Prove that LOP climb is more efficient

[testwest]

Trying to upload my thesis, the uploader barfs after momentarily showing the upload. Anyone wants a copy just PM me, it is a 12.7mb PDF file.

[WardHolbrook]

BTW, I wonder if flying lighter by going LOP helps with anything? Say you're going somewhere that would normally require full fuel but LOP you can take 30% less fuel. If you actually do that and not top it, you probably save even more by having less weight to haul around?

Didn't you just answer your own question? It's pretty much SOP to NOT automatically top off aircraft fuel tanks in aircraft that are larger than your typical 2 - 4 - 6 seat light SEL airplanes. Once you get up into the heavier light-twins and above you very seldom fly with full tanks. Landing with more than 60 mins worth of full is one of the more inefficient things we do as pilots - carrying around unnecessary weight saps aircraft performance and costs money. However, there are many legitimate reasons to do so - IFR reserves, fuel pricing, etc; but to just automatically do it is sloppy flying.      

[Hank]

Norm--

 

The published Vy for my C is 100 MPH at sea level, with a straight-line decrease to 91 MPH at 10,000 msl; I approximate as 100-[Alt in 1000's], and try to stay within Vy to Vy+5 during climb. My limiting factor is almost always Oil Temp, but only when it's warm outside.

[testwest]

Thanks for posting that. The chart says the configuration for Vy is 15 deg of flaps, is that what you do? Is there a climb chart published with flaps retracted?

[Hank]

No, I only use flaps when loaded heavy and raise them after I'm clear of the trees. That's the only climb chart I have . . . I did go to 16,000 msl once, to see how I liked oxygen and how she handled. The last few thousand feet were s-l-o-o-w, with a few level-offs to build speed. I calculated DA of 18,800'. Did I mention it was in August? Flaps up on that one, too. Then some emergency descents, both max speed and max rate of fall. Fun!

 

Here's what the OM says under Normal Procedures/Takeoff and Climb:

 

Retract the landing gear only when safely airborne and in good control. Retract the flaps when the aircraft has cleared all obstacles and has gained an indicated airpspeed of about 80 to 90 MPH.

 

Then comes the following page. Sorry, OM's in 1970 were not heavy on data.

[aaronk25]

My C climbs faster than that on 20 less hp! WOT/2700/Full Rich, at Vy is 1000+ fpm at home.

 

You need to recheck your math . . .  10 minutes is 1/6 of an hour; 1/6 of 3.5 gph is not 1, it is 3.5/6 = .58, a half gallon. There's no need to lean in the climb unless you use the Target EGT method, as your temps will all rise until you get below peak. See above, I rarely climb for 10 minutes and don't flight plan where ½ gallon makes a difference. I respect the "golden hour" and plan to land with at least 9 gallons, so far haven't been below 11.

Good for descents. I maintain cruise MP & EGT all the way down, easing throttle back and mixture forward. Makes for nice groundspeed. I learned the first time I flew an F that procedures don't always transfer well between carbureted and injected engines.

 

I'm supposing that the 115 KIAS climb speed (Vz) is Carson's speed, which I always thought was used as an endurance cruising speed rather than a climb speed. I climb as close to Vy as Oil Temp will permit on the green stripe, and can easily be at 9000' msl, power set and trimmed, within 15 minutes of turning the key. Home field = 567' msl. You injected folks with more power should easily beat me.

 

If a simple Mech. Engineer could work his way through your MS thesis on efficient flying, could you post a link or send me an abstract or something? I apparently didn't absorb as much from the previous Carson discussions here and elsewhere as I thought I did.

 

I tell you what guys I'm gonna go out to my airport RST and go do 2 identiall climbs back to back to 8000 feet with one being ROP and the other LOP.  Ill make sure to do target egt climb on the ROP climb.  I will report the difference in a couple days depending on when I can get out of the office.

 

My point is if you climb ROP your fuel flow on a io-360 200HP is  17ish gallons per hour everything forward, reducing to around 14gph at 6000ft, if you maintain the target egt,  LOP it is 10.6gph reducing to mid 9s at 6K.  

 

I think I only loose about 10-15% of the available horsepower by climbing lean of peak, but save 40% of the fuel.  I also reduce the amount of how LOP the engine is as I climb.  For example at 1000AGL 10.6 is 50 degrees LOP or so.  At 6000 9.8gph is 15LOP.  The CHTs will be some degree cooler than ROP climb.

 

It so hard to sit here at my desk and try to remember all the exact parameters as to what is what, because there are those who will pick anything apart. Tell you what, I'll do the back to back LOP and ROP climbs and then post exactly what my Fuel burn was for both climbs to 8000.  That should solve it right???

 

One other thought it was said the the "C" model out climbs my J, but what wasn't discussed was loading, temp ect.  I was trying to recall gross operating weights, so I could have been off, but at least it makes your C sound like a hot rod  .

[jetdriven]

10.6 GPH LOP is only 80% power, and then you lose the prop efficiency by climbing at a slower airspeed.  So call it an effective 75% power.  And 75% of the fuel flow.  But you still don't climb as well.

 

Also, check the time to climb and the distance from takeoff airport.  Fly the same distance LOP after the ROP target climb level off.  THen record fuel used.

[testwest]

A couple of additional items for aaronk25: it sounds like you are trying to maximize mpg (least fuel used). If you are maximizing mpg on climb, it also makes sense to fly maximum ENDURANCE speed (min fuel flow) on your cruise. At cruise, that is a very low power setting, and the specific fuel consumption is higher than it would be for a  ~65% cruise.

 

As Byron said, your LOP climb will result in a longer distance to climb. If you then do a ROP climb next, after level off you are not at the same point from takeoff. You will most likely be closer to the takeoff point. Evaluating fuel used at that point is incorrect, because you are not at the same point in the sky. You will have to cruise some to get to the top of climb point for the LOP climb you just accomplished.

 

Again, your measure of efficiency is not rigorous unless you factor in the velocity made good into the evaluation. Speed has a value, just like fuel. The CAFE parameter I have written about extensively is, in my opinion, the most valuable measure of merit when discussing small airplane efficiency.

 

You will need to hold every other parameter nearly constant to do a comparative performance analysis. That will include flying back to the airport after your first climb and refueling so your first and second takeoffs result in the airplane weighing the same for both. Flying the second flight 30lb lighter will invalidate your results. Same thing with weather, you need to fly the points back-to-back during a time of day in which the temperature, winds and barometer setting are pretty much the same.

 

Once you note the time, fuel and distance to the same point using both techniques (assuming you are using about Vy (88KIAS or 86KCAS for the J), evaluate it this way:

 

Velocity Made Good = Distance/Time. You will get some airspeed number. Raise that number to the 1.3 power.

 

MPG = Distance/Fuel Used. Then multiply Vmg**1.3 x MPG. That number is the CAFE parameter. The higher number is more efficient.

 

You should be able to produce a data table like the one below. Also, if you are savvy with the track log function of a GPS and Google Earth, you should be able to produce a visualization of the flights like the photos shown below. There are two flight tracks in the photos. The Vy one is in magenta, and the Vz one is in white. Vz top of climb used 4.1 gallons. Vy climb was 3.5 gallons. Is that more efficient? No. The airplane is 7.5 miles closer to takeoff. Flying down to the Vz top of climb point in cruise used .6 gallons. The fuel to the same point in the sky was the same, but the Vz climb velocity-made-good was 95 knots, the Vy was 76. 19 knots faster on the same gas....achieved solely due to pilot technique. This particular test day had a very strong headwind for the climbout path. However, since you are after comparative data, the test day conditions don't need to be normalized to standard day conditions. You may wind up with higher CAFE scores due to a tailwind, but you can only compare data obtained under nearly identical conditions.

 

I have gotten similar results with an M20K (with STCed wastegate and intercooler) and an Encore.

 

Also attached is the test card used to hand-record some of the data on the flight. Hope this helps. Look forward to your report!

Vz Flight Card.pdf

[jetdriven]

Here is a post from BT from Walter Atkinson, one of the owners of APS:

"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.":

 

These are bigger engines and as such, I bet would have a bigger difference in fuel wasted during a ROP climb. They saved a half gallon in a LOP climb. I bet in an M20J the results would be that or less. Now, if climbing into a headwind, higher is worse. In that case, climbing LOP (slower FPM climb) would be beneficial from a fuel per trip standpoint, but perhaps half or more of the benefit is the less exposure to headwinds during the climb, not the LOP operation itself. 

 

The whole thread is here: http://www.beechtalk.com/forums/viewtopic.php?f=37&t=66527&p=730281&hilit=range+altitude#p730281

 

good reading.

[testwest]

Very interesting, indeed. I have not done a sensitivity analysis on LOP climb for Vz, however the very stark increase in prop efficiency and lower drag factors (not speed, obviously, but less cooling drag from wide-open cowl flaps and less drag induced from counteracting sidewash) while on the Vz profile tells me choice of climb speed is far more important than using an LOP climb versus a Target EGT ROP climb.

 

Still waiting for aaronk25's flight test report.

[testwest]

Bumping this up to the top to refresh the thread, and to support another post.

[PTK]

LOP climb requires that your mixture is sufficiently lean. Down low you'll be at some really dangerous power settings which require very close attention to mixture control. The mixture will get richer as you climb especially because you don't have an alt compensating fuel pump. For this reason and because of the reduced power I never climb lop. I don't see any good reason to climb lop. Fuel is the cheapest thing in my airplane. Target egt climb as suggested by Norman is the way to go for me.

[jetdriven]

There won't be any dangerous power settings. Simply lean to 11 GPH, or to 10 GPH of you are chicken of 83% LOP. You know what your peak EGT is, for us it's 1510. So as you climb, keep the ff below 11 GPH and keep your EGT 50 LOP at low altitude and 15-25 LOP above 5000 feet.

The problem with LOP climb is it is much more work for what I suspect is zero benefit.

[201er]

There won't be any dangerous power settings. Simply lean to 11 GPH, or to 10 GPH of you are chicken of 83% LOP. You know what your peak EGT is, for us it's 1510.

Doesn't peak EGT vary depending on altitude, temperature, and pressure?

[testwest]

True dat, Jet. It is better to get to your planned altitude for best cruise with respect to winds with as much power as you can get and the best forward speed to match.

[jetdriven]

Doesn't peak EGT vary depending on altitude, temperature, and pressure?

 

Correct. However, in the 75% on up power range, its pretty consistent. If leaning and not sure what number to use, go to target EGT for ROP, or  for LOP based on the 75% EGT value, which for us is 1510.   It will keep you safe.

[PTK]

There won't be any dangerous power settings. Simply lean to 11 GPH, or to 10 GPH of you are chicken of 83% LOP. You know what your peak EGT is, for us it's 1510. So as you climb, keep the ff below 11 GPH and keep your EGT 50 LOP at low altitude and 15-25 LOP above 5000 feet.

The problem with LOP climb is it is much more work for what I suspect is zero benefit.

 

The problem with LOP takeoff is that my engine is making less than maximum power, and I always want maximum power at takeoff for maximum safety. Also, the takeoff performance charts in my POH are predicated on using maximum power, and if I takeoff with partial power I'd be a cheap test pilot!

[jetdriven]

You takeoff full power ROP and do the mixture pull to lop after takeoff

[201er]

Doc, no one ever suggested taking off LOP! It's only in question in the climb once comfortable.

 

Byron, how do you know what your peak EGT is at full power? I'm too chicken to do a proper "mixture leaning" above 75% to find peak because of detonation threat. When you pull quickly, EGTs never fully reach peak.

[jetdriven]

For us it's something above 1510 degrees, probably 1550. But if you use the 1510 and stay 50 lean or well rich of that nimber, its a conservative strategy.

[PTK]

Doc, no one ever suggested taking off LOP! It's only in question in the climb once comfortable.

I see that now Mike. The discussion was referring to climb. Thanks.

There is no safety issue with LOP climbs once at a safe altitude. It would be a high-workload exercise because it requires close attention to temperature management. Especially in a tc airplane keeping TIT below red line.