. Hot starts just fine. Hasn’t even thought about shutting down.

Before those mods I was terrified I was going to end my life on short final.

I posted videos of all this on YouTube. https://youtu.be/187jbCLdEoQ

What kind of fuel are you running in your Sonex?

[GraemeSmith]

I think there are two completely different issues.

1. The vaporization issue. Well documented and lots of solutions with fire sleeving and insulating and keeping fuel lines cooler. Lots of posts about this.

2. A heat rise on landing issue. As you land and slow - there is a sudden heat rise inside the cowl as the cooling air FLOW goes away. And the air suddenly gets very hot - which makes it a lot less dense. So the carburetor is suddenly going to be starved of air and very rich in the remaining hot air. Proof of this would be to lean aggressively as you land and see if that keeps the engine running. This is why I introduced a NACA vent in the underside of the cowl and directed the air at the air filter. My stumbles on landing went away.

The problem is that they have opposite "cures". The first needs you to get fuel into the lines and to the carb. Full Rich. Get fuel there.

But the second requires you lean dramatically to get the mixture to match the the less dense air. Which is the complete opposite of "Go rich prior to landing for a go around if needed".

--

I wonder how many unexplained power losses have been because the engine was stumbling in a too rich environment?

[Pizza Boy]

Where one may be surprised, again only speaking from the experience of operating my airplane, is a relatively (compared to say a C-152 or Warrior ect.) high sink rate that develops about 15-20 mph above the stall speed.

Generally, in most airplanes we approach at 130% of the stall speed and bleed that extra 30% of speed during the flare to carry us safely to one inch off the ground at the stall speed (ideally). This value may not be applicable to your airplane.

I've found that if I use 1.3 X Vs, then excess power is almost always required to maintain my desired glidepath. Therefore, I have developed the following technique from experience.

My trick is to bug a speed on my EFIS airspeed indicator that I call the "minimum flare speed". It's a speed that is in essence the beginning of the "sink" range and guarantees adequate pitch control through touchdown. I will not mention that speed here because it will be different for every airplane because of many variables. You can find this speed by entering the flare at different speeds until no power is required to correct a mushy, sinking touchdown. I figure that if I ever have to perform an unscheduled power-off landing, I will use this speed as a safe maneuvering target. In fact, I use it on every landing. I don't look at any particular number on final but rather my margin above my "target" speed. Ideally, I'll be at 10 feet AGL at idle power on my target speed. Any faster and I'll needlessly float, any slower and the elevator authority will be too mushy.

Thank you for this excellent post. I was trained in a C150 and am considering a Sonex kit.

Ive read about the high sink rate at lower speeds of short-winged aircraft such as Vans and Sonex.

I think best stall speeds are something like:

40 mph Sonex
49 mph C150 (for reference)
55 mph RV6

Obviously the lower the number, the better. But should I not consider this an apt comparison?

The lower the stall the better, because this theoretically lowers the groundspeed during an engine-out off-airport touchdown. But with the high drag condition of the Vans/Sonex at the lower airspeeds, I wonder if perhaps it would necessitate a more rapid and difficult flare/rotation to arrest the sink rate and reduce groundspeed right at touchdown. Or maybe not, maybe the touchdown flare requires more skill to achieve absolute minimum landing speed, but it's not really a big deal.

But then I read your comment about actual loss of elevator authority in the high sink rate condition right above stall. And maybe it's not even possible to arrest the sink rate, thus slamming the landing gear when using 40 mph as a touchdown speed.

Maybe I shouldn't think of the sonex as having a 9 mph advantage over the C150, in terms of absolute minimum landing speed. Maybe a more fair assumption would be like 4 or 5 mph.

Perhaps when we see these stall speeds for Sonex, RV6 etc, we need to understand the data isn't the same thing as the stall speed for the C150 that we're used to?

[Bryan Cotton]

Any airplane besides a 150 will require some transition training or experience to be safe. And for analysis stall speed is just one metric. I'm not at stall speed until I'm practically on the ground. To be at stall speed in anything while still at 20+ feet is asking for trouble.

What I'll say is where you can float for a long time in a 150 from being a bit fast close to the ground is different in a Sonex (my perception). It doesn't take as long to chew up airspeed in the flare.

I would make the RV6/Sonex/whatever decision based on your likes, mission and budget. They all land fine.

Welcome to the forum!