That is fairly normal low level cruise. 23" 2400rpm 11.5usg/hr gives me 138-140kt. To get 143, maybe 11.8usg/hr.
I know of two much older TB20s which have newly re-done engines and do the same.
What does yours do?
What does yours do?
I'm not sure for the exact setting - I guess few knots less. I'll check next time I fly and post.
As I promised, I checked few combinations during last few days:
- 2300/22, 8000ft, IAS 125, TAS 142, 42 lph (peak EGT)
- 2400/21, 8000ft, IAS 126, TAS 143, 42 lph (peak EGT)
- 2400/21, 8000ft, IAS 128, TAS 146, 47 lph (ROP)
- 2400/22.5, 3000ft, IAS 135, 52 lph (ROP)
- 2300/23, 3000 ft, IAS 130, 43 lph (Peak EGT)
[edited to tabulate the results - use 2 spaces at the end of each line to achieve a line break]
Taking just your last line, I would be doing 138kt, and so would be two other TB20s I know about.
There is something not right. 130kt v 138kt is a huge loss of power - of the order of 10%. I might suggest that you
Isn't the most likely reason (if the ASI is not at fault) a rigging issue? A control surface not adjusted correctly? Such small aerodynamic issues can have a huge impact. If I open the cowl flaps of my TR182 during cruise, I lose about 3 knots.
Engines very rarely do not produce rated power. Even a rotten engine with 20/80 compression usually makes its BHP.
I agree.
Maybe the landing gear is not retracting fully. That would make a big difference.
I do think mag timing could screw things up sufficiently...
Could also be massive damage to the camshaft. In this case there was 40% missing off the camshaft lobes, resulting in an approx 10% power loss. So, cut open and check oil filter (use a different shop to the one which normally does it, because some shops pretend to do it but don't) and do oil analysis. Unfortunately I don't think one can view the camshaft (not even with an endoscope) at all without pulling at least one cylinder.
•check the ASI (3 x GPS GS method)
•check fuel flow is accurate (you have a totaliser?)•if that is all OK, check the mag timing
Maybe the landing gear is not retracting fully.
I checked ASI few times and I get results consistent with IAS/TAS.
I have the same figures at analog fuel flow and totaliser and what fuel is left on board after flight is consistent with the number shown by totaliser within 2-3 liters. New magneto on new engine (bellow 200 hrs) - I don't think this is an issue but if you think it's worth of checking I'll do that. What should I tell to mechanic to do? I saw landing gear fully retracted while aircraft was on the jacks. The only difference I see is airframe TKS but I don't know if this can produce so much difference in airspeed.
Your TKS option will not make the airplane faster, that's for sure. As to whether that is expected to cause a penalty of 8 knots, I highly doubt.
Rigging is something the mechanic should be familiar with. Best to find a shop that knows how to do this on a TB20 and fly there. The maintenance manual will contain a lot of information about how exactly the control surfaces should be positioned or how the landing gear should retract.
I doubt it's your engine. If the magnetos are not adjusted correctly, you would also see different CHT/EGT values than expected. Do you see book takeoff roll numbers?
Another test you could perform to see if it's a rigging issue: put the aircraft in glide at the speed for best gild and check if you get the rate of descent given in the POH. Incorrect rigging should produce a higher than normal rate of descend (more drag).
I did a quick search of the Socata owner site. I suspect it is an FAQ but I could not see anything clear on a performance loss due to full TKS... maybe 3kt.
I would check the magneto timing. This is nothing to do with the mag itself which can be brand new. The timing is done by rotating the magneto in its mounting hole. It's a really basic aviation maintenance procedure. Then I would check for metal.
Rigging... yes sure. Make sure the flaps are all the way up during flight. Not even a 1mm gap. But my experience (having suffered bad rigging) is that this won't take 8kt off.
could it be the tachometer (RPM) ? engine turning slower than indicated - your mechanic could easily check it with a strobe.
