True Air Speed?

[Northern Mooniac]

I have an 81 M20K. New to me with about 20-30 hours on it so far, so still trying to figure it out.

The plane has TKS, merlyn waste gate, intercooler and gami injectors.

My aspen will usually show a true airspeed speed of 155-160kts between 9000 and 12,500. Is this pretty normal or am I missing a bit of speed?

I also find that I'm burning 14-16gph.

still playing around with settings but doing about 33.4 and 2400rpm at 10500 on the way home from Oshkosh gave me about 160kts true.

Temps at 10500 were about 13 degrees so my middle cylinders were running at about 390, could have probably opened up the cowl flaps a bit.

Does this sound like normal operation?

I did also recently put in new baffles from bee gee and they seem to be working much better, however on climb i go back to 36" and 2600 rpm and I can usually do about 500-700fpm and keep my #1 cylinder under 400 degrees.

 

any tips are appreciated!

[milotron]

Hi, not sure what the power HP% settings you are using, but in my 1981 262 with TKS Iast week I got 150-160KTAS at 9000' at 65% power LOP, 10 GPH. No Gamis, and a huge spread of 1.2gals.  Air temps were about 12 deg C. Cylinder temps were 360 or lower with 1/2 cowl flaps.  Not a direct comparison, but HP for the airframe should be similar.

TKS typically eats a couple of knots, but not for all aircraft it seems.

Are you actually running LOP? Those seems like rich fuel flows.

 

iain

[KLRDMD]

2 hours ago, Northern Mooniac said:

I have an 81 M20K. My aspen will usually show a true airspeed speed of 155-160kts between 9000 and 12,500. Is this pretty normal or am I missing a bit of speed? I also find that I'm burning 14-16gph. still playing around with settings but doing about 33.4 and 2400rpm at 10500 on the way home from Oshkosh gave me about 160kts true.

That's a lot of fuel. At 10,000 ft I run 30", 2500 RPM and 9.0 GPH for 160 KTAS. That's 59% power, LOP with my CHTs in the mid 300s and TIT in the mid 1400s. Cowl flaps full closed.

Sounds like you need to get to the church of Lean of Peak.

[Northern Mooniac]

Yes, I agree I do need to learn LOP.

what TAS do you hit st 75% power?

[Bryan]

I have a Intercooled and Merlyn wastegate, too, but no TKS and no Gamis.

My go-to power settings are 29", 2500 RPM at 50-75 ROP at 11.5 - 12 GPH, cowl flaps closed unless i see CHT creap up past 380.  I need to get on the LOP bandwagon but I have been doing most of my flying for my IFR rating at or below 3000 msl shooting approaches.  Now that I have my IFR, its time to start doing the Gami Spread and learning LOP.

[johncuyle]

What KLRDMD said. I'm new to mine as well but my default cruise at pretty much any altitude in my '80 K is 28" and 2500 RPM. Fuel flow gauge says I'm running just under 10 GPH but math over the last year says I can't be burning more than 9 in reality. I true out around 150kt, maybe a little less, in the 11,000' range with CHT in the mid 300's and TIT around 1400, cowl flaps closed and engine happy. I've got a hot prop, which costs some speed. No intercooler for me, but I have the Merlyn. I don't have a proper engine monitor yet (and I guess I won't be getting one soon since I'm busy hoping for Skyview or G3X integrated solutions) so I plan to operate the engine conservatively. Mine also seems to be really happy if I configure this cruise setting and then dial prop speed back to 2400. Indicated fuel flow drops to about 9GPH, airspeed drops very little, and CHT doesn't seem to rise, so I may experiment with this cruise setting some more.


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[KLRDMD]

14 hours ago, Northern Mooniac said:

what TAS do you hit st 75% power?

Never fly a TSIO-360 series engine at 75% power in cruise unless you want to do at least one, and maybe two top overhauls before TBO. 65% power, LOP with no CHT above 380º and they live a long and happy life and will probably exceed TBO without a top overhaul.

[Northern Mooniac]

So much for flying fast!

 

what do you true out at with 65%

[Northern Mooniac]

On 2017-08-06 at 5:47 PM, KLRDMD said:

That's a lot of fuel. At 10,000 ft I run 30", 2500 RPM and 9.0 GPH for 160 KTAS. That's 59% power, LOP with my CHTs in the mid 300s and TIT in the mid 1400s. Cowl flaps full closed.

Sounds like you need to get to the church of Lean of Peak.

I need to get up ab learn lop. You are running faster speeds, less power and significantly less fuel. Holy smokes!

[Hank]

Your turbo will really shine when you take it up into the flight levels and catch those great tailwinds! Things I can only dream about . . . .

[KLRDMD]

6 hours ago, Northern Mooniac said:

I need to get up ab learn lop. You are running faster speeds, less power and significantly less fuel. Holy smokes!

Less fuel is simply LOP. The same percent power (ROP or LOP) will give the same true airspeed. If one airplane is faster on less power than other, the second airplane may not be in rig, may not be loaded the same (both with respect to total weight and location of that weight) may have instrument errors, may have more drag for some reason, etc. 

[Steve Dawson]

Do you still have the micro generators on? How much does that hurt your speed? Is it rigged properly? 

[Northern Mooniac]

yeah I do have the VG's still on it.

 

any idea how much those could slow it down?

[Guest]

VG's should have less drag at higher altitude in thin air. Down low in thick air everyone pays a drag penalty.

Clarence

[johncuyle]

So much for flying fast!

 

what do you true out at with 65%

Tricky question. Running LOP power output is determined entirely by fuel flow. My power output estimates are only as accurate as my fuel flow estimates, and I'm not really confident my fuel flow gauge is an accurate indication of actual fuel consumption in cruise. With an indicated 10GPH, LOP, that should be a 65% power setting. The last picture I took of my instruments in cruise shows 151kt on an indicated 9.8GPH at 14,500' 8c OAT (28" MP and 2500RPM). GS was 162kt thanks to a bit of a tailwind. Every plane is a little different. Mine might be a bit on the slow side. Or my fuel flow indication in cruise is high by enough that I'm actually running something closer to 55 or 60% power and it's actually a pretty average example of the model. If you want fast, you can get fast at 65% power, just not at low altitudes like 12,000'.

 

 

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[carusoam]

There is value in transition training...

you can actually buy training with a CFII that flys an M20K.

There are some pilots that want to fly fast.  The cost of a set of cylinders at the half way point is the cost of great speeds....

Flying LOP with a Continental engine isn't too challenging.  @jlunseth Is one of my favorite authors on the subject around here...

ideas that come to mind...

Best regards,

-a-

[jrwilson]

If you have an inter cooler you might be running too high mp; you can't use book numbers and you shouldn't be using more than 36" for take off.  

Use 252 book settings, or about 28" for cruise for most altitudes.  Your fuel flow seems high too.

you seem about 5 kts slow at those altitudes 

[Northern Mooniac]

Well did a 2 hour flight today.

lop I did 30in and 2400-2500 rpm 10.5gph and got about 144-148 true.

rop I did 33.2in and 2400rpm and was 17.1gph but 159 true.

this was all at 10500 and +7 celcius

i ran the lop with a turbo tit of 1590 and rop at 1475

is that too high for the turbo?

[Bryan]

I would bump up your RPM to 2500.  Everything that I am reading says 2500 is optimum for our engines with a 2-blade: Mapalog M20K, 231

[Northern Mooniac]

I did try that, but it seemed to run smoother at 2400. The engine as a whole runs so much cooler and smoother, I just loose some speed. I guess when i'm in a real hurry I can run ROP and put the hammer down.

[jrwilson]

45 minutes ago, Northern Mooniac said:

Well did a 2 hour flight today.

lop I did 30in and 2400-2500 rpm 10.5gph and got about 144-148 true.

rop I did 33.2in and 2400rpm and was 17.1gph but 159 true.

this was all at 10500 and +7 celcius

i ran the lop with a turbo tit of 1590 and rop at 1475

is that too high for the turbo?

Again, check your aftermarket intercooler POH...I think you might be running too high of manifold pressure...But, hey, it's your engine, do what you like.

[Northern Mooniac]

I was, it was right on spec for 65% lop and 75% rop

[jrwilson]

Hmmm, way different than mine, but it could be because you're using 2400 rpm and I'm using 2500...

You're not using 40" for take-off are you?

[Northern Mooniac]

Nope 37 full prop full mix for take off

[johncuyle]

I was, it was right on spec for 65% lop and 75% rop

That sounds wrong. 10.5 GPH is a 70% power setting LOP without the intercooler. The intercooler shouldn't make your engine less efficient. How far ROP were you with that fuel flow? That looks like it should be closer to an 80% or more power setting, and very rich (but not rich enough for power settings over 75%, which call for operating full rich.) Also, what were your CHT? TIT looks fine.


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