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  #1  
Old 02-05-2020, 01:07 PM
Strappe Strappe is offline
 
Join Date: Jul 2017
Location: Omaha, NE
Posts: 42
Default Engine quit while practicing stalls

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.
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  #2  
Old 02-05-2020, 01:42 PM
rsr3 rsr3 is offline
 
Join Date: Feb 2018
Location: -
Posts: 79
Default

How hard are you pushing on the recovery? Enough for negative g?
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  #3  
Old 02-05-2020, 02:11 PM
Sam Buchanan's Avatar
Sam Buchanan Sam Buchanan is offline
been here awhile
 
Join Date: Dec 2004
Location: North Alabama
Posts: 4,466
Default

Quote:
Originally Posted by Strappe View Post
.......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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Last edited by Sam Buchanan : 02-05-2020 at 02:47 PM.
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  #4  
Old 02-05-2020, 02:37 PM
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tomkk tomkk is offline
 
Join Date: Apr 2014
Location: Port Orange, Fl
Posts: 931
Default

How much fuel did you have in the tank?
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RV-12 N121TK ELSA #120845; first flight 06/10/2015; 700 hrs as of 02/2020
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  #5  
Old 02-05-2020, 02:47 PM
slngsht slngsht is offline
 
Join Date: May 2016
Location: Purcellville, VA
Posts: 286
Default

I would've landed after the first stall and thought through how to diagnose. Glad you made it ok.
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  #6  
Old 02-05-2020, 03:27 PM
David Paule David Paule is online now
 
Join Date: Dec 2009
Location: Boulder, CO
Posts: 5,070
Default

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
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  #7  
Old 02-05-2020, 03:47 PM
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DaleB DaleB is offline
 
Join Date: Sep 2012
Location: Omaha, NE (KMLE)
Posts: 2,331
Default

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.
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Omaha, NE
RV-12 # 222 N980KM "Screamin' Canary" (bought flying)
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Previous RV-7 project (sold)
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  #8  
Old 02-05-2020, 04:52 PM
Sue Sue is offline
 
Join Date: Nov 2012
Location: Ok
Posts: 99
Default Stall

6500 feet and full rich, really?
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  #9  
Old 02-05-2020, 05:38 PM
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Tankerpilot75 Tankerpilot75 is offline
 
Join Date: Jan 2015
Location: Oklahoma City, OK
Posts: 683
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Quote:
Originally Posted by Sue View Post
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).
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Superior XPIO-360, Hartzel CS prop, Dual GRT Horizon EX with ARINC, EIS, Garmin 340, 335 w/WAAS gps, Dual 430s (non-WAAS), TruTrak 385 A/P with auto-level & auto-trim, Tosten 6 button Military Grips, FlightBox wired to EX, Dynon D10A w/battery backup, 406 MHz ELT. Custom Interior, New TS Flightline hoses, Great POH!
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  #10  
Old 02-05-2020, 06:20 PM
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rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,665
Default

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
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