Turbo - Static MAP vs. in-flight MAP?

Discussion of the Aerovee kit engine.

Re: Turbo - Static MAP vs. in-flight MAP?

Postby SonexN76ET » Fri Apr 13, 2018 7:26 am

Noel,

Sonex has repeatedly warned not to run the engine at high power, even for a short time with the cowling off. You can burn up your engine because the heads and cylinders are not getting pressurized cooling air, regardless of what the temperature probes are indicating. Airflow is not going through the cooling fins and ports in the heads.

Jake
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Re: Turbo - Static MAP vs. in-flight MAP?

Postby XenosN42 » Fri Apr 13, 2018 10:10 am

Hi Noel,

Thanks again for the files, they were very valuable.

You will find the specifications for the MGL ‘Black Box’ data recording file at: http://kb.mglavionics.com/getAttach/194/AA-00807/MGL+EFIS+data+feed.pdf It contains the units (Fº or Cº for example) and any scaling applied.

Have fun reading that document. There is good news however. I’m currently finalizing an application that reads the ‘Black Box’ recording file and displays all the data in a very user friendly manner. Features include: graphs (CHT, EGT, RPM, pressures, airspeeds, etc.), a table showing values recorded each second, ability to change display units (this is for users that would like to see speeds in knot vs MPH, or temperatures in degrees C vs F) DVR type playback of events, and integration with Google Earth. I’ll release some marketing material in about 3 weeks, and the product will be available for purchase in about 6 weeks.

Oil pressure is expressed in BAR when exported. If you are parsing directly from the binary file it’s expressed in a 10th of a BAR (so you’ll need to divide by 10 to get the actual value).

Oil temperature is in Cº. In fact all the temperature values are in Cº.

Fuel flow is in liters/hour. If you are parsing directly from the binary file it’s expressed in a 10th of a liter/hour (so you’ll need to divide by 10 to get the actual value).

Manifold pressure is in MBAR (milli BARS). If you are parsing directly from the binary file it’s expressed in a 10th of a MBAR (so you’ll need to divide by 10 to get the actual value).

Hope that helps.

 Michael
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Re: Turbo - Static MAP vs. in-flight MAP?

Postby NWade » Fri Apr 13, 2018 2:39 pm

All -

Thanks for the info and suggestions. Let me try to respond to a few of them...

Fuel Burn: As I mentioned, I think it took a moment for the flow meter to "catch up" to my push up to WOT. I saw 27.3 Liters/Hr just as I throttled down. That relates pretty closely to the "28-30 L/hr" that Brett mentioned @ 35" of MAP (which is what I'm seeing at WOT). Furthermore, at high-idle (~1600 RPMs) I have to pull the mixture control out 3/4 to 7/8 to get max RPMs. Similarly, at 2200 - 2400 RPMs I see max RPMs at about 1/2 mixture. So I don't think I'm running TOO lean. In the past I've had the needle go too lean and heard the engine stumble and struggle when I applied throttle; but that was back when I was trying to crank down hard on the locking screw in the aeroinjector. Then I discovered that doing so pushes the needle leaner than intended (the locking screw and the needle carrier both spin as you're tensioning one against the other). Nowadays I spin the locking screw up to the needle carrier until they bump (just snug, without applying any real torque). I find it holds things in place without causing an unintended mixture change. TL;DR, I don't think I'm too lean, given the mixture adjustments I have to make at mid-throttle settings.

MAP Calibration: As I've mentioned a couple of times, with the engine off the MAP and BARO read-outs on my MGL are within 0.10" of each other, both before and after engine runs.

High Power runs: I specifically called Sonex tech support and asked them about AeroInjector tuning with the cowling on or off. Their advice was to tune per the instructions with the cowling off, for easy access. And the instructions specifically call out tuning at WOT. Obviously you want to limit the time at high throttle to a very brief period, to keep the heads from cooking. This is why I only let the engine stay at WOT for 5-15 seconds at a time before throttling back to idle, then I shut off the engine and let it rest until the CHTs are reporting under 200 degrees F (with the engine off, so no prop-blast). Furthermore, on the ground the engine is likely to see _more_ cooling air with the cowling off than with it on. This is because there's no forward airspeed to create low pressure at the cowling exits (and the root of the prop is also unlikely to create enough high-pressure flow at the intakes; but the exit is really the key here). Without that good delta in pressure between the cowling intake and outlets, you're unlikely to get proper airflow through the cowling and thus through the heads/fins at zero airspeed. Exposing the engine to the cool outside air and the prop-blast is likely to be better than creating a "heat bubble" inside the cowling with zero forward airspeed. But let me wrap up this point by reiterating that there's no way I am endorsing long engine runs or running the CHTs up to their limits while exposed to the prop-blast. I am being very conservative and trying to keep the reported CHTs under 330 degrees F and the WOT period to less than 15 seconds.

We have crappy weather in the northwest right now, but if I get a break this evening I'll add tracerline to the fuel and see if I can find any evidence of intake leaks.

Additional suggestions or ideas are appreciated, though!

--Noel

P.S. With AeroInjector settings being so variable, I hesitate to ask - but can any Turbo owner/operators tell me what AeroInjector needle they're using? I'm curious if there's a strong consensus out there...
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Re: Turbo - Static MAP vs. in-flight MAP?

Postby SonexN76ET » Fri Apr 13, 2018 3:52 pm

Noel,

You must have misunderstood Sonex on running the engine with the cowling off. Check Joe Norris's earlier post on it from about a year ago on this forum.

http://www.sonexbuilders.net/viewtopic.php?f=33&t=2465&p=18432&hilit=without+cowling#p18427

Jake
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Re: Turbo - Static MAP vs. in-flight MAP?

Postby lutorm » Fri Apr 13, 2018 5:26 pm

The linked post also says it's fine to run it briefly at WOT without the cowling.

I personally think the risk is overblown; if some part of the heads got way hotter than where the CHT probes are located, the temp reading would tend to continue climbing after you throttle back as the heads go into thermal equilibrium, but I have never seen the CHT climb more than a few degrees after throttling back to idle after a WOT run, with or without the cowling.

My experience is that you can't run it WOT on the ground for more than maybe 30s, cowling on or off, before hitting CHT redline anyway. That's barely enough for a mixture pull while allowing fuel flows and EGTs to come into equilibrium for a reading. If someone went flying without a cowling, either they must not have had CHT probes or they ignored them. That seems like a very bad idea.

One thing though: I've been covering the probes and the first half inch of their leads with RTV, so they're not directly exposed to the cool air flow. Without doing so, I suspect they will underestimate the true temperature of the head where they're screwed in. (I should test this assumption, actually...)
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Re: Turbo - Static MAP vs. in-flight MAP?

Postby daleandee » Fri Apr 13, 2018 5:53 pm

lutorm wrote:The linked post also says it's fine to run it briefly at WOT without the cowling.

I personally think the risk is overblown;


The initial break-in of Corvair engines is 30 minutes and is done on the ground using a shroud. Overheating isn't a concern. Perhaps using a shroud on the VW would allow longer ground run times. Doesn't look too difficult to construct:

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Re: Turbo - Static MAP vs. in-flight MAP?

Postby NWade » Sat Apr 14, 2018 1:18 am

SonexN76ET wrote:Noel,

You must have misunderstood Sonex on running the engine with the cowling off. Check Joe Norris's earlier post on it from about a year ago on this forum.

http://www.sonexbuilders.net/viewtopic.php?f=33&t=2465&p=18432&hilit=without+cowling#p18427

Jake


Jake -

In that quote he specifically calls out *flying* the airplane without the cowling on.

He also says

Sonerai13 wrote:Running on the ground for short periods of time without the cowling is ok. You just don't want to run it too long, and only VERY briefly at high power settings. You have to do this in order to dial in the AeroInjector, but just use your best judgement and keep it to a minimum.


--Noel
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Re: Turbo - Static MAP vs. in-flight MAP?

Postby SNX1508 » Sat Apr 14, 2018 6:17 am

I fabricated a temporary cooling shroud for running the engine on the ground. Allows for somewhat longer engine runs on the ground.

I saw a similar cooling shroud installed on the factory turbo while it was in the test cell area, here is a link to video of same -

https://www.youtube.com/watch?v=DBl4DhTUta4

And links to PIC's of my cooling shroud -

http://www.mykitlog.com/users/display_l ... 273&row=22

http://www.mykitlog.com/users/display_l ... 612&row=14

My first engine run, with shroud -

https://youtu.be/K9wP77IqoZ8

I have had more than one visitor to my hangar comment .....you can't fly with that installed !!
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Re: Turbo - Static MAP vs. in-flight MAP?

Postby DCASonex » Sat Apr 14, 2018 8:26 am

Do not know how much of this applies to Aero-Vee engines, but on Jabiru /CAMit engines, the steel cylinder walls are quite thin and steel does not conduct heat as well as aluminum with result that hot spots can develop very quickly on the cylinder walls when there is insufficient air flow over the cylinder fins even as head temperatures continue to show safely in the green. This can happen in flight as well. Scored a cylinder two years ago when during my BFR, examiner asked for full power on stall. With a 3300, it mostly just hung on prop at about 45 degree angle, and kept it there a few seconds too long.

The shroud looks like it would be a quick and easy improvement for full power ground testing, but even then would be careful and try to monitor for cylinder hot spots, particularly on under sides of cylinders, with one of the remote sensing infra-red gauges.

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Re: Turbo - Static MAP vs. in-flight MAP?

Postby lutorm » Sat Apr 14, 2018 3:29 pm

DCASonex wrote:Scored a cylinder two years ago when during my BFR, examiner asked for full power on stall.

I don't think a hot spot on the cylinder wall can cause scoring, since overheating the cylinder will only make it expand more. My understanding is that scoring can happen if you suddenly go full throttle without letting the cylinders warm up, since the aluminum piston will heat up faster, and expand more, than the cylinder thus making the piston-barrel clearance insufficient.
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