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252 Cruise Speed


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Hello all,

After the worlds longest pre-purchase it is time for me to come out of the "lurker" closet. As of today I am a brand new proud owner of C-GKRP, a 1986 252. I have been flying it for several months while the seller and I worked the bugs out, so I am feeling pretty comfortable by now. During that process I have learned an awful lot about Mooneys by reading this forum. Nice to have such a great source for advice and opinions.

She's pretty nicely equipped with Aspen, 530W, XM weather, EDM830, TKS, Stormscope, Radalt and a 3 blade hot scimitar. The only big thing left to do is ADS-B out, but being in Canada I can afford to wait for a while. The piggy bank is kind of depleted after the purchase.

I ran the GAMI spread test and sent it to folks at GAMI. They tell me I already have a .3 spread and they wouldn't try to improve it. Bonus!

There are two things I want to change, based on advice I have read on this forum. I want to switch to Tempest Fine Wire plugs. Getting my mag timing checked will also be a part of the process. I can't currently get more than about 15 degrees LOP before it starts feeling rough and my TIT is uncomfortably close to 1650 at that setting. That's starting from 65% (27" 2500 rpm) and leaning to about 10.2 GPH. 

I also plan to replace my baffle seals with a set from Guy Ginby this winter. Right now I have to trail the cowl flaps 1/2 way open to get stay below 380 CHT at 65%. I am running 100 degrees ROP until I can get the plugs changed which gives me about 14 GPH.

So finally to the question: At 8000 ft, 65% and 100 ROP I am seeing about 156 KTAS. (OAT was 14C) I know TKS can cost some airspeed, as can a hot prop, and I am probably losing 2-4 knots with the cowl flaps half open, but that seems a little slow compared to some of the 252 numbers I have seen mentioned on this forum. Any 252 owners care to comment?

Regards,

MarkIMG_0332.thumb.JPG.02147a7f0da1aec534cd8f74ff63b371.JPG

 

 

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Welcome out into the posting open, Mark.

We have a few threads regarding turbo ops.  With and without intercoolers and various pressure controllers.

You can search to find things like LOP for M20Ks there are a few interesting authors that have covered the topic....

Best regards,

-a-

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More Canadians! Woo hoo eh!

 

I have a 1981 M20K with the 262 upgrades and TKS so very similar to yours but with 2 blade prop.

My last flight was that altitude out and back and was 160KTAS or so ( although flight aware says it was 173kts...IDK ) .  I also use LOP at 65% and see 10GPH. My GAMI spread is about 0.6GPH so you should have no issue doing that. I see 1600 TIT using 2400 and 25" or so.  I need about 1/3 open cowl to maintain below 380.

I added the fine wires and had better high altitude performance without a doubt. Expensive, but they last forever. Didn't really impact lower LOP ops though.

You noted TIT of 1650. What power setting was that at?

 

iain

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Hi Mark,

that cruise speed is good for 65% and 8,000. If you look in the poh, you'll see. On the other hand, you should be burning around 12 gph at 100 degrees rop. I burn 12.5 at 125 rop, but have 10 extra hp. I have seen MP gauges seriously out of calibration, or your timing could be seriously retarded. The timing issue would account for higher tit numbers and not running lop, but yor chts would be lower as well. 

At 65%, my chts really never get much above 350 with the cowl flaps closed regardless of outside temp. 

I had tks installed at the CAV facility. I didn't notice much change in cruise speed. 

Jack

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That speed sounds really good for a TKS, hot prop, three blade. You're burning a lot of fuel and with that GAMI spread you really ought to be able to run leaner. I've got a 231 with Champion massives all around and probably a worse spread (no engine monitor) and I can run fifty to seventy five lean. I don't get anywhere near that speed  (two blade hot prop no TKS, with intercooler and Merlyn) at 65% and 8000', but running LOP I'm showing 10gph.

Given your fuel flow I also wonder if your MP gauge is off and you're running more like 70% power.

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That speed sounds really good for a TKS, hot prop, three blade. You're burning a lot of fuel and with that GAMI spread you really ought to be able to run leaner. I've got a 231 with Champion massives all around and probably a worse spread (no engine monitor) and I can run fifty to seventy five lean. I don't get anywhere near that speed  (two blade hot prop no TKS, with intercooler and Merlyn) at 65% and 8000', but running LOP I'm showing 10gph.
Given your fuel flow I also wonder if your MP gauge is off and you're running more like 70% power.

Same setup as me minus the intercooler and I'll do 160-164 TAS at 8-9000. Was -9C at 9000 ft cruise today and about 2800lbs. Burn was 10.4 gph. So I'd take a look at those power setting gauges.


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I have a stock 1987 252...210-hp Continental, two-blade McCauley, no TKS, no VGs, etc. I use the MAPA Mooney Manual's "Key Number" concept (53 for 75%, 49 for 65% and 45 for 55%) for setting cruise power initially, but then refine it with the POH (sun visor numbers) each time. In cruise, I lean based on TIT, not EGT, and I'm a 50 ROP TIT guy. I see 175-178 KTAS at 11-12,000' where I often cruise using 75% (key # 53...28", 2500 RPM and 13 GPH)...this is where I usually fly it. Although 1650 is the TIT red line, I use 1600 as my red line; my CHTs always run cool (just under 350) and my oil runs too cool sometimes (~150-160).  Same power (53) and fuel flow (13) gives me 190+ KTAS in the high teens to low 20s. If I'm trying to extend my range, I'll set 65% (key # 49...24”, 2500 RPM and 11 GPH) for 170 KTAS. If I'm taking someone on a local sight-seeing ride, I pull it back to 55% (key # 45...23", 2200 RPM and 9.5 GPH) for about 130 KIAS...

This is a fast bird combined with excellent efficiency...the Mooney guys got it right! The operational capabilities now available above and beyond what the J allowed is what really makes it a sweet deal for me.

We had a J model for 5 years before getting this 252. Though we loved the J (and still do), we're VERY happy we made the switch. 

Feb2017-14.jpg

Edited by Jsavage3
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Thanks everyone for all the good feedback.

I am getting a better picture after recording data on a few more flights. First, it appears I was running significantly higher power settings than I thought was. This goes a long way to explain the higher temps and fuel flows I was seeing. 

For the last couple of flights I have used POH settings and am seeing almost exactly the POH speeds at the POH 65% and ROP.  Fuel flow at that setting is around 12.5 GPH or less at 100 degrees ROP and 9.5 GPH at 20 degrees LOP. It runs a little rough at LOP so I will wait until I have timed the mags and installed new plugs before operating that way on a regular basis. I can also fully close the cowl flaps now and keep CHTs under 380 now.

My EDM 830 will evidently need some tweaking. A 65% power setting from the POH at lower altitudes shows right on 65% on the EDM, but at higher altitudes it shows lower settings. At 10,000 feet today on an ISA day, 65% POH settings showed 59% on the EDM. Looking back on some notes I took at 15,000' some weeks back, my EDM showed 65% but by the POH I was actually running 75% or higher. That explains the high temperatures and fuel flows I was seeing.

Lesson learned? Verify my power settings with the POH. I was far too trusting that my EDM was set up properly. 

Any EDM users have any tips on getting it tuned up? Before I start messing with the Horsepower Constant I want to be sure it is getting good input data. RPM and MP match my primary gauges almost exactly. OAT does not. I am not sure where the OAT probe is, but it reads much higher than the OATs displayed on the Aspen and the analog gauge. According to the ADM manual, it needs RPM, MP, FF and OAT to calculate %HP. If the temperature is over-reading, I am guessing that my % HP will get more inaccurate as I climb.

 

 

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Make sure you get new probes for the edm every 400-500 hrs. This is often overlooked and the probes degrade over time with the result that temps will read erroneously low. I think this is very important for a turbocharged bird.

What?! I have to buy probes every 2 years? I assume you are just talking about EGT probes?
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On ‎10‎/‎14‎/‎2017 at 9:08 AM, Jsavage3 said:

I have a stock 1987 252...two-blade McCauley, no TKS, etc. I use the MAPA Mooney Manual's "Key Number" concept (53 for 75%, 49 for 65% and 45 for 55%) for setting cruise power initially, but then refine it with the POH (sun visor numbers) each time. I lean based on TIT, not EGT and I'm a 50 ROP TIT guy. I see 175 KTAS at 11-12,000' where I often cruise using 75% (28", 2500 RPM and 13 GPH)...this is where I usually fly it. Same power and fuel flow gives 190+KTAS in the high teens to low 20s. If I'm trying to extend my range, I'll set 65% (25", 2400RPM and 11 GPH) for 170 KTAS. If I'm taking someone on a local sight-seeing ride, I pull it back to 55% (23", 2200 RPM and 9.5 GPH) for about 160 KTAS...I say about because I'm sight-seeing and not paying as much attention to my actual cruise speed... 

This is a fast bird combined with excellent efficiency...the Mooney guys got it right! The operational capabilities now available above and beyond what the J allowed is what really makes it a sweet deal for me.

We had a J model for 5 years before getting this 252. We're VERY happy we made the switch. 

Feb2017-14.jpg

Happy you made the switch too Savage!

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5 hours ago, teejayevans said:


What?! I have to buy probes every 2 years? I assume you are just talking about EGT probes?

 

5 hours ago, teejayevans said:


What?! I have to buy probes every 2 years? I assume you are just talking about EGT probes?

 It’s my understanding that they all degrade over time. With a turbocharged Airplane, you are much more interested in what your cylinder head temperatures are doing than  EGT’s. I don’t pay much attention at all to EGT other than the the differential as between all cylinders. In any fuel injected engine, you want to see the spread between the lowest and highest at less than 100°. In the bravo, I lean to CHT and in my normally aspirated Saratoga, I lean to EGT. The probes are relatively cheap, and I want to be sure that my readings on the JPI are as close to correct as  possible. 

Edited by Bravoman
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 It’s my understanding that they all degrade over time. With a turbocharged Airplane, you are much more interested in what your cylinder head temperatures are doing than  EGT’s. I don’t pay much attention at all to EGT other than the the differential as between all cylinders. In any fuel injected engine, you want to see the spread between the lowest and highest at less than 100°. In the bravo, I lean to CHT and in my normally aspirated Saratoga, I lean to EGT. The probes are relatively cheap, and I want to be sure that my readings on the JPI are as close to correct as  possible. 

You can check the accuracy of your temperature probes before starting the engine, they should read the ambient temperature.
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34 minutes ago, teejayevans said:


You can check the accuracy of your temperature probes before starting the engine, they should read the ambient temperature.

Good idea, but are they that accurate at the bottom of their range? I know mine suggest that the ambient temperature is about 90 deg C.

 

iain

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Hey Mark,

i flew up to KRUT(Rutland, VT) on Wednesday to do some fall hiking. I wanted to check out 65% at 8,500. See photo below. If you figure an additional 2 kts per 1000 ft, you're at 160 at 10.5k. Any plane that can do 160 burning between 10 & 12 gph is nothing to sneeze at. 

My edm930 is accurate as far as %hp is concerned, the power numbers adjusted to oat do indeed come to 65%. 

Jack

 

IMG_0101.JPG

Edited by jackn
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Nice data collection, Jack.

12.3 gph is ROP for your bird, right?

 

For those reporting odd OAT and CHTs while shut down...

Both J and K type thermocouples will read OAT correctly while on the ground...

If you have a 50°C offset on the ground, you might expect the same offset while operating... consider it room for improvement...

check the settings on the JPI for thermocouple type. Clean the connections.  That kind of thing...

 

http://www.thermometricscorp.com/thermocouple.html

a K type thermocouple has a really wide range of operation... -200°C to 1260°C

This topic is so confusing, the site I quoted has arbitrarily dropped the minus sign a couple of times on their -200°C spec...

This one had trouble converting °C to °F and the data doesn't match....   http://www.thermometricscorp.com/thermocouple.html

This one should be a little more reliable with peer review...    https://en.m.wikipedia.org/wiki/Thermocouple

 

There is also a different spec range for extension wires.  I'm not sure what is causing that...

 

Best regards,

-a-

 

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6 hours ago, carusoam said:

 

 

There is also a different spec range for extension wires.  I'm not sure what is causing that...

 

 

 

I have had some issue with the bolted splice connections between the leads and wiring harness.Sometimes tough to get a good connection with them. In the milli volt range that these run in, it doesn't take much resistance to cause inaccuracy.

I think I need to review my CHT 'issues' on this basis.

 

iain

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Thanks Jack,

Looks like my OAT on the EDM830 is over-reading by about 20C in flight. It's accurate on the ground before start so I suspect the probe is too close to something hot. 

Interestingly, the POH says to add about 1" of MP for each 10C above ISA to get the required %HP. I was running about 2" MP higher than POH to get the EDM to show 65%.  I think I need to find a better location for my OAT probe.

Cheers,

Mark

7 hours ago, jackn said:

Hey Mark,

i flew up to KRUT(Rutland, VT) on Wednesday to do some fall hiking. I wanted to check out 65% at 8,500. See photo below. If you figure an additional 2 kts per 1000 ft, you're at 160 at 10.5k. Any plane that can do 160 burning between 10 & 12 gph is nothing to sneeze at. 

My edm930 is accurate as far as %hp is concerned, the power numbers adjusted to oat do indeed come to 65%. 

Jack

 

IMG_0101.JPG

 

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