Last night I flew 1135nm non-stop from home base, Santa Maria, California (smx) non stop to Mineral Wells, Texas (MWL) in N8065J, a low compression "U2A" powered 601p/700.
I left solo with 209 gallons. I climb full power (390 max cht) at 82 gph to 17,500, at 2,000 fpm, 145kias.

https://flightaware.com/live/flight/N8065J/history/20181212/0129Z

At 17.5k' I level off and power back to 30", 2000rpm, 14gph/side, TIT 1650, 200 LOP, KTAS 190. (55% power?)
CHT's are 290-320f. Ground speeds were 180 (headwinds) rising to 235 knots second half with tailwinds.
Descent was at 500-1000 fpm at 10gph/side as I pulled power down 28" initially (otherwise it rises) then to 25" in the pattern.
I landed after 5.5 hours burning 174 gallons and had 35 gallons remaining.

Cruising at low power allowed me to make the trip nonstop.

Block speed and fuel was 207 knots 32gph, 6.5nmpg.
Returning westbound against a headwind I expect an extra hour block time and will stay down as low as possible.

I cross fed the left engine to keep wing tanks balanced.
Attached are photos of fuel guages showing wing tanks a bit higher than the fuselage tank.
Any Yaw on final would illuminated the "low fuel" warning light.

Based on what I read from straight 601p, this niche regime style of flying favors
the straight 601p whose high compression efficiency puts out more hp at
lower fuel flows compared to the 700. Possibly 25-35 knots faster at 6gph higher flows...

The 180k gs for the three hours was a little discouraging and felt very un-aerostar like,
but she made up for it with 2.5 hours after that at 230+ gs!

John,

At such low power the difference in compression is largely immaterial. Where the compression comes in is when you want to run fast. On the UA2 it is really hard to run LOP above 55% power without cooking the turbos and/or the engine. While on the higher compression engines you can run as much as 75% power LOP without an issue. Here is the trick though:
55% of 350 = 192.5
65% of 290 = 188

The high compression engines you can match LOP up to about 65% for them and 55% for you. But they can get another 10% power easily before they need to go ROP.

To get the longest range, you want KIAS to be around 135 (going on memory).
Go to the http://aerostar-forum.com/ where Bob/Forrest and a few others hang out and can get into the details with such concepts as Vz

Tim

I believe the vast majority of Aerostar operators would be very uncomfortable with your indicated TIT’s at 1651 and 1655, regardless of your CHT’s. Both are above redline. Many plan on keeping the TIT around 1550. Some say that just wastes gas, but if it were my turbos, I wouldn’t select 1650 as my target TIT. And what do you mean when you write “200 LOP”? Are you suggesting you think you are running the plane’s engines at 200 degrees lean of peak EGT on the highest cylinder? How do you figure that? Do you do a lean find as per the JPI manual? Do you use GAMI injectors?

Thanks Tim,
I'm most interested in the fastest trip time. On this flight, the lower power resulted in range eliminating a fuel stop.

Regarding the 28gph=only 185ktas @ 17.5 though...

I thought this lower tas was the low compression engine being less efficient in converting 100ll & O2 fuel to energy. And having to run 200-300 LOP on the u2a seems inefficient...

Earlier in the thread I read that the normalized 601p drivers are effectively seeing 30 knots faster on that same flow:



...Could the heavy weight (full aux tank) contribute to the 700 being 30knots slower than the 601p when both running 30gph in the teens ?

Thanks Thomas,
I agree on that! My TIT alarm is set for 1650 and I run it at that limit as in this photo only when LOP at Low power setting and stabilized. The other photo showed 1630 ish.
I have 4 TIT's and the other secondary TIT's are always 10-15 degrees cooler.
Running at 1650 TIT only at low power and LOP is based on discussions with GAMI at their seminar and writings in this thread by Jim Christie and yes I have Gamis installed.

For ROP I never pass above 1550F TIT and use that as my max TIT.

By 200 LOP, I mean generally and approximately that 1650 is several hundred degrees below Peak TIT Temperatures shown when going from ROP to LOP. I routinely see High 1700's when pulling the mixture and have recorded up to 2100F TIT on the JPI... BTW, after seeing 2100F I sent the turbo to Main Turbo and he said it looked fine.

Also, being 200+ LOP I feel like I am wasting O2! Feels like she is just sucking, compressing, and pumping out unburned o2. In the racing world they say "heat is horsepower" but with these low compression engines I feel stuck running low hp/low heat when lop. And the cylinders are below 300F at that 1650 TIT setting.

Thanks for the feedback.

Please remember that running Lean of Peak refers to the degrees on the lean side of the power curve as it applies to Exhaust Gas Temperature. Not Turbine Inlet Temperature. If I were you, when doing this LOP experiment, I’d use the JPI “Lean Find” for LOP ops and follow that process. TIT is only indirectly related to the EGT level and has a lot of variability depending on the location of the probe (as is evidenced by your variability among the 4 probes). If you have one relatively hot EGT and another that’s rather cool (not real likely with GAMI’s but still possible), they will average out in the TIT and you could be playing with a detonation event without knowing it. My Aerostar had highly variable TIT’s on the different banks.

Thanks very much Thomas,
I appreciate your input and your deep Aerostar experience, and I learn something from every one of your posts.

I read about this process just now on the JPI website. It instructs me to set power at 65-75% and rich of peak egt and start leaning...to peak egt...and hold it there for a minute....Leaning to peak at that power setting is probably too hot for the exhaust...did you modify this process ?Am I missing something there?

https://www.jpinstruments.com/FAQ/lean- ... procedure/

How I lean now:
At 30" and 2000 rpm, I do the BMP back to 12gph and add MP back to 30" and enrich until the tit limits I am comfortable with (1650) are reached, about 13gph at sea level and 14gph at altitude--ie 17.5k' (not sure why it is that way, as someone said, how does the engine know what altitude it is at?), enriching from the lean side of peak.

EGT's are flat and stable on the lcd bar graph and at 1600-1650 it is very sensitive to even a tenth of gallon per hour changing the TIT 10-20 degrees. That is why if it is stable at 1651, a degree or two above the manufacturers redline (and I have inconel exhaust), ...I am not going to fiddle with it for a few minutes until the gph lands on the exact tenth of an hour that gets my the elusive 1649f goal...

On my next flight, I will experiment above the tit limits briefly and see what the peak EGT is at 55% power setting but for now, from my JPI data:

Peak EGT is about 1580 without getting past 1650 TIT limit.
Richest cylinder is 10 lop at 1570
leanest cylinder is 125+ LOP at 1443

I asked around at Gami/APS what other aerostar u2a drivers were doing LOP wise and answers indicated even slightly higher (60% power) MP and TIT's so I am still conservative to other U2A lop followers at 50-55% power. I am open to higher power LOP on the U2a if I had more data and experienced mentors, but for now, I am at the target fuel, speeds, and TIT that Jim Christie Illustrated (28gph LOP and 1650 max tit) and am very comfortable there. The engine runs smooth, Oil analysis is night and day better than the last operator's numbers, ie metals are way down/back to normal, oil consumption is down to 5 hrs per quart.

I speculate that the majority of U2a A* Drivers that are concerned with 1650 TIT are at 60% power or better, and not operating their engines at 2000 rpm, 30", LOP and aiming for 1275nm legs like I am. When you descend at this reduced power setting all cht's are well into the 200f range.

What should I look out for do you think when operating this way? (coking, deformation of the turbine, warping the housing?) Because I am certainly willing to take apart a turbo for inspection and see if it is there. I don't fly as much as you, but I do fly that 4000nm mile circuit quite a bit. And for only half hour penalty per leg going 20 knots slower it seems worth it to get there faster and for way less fuel.

Another question, what # is Peak EGT that you mention could risk detonation? Because peak EGT seems to change with Fuel Flow. At lower power settings the peak egt is much lower than peak egt at higher power settings.

I ask because at 50% power settings I fell into the routine of enriching until I hit TIT limits and not every worrying about too high of an EGT, calculating (possibly incorrectly) that It would be impossible to encounter a dangerous EGT at that low power setting and fuel flow.


In other words, at 55% power I use the red knob to get as much power out of the engine as I possibly can without exceeding the TIT limits. I was under the impression that CHT was the primary indicator and corollary to detonation. In my past detonation case, it was caused by a 750 hr TIS cracked champion fine wire where cht spiked to 500 and egt dropped to 1100 iirc during full power takeoff climb. Needless to say, I shelved all 24 of those gold champions and now run massive tempests exclusively with confidence.

Insights appreciated!

Here's another example of what a SS700 with U2A's can do:
https://flightaware.com/live/flight/N72 ... /KLAL/KRNP

I took off with 220 gallons of FOB. I landed with 40 gallons. 180 gallons of burn for 900 miles wasn't bad, considering the first half of the trip I had a headwind. The opposite direction was four hours even.

Both ways were at 60% power, burn was around 33GPH once I was in cruise flight. 1550 EGT, which was about 100 ROP. Takeoff was at gross weight with three on board.

I would have gone higher, but I'm ready for two turbo's that will get overhauled next month...

Jason

Good morning John, thanks for your detailed response...you're up late.
My main reason for writing a response to your post was that I was concerned you were conflating EGT with TIT when discussing your engine's status as "200 LOP." In reading your more detailed response, I see you understand the difference! I do have concerns that you may be straying into a bit of uncharted territory since I don't think the actual position on the power curve is known at the state you are operating. It appears you are making some assumptions about where the engine is as you approach the LOP state from the lean side. Your experience and perspective is just much different than mine in a lot of ways, not saying you're doing damage to your engine components, I'm just not sure.

On LOP utility in a 700: My Superstar had low compression S1A5-MM engines, not U2A's so there may be a slight difference there. When I approached GAMI with my plane, they told me that I can't run LOP with that engine anyway so I shouldn't purchase their injectors.

On spark plugs: Most folks I have spoken to (and my personal experience) indicate that the fine wire plugs work better than the massive plugs, especially in high powered aircraft operating at altitude. Your experience apparently was different.

On TIT: Unlike the concept of EGT leaning and cylinder head pressures etc., when it comes to TIT, it's just plain heat. GAMI says that 1650 is already conservative and that you can fly around at that peak temperature in an Aerostar all day long without doing damage. Many others disagree. Thermal stress is thermal stress. Your turbos don't care whether you are LOP or ROP. You note that you target is 1550 ROP and 1650 LOP but I'm not understanding why (unless it's secondary to other things you're seeing in the engine monitor). I know in the jet-turbine world, folks don't normally operate their engines at max allowable temp. But a 1st stage turbine wheel is around $80K compared to an Aerostar turbo at around $3.5K...so less financial risk. Still, I'm pretty sure your turbos will have a lower life when operated at 1650 than a more conservative temp.

On LOP ops in the -700 Aerostar: I found that it was not possible to just set my engines up with the TIT near redline and leave them there. As you note, even a 10th of a gallon one way or another made a difference. Similarly, slight updrafts and downdrafts changed RAM pressure and made huge swings in the TIT at altitude. In my plane, it just didn't work well...I'd spend my whole flight staring at the JPI. Also, because I could not do a lean find operation on my engines without sending the TIT through the roof, I didn't fly the Aerostar LOP...It's not that I don't like LOP (I drank the Coolaid long ago and flew my old T210's TSIO520 that way for a decade). For the Aerostar, low power ROP seemed to work OK. At 17,000 MSL: 33.7gph (total), 27.5", 2100, 1585 TIT = 200kts. At FL250: 35gph, 27", 2100, 1565 TIT = 214kts.

On detonation: It's quite true, as you note, that detonation is less common at low power settings, low CHT, and also with low compression engines. But as you note, it is not easy to ascertain where peak EGT is in the low compression planes because your TIT goes through the stratosphere before you can find out (except maybe in very low power settings). I'm not sure we know how many degrees LOP you are operating...so you might be fine, or you might not, I think it's a bit of an experimental zone. IMO, you are most likely fine on your cylinders/pistons, but decreasing the life of your turbos. Perhaps the turbo/exhaust wear is worth it for the operation you desire? It sounds like you are having lots of fun with your Aerostar... Enjoy it, they are amazing aircraft.

John,

Your RPM is likely way to low. I am going on memory since I sold my Aerostar 4+ years ago.

The prop effectively has an inverse bell curve for efficiency. When the prop is too far course and you increase drag (vortex and pressure differentials), to fine and you increase drag (prop tip speed). Basically, the props are designed for a specific speed range, outside of those ranges the constant speed prop is a compromise. I found the best speed in the Aerostar as indicated by KIAS varied by altitude, so I would run closer to 2200 in the mid teens, and 2300 in the FL (those are the numbers I recall, question is if I have them backwards or not).

Since you have been to APS, you know when LOP power is constrained by fuel. So get setup at 12 or 13 GPH and vary the MAP and RPM and see what that does for performance; make sure to let the plane stabilize for five minutes or so to get the new speed.

In terms of the red box/fin; the U2A engines really need to be closer to 50% maybe 55% to switch to LOP in the U2A. There just is not enough "head room" for the TIT to stay in the acceptable range at higher power settings. Note: I did the vast majority of my low power LOP testing closer to 45% power.

Tim

Agreed. "The book" says you should be at 2100+. I think lower RPM with higher MP puts too much stress on the prop blades, so although you may be getting better efficiency, you could also be doing damage. I am not an expert -- far from it -- and that's why I use this "aerostar for dummies" chart.

Software is the future of cameras. The Night Vision and Super Zoom stuff from Google is absurd.

I flew the aerostar about 100hrs last year.
Went to Alaska twice and all over the west coast.

It looks like I have a project in 2019 that is going to burn a ton of personal time.
I'm probably going to sell the beast...
601P with short props and intercoolers.
G500, GFC-750, ADSB in/out XM Wx and music.
~2800hrs TT.
~100hrs Since Factory reman on left, about 1400hr on right.
about 100hrs on all new(x4) turbos.
All LED lights.
Electric A/C (inop, but I have all the parts to fix)
PM me if your interested before I go to market it in a more formal way.
Other than A/C no known issues.
Paint is a 6, interior a 7 or 8.

Is there a performance chart somewhere for intercooled 601p?

I climb at about 900 fpm and 145 to 150Kias. Burning 45 to 50 gph.
Then at 17,500 I cruise between 208 and 215 true burning about 32 gph.
At 24,000 its more lie 225 to 230 true and same fuel.

I am hesitant about runways shorter than about 4000 to 4500 ft.

I have GAMI injectors, but have not done the work to get them balanced well enough to run lean of peak.
I have a JPI with CHT and EGT for each cylinder.