Turbo - Static MAP vs. in-flight MAP?

[NWade]

Another Update:

Sonex shipped me a new wastegate actuator, free of charge, to test with. Upon installing it today I noticed that the spring is slightly stiffer than the previous unit.

However, I performed an engine test and found that again the MAP plateaued before reaching WOT. This time it hit 36.8" - an improvement of about 1" over the old system, but definitely not where it should be.

After the engine run I recorded this video of me wiggling the wastegate. Anyone spot anything obviously wrong or problematic? I'm running out of ideas here!
https://flic.kr/p/GTmnsF

Thanks,

--Noel

[NWade]

Another update in this saga:

The only reason I could think of for why the wastegate actuator would open below the level I was seeing on my MAP sensor (having already cross-checked it with a mechanical gauge) was that there is an air leak happening somewhere in the turbo or the intake tubing between the turbo and the manifold where the threaded port is for the MAP tubing. In such a situation, higher-pressure air would go through the air-balance line than what I was seeing at the MAP sensor (with the leak causing a loss of pressure in-between the two measurement points).

So I cut the air-balance line and spliced in a "T" fitting. I then mounted the mechanical boost gauge to the "T" fitting and performed an engine run.

https://flic.kr/p/23V3oSS
https://flic.kr/p/25iigtD
https://flic.kr/p/25iifQz

I *did* see moderately different boost/PSI readings between the air-balance line and the MAP sensor at idle (when the system is under pretty heavy vacuum). But at mid-range and high throttle settings I saw very little difference.

Nearing WOT, the MAP sensor topped out at 36.8" while the mechanical gauge (on the air-balance line) topped at 4 PSI, then I believe the wastegate opened up as the engine showed its typical minor drop in MAP reading and all gauges and readings plateaued over the final movement range of the throttle lever.

Converting 4 PSI to "HG, we find that's the equivalent of about 38" of manifold pressure. So the air-balance line _does_ show slightly more pressure than the MAP sensor, but still well below the ~44" that others claim their turbo units spool up to before the wastegate actuates (i.e. the equivalent of 6-7 PSI of boost).

So I'm pretty well stumped at this point! :-(

--Noel

[thomas]

Hi Noel,

Are you able to observe (e.g. video camera) the waste gate arm during full power? Given its orientation, could there be any torsional vibrations at WOT that would induce the mass of the actuator linkage to unseat the waste gate? I know it's a long shot but I'm always amazed at how slight changes in the stiffness of motor mounts or different propellors or even the mounting of a 2-blade propellor relative to TDC can make a difference in resonance patterns.

I have a complete Aerovee Turbo kit sitting in my office while I decide whether to build it or cut my losses and sell it. Thanks for all you've shared on these threads - it's been invaluable info to me!

Paul

[John keith]

Hi Noel,
Not sure if you have fixed this problem yet that your having with low turbo boost but I had the same problem. How I fixed it was to take apart the waste gate actuater and place a washer underneath the spring so that it would take more pressure on the diaphragm pushing against the spring. I had tried everything, adjusting aero injector, putting larger air filter etc... to get 40" MAP all along it was nothing more than a weak actuater spring. Now when I go to full throttle it goes to 38-39" and stays, witch is close enough.

Sonex 1709
Aerovee Turbo

[marsolgp]

Noel,

Sounds like you've already found the problem..... (wiring waste gate shut) just increase preload on waste gate actuator arm, 1/2 turn at a time. As stated earlier, the boost is actually controlled by the throttle/pilot, waste gate just offers "back-up" protection. This worked on mine.

[John keith]

G.Marsolais,

Thanks for posting, don't know why I didn't think of that. Ya that's a lot better way of adjusting then what I suggested. Guess that's why we have a forum.

[lutorm]

It's worth noting that having to close the throttle to avoid overboosting, so the turbo compressor is working against a partially closed throttle, increases pumping losses. I don't know if it's even noticeable on fuel consumption, but it is a source of inefficiency, so it seems optimal to have the wastegate preload adjusted such that you basically hit max MAP at full throttle.

[marsolgp]

lutorm, you are right. But this system isn't as sophisticated as some. I believe that this turbo will produce the 40" way before throttle is full open AND the spring in the waste gate controller is the lightest one made by the maker of the controller. It actually starts opening at about 44". So in reality if you don't control boost with the throttle you could possibly do some damage to the engine.

As an experiment, early on in my installation, I installed a 'helper spring' and collar on the outside of the controller to assist the controller in opening closer to the 40" max recommended and I installed a stop bolt on the throttle quadrant and adjusted it so I can just slam throttle full forward, the combination of the stop and 'helper spring' I never see more that 41". you've gotta love an EXPERIMENTAL.

[NWade]

All -

So I got a new job and that's kept me away from the Sonex for a bit. To answer questions / fill people in on the latest:

• Adjusting the pre-load on the actuator arm never solved my problem - even with the arm as short as possible. That led me to think that perhaps the actuator spring was too light.
• So Sonex/AeroVee shipped me a replacement actuator to test with. Sadly, it had almost no effect; max MAP was only increased by ~0.5" to 1" (about 38.5" at best)
• Based on photos and exchanges with Tech Support, they believe that the problem may be that the wastegate actuator sits at an angle to the wastegate lever (on the turbo itself).
• Tech Support showed me a photo of a turbo they had on one of their factory aircraft, where they'd bent the wastegate lever (on the turbo) in order to resolve this angle mismatch.
• I am being instructed to try to bend the wastegate lever, or mod my actuator mount, in order to eliminate the angle between those components.

I don't like the idea of *bending* part of the turbo, but my new job has left me with little free time to try to fabricate a new wastegate actuator mount. And with the main part of glider/soaring season happening, I will be out of town over the next month at various contests in the Western US (either volunteering as an organizer, or competing in them).

I'll update this thread again when I've had a chance to work on the bird some more... :-/

--Noel

[NWade]

Just a quick update on this saga:

Changing the wastegate lever made no difference, so I partially disassembled the turbo and made a video of me poking around and moving the various parts. Sonex tech support didn't identify anything obviously wrong; but they shared it with the turbo manufacturer, who reportedly spotted some kind of "machining error".

Just before Airventure I shipped the turbo back to Sonex at their request. They forwarded it on to the turbo manufacturer who did some cleanup and re-machining around the wastegate area, and put in a new wastegate cover & lever-arm. I can't see exactly what they may have done to make the situation better; but we'll see when I run it up!

I got the unit back a few weeks ago, but decided to delay installing it until I'd worked out how to set up the whole turbo cooling system on my (crowded) Sonex firewall (with a big oil breather can & MGL RDAC blocking most of the space that could've accommodated the radiator & catch-can. I finally got everything reassembled and buttoned up tonight, but while working out where to install the catch-can I broke one of the tubes and will need to get someone to weld it back on... D'oh!

With any luck, she'll fly before the end of the year - but its becoming quite a slog to get this bird wrapped up!

--Noel
Sonex #1339