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Engine quit while practicing stalls

Strappe

Member
On a clear sunny Groundhog and Super Bowl Day I went for the first test flight to set up SV-AP-Panel and AoA system.
Barometer was 27.81, OAT 54℉ on the ground, winds calm.

Equipment:
2015 RV-12
ROTAX 912ULS
Dynon Skyview Touch with 2 axis-AP
SV-Knob Panel (installed 5/2019)
Gen3 HACman mixture control (installed 7/2019)
Silent Hektik VR (installed 9/2019)
SV-AP-Panel (installed 11/2019)
AoA retrofit kit (installation finished 1/28/2020 ? required removal of wings and fuel tank.​

Scenario:
In level flight at 6500 MSL, OAT 29℉, electric fuel pump on, HACman mixture set to full rich, I lowered engine RPM to 3,000 and began first stall to calibrate AoA. With RPM at 2500, nose up steeply and near the stall, the engine RPM fell and the engine began to run roughly. I lowered the nose right at full stall, logged the stall in Skyview (of course), lowered the nose, eased throttle forward then leveled out after full recovery. Engine recovered full RPM and smooth running, but only after 30-45 seconds of roughness with nose level.​

I decided to add a second stall to the calibration. Entry to stall was similar, but of a longer duration and at full stall, RPM began to fall and in 2-3 seconds, the engine quit. By full recovery from the stall, the prop stopped. Initial attempts at using the starter failed to restart the engine. I did the usual system checks (fuel on, electric pump audibly clattering away and making good fuel pressure, all active engine monitors in the green, HACman still full rich) and began to set up an approach and landing at the paved airport less than 3 miles away. My altitude by then was over 5,000 MSL, about 3500 AGL. After several more attempts with the starter, the engine roared to life after about 3 minutes in glider mode. I re-established cruise RPM slowly and leveled off, only to have the engine quit again. This time it restarted within 10 seconds or so of running the starter.​
.
I flew back to my home airport (> 30 miles away) without further incident, did a full stall landing. The newly calibrated AoA and the stall warning agreed on the moment lift was lost. The engine ran fine during landing stall and taxi.

The electric fuel pump appears to be running fine, with good pressure at all times (although, I did not check it during the drop in RPM/rough running moments; only after stall recovery). The fuel tank was full at takeoff and I have no evidence of any leaks in the fuel system, but I have not yet removed the cowling or floor boards to do a full inspection. I completed last CI in late August and two carb floats were heavy, so I replace them with new.

I emailed Green Sky Adventures on Monday and am awaiting a reply. One local RV-12 owner with HACman installed has never noted any issues like this. Reading the install instructions and operational information (and warnings) however, engine stoppage from what they state are incorrect installations can occur. Obviously, I need to check the entire fuel system if I can't find an issue with the mixture controller. Carb floats seem always on the list of suspects. This doesn't seem like an ignition issue, however. Or does it?

I'm looking for suggestions. I do not want to fly the plane until this is resolved.
 
.......I re-established cruise RPM slowly and leveled off, only to have the engine quit again. This time it restarted within 10 seconds or so of running the starter. [/INDENT].
I flew back to my home airport (> 30 miles away) without further incident.......

What?

The engine stops twice for unknown reasons leaving you in glider mode and you left an airport a couple miles away to fly 30 miles to another airport?????

Wow........glad you had a safe return.
 
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I would've landed after the first stall and thought through how to diagnose. Glad you made it ok.
 
Is this HACman system an add-on to the existing mixture control system for a Rotax 912ULS in an RV-12 or does it replace that?

In either case, was the mixture setting appropriate for the conditions?

Aren't the 912ULS carbs altitude-compensating all by themselves? If this device is in series, wouldn't it lean the motor excessively?

Did you adjust the HACman's setting between the events? How about after the second?

Have you ever flown slow-flight at high angle of attack for a period of time with that system?

Did you make a ground nose-high fuel flow verification before flying the plane? I didn't see it in the PAP but this is a modified engine installation and it might be appropriate.

Is the tank vent system working and stock?

Can you remove the after-market modifications and return the engine to its factory-designed installation? That might be the way to go....

I haven't a clue what the issue is, but these questions came to mind. To me it sounds more like a fuel than an ignition issue, though.

Then you figure it out, please let us know.

Dave
 
Bet that got your attention. By sheer coincidence, I was also out in that same ares (assuming south of Wahoo) also doing fairly high AoA stalls in an RV-12 that day. Didn't manage to log any glider time though.

If I understand the HACman system correctly, "full rich" simply shuts off the added vent system and allows the Bing carbs to operate as if there were no added mixture control. Assuming you installed it correctly, I suppose a leak could lead to an overly lean condition -- don't suppose you noticed the EGT at the time, or have data logged from that flight? Of course there could be something wrong with one or both carbs that would cause it with or without the HACman. I'm guessing you haven't spent a lot of time flying at very low throttle settings at that altitude; I know I haven't. I wonder how much, if anything, the high AoA had to do with the engine not performing as expected.

Dave, the Bings do some altitude compensation, but they seem to always be a bit on the rich side. There is no manual mixture control, it's all "automatic" by means of a diaphragm. There is another RV-12 at our airport that's had that system installed for a few years now; the only real difference is higher EGTs and lower fuel consumption when it's leaned out from the normal non-adjusted state. They don't seem to be super common on RV-12s, but I've heard about them on other airplanes that use 912 series engines.
 
6500 feet and full rich, really?

When practicing stalls I also usually do it ?full rich? between 5,500 and 6,500 MSL (4,000 to 5,000 AGL) especially if they?re high nose up/AOA, power on stalls. Typically that?s the configuration I?d be in during initial takeoff / climbout / aerobatics and became distracted resulting in a very nose high attitude, low airspeed condition (which is what I?m simulating).

Approach / cruise (low power) stalls are practiced with and without flaps and done both at lean and rich configuration depending on how I feel that day. I monitor CHTs to ensure temps stay at or below 385 degrees (my target).
 
This thread should probably have been started in the RV-12 forum.
Then maybe more people would realize that the post was about a Rotax 912, not a Lycoming:rolleyes:
 
Also consider bad fuel especially if you are using auto fuel with alcohol. I was always careful to use my fuel in a couple of weeks but one time bad weather caused the fuel to age to close to 6 weeks. Engine did not quit but went to mostly the right cylinder bank causing loss of most power and a lot of shaking. Shut off engine when close enough to airport for a little glider time with a dead stick landing. A fuel system flush and a switch to 100LL took care of it.
 
What?

The engine stops twice for unknown reasons leaving you in glider mode and you left an airport a couple miles away to fly 30 miles to another airport?????

Wow........glad you had a safe return.

I circled at 4500 MSL for long enough to be sure. The issue only occurs when in a steep, nose-up attitude.
 
I have no idea about cause and effect, but since you just had the fuel tank out, I?d look hard at any connections that were undone.
 
6500 feet and full rich, really?

That is the setting on the HACman to shut it off and allow the carbs on the 912ULS to do its normal automatic adjustment. SOP of the HACman is to only adjust it out of full rich when in level cruise flight.
 
Bet that got your attention. By sheer coincidence, I was also out in that same ares (assuming south of Wahoo) also doing fairly high AoA stalls in an RV-12 that day. Didn't manage to log any glider time though.

If I understand the HACman system correctly, "full rich" simply shuts off the added vent system and allows the Bing carbs to operate as if there were no added mixture control. Assuming you installed it correctly, I suppose a leak could lead to an overly lean condition -- don't suppose you noticed the EGT at the time, or have data logged from that flight? Of course there could be something wrong with one or both carbs that would cause it with or without the HACman. I'm guessing you haven't spent a lot of time flying at very low throttle settings at that altitude; I know I haven't. I wonder how much, if anything, the high AoA had to do with the engine not performing as expected.

Dave, the Bings do some altitude compensation, but they seem to always be a bit on the rich side. There is no manual mixture control, it's all "automatic" by means of a diaphragm. There is another RV-12 at our airport that's had that system installed for a few years now; the only real difference is higher EGTs and lower fuel consumption when it's leaned out from the normal non-adjusted state. They don't seem to be super common on RV-12s, but I've heard about them on other airplanes that use 912 series engines.

EGT fine in cruise, and after recovery. I did not check actual temp readings during stall and engine stoppage, but they were not out of green area.
 
I have no idea about cause and effect, but since you just had the fuel tank out, I’d look hard at any connections that were undone.

I removed the access panel where fuel tank connects to fuel lines. Those are the only connections touched when removing tank. No leaks.

This was the first time I’ve done stalls after installation of HACman.

I’m mostly looking for others who may have had issues with HACman for any reason.
 
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i had a hacman on a jab 3300. the jab had an altitude compensating bing. it would ''compensate '' to 4 or 5000 feet as i remember. when the op said ''full rich'' he meant the hacman valve was closed and it was as if the system wasn't even there, the engine was operating only with what the carb was doing [leaning] . as someone else mentioned it is possible there is a leak in the hacman plumbing, that would simulate leaning with the hacman.
i never had an issue with how the hacman performed .
 
I'd pull the float bowls, and weigh your floats, first.

Then I'd switch to 100LL and Decalin and repeat tests, just to see if it's fuel related with the Mogas you are running.

You didn't mention your fuel pressure readings or your gals/hr readings when the engine quit. Try to catch that if it quits again.
 
Ignition Modules

I had experience when rough running was due to failing ignition modules. The high angle of attack could be triggering a fault on the ignition system. How many hours on the engine?
 
If I'm not mistaken, the RV-12 fuel tank is back in the baggage compartment. At a high pitch angle, doesn't that place it below the level of the carburetor? If not gravity, what pumps the fuel up to the engine? You were probably a little busy when your engine quit, but I wonder what the fuel pressure was at the time.
 
If I'm not mistaken, the RV-12 fuel tank is back in the baggage compartment. At a high pitch angle, doesn't that place it below the level of the carburetor? If not gravity, what pumps the fuel up to the engine? You were probably a little busy when your engine quit, but I wonder what the fuel pressure was at the time.

You can dump that data out of Skyview and look at it offline ...
 
"HACman mixture control " Is unique to RV12 or Rotax? Is this standard fuel system device on Rotax?

http://greenskyadventures.com/mixture-controls.html

My short research on this, I'd start by eliminating this HACman thing and do what ROTAX requires for their 912UL fuel installation. See if that fixes your issue. This looks like an aftermarket work around for mixture control by lowering FF to the float bowl. My "What The Heck", senses are kicking in.

This aftermarket accessory looks like it is more for ultra-lights. I would look into eliminating this device. If your Rotax Carb has Auto lean there is a reason for that. If it is too rich or lean, re-jet it.

PLUS all those plastic barb fittings for fuel lines in the cockpit (Gen 1 and 2 of this gizmo) .... Ahaaaaaa yeah no. If you have plastic fittings in your fuel system replace them with metal please ASAP. Their Gen 3 fuel gizmo apparently went to brass fittings and has O-rings that do not leak like their previous 2 Gens? Beauty.

Fuel mixture is controlled by separate fuel metering circuit in a Carb... fuel level in the bowl is automatically maintained. You don't starve the bowl for fuel to lean the engine.

Also it is made by "Green Sky Adventures".... No bashing but usually Sky is blue, and if your sky is green you might be inverted.... :D
 
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What?

The engine stops twice for unknown reasons leaving you in glider mode and you left an airport a couple miles away to fly 30 miles to another airport?????

Wow........glad you had a safe return.

I think after 2 events related to stalls it was pretty clear that this was related to the maneuver he was doing. The engine went back to normal afterwards. I think it was a reasonable decision. It is one of those things that you will never get everyone to agree on. We all have different thresholds of what is an acceptable level of risk. It is not impossible that something could have happened on the way home, just improbable so I don't expect my words to convince anyone else and that is fine.
 
You can dump that data out of Skyview and look at it offline ...

+1!

Pull the Dynon logs and upload them to Savvy (or any other service that allows you to look at them) assuming your Dynon is wired for engine monitoring. Setup a very simple password for your Savvy account and have your mechanic and trusted friends review the files. There should be a ton of recorded parameters and it is much easier to look at them on your couch than when flying your glider.

Good luck!
 
+1!

Setup a very simple password for your Savvy account and have your mechanic and trusted friends review the files.

You don't need to do that. Savvy let's you share specific flight data logs/graphs with others without the need to compromise security.
 
No Fuel in cockpit

"HACman mixture control " Is unique to RV12 or Rotax? Is this standard fuel system device on Rotax?

http://greenskyadventures.com/mixture-controls.html

My short research on this, I'd start by eliminating this HACman thing and do what ROTAX requires for their 912UL fuel installation. See if that fixes your issue. This looks like an aftermarket work around for mixture control by lowering FF to the float bowl. My "What The Heck", senses are kicking in.

[/B][/U]. This aftermarket accessory looks like it is more for ultra-lights. I would look into eliminating this device. If your Rotax Carb has Auto lean there is a reason for that. If it is too rich or lean, re-jet it.

PLUS all those plastic barb fittings for fuel lines in the cockpit (Gen 1 and 2 of this gizmo) .... Ahaaaaaa yeah no. If you have plastic fittings in your fuel system replace them with metal please ASAP. Their Gen 3 fuel gizmo apparently went to brass fittings and has O-rings that do not leak like their previous 2 Gens? Beauty.

Fuel mixture is controlled by separate fuel metering circuit in a Carb... fuel level in the bowl is automatically maintained. You don't starve the bowl for fuel to lean the engine.

Also it is made by "Green Sky Adventures".... No bashing but usually Sky is blue, and if your sky is green you might be inverted.... :D

The HACman valve and lines aren't plumbed to fuel lines. One line is plumbed to a manifold pressure sense port and the other is plumbed to to the float bowl vent. The device works by using manifold vacuum to lower the air pressure inside the float-bowl, thus reducing the fuel head-pressure to the main jets.

Skylor
 
The HACman valve and lines aren't plumbed to fuel lines. One line is plumbed to a manifold pressure sense port and the other is plumbed to to the float bowl vent. The device works by using manifold vacuum to lower the air pressure inside the float-bowl, thus reducing the fuel head-pressure to the main jets.

Skylor
Thank you for explaining...control the vent to lean or enrich mixture... What is
worst case failure mode? :eek: :rolleyes: It may be a perfectly fine product, but if it is an
optional device, I'd bypass it see if that helps..... Intermittent loss of power for
unknown reasons should be addressed before further flight.... be safe my friends.
 
Just a little history from a different airframe which might (or might not) be useful. The original 1984 Lancair 200 sported a Continental O-200 engine which, I have been told, didn't have a mechanical fuel pump. So Lance built in a header tank to feed the engine by gravity. Later versions like my 235 kept the header tank (most of them, anyway). Just sitting on the ground, I get 2 PSI of fuel pressure at the carburetor with the engine not running. Even in a high pitch attitude, I still have gravity fuel pressure to the engine. (I demonstrated that prior to my first flight.) I just wonder if the RV-12 has gravity fuel pressure in a nose-high attitude.
 
The RV-12 has an electric boost pump in addition to the Rotax 912ULS engine-driven mechanical fuel pump.
 
What?

The engine stops twice for unknown reasons leaving you in glider mode and you left an airport a couple miles away to fly 30 miles to another airport?????

Wow........glad you had a safe return.

Sam, that's exactly what I was thinking !!!! :eek::eek::eek:
 
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