Austintatious

LOP and oversquare

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On 9/30/2019 at 7:59 PM, aviatoreb said:

Oops - I did the math wrong...

That’s not very professional of you to let on :)

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46 minutes ago, FloridaMan said:

That’s not very professional of you to let on :)

:-)

Actually I feel strongly, as a professional mathematician - it is much more professional to announce your mistake and fix it, rather than to dig in or hide it.  Everyone makes mistakes - its how you deal with it.

E

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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

200hp Lyc is actually 8.7:1 so a calculated multiplayer of 15.13. Trivial I know but good for a few little less fuel on the same power. 

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On 9/28/2019 at 11:46 PM, 65eTurbo said:

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.

Are you running low compression pistons?

Edited by Shadrach

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24 minutes ago, Shadrach said:

200hp Lyc is actually 8.7:1 so a calculated multiplayer of 15.13. Trivial I know but good for a few little less fuel on the same power. 

Thanks Ross for bringing that up, there are quite a few (depicted beow) engine models with a CR 8.7:1; then there are also the HIO-360's with both 8.7:1 & 10:1 CR's

image.thumb.png.e04010a4ab847f74eba1f57993718113.png

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4 minutes ago, kortopates said:

Thanks Ross for bringing that up, there are quite a few (depicted beow) engine models with a CR 8.7:1; then there are also the HIO-360's with both 8.7:1 & 10:1 CR's

image.thumb.png.e04010a4ab847f74eba1f57993718113.png

I’ve never understood why the Helo engines with 10:1 CR make less power at higher RPM than 8.7:1CR  fixed wing engines at 2700rpm. Timing is retarded a bit to  20° But that should not make a huge difference.

E6AACF3B-AC99-4CFA-AE1C-E7B546C866ED.thumb.jpeg.4bd1227f0c28be033e67646bc521eaf5.jpeg

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Anyway, back to the original post....regarding oversquare on a 550 Continental, not a 360 Continental, and not a 360 Lycoming-

I would take the advice from Continental, and not operate the RPM in the range that seems to have ruined more than a few crankshafts.

When they do fail, they destroy the engine quickly, so you won't get much warning.

 

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If  back to the original topic, I can share this from prior discussions with Mike B. The Cape Air failures that resulted in Continental CSB09-11A. It's a service bulletin, not an AD, so it is not an operating limitation, just a suggestion. CSB09-11 arose out of accelerated crankshaft counterweight pin/bushing wear that occurred in the Cessna 402C fleet operated by a Part 212 air carrier called Cape Air. The problems occurred in turbocharged TSIO-520 engines that were operated very far oversquare and with worst-case ROP mixtures. The Cape Air operations were very unusual -- extremely high-cycle ops, very short flights, worst-case leaning procedures. 

To the best of Mike's knowledge and belief, no similar accelerated counterweight pin/bushing wear has ever been observed in normally aspirated Continental engines, nor in engines operated primarily LOP. The intensity of power pulses (and thus torsional stress on the crankshaft and motion of the counterweights) is greatly reduced during LOP operation. 

Mike has literally thousands of hours flying TSIO-520 engines LOP at RPMs in the 2100-2200 range and no unusual counterweight pin/bushing wear was observed at teardown.

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10 hours ago, Shadrach said:

I’ve never understood why the Helo engines with 10:1 CR make less power at higher RPM than 8.7:1CR  fixed wing engines at 2700rpm. Timing is retarded a bit to  20° But that should not make a huge difference.

E6AACF3B-AC99-4CFA-AE1C-E7B546C866ED.thumb.jpeg.4bd1227f0c28be033e67646bc521eaf5.jpeg

It’s called derating... they do it for a myriad of reasons... tbo increases sometimes, transmission weakness, rotor issues, airframe.

but mostly to keep those helicopter pilots humble. Kidding... that’ll be the day.

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7 hours ago, Sandman993 said:

It’s called derating... they do it for a myriad of reasons... tbo increases sometimes, transmission weakness, rotor issues, airframe.

but mostly to keep those helicopter pilots humble. Kidding... that’ll be the day.

I understand what derating is and I have a basic understanding of physics/combustion science.  Normally when an engine is derated steps are taken to decrease power like say limiting RPM (eg the M20S’s IO550 is limited to 2400rpm which derates it to 244hp). Increasing the C/R and spinning an engine faster seems like an odd way to make less power. I’m sure there is more to the story.

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On 9/28/2019 at 8:57 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

I'm sure a lot of you know this, but just in case some don't ...

It's not really the compression ratio; that's just a proxy for BSFC (brake specific fuel consumption). The reason that LOP is efficient is that there is a minimum in the BSFC when LOP, and the reason that fuel flow can be used to determine approximate horsepower when LOP is that the this minimum is nearly constant over a fairly wide range of LOP fuel flows. So if you want the exact number you need the BSFC curve for your engine. It turns out that all these engines have similar BSFC curves with the higher compression engines being more efficient and so a further approximation can be made by using the compression ratio in the calculation since compression ratio is readily obtainable. But this is an approximation on top of an approximation, so there is no need to carry it to two or more decimal places. 

Skip

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On 10/13/2019 at 9:51 AM, 65eTurbo said:

No.  8..7.  I'm using the numbers from ADA.

Yes, I’m familiar with their work. The 14.7 multiplier you mention does not match any number that I’ve seen them use. As was pointed out earlier, these multipliers are approximations, but given we’re using math we might as well apply the right numbers. For what it’s worth, the 8.7 CR would use a multiplier of 15.1 not 14.7. The multipliers are driven by compression ratio. Thermal efficiency increases with compression ratio.

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Here's the APS methodology for calculating LOP power using fuel flow that I got back in 2007 at a seminar in Ada.  Remember, this is an approximation.

Skip

908269635_APSpowermultipliers_20191019_0001.thumb.jpg.f8231fdcdef7b7bab0f49fcaccf41625.jpg

 

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On 10/5/2019 at 11:51 AM, Shadrach said:

I’ve never understood why the Helo engines with 10:1 CR make less power at higher RPM than 8.7:1CR  fixed wing engines at 2700rpm. Timing is retarded a bit to  20° But that should not make a huge difference.

 

Certification is different for heli engines. Also, heli engines drive a large HP consuming cooling blower. Heli engine certification requirements include sustained operation at 105% and 110% of rated power. To achieve this, the ratings must be "adjusted". As you'd never be able to wring 220HP out of a 200HP (really 195HP) IO360 angle valve Lycoming under any conditions. But if it were de-rated to 170, you could then get the 17 additional HP necessary for the 110% certification requirement. 

 

The higher RPM is also driven by both practical requirements and certification. As 70% power must be available at 70% RPM, and it must be available at an altitude above sea level. From a practical point of view, any helicopter must be able to hover out of ground effect at 5000 feet, or 25 inches of manifold pressure. 

In real world terms, similarly built heli and airplane engines make the same HP. 

EDIT, Note: the higher RPM results in reduced volumetric efficiency. Meaning the torque curve declines as RPM increases. This leads to a favorable characteristic of increasing torque as RPM decreases from redline. 

Edited by cujet
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18 hours ago, cujet said:

Certification is different for heli engines. Also, heli engines drive a large HP consuming cooling blower. Heli engine certification requirements include sustained operation at 105% and 110% of rated power. To achieve this, the ratings must be "adjusted". As you'd never be able to wring 220HP out of a 200HP (really 195HP) IO360 angle valve Lycoming under any conditions. But if it were de-rated to 170, you could then get the 17 additional HP necessary for the 110% certification requirement. 

 

The higher RPM is also driven by both practical requirements and certification. As 70% power must be available at 70% RPM, and it must be available at an altitude above sea level. From a practical point of view, any helicopter must be able to hover out of ground effect at 5000 feet, or 25 inches of manifold pressure. 

In real world terms, similarly built heli and airplane engines make the same HP. 

EDIT, Note: the higher RPM results in reduced volumetric efficiency. Meaning the torque curve declines as RPM increases. This leads to a favorable characteristic of increasing torque as RPM decreases from redline. 

Thank you for the explanation.  I understand the relationship between RPM and volumetric efficiency.  I also understand the relationship between torque and horsepower. While the torque per cumbustion event may decrease as rpm increases, the cumulative effect is still typically an increase in power due to the increased number of combustion events. This was why I wondered how a higher compression (10:1) angle valve, spinning 500rpm faster, would make less power than a the the lower compression (8.7:1) engine while turning 500rpm slower.

Edited by Shadrach
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On 10/4/2019 at 8:49 PM, Sandman993 said:

That’s bs! Pie aren’t square... they are round!

Cornbread are square!

<sorry, I'm out in the country, and we use our skillets on the stove, not in the oven>

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2 hours ago, Hank said:

Cornbread are square!

<sorry, I'm out in the country, and we use our skillets on the stove, not in the oven>

I’m with you brother! I tease my real brother about living in the city... heck, if you run out of toilet paper, just pound on the neighbors bathroom window to mooch a roll. Love those zero lot lines!

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6 minutes ago, Sandman993 said:

I’m with you brother! I tease my real brother about living in the city... 

This is where my mail comes from; note tgat it's  a "town" not a "city." I'm 8 miles out into nowhere from the Post Office . . . .

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On 10/20/2019 at 6:22 PM, Shadrach said:

 This was why I wondered how a higher compression (10:1) angle valve, spinning 500rpm faster, would make less power than a the the lower compression (8.7:1) engine while turning 500rpm slower.

It really does not make less power. In fact, the simple change from 8.7 to 10:1 pistons in a typical angle valve IO360 brings real world 2700 RPM output from 195 real world HP to 210HP. 

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FWF claims up to 25hp increase with their 10.1 cr pistons stc. Volumetric Cylinder match when new cylinders are used as in my case. I don’t have any provable science to back up my explanation... and my only previous experience with the a3b6d was about 400hrs running around with intake valves that were not opening all the way. I bought this ship with a new cylinder recently installed... I suspect the previous owners got a look at the cam while the cylinder was removed and hung a for sale sign on it. Oh, they conveniently forgot to disclose... And at the time, I had not yet become wise to cams.

Whatever, I’m pleased with the cruise and climb numbers... also added a power flow exhaust to diminish the hp loss of a stock muffler. She’s a grin maker now!

Just received Blackstone oil analysis at 155hrs smoh and they say everything looks great and engine is healthy. Was asked a week ago to deliver a pilot back to his home town 130nm away and while he was drooling about several things, among others, he mentioned how smooth the engine ran.

FWF rocks!

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10 hours ago, cujet said:

It really does not make less power. In fact, the simple change from 8.7 to 10:1 pistons in a typical angle valve IO360 brings real world 2700 RPM output from 195 real world HP to 210HP. 

That was my take from your first explanation. Power on paper and power at the crank are not the same.

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