1978 J numbers

[wishboneash]

Sorry for hijacking another thread yesterday and posting some numbers off the top of my head which were clearly not accurate. I downloaded data from my engine monitor today and looked at the data carefully again. This was a a flight from Livermore to Sacramento Exec (it was IMC part of the way, so I wasn't paying focussed on the monitor as much). But I did run LOP and ROP on the onward and return journey respectively.

For KLVK to KSAC

MAP: 22.7", RPM: 2458, FF: 8.3, OILT: 182, CHT: 303-318, EGT: 1455-1505 (~10 deg LOP), HP: 62%, ALT: 5000, SPD(GS): 148KTS

For KSAC to KLVK

MAP: 25.5", RPM: 2488, FF: 11.5, OILT: 188, CHT: 344-368, EGT: 1460-1504 (~25 deg ROP), HP: 76%, ALT: 4000, SPD(GS): 152KTS

It seems I could burn another 1 gph either LOP or ROP, bump up the RPM another 50 or so and gain a few more knots. Would like to get some data points before I start thinking of some easy mods to get boost the speed. Thanks.

[ArtVandelay]

Ground speed is variable depending on winds, what was your weight, you lose about a knot/100lbs?

Try flying higher, 6000', WOT, 2600 RPM should give you about 165k depending on weight, at 8000' you'll improve your FF a bit. The ? is how does it compare to POH?

These look pretty close to my 78, I never cruise at ROP, rarely below 7000' unless it's a short trip.

[wishboneash]

33 minutes ago, teejayevans said:

Ground speed is variable depending on winds, what was your weight, you lose about a knot/100lbs?

Try flying higher, 6000', WOT, 2600 RPM should give you about 165k depending on weight, at 8000' you'll improve your FF a bit. The ? is how does it compare to POH?

These look pretty close to my 78, I never cruise at ROP, rarely below 7000' unless it's a short trip.

I should experiment with some POH settings and other altitudes as you suggest - but interpolating I get about 5-7 KTS slower than book. Weight was around 2500lb, winds were fairly light out of the west (my flight was generally north-south). Can't complain too much.

[ArtVandelay]

Don't forget the POH numbers use standard temps, so if it's warmer than standard you performance won't be as good. Also if traveling north or south and winds from west to east, you speed will be less because you'll be fighting the winds to remain on course, that's why winds hurt more than help.

[wishboneash]

I used the POH graph that has the temperature axis as well. Not too far from standard at this time of the year. Agreed about fighting the winds.

[bonal]

Wishbone, I would definitely get out and do some 3 or 4 course GPS runs at higher altitudes I bet if you did your numbers would be improved from your recent run. I did mine at 8000 and was pleased with my results plus it's FUN 

[Bob - S50]

Instead of recording GS, record IAS, then use your trusty E6B to calculate density altitude and TAS.  Do it at several altitudes and power settings.  Then after you do your mods, you can compare TAS at similar power settings and density altitudes.

[bonal]

IAS with E6B would work assuming your airspeed indicator is accurate. I doubt you could be as precise as combined GPS runs and not as much fun.

[wishboneash]

I guess multiple input source s are a good way to corroborate ones calculations or measurements. I did recall the IAS for my RTB flight at 4000 ft. It was 144KIAS that roughly translates to 153KTAS.

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[cnoe]

On 12/8/2015 at 4:11 PM, teejayevans said:

Try flying higher, 6000', WOT, 2600 RPM should give you about 165k depending on weight,

That's a fast J from what I've seen/heard. Maybe 160 for an average-type J?

[Steve Dawson]

I've gotten 165K at 7K

[Brandontwalker]

I true out at 158k. Thought I was doing good until reading above...

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[cnoe]

I true out at 158k. Thought I was doing good until reading above...

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At least you and I aren't flying a (insert brand/type here).

I'll take 180 mph over 120-150 mph any day!

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[ArtVandelay]

On 12/8/2015 at 4:11 PM, teejayevans said: Try flying higher, 6000', WOT, 2600 RPM should give you about 165k depending on weight,

That's a fast J from what I've seen/heard. Maybe 160 for an average-type J?

I pulled that from the POH which I've found to be pretty close to spot on, but haven't tried it myself.

[mike_elliott]

I take care of a  J that does 158 TAS on 8.5 LOP...oh and the pics to back it up...

[wishboneash]

2 hours ago, mike_elliott said:

I take care of a  J that does 158 TAS on 8.5 LOP...oh and the pics to back it up...

Quite an impressive benchmark. I see you are running 21.5", 2400 rpm with OAT=5C at 9,500 ft.

[mike_elliott]

7 minutes ago, wishboneash said:

Quite an impressive benchmark. I see you are running 21.5", 2400 rpm with OAT=5C at 9,500 ft.

13.8 deg C (57F). It is a fast 1984 J.

[Mooney1401]

I can bank on 155kts true EGT 1300  2400 rpm and 23"  about 10.5 gal