LOP in the Check Ride

[201er]

Ops below 3500 is where I find LOP to give the biggest bang for the buck. My bird will burn a lot less gas LOP at 1500ft than it does ROP and it stays nice and cool. But then many folks are uncomfortable running LOP above 65%, I'm not one of them... I often climb LOP on hot days to keep temps down.

The trouble with climbing LOP on a hot day is that you're not climbing so well in the first place...

[Shadrach]

The trouble with climbing LOP on a hot day is that you're not climbing so well in the first place...

If I have to take 500FPM to get my #3 CHT below 375, I'll take it.

[jetdriven]

Shadrach, the guys over on BT, namely Walter Atkinson, have done extensive testing on LOP climb.  At the point the LOP climb airplane reached top of climb at 100NM donwrange, and 10K, the ROP/target airplane was already in cruise at high speed.  IIRC the total fuel used at that exact same point (top of climb and accelerate to cruise speed for the LOP plane, and the ROP plane at that point in space as well) was only a half-gallon more for the ROP/target airplane, and this was an F33A Bonanza. A Mooney would save less.

 

"We used two F33As with the IO-520s. Set a GPS point 100nm downrange. Took off in formation. One climbed at the Target EGT ROP to 10k; the other went LOP at 500 feet AGL and made the same climb to 10k-- at 500fpm (or less) as altitude increased. Both used the same Target IAS. The ROP climbing airplane reached the 100nm point first and had burned less than .5 gallons more than the LOP-climbing F33A. If the half-gallon is important, go for it.

The LOP engine does run cooler, but the ROP engine using Target EGT runs adequately cool itself.  Walter Atkinson" source:  http://www.beechtalk.com/forums/viewtopic.php?f=37&t=66527&hilit=lop+climb&start=0

 

 

 

It is more efficient from a fuel standpoint, but from a cost standpoint the target EGT ROP climb is more bang for the buck.

 

If climbing into stronger headwinds aloft, the LOP climb saves more, because your headwind component during climb is less due to the lower climb rate.  If there are increasing tailwinds aloft, then LOP climb may burn more for the trip than a ROP/target climb, due to lost opportunity of the tailwind, you get it later in the flight.

 

Turbocharged, high output piston singles and twins with a lively climb rate (They make rated power until top of climb), such as the TAT TN-A36 (Atkinson says 3 savings gallons on the TN-A36) , P-Baron's, light weight C414A's, 421Cs, etc I think there is some definite savings in fuel for the trip, but the dry rate costs of these twin engine airplanes are in the >100$ per hour range, and it takes a lot of fuel savings to offset an additional 20-30 minutes on the airframe.  

 

Total marginal trip cost = (cost of fuel) + (cost of time).  Our particular M20J is 34$ an hour dry rate plus fuel. In reality it is twice that. So, save 1/2 gallon for the climb, add 5 minutes to the trip.  +$3.00 for the fuel and -$2.83 to $5.67 for the dry rate.  A loss. 

 

That said, I will do a LOP step climb 1000' in cruise, and I will do a LOP takeoff and climb if absolute range is critical, such as 800 NM or more. 

[Shadrach]

Byron,

I'm well aware of the trade offs. I typically do use target EGT. However, if my CHTS are 370 trending up and I'm already full rich, pulling the mixture back to LOP will bring CHTs down much, much faster than dropping the nose...

[Shadrach]

Byron,

I'm well aware of the trade offs. I typically do use target EGT. However, if my CHTS are 370 trending up and I'm already full rich, pulling the mixture back to LOP will bring CHTs down much, much faster than dropping the nose...

[xftrplt]

Whatever's easiest for YOU.

Remember, KISS.

[Shadrach]

It isn't complicated!

[DaV8or]

I haven't bothered to read all the responses, but if it were me, I would just run ROP for the check ride. Don't lean in the climb, use the lean to rough and richen to smooth technique in cruise and then full rich in the pattern at GUMPS. This way you won't get any flak and your engine will survive all this horrible abuse for the duration of one short flight. You really don't need to try to educate the examiner about engine management and you also don't need a lecture about detonation and burned valves. The examiner might even make a suggestion to their favorite engine management technique and you can be duly impressed with his/her wealth of knowledge.

[DS1980]

How many degrees ROP and LOP were the target and LOP airplanes? My thinking is that the fuel flow is only close if one is running JUST rich enough and the other is running JUST lean enough.

[mike_elliott]

How many degrees ROP and LOP were the target and LOP airplanes? My thinking is that the fuel flow is only close if one is running JUST rich enough and the other is running JUST lean enough.

If I understand what you are asking, Targeting EGTs LOP is just an end to really get to Fuel Flow. Using fuel flow is a faster, more precise means to get to the percentage HP you want. While not as precise for HP ROP, MP and RPM will get you where you want to be ROP, just keep the EGTs 100 below peak. You will have a FF number for your engine here, and once you know what it is, you can lean to it vs EGT.

[201er]

I don't think this is so. While the FF will define your HP (at least in theory), it will not define how far from peak your EGTs are. As altitude and possibly other factors change, as well as rpm/mp combination, the same FF can be putting you at peak vs 100LOP in different conditions. Target LOP EGT ensures detonation margin, cooling, and best power to economy ratio. Who can explain this better?

[aaronk25]

I don't think this is so. While the FF will define your HP (at least in theory), it will not define how far from peak your EGTs are. As altitude and possibly other factors change, as well as rpm/mp combination, the same FF can be putting you at peak vs 100LOP in different conditions. Target LOP EGT ensures detonation margin, cooling, and best power to economy ratio. Who can explain this better?

You did a great job of explaining it. To even take it to a further extreme at fl180 on my m20j peak is at 7.4gph at 2700 rpms! Where at sea level peak is at 11.5 gph it all varys with altitude! But on a io360 8.2gph is about 55% 9.2gph 65% and 10.2gph is 75%.

However obviously putting the fuel flow at 10gph isn't going to get you 75% power at 10k feet. Once you go to the dark side past peak it makes 3% more power at 80rop but that's it. Need turbo to bring MP up to go faster something I am lacking

[Shadrach]

Target EGT method in climb is simply a way to simultaneously maintain max power at a safe ROP mixture (though there is no reason why you could not do the same thing LOP at the expense of reduced climb performance). Nothing more. The Bendix RSA at full rich at SL on a standard day should translate to a mixture setting ~250 ROP (+/- 25df) this is a safe place to produce full power ROP. Whatever that raw number may be in terms of EGT (in my plane it's about 1175df or ~265 ROP depending on temp and DA) should be the target you lean to as you climb. you can go a little leaner as power starts to drop off above ~3000ft (I shoot for 1225 or so CHTs permitting). As you climb, peak EGT happens at a lower temp so while a taget EGT of 1225 (in my case) may be 215df ROP at 4500ft it may only be 175df ROP going through 9500ft. If CHTs are low, you may choose to increase the target number by 25df. Target EGT method of climb ensures robust performance, and ideal fuel flow for ROP climbs.