Peter wrote:
A lot of TB21 owners had lots of downtime due to turbo issues and a lack of expertise among European dealers.However, others say the turbo installation is straightforward…
It’s an older thread now, but I will answer anyway for the record.
First, I would say the turbo installation on TB21 is straight forward.
Second, on to the original subject here: I have a few pictures and Measurements from a full power climb the other day, even though I usually use a more gentle cruise climb.
So at full power and full mixture my FF was 102 Liters/hour and MP 33,5. Passing 2000 feet the highest CHT was 186 C (367 F), OAT 5 C. Close to 10000 ft highest CHT had risen to 210 C (410 F), OAT -3. The plane was lightly loaded and climbed with about 1500 ft/min all the way up with speed around 90 KIAS. (disregard the CHT 6 reading from the engine monitor – its not reading correct due to the factory installed probe).
I have found that CHT correlate to OAT quite a bit so naturally these temps would be higher had I done the same thing during summer.
So assuming the engine has been broken in I would consider the CHTs reported from placido on the high side too. To maximize engine life it makes sense to troubleshoot to get the temperature down. A nice seal of the baffles helps and easy to fix. I would get the MP adjusted as both FF and MP look too high. And verify the timing of magnetos is correct, even a few degrees early can cause high CHT.
Out of curiosity @placido since this an old thread, have the problem been solved?
placido wrote:
So I guess that nobody really touched the magneto but nevertheless I will ask the mechanic to also look at this.
THen magneto internal timing would not have changed, but magneto-to-engine timing was adjusted again when it was reinstalled on your engine. Perhaps it was checked subsequently at your annual or 100hrs inspection, but checking again is a small job and cheap insurance.
Dear all it will be a couple of weeks before my mechanic can work on the airplane so i won’t have any news short term. I will ask him to also look at timing but I don’t think this will be the issue as the magneto was not overhauled during the engine overhaul as I had replaced the magneto with a newly overhauled one just 6 months prior to the engine being overhauled. So I guess that nobody really touched the magneto but nevertheless I will ask the mechanic to also look at this.
I have talked to the overhauler on Friday and his take is to adjust the density controller so that it shows the correct values on the ground and to also close the gaps around the metal sheet that contours the engine case.
I will let you know if this will have fixed my issues. thanks to all for your valuable contributions.
tmo wrote:
You get better feedback, but admittedly possibly spend more money chasing a problem, when you change one parameter at a time.
That is a good point. If @placido has good access to his mechanic, then the feedback may be of interest, but it may take several iterations.
If not, he just needs the problem fixed in one go.In such case, I would do ignition timing, MP and FF adjustments (since FF indication seems to be good) all in one go. Maybe we will not know what fixed it, but hopefully it will be fixed or at least mitigated.
I agree with Off-Field, Timing directly affects CHT.
I can’t find it but last year an article regarding someone’s struggle with temps was written about the subject.
Maybe the overhaul is ‘smokescreening’ something straightforward as Timing.
If MP increased and FF is at the same level as it was at the lower MP, you’re running leaner. High CHT might indicate too lean. I believe the FF is set at the fuel servo, the MP between the wastegate and density controller. As Antonio wrote, it is much better to be over rich than not rich enough. I thought your MP appears to not exceed limits, so if not broken, perhaps don’t fix. You get better feedback, but admittedly possibly spend more money chasing a problem, when you change one parameter at a time.
I do have an insight avionics fuel totalizer and the fuel flow seems to be correct and it looks identical to before the overhaul. I have failed to look at TIT or EGT numbers in particular during take-off. I can surely say that TIT never exceeded its limits but I couldn’t tell you now whether the take-off TIT numbers are higher now than what they were before.
What is it that the mechanic should look at to correctly set MP/FF for take-off. It is the waste gate or the density controller or both?
Antonio wrote:
That is not necessarily representative of what should happen if things were set right, since this requires a throttle position different from WOT, and throttle position affects fuel richness.In other words: what Placido needs is correct richness at WOT, and not another throttle position, which is the standard take/off+climb regime. hence you are correct that he needs the MP setting of his wastegate to be correct, but at WOT, then he can figure whether FF is correct.
I agree Antonio. My suggestion was based on the question whether then excessive MP he gets is overboosting the engine, which by now we know it isn’t. However, if a faulty wastegate is the problem, it could help in a situation where he has to ferry the plane. I recall from planes with fixed wastegates (Seneca II, Arrow 3T) you have to set take off power manually (not WOT) in order not to overboost the engine. That was my thought process.
Antonio wrote:
And even with correct baffling (a must, yes) , a 10% excess MP/pwr will drive your CHTs away as the design cooling capacity is exceeded.
Exactly. So a power reduction at least after take off might be a temporary solution to that.
Clearly, if he is involving the overhauler as well as any maintenance, he needs to give them all the data he has, ideally the data from his analyzer. But the data he has shared here is sufficiently irregular that something must be amiss.
