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Darren S

Well Known Member
Hi group,

I've had my "new to me" -7 for a month. It has an IO-360, Constant speed prop. It also has an Advanced 2002 EIS. I live in Western Canada and my home field is about 3400 feet.

I typically cruise at about 5500 - 6000 ASL. At this height I get 160 knots cruise at 22" MP and 2350 RPM. Fuel burn is 9.5 gph when leaned to 100 degrees ROP. Peak EGT is around 1450'ish so I shoot for EGT's in the 1350 range. All right in line with the POH.

This morning I took a little foray into the mountains. On the way home I climbed up to 9500 feet to clear some peaks. At this altitude I was full throttle at about 21" MP so I turned the prop till the RPM was 2250. I leaned to peak (engine starts to stumble) then richened to 100 degrees ROP, as per usual. EGT's were in the low 1200's and my fuel burn was in the 10.5 gph range.

Here's what I need a little help with. Are these typical numbers ? Is my process of leaning to peak and then richening to 100 degrees ROP correct ? Why such low EGT's at 9500 ? Why such high fuel burn at 9500 ? At 9500 I don't think I could get EGT's of 1350.

I know this is elementary to some of you out there. If you could share your wisdom, I would appreciate that.

Thanks,

Darren
 
I just looked at one of my 9500' pics. MP just under 20, 7.6 gph, and prop set 2300 rpm. I must have the throttle pulled back a bit. EGT on #3 is 1290 F. I'm only able to measure #3 at this time. I usually lean to rough, and then about three turns rich. This gets me in the ballpark & plugs always look good, and the engine runs smooth. Most of the time, my EGT on #3 will usually be between 1300 & 1325.

L.Adamson ---- RV6A
 
EGTs are, in part, a function of the probe location, so I wouldn't use exact numbers for comparison to another engine. Seems to me that you're burning way too much fuel. If I'm cruising at 8000 ft (airport is 5000, so I can't easily cruise there and usually I'm higher than 8000) I typically run ~2400 rpm, ~7.5 gph fuel burn, when leaned out. My leaning procedure is to lean through peak to about 50 degrees lean on the leanest cylinder. Typically, this results in maybe 10-20 rpm drop. Much further lean and the engine starts to run a bit rough. My temperatures, for what that's worth, are typically in the 1400 degree range at peak, and my probes are 6 inches from the port. At higher altitude, peak EGT is usually lower, and at a couple thousand feet they will run 1450 or a slight bit higher.

I'm not sure why your EGTs are so low at altitude, other than possibly you are far too rich. I know that if I richen the mixture, it doesn't take much to increase fuel flow dramatically (I can easily see 9-10 gph and 1200 EGT at 9000 feet if I'm way too rich).

Caveat is that I have a FP prop, but I don't see any reason why that would be significantly different than your CS in cruise mode.

Hope this helps.

greg
 
Thanks for the help so far.

So it seems that it is normal for EGT's to be lower at higher altitude. Also, it appears that I am running pretty rich.

I don't think I want to go 50 degrees lean of peak. I understand that some folks prefer this method but I think my limited understanding may be detrimental and I may end up wrecking something.

I was shooting for 20" MP and 2250 RPM because the POH showed this as 55% power. This is also why I cruise at 22" MP and 2350 RPM as this is 65% power.

I also didn't necessarily have to run WOT. I guess I could have backed off but then I wouldn't be getting 20" MP so would I set my RPM to 2150 or go higher to 2400 ???

I was aiming for the 100 degrees ROP as I do at 6000 feet.

So...... I guess now I'll search to find what MP, RPM settings others are choosing at different altitudes.

I don't mean to make a mountain out of a mole hill. Just looking for a good, economical setup that is "engine friendly".

Thanks again,

Darren
 
Can't hurt the engine at those power settings

At those low power settings, you can't hurt the engine no matter what you do. Normal Lycoming procedure results in running just about right on the peak, and thats Ok at those MAP and RPM. I'm not saying its the best point to run the engine, but you can't hurt it there.

Don't be afraid to go lean - the engine loves it.

My EGT's seem to be sensitive to altitude and ambient temperature. I have not recorded enough points to understand the trends, but at the same MAP and fuel flow, I see some variation in EGT based on altitude and OAT.
 
If all else allows, things are more "efficient" oversquare e.g. we cruise at 2300RPM / 25" [180HP FI / C/S / RV-8]. I find it easier to establish LOP in that regime as well. It gives at lower levels ~145-150KIAS on ~8.3USG/hr, and the Dynon says ~71%-72%. That is with 2 x Mags and FI, EI would clearly be more efficient.

There are as many opinions about "oversquare" / "overboosting" as posters on this forum :eek: But the authoritive manuals I have seen indicate going to 4"-5" oversquare is fine, and a rule of thumb of max 2" is fine, even conservative.

Reducing RPM also tends to reduce EGTs.

Andy
RV-8 G-HILZ
 
flow meter

Also, make sure your fuel flow meter has been calibrated. They all are calibrated at the factory, but matching recorded fuel used with actual fuel burned may give you a slightly different k factor number for the fuel flow meter and how it reads in your particular application.
 
Just another datapoint. My Lycoming manual for my parallel valve IO-360 says I can run at peak below 75% power. I usually run lean of peak, but basically below 75% power you are not going to hurt anything.
 
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DakotaHawk said:
This is the best series of articles I've ever read about leaning and engine management. I've been running my engine based on these articles and have been very happy with the results.

http://www.avweb.com/news/pelican/182179-1.html
Click to expand...

Here's a link to a whole series of Deakin articles. I can't recommend these enough. All the myths about LOP and "over square" operation are dispelled and with facts and backed up with real world data.


http://www.avweb.com/news/pelican/182544-1.html
 
Darren S said:
...I don't think I want to go 50 degrees lean of peak. I understand that some folks prefer this method but I think my limited understanding may be detrimental and I may end up wrecking something...
Click to expand...

Not to pick on you, but what exactly do you think is going to happen? Perhaps we can dispel some of that fear?

As several have said, there is nothing you can do to the mixture at that altitude that will hurt the engine. Lycoming even recommends peak EGT - so 50 LOP is LESS temperature and LESS internal pressure than that approved by the engine manufacturer.

And BTW, WOT at altitude is best for reducing pumping losses. Many here don't believe this, but here's what the folks at Tornado Alley have to say:

...Every internal combustion engine operates more efficiently with the throttle wide open, than any other position. However, this does not mean that the engine will be operating at 100% power. On the contrary...
...both the MIXTURE control and the propeller governor can be used to reduce or "modulate" the horsepower produced by the engine.

...THEREFORE, we suggest that, in general, in cruise, that the engine be operated with the throttle in the WOT position, and the horsepower be controlled by appropriate use of the mixture and propeller governor controls...

Botom line is that LOP, nor "oversquare" operation is much of a black art once you get your head around it and stay clear of just a few "gotcha's".
 
Thanks to all for the help and for the references to the Deakin articles. I'm reading through them and getting a better picture of what I am to be doing when flying at altitude.

He writes the articles in a very easy to read way, and cuts through alot of the mystique. Great stuff for all to read.

Darren
 
Ok, me again. It's been a long day of reading and understanding, I think, on what I am going to try on my next flight.

Normally I would set up cruise at 6000 feet as such. MP 22", RPM 2350, lean out till engine stumbles, note the peak EGT and then richen to 100 degrees ROP.

The articles by John Deakin have been eye opening to say the least.

Here's what I will try next time out. Takeoff and leave throttle wide open. Set prop to about 2500 RPM for climb. Level off at 6000 feet. Lean mixture to 25 degrees LOP and decrease RPM to ?...... Not sure.

One thing I'm not sure of. I've never leaned my engine to LOP. I thought that peak was when the engine starts to stumble. If I continue to lean the engine beyond this point, isn't the engine going to shut off ???!!

Darren
 
I've never leaned my engine to LOP. I thought that peak was when the engine starts to stumble.
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If you have leaned until the engine stumbles, then you have most definitely been LOP. If fact if you enrichen from the stumble, say 50-100 degrees, you may well be around peak EGT. (and power)
 
Gotta go slowly on the leaning - a tiny bit of mixture can cause significant changes. Starting at full rich, lean while watching the EGT. As soon as one cylinder goes beyond peak, continue leaning to about 50 degrees lean (of course don't do this if the engine is coughing!) and you should be about right. If I recall correctly, you have a 360 engine. I would guess that you should be around 7.5-8 gph properly leaned (again, I have a FP prop, so not sure how this might change with a CS, but I wouldn't expect much difference).

Cheers,
greg
 
PIN 37 said:
If you have leaned until the engine stumbles, then you have most definitely been LOP. If fact if you enrichen from the stumble, say 50-100 degrees, you may well be around peak EGT. (and power)
Click to expand...

Exactly... The stumble is because the engine is so LOP that combustion can't be supported any longer. A strong ignition will delay the "stumble" much longer (cooler) than a weak one, which is why EI works so well LOP. Where the magneto is falling on its face (say, 50-75 LOP) the EI may still be smooth.

Picking the RPM for cruise is really a function of experimentation and how much of a hurry you are in - BIG hurry, lean for best power (ROP) and max RPM; best economy, as lean as you can stand and 2300 or so. Should be WOT though.
 
read deakin carefully

You are right PIN 37. If you lean to rough running, you are past and below peak EGT on the lean side.

However, I believe you are wrong on peak EGT. According to Deakin, peak EGT is not peak power and peak EGT is to be avoided above 65% power. Peak power is 150 - 100 ROP (depending on % power). Deakin describes peak EGT as a place to avoid at any operation above 65% power. Besides, there is no reason to run there. It is not best power, it does not get you the advantages of LOP, and again, it is to be avoided above 65% power (peak EGT generates High temps and high internal pressure and possible damage).

Per cent power is important. Below 65% Deakin says you can run at any EGT without damage. At 75%, you must avoid above 125 (or so) ROP and below more than 25 LOP. Above 75% power, never above 150 ROP (best power).

Deakin says During climb, Run 150 ROP until the altitude degraded MAP in combination with your chosen RPM is less than 75% power. Then you can go to 125 -100 ROP for best power to climb. Once level you can stay at best power ROP for fastest cruise, or lean 25 LOP for economy.

If leveling off at below 65% power, you can go to 100 ROP for best power and fastest cruise, or lean to 50 or more LOP for best economy. I find it easiest at 65% or less power to lean to rough running and richen back to smooth. You'll be somewhere between 25 and 50 LOP.

It is a bit confusing, read deakin carefully and think it through. Never a good ida to be at peak EGT.
 
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Thanks Gary, I re-read the cruise article and I follow his graphs.

Two other things:

First, I have two Slick mags. No electronic ignition. How will this affect my LOP settings ? Are they going to get really HOT !! ???

Secondly, he talks about the "big pull" from rich to lean. I don't know about this. I think I will do as Greg suggested. Go slowly and lean till peak, then go beyond this point till all cylinders are 50+ degrees LOP.

I am excited to try this. Better fuel economy and cooler running engine...... kinda wish I knew this earlier.

Darren
 
Oh and Darren

at level off, reduce RPM first, then lean. What RPM depends on what you want - fastest cruise or some economy. As Toolbuilder said. If fastest cruise is what you want, set RPM at whatever feels comfy and lean to best power 150 - 125 ROP.

If better economy is what you want, set 75% power or less. For our engines and typical altitude (6000 - 11,000) the rule of 48 is pretty accurate. Search the threads for that definition.

Slick mags should'nt matter. It all still works.

Not sure about the "big pull" either, just don't dally un-necessarily in the peak EGT area. Greg's also right about the fuel flow, it'll be around 7.5 GPH for a 360 and around 70% power.
 
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gereed75
I agree with you about peak power and peak EGT not being in the same place. Dont know why I added the bracket really.
Slight thread drift maybe, but I used to have FADEC on my engine, since removed, but my reading of the manual suggested that it ran peak EGT all of the time. Makes me wonder now how the engine (360) would have taken that seeing as how a lot of time is spent at above 75% power, takeoff, climb etc
Hmmmm
 
Darren,

To carry on with the Deakin theme, let me tell you how I run my IO-360/CS prop on my RV-7.

On take off, Mixture/Prop/Throttle are all full forward. If I'm at more than about 3000' agl airport elevation, I'll keep everything forward on the start of the takeoff roll, and then carefully pull the mixture back while I'm on the roll. Not too far - just until I hear the prop speed up about 50 rpm. Below 3000 agl - don't mess with the mixture.

On climbout, I'll fly at 2700 rpm for about the first 500' climb, and then (as soon as my climb is stabilized) I'll pull the prop back to about 2600 rpm to continue my climb. At about 1500' agl, I'll pull the prop again, this time back to 2400 rpm - and I'll leave it there for the rest of the flight!

So now I'm at 1500' agl with the prop at 2400 rpm. I'm still climbing. My fuel flow is showing about 16.5 gph. At this point, I'll pull back on the mixture until I'm showing about 12.5 gph - which I know from experience puts my engine at about 150* ROP. Watch CHT to make sure you're not overheating your cylinders. All that extra fuel is cooling your cylinders. I use 425* as my hint to richen the mixture to prevent overheating my cylinders. I'll continue my climb at 12.5 gph until I level out or climb above about 6500' msl.

At 6500' msl, I'm either thinking about transitioning from Vy to a conservative cruise climb, or I'm leveling out. After leveling out or reducing my climb rate, I start jockeying my mixture back. Deakin calls it "the big pull". I don't make a big issue of "the big pull". I just start pulling the mixture slowly (it takes a couple of seconds for the fuel flow indicator to indicate new flows) until I'm showing about 9.5 gph. Again, from experience, I know that I'm LOP here. After letting the fuel flow settle out, and letting CHT and EGT settle out for about a minute or two, I'll make bare minimum pulls on the mixture until the engine starts to stumble just a little. Usually the IO-360 runs so smooth that just a little stumble is noticeable. Push in mixture just enough to get rid of the stumble, and I'll find myself at about 8.0 to 8.5 gph, and about 50* LOP. My RV-7 cruises at about 175 mph at 2400 rpm, 8.0 gph at 7,500'.

Did you notice that through the entire take-off, climb, and level out that I haven't touched my throttle? It's still WOT!

Carrying on... When it's time to descend, just leave the throttle/mixture/prop where they are and descend. Unless my engine starts to run rough, I don't touch anything until I'm at pattern altitude and need to start slowing down (I like my CS prop!). Since my prop is unloaded on descent, the engine isn't working as hard so mixture usually isn't a problem.

As I approach pattern altitude, I'll push mixture full forward and pull the throttle way back. Prop is still at 2400 rpm, I couldn't tell you what MAP is. When I pull the throttle back, the prop will stay at 2400 rpm and begin to provide braking. By the time I'm on the 45* to downwind, I'll have the throttle just about all the way out - still using the prop to slow the plane down. At this point, the prop is flat-pitch and I can treat the plane like a fixed pitch for the rest of the landing phase. Finally, just abeam the numbers I'll push the prop full forward in preparation for landing. My goal is to be at Vfe (100mph) just abeam the numbers.

Hope this helps...:D
 
Hey Scott, a big thanks for running through how you set up your LOP flying and for the previous link to the articles. I too have an IO-360 and a Hartzell C/S prop so I think our numbers will be pretty close.

You mentioned twice that you "know" what fuel flow gives you either 150 ROP or 50 LOP. Since I have never run LOP and I don't know these numbers for my engine, below is a proposed way of getting to 50* LOP without spending too much time right at peak EGT.........?

Before I get to my proposed way of finding 50* LOP, let me ask you and the forum this other question...... I fly out of a strip that is 3400 feet ASL.

On my runup at 1700 rpm, can I lean out the engine till it stumbles a little then enrichen till smooth and leave that mixture setting for take off? Do you think that this mixtures setting would be too lean ? We've all done it in the Cessna's we flew in flight school.

Ok, now my proposed way of finding 50*ROP for my engine.

I usually level out at 6000 feet ASL. Once level, and WOT, and prop back to say 2350, I will keep leaning out till I detect a slight stumble. This is easy to find. Then enrichen slightly to smooth out. I'll make a note of this EGT and fuel flow rate. Then I'll continue to enrichen to hopefully see the EGT's peak. Now I SHOULD know where peak is, and where LOP is, and what fuel flow gives me LOP operation.

Anything wrong with this ? Sounds good on paper, hope it works ?? :)

Thanks again,

Darren
 
Darren,

I've found flying out of 5000 (elev) at Reno, that if I lean to peak RPM during runup, richen just a little and take off, that I end up with hot cylinders, so I generally lean to peak and check mags, but then richen the mixture considerably just before taking off. This helps considerably with engine cooling. Cooling might just be an issue with FP prop (?) I don't know.

greg
 
Darren,

If you look at the amount of work that your engine is producing (and therefore the amount of heat that needs to be cooled), the takeoff creates the most work/heat! You asked
On my runup at 1700 rpm, can I lean out the engine till it stumbles a little then enrichen till smooth and leave that mixture setting for take off? Do you think that this mixtures setting would be too lean ?
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I would recommend that you do your runup and lean to stumble, and then really richen the mixture. Not just until it's smooth. Smooth gives you "Best Power". You want to richen beyond "Best Power" until you get "Best CHT/EGT Cooling".

The rest of your plan sounds good to get started finding some rough numbers for reference.

Remember that (according to Deakin's information) you can't damage your engine as long as it's operating below 75% power. So you can find your TRUE EGT PEAK by simply setting up WOT/2350rpm at 6000'. Then slowly pull your mixture. You should allow about 30 seconds between each pull to allow temps and fuel flow to stabilize. Watch EGT's after each pull - they will creep up. Watch for the first one to peak. Note that the first cylinder to peak may not be the highest temp cylinder.

Once the first cylinder peaks, note the EGT temp (remember to let everything settle out for about 30 seconds here), and then continue to pull mixture to get 50* LOP. You'll notice that the engine has a different "feel" as you change the mixture. Try to get a feel for how it "feels" at 50 LOP.

As you climb higher, your fuel flow will change as well. I use my "known" fuel flows as a starting point, and then continue to adjust mixture to keep the feel the same as I climb. For example, at 7500', I flow about 8.0 gph. At 12500' I'm down to about 7.5gph.

Caveat: I've only got 150 hours on my RV-7. I've never flown a CS prop before that. In fact, my whole flying experience consists of a slow, draggy airplane with an 85hp engine and fixed pitch prop. Couldn't climb high enough to ever use my mixture in that airplane!
 
Darren S said:
...On my runup at 1700 rpm, can I lean out the engine till it stumbles a little then enrichen till smooth and leave that mixture setting for take off? Do you think that this mixtures setting would be too lean ? We've all done it in the Cessna's we flew in flight school...
Click to expand...

Almost right, but you are missing an important point: If you set the mixture at 1700 RPM, it is only set for that angle of throttle opening - any increase in throttle opening will be progressively leaner. If you are looking for best takeoff power at a high altitude airport, you must set the mixture for takeoff power and RPM by actually going to WOT and high RPM. Anything less is just a guess.

This is illustrated easily by leaning very aggressively on the ground. I am so lean at idle that almost any throttle increase causes the engine to die. This is also a good way to make sure you don't forget to set the mixture before takeoff.
 
Darren S said:
Ok, now my proposed way of finding 50*ROP for my engine.

I usually level out at 6000 feet ASL. Once level, and WOT, and prop back to say 2350, I will keep leaning out till I detect a slight stumble. This is easy to find. Then enrichen slightly to smooth out. I'll make a note of this EGT and fuel flow rate. Then I'll continue to enrichen to hopefully see the EGT's peak. Now I SHOULD know where peak is, and where LOP is, and what fuel flow gives me LOP operation.

Anything wrong with this ? Sounds good on paper, hope it works ?? :)
Click to expand...

Sounds good but keep in mind a couple of things: Don't get too caught up in using FF numbers from other members as any form of fine tuning untill you have a LOT of experience with the airplane because FF is a RESULT of the mixture at various RPM, altitude, temperature, etc. Using other peoples experience is about as effective as arbitrarily marking your mixture control knob at "8.6 GPH"...

The only thing that matters is peak EGT on YOUR AIRPLANE and how far from either side you run that. And on that note, you don't even care what the value of peak EGT is, just that it is peak.

On another note, we have heard experience that the LOP mixture should not be touched on descent because the engine is unloaded going downhill. This is not true with a C/S prop. If you have set 2400 RPM, the engine does not much care that you are in a vertical climb, vertical dive or tied to a tree on the ground. The only time the prop gets to unload is if it reaches its high pitch stop and simply can't twist the blades any further to compensate for the increased airspeed. In most cases, this will be well past Vne.

With that said, if you are sitting up at 8500 feet, WOT and 2400 RPM you will have a certain % of power. Without touching anything, if you descend lower, your MP will increase as a function of "thicker", more oxygen laden air, and your mixture will go leaner for the same reason. But the "gotcha" here is that you are also increasing your % of power, and you are getting closer to your detonation margins. Since you are still LOP (and getting leaner), detonation can't happen, BUT... you have to be careful about richening the mixture at this power setting because you could drop right into detonation as you are going from too lean to "safely" rich.
 
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Ok Michael, good stuff. Thanks for the clarifications. Fuel flows vary from aircraft to aircraft and EGT's vary because of probe positions so don't get too hung up on a number. Just watch for peak EGT. As Scott said, get a feel for what 50* LOP feels like.

So Michael, what do you suggest I do with the mixture on decent?

Say I am 6000 feet, WOT, 2350 RPM and it's time to come down. Do I descend and keep richening the mixture to keep that 50*LOP EGT setting, or do I do a "big push" and go to a 100 - 150 ROP setting? What do you do ?

Deakin said something about shock cooling an already cooling engine by dumping a bunch of fuel into it.

I've never done it, but descending at WOT and 2350 RPM seems dang fast. Do you guys come ripping over midfield at 150 knots and then somehow slowdown for downwind ? :)

Thanks again for all the good help. I'm anxious to try something new next time out.

Darren
 
Darren S said:
I've never done it, but descending at WOT and 2350 RPM seems dang fast. Do you guys come ripping over midfield at 150 knots and then somehow slowdown for downwind ? :)
Click to expand...

You only go 150? ;)

Well, here's what works for me on descent - there are hopefully others who have different opinions that you can draw from. I want several things from a descent profile: I want to go fast so I can get back some of the speed I lost in climb; I want to be efficient with my fuel burn; and I want to manage my temperatures.

I know that at high altitude cruise I am below 70% power there is literally nothing I can do with the mixture to cause detonation or other engine damage. At worst, I burn lots of extra fuel because the mixture is too fat, or the engine quits because I'm lean - but no "damage". So what I do is simply maintain my cruise MP setting all the way to the pattern. If I'm at 23 inches MP at the top of descent, I keep pulling throttle out as I'm going downhill until I have either reached the pattern, or my target MP. So this saves me from worrying about passing through the "high power/detonation danger zone". I think figuring out where to set the mixture is harder to explain than where NOT to set it - which is anywhere between 50 LOP and ~125 ROP when at or above 70% power. This technique is easy, and allows me to keep the EGT high and stable which is exactly what you want to prevent shock cooling.
 
Darren S said:
Ok Michael, good stuff. Thanks for the clarifications. Fuel flows vary from aircraft to aircraft and EGT's vary because of probe positions so don't get too hung up on a number. Just watch for peak EGT. As Scott said, get a feel for what 50* LOP feels like.

So Michael, what do you suggest I do with the mixture on decent?

Say I am 6000 feet, WOT, 2350 RPM and it's time to come down. Do I descend and keep richening the mixture to keep that 50*LOP EGT setting, or do I do a "big push" and go to a 100 - 150 ROP setting? What do you do ?

Deakin said something about shock cooling an already cooling engine by dumping a bunch of fuel into it.

I've never done it, but descending at WOT and 2350 RPM seems dang fast. Do you guys come ripping over midfield at 150 knots and then somehow slowdown for downwind ? :)

Thanks again for all the good help. I'm anxious to try something new next time out.
Click to expand...

Almost all of my flying is at higher mountain altitudes. I'll slowly richen up the mixture as I descend, but never go full rich, as I'm usually higher than 3000' density altitude. I can litterly tell by the sound & feel, and don't worry about looking at the EGT gauge. I've got to the point to where my engine is always running smooth, and the plugs are always clean and never fowl. Initially, I was quite good at fowling the plugs on my RV. I'd have to clear them on the mag check run up.

A few points to make, though. I'm not throughly convinced about flying WOT all the time, if I'm flying slower to stay with someone else, or care to preserve fuel. I'm not convinced that that wide open throttle plate is making that much difference, than a partially closed plate in a "four banger", when we're pumping less airflow. In other words, I do not yet prefer the WOT method, and perhaps never will.

As to the red knob setting for takeoff, we get quite use to whats a good setting, and what isn't..........depending on airport elevation and density altitude. Yet, mixture adjustment is a real habit around here.

L.Adamson --- RV6A
 
L.Adamson said:
...A few points to make, though. I'm not throughly convinced about flying WOT all the time, if I'm flying slower to stay with someone else, or care to preserve fuel. I'm not convinced that that wide open throttle plate is making that much difference, than a partially closed plate in a "four banger", when we're pumping less airflow. In other words, I do not yet prefer the WOT method, and perhaps never will...
RV6A
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Well, it is a fact that an internal combustion, reciprocating engine is most efficient unthrottled. Whether someone needs all that power is the real debate. After all, if absolute fuel savings was the primary concern, we'd all fly at best L/D speed - but who wants to fly an RV at 115 (or whatever) MPH? Taking that to its most ridiculous extreme, A very small engine which provided that same 115 MPH, but at WOT, would be a lot more efficient than a 360 inch engine with the throttle mostly closed. The benefit of the WOT is to simply make the most efficient use of the speed and HP "capability" of the airframe/engine combination, not look for absolute lowest GPH.
 
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The benefit of the WOT is to simply make the most efficient use of the speed and HP "capability" of the airframe/engine combination, not look for absolute lowest GPH.
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I have a friend who fly's a 9A, but he often likes to fly at speeds to get the best possible mile per gallon figures to the destination. In other words, it's not how fast I get there ........but how much money do I save. Do keep in mind, that even these "slower" speeds, are much faster than a typical Cessna or Piper.

But, if I do decide to fly along at these slower speeds, then it's throttle that seems to work best, and not WOT & pulling the prop rpms back.

And I did find it interesting, that when he once flew my 0360 on a cross country, while someone else flew his 0320 9A..............is that my 6A beat his 9A in fuel economy. :) Normally, I'll just fly faster, higher, and use an extra gallon or two. Oh well...

L.Adamson --- RV6A
 
RE:Engine Instrumentation

Hi Darren

I am a Deakinshead for sure. It has allowed me the info necessary to run my ECi Titian IOX360 in a practical, safe, and efficient way.

What engine instruments do you have .... very important to run that LOP efficiently and safely. I use the LOP mode in the Dynon D120. It gives great info when running the engine either ROP or LOP.

Frank @ 1L8 ... RV7A ... Flying and Tracken ... MT-RTG ...
 
Hey Frank,

I have an Advanced 2002 EIS in my -7. It of course shows 4 EGT's and 4 CHT's and Fuel flow.

I have learned so much from this thread.

I didn't realize the engine performance decreases so much with every 1000' foot of altitude gained. I fly off a field at 3400' ASL to begin with so 6000' is my playground. The Deakin "red triangle" is pretty small at this altitide so, from what I have learned, damaging the engine from running too lean is pretty tough.........relatively speaking.

I know my numbers for EGT, FF etc... may vary because of different instruments and mounting locations, but I think I have enough information to be a safe beginner and begin exploring the LOP side. I've changed my tune from my beginning posts. I never knew any of this.

I fly alot and fuel savings would be very convenient vs. having to stop at the pump every few days. I just have to see if I can live with the "decreased performance" of running LOP.

Darren
 
Not really much decreased performance at LOP, just fuel savings. I normally cruise at ~165 mph and 7-7.5 gph, depending on altitude (throttled back to ~2400 rpm). Adding mixture doesn't affect my speed significantly, but it is easy to burn 9-10 gph (and I see EGTs down from peak of ~1400 to ~1200 due to the cooling effect). I can get to 200 mph (@2750 rpm!) but my fuel burn goes to 12-13 gph. Both cases are not worth it, in my opinion.

greg
 
I anticipate a good experience on my next flight with running 50*LOP. After 250 hours of running at least 100*ROP I assume there is a bunch of carbon junk built up on the valves and in the combustion chamber ?

Does this stuff get burnt off eventually or is it there for good ? Deakin didn't mention anything in this regard.

Darren
 
Greg Arehart said:
...Not really much decreased performance at LOP, just fuel savings...
Click to expand...

Depends on your perspective. The difference between running peak and 50 LOP on in the -8 can be seen on the airspeed indicator. It's easily 5 MPH, and to me, that is significant. The further you go LOP, the faster the speed falls too (until you are gliding, then the speed/mixture relationship is pretty constant) ;) Of course the FF is much lower too. The goal is to strike the balance between speed and economy that you want.
 
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L.Adamson said:
I have a friend who fly's a 9A, but he often likes to fly at speeds to get the best possible mile per gallon figures to the destination. In other words, it's not how fast I get there ........but how much money do I save. Do keep in mind, that even these "slower" speeds, are much faster than a typical Cessna or Piper.

But, if I do decide to fly along at these slower speeds, then it's throttle that seems to work best, and not WOT & pulling the prop rpms back....RV6A
Click to expand...

There is a difference between "efficiency" and "economy". If you fly an airplane that is capable of climbing and cruising faster than you need (overpowered), you can certainly extend your time aloft by throttling the engine, but this is not the most "efficient" use of this engine/airframe combination. Sure you can throttle back and perhaps reduce your fuel flow by 10%, but if your speed decreases by 12%, you are LESS efficient in the utilization of that combination.

Looked at another way, my Corvette needs about 35 HP to push it along at 70 MPH, yet it has more than 435 HP available. While it gets fantastic MPG on the highway at less than 10% power, it would get far better mileage with a 35 HP engine running 100%/WOT. The reason is because the big 435 HP engine is suffering tremendous pumping and friction losses compared to the much smaller engine.

The WOT technique is used for any given airplane as a transportation device, not a plaything. If you don't need all the cruise performance of a particular airplane, you can certainly fly slower and cheaper by throttling, but you are leaving something on the table by dragging all that untapped capability around.
 
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