J Speeds

[aaronk25]

Ya at 1500 ft on a 15c day full power for short burst my IAS needle will go a needles with last 170kts. But that's not a power setting I'd want to run long cause have to lean to 80rop to do it.


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[aaronk25]

One last thought the plane does the same as most other moneys when slowed up. 135kts on 7.2gph, 148kts on 8.2-8.5gph. 152kts on 9ish. Just for whatever reason it really comes alive at 2700rpms.....


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[mike_elliott]

3 hours ago, MyNameIsNobody said:

Original poster, B.S. Alert.  Anything over 155 knots in a J should be HIGHLY suspect

hummm...are you saying  the pics I posted of Joe D's J doing 158 TAS on 8.5 LOP are fake?

[MyNameIsNobody]

Yes.  I call B.S. On 158knots at 8.5GPH at 9000 feet.  I don't question that it will do 158knots at 9000'.  Not at that fuel flow.  I am a NON-Believer.  With a tailwind?  Yes.

3 hours ago, aaronk25 said:

 

Hey there long lost friend.....

2700rpm, and at the lowest fuel burn for those speeds is about 9.8gph but more like 10.2-10.8gph.

The power flow works the best at higher rpm. Sure there is a little benefit at 2400-2500 but wow what a difference in cruise pre power flow to post power flow especially at 2700rpm.

If the rpm is brought back to 2500rpm my plane is at the slowest at max gross 155kts on 8.8-9.2gph but real world is closer to 157-158kts. Temp plays a factor.

A side note is I have a once piece belly, head doors and flight surfaces are near perfect rig and have a round tip propeller,not the square original prop and challenger air filter.

Hey Mr. Iowa I got a $100 bill that says I got those speeds with you aboard in a 4 way average.......wanna go to breakfast?


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Hey.  Not "hiding".  I get to choose the altitude for your "8.8-9.2GPH for 157knots@2500RPM?"  If yes then I will take that bet and if it is 156 you lose.  Not in the winter when 1000 climb to cruise is doable.  On a flying season day in the Midwest.  My plane can do 150knots up high with that fuel flow...

Mr. Flatland would be a better moniker...

I just "reside" here.  I am livin' when I am UP NORTH...

[Steve Dawson]

Can't remember what the fuel flow was but so I'm guessing at 10 gph

[mike_elliott]

1 hour ago, MyNameIsNobody said:

Yes.  I call B.S. On 158knots at 8.5GPH at 9000 feet.  I don't question that it will do 158knots at 9000'.  Not at that fuel flow.  I am a NON-Believer.  With a tailwind?  Yes.

Well, How do you like your crow?

Here are the pics again...take a look at the JPI for the fuel flow, the aspen for the TAS. Notice it is in level flight. N984VW will do this, and this is on a 1700 hr engine. Yours must be slower I take it. A shame. Next time I fly her, Ill open it up to see what her top speed is ROP down low.

 

[Ftlausa]

96 J, 3 blade prop.  155kts at 10.5 gph at 8k flying ROP. 

[MyNameIsNobody]

1 hour ago, mike_elliott said:

Well, How do you like your crow?

Here are the pics again...take a look at the JPI for the fuel flow, the aspen for the TAS. Notice it is in level flight. N984VW will do this, and this is on a 1700 hr engine. Yours must be slower I take it. A shame. Next time I fly her, Ill open it up to see what her top speed is ROP down low.

 

NOPE.  That is a Ground Speed.  I can do that do in level flight.  Doesn't mean that is the speed at that fuel flow except on that day.  Glad that day gave you good speed over the ground.

[mike_elliott]

Just now, MyNameIsNobody said:

NOPE.  That is a Ground Speed.  I can do that do in level flight.  Doesn't mean that is the speed at that fuel flow except on that day.  Glad that day gave you good speed over the ground.

NOPE that is 158 TAS on the aspen. it is 160 GS on the Garmin.

What do you like with your crow?

[MyNameIsNobody]

10 minutes ago, mike_elliott said:

NOPE that is 158 TAS on the aspen. it is 160 GS on the Garmin.

What do you like with your crow?

Skeptics will try anything, including crow, but they don't except that crow is "good" until they taste it themselves...

[Guest]

Here's what the hangar cat says about those numbers.

Clarence

[mooniac15u]

And here's @Marauder's cat.

[Marauder]

And here's @Marauder's cat.

Meow!


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[Marauder]

And I did this at 1950 RPM on 2 ounces per hour. F models rule! Vrooom, Vroooom!




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[bradp]

Mike I wonder - at 9500 I'd expect to be running LOP at 8.5 GPH and 2450 rpm. But but but those CHTs seem rather high for anything LOP even though it seems like a summer Florida day at that altitude. Other possibilities are the K-factor on the FF transducer is inaccurate. My bet would be that based on the CHTs this is peak or a bit on the rich side


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[gsxrpilot]

9 minutes ago, bradp said:

Mike I wonder - at 9500 I'd expect to be running LOP at 8.5 GPH and 2450 rpm. But but but those CHTs seem rather high for anything LOP even though it seems like a summer Florida day at that altitude. Other possibilities are the K-factor on the FF transducer is inaccurate. My bet would be that based on the CHTs this is peak or a bit on the rich side


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CHT has nothing to do with ROP or LOP.

[Guest]

21 minutes ago, gsxrpilot said:

CHT has nothing to do with ROP or LOP.

I thought that one prime advantages of LoP operations was lowering CHT's?

Clarence

[Bob_Belville]

24 minutes ago, gsxrpilot said:

CHT has nothing to do with ROP or LOP.

Really?

https://www.jpinstruments.com/wp-content/uploads/2013/05/Mike-Bush-Red-BoxRed-Fin.pdf

[gsxrpilot]

Just now, M20Doc said:

I thought that one prime advantages of LoP operations was lowering CHT's?

Clarence

True... but lowering from what number? The CHT numbers in Mike's JPI could be the result of anything from full rich to 60 - 70 degrees LOP. You can't tell from the CHT number.

Just now, Bob_Belville said:

Really?

https://www.jpinstruments.com/wp-content/uploads/2013/05/Mike-Bush-Red-BoxRed-Fin.pdf

Both of you are somewhat correct. Of course, full disclaimer, I'm a disciple of John Deakin and his Advanced Pilot Seminar. It's interesting that evidently Mike Bush has sat through the APS course three times and can't disagree with APS, but still pushes his version of Leaning based on CHT. APS has discredited that method to my satisfaction.

Running "far enough" LOP will reduce CHT's as well running "rich enough" ROP.  But there isn't anyway to measure LOP or identify LOP or ROP from CHT's. That was my point. I was responding to Brad who said based on the CHT's he thought the engine was running AT peak or slightly ROP. My point is that can't be determined by reading CHT. According to the guys at APS, while the variance of CHT's from full rich to say 60 degrees LOP, will follow a prescribed arch, the actual numbers will be affected much more by baffling, OAT, Altitude, etc.

[Bob_Belville]

Just now, gsxrpilot said:

True... but lowering from what number? The CHT numbers in Mike's JPI could be the result of anything from full rich to 60 - 70 degrees LOP. You can't tell from the CHT number.

Both of you are somewhat correct. Of course, full disclaimer, I'm a disciple of John Deakin and his Advanced Pilot Seminar. It's interesting that evidently Mike Bush has sat through the APS course three times and can't disagree with APS, but still pushes his version of Leaning based on CHT. APS has discredited that method to my satisfaction.

Running "far enough" LOP will reduce CHT's as well running "rich enough" ROP.  But there isn't anyway to measure LOP or identify LOP or ROP from CHT's. That was my point. I was responding to Brad who said based on the CHT's he thought the engine was running AT peak or slightly ROP. My point is that can't be determined by reading CHT. According to the guys at APS, while the variance of CHT's from full rich to say 60 degrees LOP, will follow a prescribed arch, the actual numbers will be affected much more by baffling, OAT, Altitude, etc.

I think you're making it more complicated than it needs to be. "Peak" means maximum value. As you lean, pull the mixture back from full rich to the point that the engine stumbles, both CHTs and EGTs will "peak" at some point and then decline. According to the graphs I've seen the CHTs peak first, i.e. at a higher FF and since "peak" means maximum as the mixture is further pulled out the CHTs will decrease. At some (leaner) point the EGTs will peak and start to decrease. Since EGTs peak after CHTs, any mixture setting that's LOP (EGT) will always be LOP (CHT). 

Nothing above says anything about the absolute values of CHTs. Other factors are involved: % power, OAT, cooling inefficiencies, etc. So... if you've leaned as much as you are able due to a rough running engine or an unacceptable loss of power/TAS, and if the CHTs are higher than you're comfortable with >380F, or >400F - whatever you target, you will open cowl flaps and/or reduce power by decreasing RPM or pulling back the throttle. 

[mike_elliott]

1 hour ago, bradp said:

Mike I wonder - at 9500 I'd expect to be running LOP at 8.5 GPH and 2450 rpm. But but but those CHTs seem rather high for anything LOP even though it seems like a summer Florida day at that altitude. Other possibilities are the K-factor on the FF transducer is inaccurate. My bet would be that based on the CHTs this is peak or a bit on the rich side


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yea they were high. The back baffling was folding down and allowing a lot of the air to escape behind where the mag and vacuum pump is. It was corrected and temps are normal once again. I had to keep opening the cowl flaps up to keep them under 400 even LOP on the way back. Once I decowled it, I could see a "section" of the baffling that wasn't making contact with the cowl, so a "stiffener" was added. Fairly common on J's to have this happen.

Good catch, Brad, I was 25 LOP 

[gsxrpilot]

Just now, Bob_Belville said:

I think you're making it more complicated than it needs to be. "Peak" means maximum value. As you lean, pull the mixture back from full rich to the point that the engine stumbles, both CHTs and EGTs will "peak" at some point and then decline. According to the graphs I've seen the CHTs peak first, i.e. at a higher FF and since "peak" means maximum as the mixture is further pulled out the CHTs will decrease. At some (leaner) point the EGTs will peak and start to decrease. Since EGTs peak after CHTs, any mixture setting that's LOP (EGT) will always be LOP (CHT). 

Nothing above says anything about the absolute values of CHTs. Other factors are involved: % power, OAT, cooling inefficiencies, etc. So... if you've leaned as much as you are able due to a rough running engine or an unacceptable loss of power/TAS, and if the CHTs are higher than you're comfortable with >380F, or >400F - whatever you target, you will open cowl flaps and/or reduce power by decreasing RPM or pulling back the throttle. 

No, actually to be correct about it, the Peak in ROP/LOP discussions ONLY refers to EGT. There are very specific reasons for this that are mathematical, but a bit too deep to go into here. 

Certainly as EGT moves towards or away from peak temperature, other measurements such as CHT, BHP, ICP, etc are all affected. But the determination of Peak is based solely on EGT.

And... it looks like Mike just weighed in and confirmed my original point. ;-)

[Bob_Belville]

4 minutes ago, gsxrpilot said:

No, actually to be correct about it, the Peak in ROP/LOP discussions ONLY refers to EGT. There are very specific reasons for this that are mathematical, but a bit too deep to go into here. 

Certainly as EGT moves towards or away from peak temperature, other measurements such as CHT, BHP, ICP, etc are all affected. But the determination of Peak is based solely on EGT.

And... it looks like Mike just weighed in and confirmed my original point. ;-)

Whatever.

[mike_elliott]

1 hour ago, M20Doc said:

I thought that one prime advantages of LoP operations was lowering CHT's?

Clarence

That's the real reason to run LOP. It helps when the baffles are right  

[bradp]

I was trying to figure out why - for a plane with a nearly identical engine, fuel servo etc., how it could be getting a TAS that seemed quite high while supposedly running LOP. Gsrxpilot is absolutely right that LOP or ROP doesn't determine an absolute CHT number. Also right that you can't infer where you are on the mixture curve based on CHT alone.

However since I run the same engine and presumably have a similar airframe I can infer that those CHTs are not typical for LOP (meaning, say -10 F for the richest cylinder) or even peak mixtures at that altitude and RPM/MP combination. They seem high and in this case they are due to inadequate air cooling. I'd have to actually try hard running maybe 25-50 ROP to get those CHTs at that alt MP and RRM combination. That's why I was questioning where he was on the mixture curve.

I think, based on whatever data we've consumed, that most of us will subscribe to the idea that the cylinder pressure and CHT will be lower for a given value LOP as for the same value ROP.


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