Austintatious

LOP and oversquare

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So I have been watching a LOT of Savvy aviation videos.  I decided to try some of the stuff I learned.  Here is what I was able to achieve in my rocket:

32"  2100rpm  13.5 gph  172 knots (4 way verified) at 8000 feet.  This should equate to around 190 knots at FL180.  CHT's looking phenominal.


Here is a video if you are interested.  https://www.youtube.com/watch?v=A1fmNFWNHD4&t=4287s

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10 minutes ago, Austintatious said:

So I have been watching a LOT of Savvy aviation videos.  I decided to try some of the stuff I learned.  Here is what I was able to achieve in my rocket:

32"  2100rpm  13.5 gph  172 knots (4 way verified) at 8000 feet.  This should equate to around 190 knots at FL180.  CHT's looking phenominal.


Here is a video if you are interested.  https://www.youtube.com/watch?v=A1fmNFWNHD4&t=4287s

LOP AND over square.  There is an old wives tale that says LOP is bad.  There is another old wives tale that says over square is bad. So what is going on that you put those TWO different old wives together in same thread?  Are they going to fight and maul each other or get along and make for great performance?

There is an SB for big continental engines in general that suggests running even 2200 is no longer advised, and that SB does not say anything about what setting in terms of power, but it was implicated in some sudden stoppage.  So .. even though 2200 is often in our POH as allowable settings I typically don't run 2200 or less but I start at 2250.  2100 makes me feel nervous at any power setting.

LOP you can calculate your actual power based on fuel flow.  Since we have 7.5  compression cylinders, then 12.7 horsepower per gph.  So at 13.5 gph you are producing 171hp.  That is roughly 56%.  So if you can burn 13.5gph with some setting a bit higher than 2200 rpm, and less than 32'' it might be good?  I forget my numbers since I didn't write them down, but something like 2250 and 29'' or 30'' makes similar fuel flow and similar speed LOP.  For me the limiter in running properly high power settings say LOP at say 17.9gph (which would be therefore 75% of 305) is that we seem to be TIT limited.  So I only run LOP at low power settings where things are cool and no damage is likely.  And otherwise I am usually running ROP.

Edited by aviatoreb

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I thought it is 14.9 hp per gph.  at the power settings I posted I am at 200 HP, roughly 65%.  I know CR changes it.  I'll go double check.

 

Also, the SB suggest not to run below 2300 rpm. Not mandatory and the circumstances of that SB are discussed in the video I posted.

I always wondered why oversquare was considered bad, you do it on every takeoff and in a tyrbocharge aircraft is it prettymuch required.

Edited by Austintatious

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I don’t think anyone knows where the fear of over square originated. 30 years or so ago I believe Kas Thomas postulated that it was a misapplication of the prohibition on radial engines to avoid operating under square. That was because low cylinder pressures can’t balance reciprocating load and the result can damage the master rod bearing. 

Skip

 

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The io 360 compression ratio equates to 14.7 hp per.gph.  I run my Rajay normalized non intercooled io 360 at 27 inches, 2400 or 2100 rpm depending on power I want.   10 gph at 27 inches 2400 at 8000 is 165ktas and at 18000 is 195 ktas.  Cool smooth quiet operation.  Between 30 and 50 lop.

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Both multipliers quoted above I believe are incorrect:

TCM Turbocharged typically 7.5:1 -> 13.7 multiplier

Lyc IO-360 8.5:1 (includes most normally aspirated engines) -> 14.9 Multiplier 

But many other CR are used; especially in turbo charged engines

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I loved the video and the links to his other work.  What he says makes perfect sense.  Apparently I have more studying to do.  When I recently did a check ride in the plane that I afterwards purchased, the friend of the owner that took us up said in the Screaming Eagle, just keep the prop and throttle pegged but did show me how to lean it out using the engine monitor.  That really didn't make much sense to me not dialing in the prop, but watching this video talks to me. 

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The regular ovation is 2400 rpm.  And pilots dial that prop back because they don’t like seeing the tach at the redline. Then when they get the screaming eagle conversion and a 2700 rpm redline, they pull it back to 2500.  Which was above the original redline that they were uncomfortable with. 

Edited by jetdriven
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15 minutes ago, jetdriven said:

The regular ovation is 2400 rpm.  And pilots dial that prop back because they don’t like seeing the tach at the redline. Then when they get the screaming eagle conversion and a 2700 rpm redline, they pull it back to 2500.  Which was above the original redline that they were uncomfortable with. 

2550! :-) 

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14 hours ago, carusoam said:

Don’t forget the FWF 10:1 CR that @Sandman993 has...

just keeping Sandman in the loop...

Best regards,

-a-

10:1 CR = 16.64HP/USG multiplier

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I cruise oversquare every single time. Engine is about a hundred hours past TBO and doing fine.  Its a turbo though, all the cruise settings are oversquare. I am pretty sure that is true of all the Mooney turbo aircraft. 

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On ‎9‎/‎29‎/‎2019 at 12:40 AM, carusoam said:

Don’t forget the FWF 10:1 CR that @Sandman993 has...

just keeping Sandman in the loop...

Best regards,

-a-

Nothing exceeds like excess.

Thanks Carusoam

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I've been toying around with DCS World, and I have to say, it's pretty freaking cool.  One of the things I noticed on the trainer-version P-51 it comes with is that max sustained MP is 46" at 2700 RPM.

Max MP is actually 60" :o

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1 hour ago, jaylw314 said:

I've been toying around with DCS World, and I have to say, it's pretty freaking cool.  One of the things I noticed on the trainer-version P-51 it comes with is that max sustained MP is 46" at 2700 RPM.

Max MP is actually 60" :o

60" is fine if you have a jap on your 6 shootin at you

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17 minutes ago, Sandman993 said:

60" is fine if you have a jap on your 6 shootin at you

Well, DCS World only comes with the TF-51 trainer version, so no guns and nobody shooting at me either...

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24 minutes ago, jaylw314 said:

Well, DCS World only comes with the TF-51 trainer version, so no guns and nobody shooting at me either...

I used to have a chick that would shoot, throw knives and then call the cops just because I came in late from the mens club...sometimes you just need 60" MP!

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9 minutes ago, Sandman993 said:

I used to have a chick that would shoot, throw knives and then call the cops just because I came in late from the mens club...sometimes you just need 60" MP!

I...don't know what to say :blink:

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18 minutes ago, jaylw314 said:

I...don't know what to say :blink:

I get that...just sayin, sometimes you gotta give the throttle a good push if you get a hostile Jap on your tail!

Way back when I started flying lessons...there was a guy that Taxied up to the ramp in a 414A Ram IV conversion...that plane was awesome sexy. When he opened the door, a couple beer bottles and one Vodka bottle tumbled down the stairs to the concrete ramp (they didn't even break). I immediately asked if there was any chance he was a CFI. His response was yep. And that's who mentored my tender fledgling time. Ever done a 220kt low pass over a house in a 414? It vibrates the windows if you get low enough...or so I'm told. I was too busy to look at the MP.

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1 hour ago, Sandman993 said:

I get that...just sayin, sometimes you gotta give the throttle a good push if you get a hostile Jap on your tail!

Way back when I started flying lessons...there was a guy that Taxied up to the ramp in a 414A Ram IV conversion...that plane was awesome sexy. When he opened the door, a couple beer bottles and one Vodka bottle tumbled down the stairs to the concrete ramp (they didn't even break). I immediately asked if there was any chance he was a CFI. His response was yep. And that's who mentored my tender fledgling time. Ever done a 220kt low pass over a house in a 414? It vibrates the windows if you get low enough...or so I'm told. I was too busy to look at the MP.

The way to really scare everyone is to pull the power and props WAY back, Dive down, preferably behind a building that block s the view of you, and then jsut before you pass push the power and props FULL.   That seems to get everyone's attention!

Edited by Austintatious

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6 minutes ago, Austintatious said:

The way to really scare everyone is to pull the power and props WAY back, Dive down, preferably behind a building that block s the view of you, and then jsut before you pass push the power and props FULL.   That seems to get everyone's attention!

I think I'll limit the SPT's to DCS World :rolleyes:

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On 9/28/2019 at 11:57 PM, kortopates said:

Both multipliers quoted above I believe are incorrect:

TCM Turbocharged typically 7.5:1 -> 13.7 multiplier

Lyc IO-360 8.5:1 (includes most normally aspirated engines) -> 14.9 Multiplier 

But many other CR are used; especially in turbo charged engines

Oops - I did the math wrong...

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6 hours ago, Sandman993 said:

60" is fine if you have a jap on your 6 shootin at you

Hmm, I'd be runnin' at least 70" in that case:D

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