[RV8Squaz]

I'm sure I didn't set any altitude or distance records, but you may be interested in the cruise data I obtained during my recent flight from New Braunfels (KBAZ) near San Antonio to Meridian, MS (KMEI), and then to Peachtree City, GA (KFFC) just south of Atlanta.
Distance BAZ-MEI 503 nm, MEI-FFC 220 nm, total distance BAZ-FFC 722 nm. If you're thinking about extended range tanks or an O2 system, this may help with your decision.

I was cruising at 17,500, OAT was -01?C, full throttle MAP was 15.7", 2650 rpm. I was burning 7.1 gph at peak EGT which ranged 1300-1375?F. This worked out to about 53% power.

I was indicating 125 knts which worked out to a true airspeed of 168 knts. I didn't have much of a tailwind, so I had ground speeds of 172-175 knts for most of the flight.

After landing at MEI, I filled up the tanks with 23.5 g. I had averaged 21.4 nm/gal during the 3.1 hour flight. I figured I would have landed with 8 or 9 gals. had I gone all the way to FFC non-stop! I decided to make the stop at MEI because the weather in Georgia was questionable when I departed BAZ. Enroute weather updates from Flight Watch and FSS supported a landing at MEI. In addition, I had already filled up my only piddle pack. It was time to land!

I encountered similar cruise performance during the second leg, but more importantly my altitude allowed me to stay in the cool, dry air and visually avoid the build-ups. I ended up filing an IFR flight plan midway during the second leg because the layered weather didn't permit a VFR descent very easily. The weather at FFC was 035 BKN upon arrival.

I know a lot of guys have good reasons for increased fuel capacity, but I never felt I have needed it. I could see it on a solid IFR day with distant alternates, out west where airports are sparse, or simply to tanker cheap gas. I haven't used my O2 system much, but I'm glad I have it and value it very much.

I hope you find this gee whiz info mildly interesting. It's just another data point in the wonderful RV world.

Jerry
RV-8 N84JE
Flying since 2007, 760 hours

 

[rv7boy]

Thanks for taking the time to share your data with us.

And...I couldn't help but notice that your RV-8 is featured this month on the Van's Aircraft calendar. I recognized your N-number because it's part of one of my passwords.

Nice paint scheme!

 

[erikpmort]

This is exactly why I'm getting o2 soon. Why would I limit myself to 5k more feet of cruising altitudes ? Nice data

 

[RV10inOz]

Gerry, good numbers, but perhaps I can help you optimise a little.

Try 10-20dF Lean of Peak for better fuel efficiency, or if you want better power and speed at that height use around 75dF ROP.

Peak is not hurting anything at that altitude but it is in-between the max HP and min BSFC.

They are awesome machine hey!

PS I assume you have a 200HP standard compression engine?

 

[texdog]

EGT

I have read that peak EGT's don't matter as much as CHT's, is that true? I keep CHT's below 380 but 50 below EGT, which sometimes is 1460 on the hottest cylinder. 0-360 A1A 8.5 compression. Fuel flow is between 7.5 and 8.5 depending on altitude. I would appreciate your input, I do not want to harm the engine, the exhaust has a nice grey color on the pipes.
Thanks.

 

[Jesse]

In my experience, the older the probes are, the hotter they tend to read. In my research, you care more about where you are in relation to peak, not what the number is. Below 65% power, you can run anywhere rich of rough and not cause damage. In the -10, 20" and I can run anywhere I want. Of course, up at 17,500, 15.?" Is the most you'll get, so lean for economy or run a little richer for speed. If you're up there, then you're probably going for economy and winds, so nice and lean and riding the winds if my idea of good economy. You'll be hard pressed to even hit 380CHT up there anyway. I usually go lean of peak or right at peak up high.

 

[RV8Squaz]

Thanks for taking the time to share your data with us.

And...I couldn't help but notice that your RV-8 is featured this month on the Van's Aircraft calendar. I recognized your N-number because it's part of one of my passwords. Your Wecome! Yes that's my bird! BTW N84JE stands for "-8 for Jerry Esquenazi."

Nice paint scheme!

Thank you very much. I worked hard to get that look!

This is exactly why I'm getting o2 soon. Why would I limit myself to 5k more feet of cruising altitudes ? Nice data

Exactly,; it's great to have the flexibility.

Gerry, good numbers, but perhaps I can help you optimise a little.

Try 10-20dF Lean of Peak for better fuel efficiency, or if you want better power and speed at that height use around 75dF ROP.

Peak is not hurting anything at that altitude but it is in-between the max HP and min BSFC.

They are awesome machine hey!

PS I assume you have a 200HP standard compression engine?

Yes, they are awesome machines. I love my RV-8! The mixture is very sensitive at that altitude. Also, much leaner than peak EGT I lost a lot of power that high. 100 deg ROP gave me about 8 gal/hr. Since I thought there was a chance I would go all the way to FFC, I decided to run at peak. During normal ops, I run 100-150 deg ROP for Best Power as defined in the Lyc. Operator's Manual. If I am trying to econmize I usually run peak EGT which Lyc defines as Best Econmy in the Manual. I found through a lot of cruise performance testing that it was not worth going more than 20 LOP. I used to run the engine 30 to 40 deg LOP. But then I had replaced a cylinder a few hundred hours ago. The cylinder was a very light tan color inside. The guys at the engine shop said if it were his engine he wouldn't run it that way. I call a few other very respected shops and they all said long term LOP operations usually result in premature top overhauls. So now I do just what the book says and the color inside the cylinders looks more normal. I do have a 200hp angle valve IO-360A1A

I have read that peak EGT's don't matter as much as CHT's, is that true? I keep CHT's below 380 but 50 below EGT, which sometimes is 1460 on the hottest cylinder. 0-360 A1A 8.5 compression. Fuel flow is between 7.5 and 8.5 depending on altitude. I would appreciate your input, I do not want to harm the engine, the exhaust has a nice grey color on the pipes.
Thanks.

EGT should be used as a relative value in relation to peak EGT. The absolute value dosn't matter much because it will vary with probe placement.

In my experience, the older the probes are, the hotter they tend to read. In my research, you care more about where you are in relation to peak, not what the number is. Below 65% power, you can run anywhere rich of rough and not cause damage. In the -10, 20" and I can run anywhere I want. Of course, up at 17,500, 15.?" Is the most you'll get, so lean for economy or run a little richer for speed. If you're up there, then you're probably going for economy and winds, so nice and lean and riding the winds if my idea of good economy. You'll be hard pressed to even hit 380CHT up there anyway. I usually go lean of peak or right at peak up high.

I agree with all that!

 

[RV10inOz]

Texdog

The absolute value is not critical for EGT, this is correct. Keeping the EGT 50dF below peak is not necessary as a rule of thumb, in fact it is very sub optimal. It is only optimal in one out of hundreds of occasions.

For example, 50dF LOP is perfect when you are running between say 75-80% power, but it would be the worst place to be if you are ROP at 75-80% power.

To gain a full appreciation for this, it takes more than can be provided in a few posts on a forum, so my suggestion is get along to the next APS class in Ada OK in October. They are running one I think mid October. The best money you will ever spend in education and aviation.....or your money back! (NB: I am not financially interested in the USA courses)


RV8squaz

During normal ops, I run 100-150 deg ROP for Best Power as defined in the Lyc. Operator's Manual. If I am trying to econmize I usually run peak EGT which Lyc defines as Best Econmy in the Manual.

100-150 ROP as per the manual is not a universally optimal setting. This is appropriate at say between 65-70% power when wanting to run ROP. At higher powers this is sub optimal in terms of ICP (internal cylinder pressure) and CHT. At lower powers this is sub optimal due to gross waste of fuel and the build up of deposits.

What you read in the manual Vs what you can determine from the engineers data in the properly drawn graphs etc is often conflicting, but you need to know how to pick the contradictions. Lets just summarise it as the engineers info Vs. the marketing department newbie.....who do you think is the better to follow?

The same goes for efficiency, the best efficiency is never at peak EGT, unless of course your engine has poor F:A ratio's, because it then will not happily run at the best BSFC because it will be running rough. This is why the marketing departments suggested peak or slightly rich of peak, because they knew they could not get their poor F:A ratio engines to run where the engineers would run them, and where the graphs (the real ones not doctored) showed the best BSFC.

Peak efficiency is around 10-20dF LOP at lower powers and up around 70dF LOP for higher powers (say beyond 75% i.e. 80-90%).

I assume you have a very well set up engine with no induction leaks and well balance F/A ratio's. (as you should)

I found through a lot of cruise performance testing that it was not worth going more than 20 LOP.

What you have found validates exactly what I have stated above. At the typical cruise altitudes and powers this is the optimum indeed, 10-20 (across all cylinders). Refer the tip below, this may help you be more precise in gaining maximum bang for buck!

I used to run the engine 30 to 40 deg LOP. But then I had replaced a cylinder a few hundred hours ago. The cylinder was a very light tan color inside. The guys at the engine shop said if it were his engine he wouldn't run it that way.

30-40dF LOP at low powers would have been less than efficient and sub optimal, but this is not harmful. The light tan colour is fine and the comments from your engine shop are inaccurate and based on misinformation. That is the polite way of saying they are simply wrong.

I call a few other very respected shops and they all said long term LOP operations usually result in premature top overhauls.

This further shows the complete lack of understanding. If only they knew better. American Airlines alone, have 400,000,000 hours of data to prove that long term very high power LOP operations actually extended TBO, not the opposite. In fact they were routinely doing 3600hr TBO's on the mighty R3350 radials, yet prior to that time the military and the very first of the airliners operating them ROP only made around 700 hours.

DO NOT believe me......believe the data!

What your engine shops are referring to is either operations that have been leaned but are not lean enough. Or they have been leaned and not rich enough. Most top end overhaul problems that they see are from poor assembly at the manufacturing stage not the pilots doings.

IMPORTANT OPERATIONAL TIP

Many people running LOP, get to TOC and then slowly lean from the rich side, watching their Lean Find function. Then as it rolls over the numbers range from say 30-10dF LOP and they say ...great, leave it there!.

The problem with this is the majority of Lean Find functions suffer from hysteresis and the alogorithims are not perfect. To compound this issue they run the CHT's up in the process and this has a negative effect on volumetric efficiency, further skewing the peak EGT point.

Secondly if you flew along like this for a while and then went to find peak again from the lean side, you would discover that you were not as close to peak as you thought and were in fact much further past your optimum target.

So the best method is to level off in the cruise, let the plane accelerate (most important) and then close your eyes and do a Big Mixture Pull, until you feel the deceleration. Now you are safely LOP, let things settle, the CHT's will roll off fairly quickly and then once all stable, sneak up on peak from the lean side, and then adjust back to appropriate setting.

Try this for yourselves, don't just take my word for it....believe the data!!!

Hope that helps everyone!

 

[RV8Squaz]

Textdog

EGT should be used as a relative value in relation to peak EGT. The absolute value dosn't matter much because it will vary with probe placement.

I don't think I fully answered your original question... EGT is used as a relative value in relation to Peak EGT to set your mxture whether you choose to go LOP or ROP. The EGT can be a good troubleshooting tool as its response to change is very quick compared to CHT. It will give you immediate indications of timing trouble, combustion loss, etc.

The absolute CHT value is critically important as it can result in reduced cylinder service life, damage, or failure. The Lyc. Operator's Manual has the Max Cyl. Temp at 500 deg F. It also states that for maximum service life to maintain the temps between 150-400 deg F during continuous operation. With the CHT, the cooler the better. No hard data, but I'm pretty certain the cylinder will last longer maintained at 325 vs 375. How much longer? No one knows. Cycles, how many times the cylinders get warm then cold, can affect service life as well, but don't know if that is documented anywhere. I'm not going to change the way I fly my airplane based on that! If CHT creeps up above 400, you should make a change by increasing fuel flow and or airspeed to get it below 400. You are not going to damage the cylinder if it creeps up above 400 for a few minutes. These things are tested at redline for extended times during certification. I hope this helps!

Jerry

 

[RV10inOz]

Jerry,

You are quite right, temps above 400 should be avoided at all times. We have a graph in the APS course that shows the strength of aluminium Vs temperature and hence our preference for sub 380dF operation and CHT alarms set at 400.

The interesting thing associated with high CHT is high ICP, and they go together (assuming you have cooling airflow that is). A few courses back a senior employee from one of the two major engine companies stated there were three things that reduced the life of a cylinder, Temperature-Temperature-Temperature. After seeing dyno data and doing the course he modified that to be 6 things, Temp-Temp-Temp & Pressure Pressure & Pressure.

 

[erich weaver]

For example, 50dF LOP is perfect when you are running between say 75-80% power, but it would be the worst place to be if you are ROP at 75-80% power.

This statement is confusing. I think you meant to say that 50 LOP is perfect at 75-80%power but that 50 ROP at this power setting is the worst place to be.

 

[RV10inOz]

This statement is confusing. I think you meant to say that 50 LOP is perfect at 75-80%power but that 50 ROP at this power setting is the worst place to be.

Yes that statement could be better written especially when read alone and not referenced to the notion of just keeping the EGT 50 below peak (either side) which was the post by TEXDOG.

Texdog

The absolute value is not critical for EGT, this is correct. Keeping the EGT 50dF below peak is not necessary as a rule of thumb, in fact it is very sub optimal. It is only optimal in one out of hundreds of occasions.

For example, 50dF LOP is perfect when you are running between say 75-80% power, but it would be the worst place to be if you are ROP at 75-80% power.

Thanks for helping clear that up!