Keep my 231 or trade up for a Rocket

[231LV]

Rockets are awesome in spite of the high fuel burn rate! I saw 200kts at 5500' with close to 2000 FPM climb out now I was at a sea level airport so might vary at a place like Sedona.

Well that delta might be worth the extra 5gph!

[cujet]

Rockets are awesome in spite of the high fuel burn rate! I saw 200kts at 5500' with close to 2000 FPM climb out now I was at a sea level airport so might vary at a place like Sedona.

 

That is incredible! 

[cujet]

I can't speak to the GB because I don't have one, but the LB runs at rated cruise just fine at any altitude so long as you have the wastegate and intercooler.  You will have Compressor Discharge Temp issues above and altitude of around 18-20k if you do not have the intercooler.  The engine has a CDT limit of 280 to protect the engine from detonation, but the CDT becomes irelevant with the intercooler in place.  Other than that, there are no temp problems.  I believe you would see temp problems in the GB above 17-18k because as noted, it is a hot running engine, and the thinner air is not conducive to cooling.

 

Overall the 231 is a great airplane.  Very fuel efficient compared to the later model turbos. 

 

So, in light of this, what cruise speed and fuel flow would you expect at 10,000 feet, rated cruise power? Clearly, the OP wants to go fast, at lower altitudes.  To me, it seems that his speed of 145Kts at 10K is way off the mark.

 

I can understand wanting a Rocket, as it really is fast. I don't see the comparison of 145Kts to 200Kts as valid though. It's more like 170+Kts vs 200Kts from what I understand. Maybe the OP would run the Rocket LOP at reduced power. And, maybe we could compare speeds another way. What's a Rocket do at 10,000 ft, LOP at reduced power, compared to a well configured LB 231 at rated cruise power?

 

 

I understand that running an engine near or against it's operational limits is uncomfortable for some. And, those that "baby" their engines may make the rated overhaul period without wearing it out. However, keeping speeds down to 145Kts results in considerably more time on the engine, per trip. Is the end result better? If I were to guess, I'd say the OP is gentle on his engine, and is unhappy with the low altitude speed provided by gentle operation. Plenty of engines run "as designed" make TBO. 

[231LV]

Well, I wanted to give an update on some different settings I used on a cross country trip today. It was not a perfect comparison because the winds were blowing early in the flight and subsided later. Nevertheless, I already know what my speeds are during

LOP operations down low. I wanted to try deep ROP down low to see what speeds I could achieve. If you recall, I was seeing speeds of around 145 KTAS below 10,000 ft running LOP at about 10 gph. Today, I was flying at 9,500ft running ROP at 80% power at 13 gph with the hottest jug at about 360 degrees and seeing about 160 KTAS. This is satisfactory and opened my eyes to running deep ROP without generating excessive heat. I did burn more fuel but that's the trade off. I understand that if I elect to run the engine at the advertised 50 ROP, I can get more speed but I refuse to run my engine at the worst settings so I will be happy with deep ROP.

[cujet]

Well, I wanted to give an update on some different settings I used on a cross country trip today. It was not a perfect comparison because the winds were blowing early in the flight and subsided later. Nevertheless, I already know what my speeds are during

LOP operations down low. I wanted to try deep ROP down low to see what speeds I could achieve. If you recall, I was seeing speeds of around 145 KTAS below 10,000 ft running LOP at about 10 gph. Today, I was flying at 9,500ft running ROP at 80% power at 13 gph with the hottest jug at about 360 degrees and seeing about 160 KTAS. This is satisfactory and opened my eyes to running deep ROP without generating excessive heat. I did burn more fuel but that's the trade off. I understand that if I elect to run the engine at the advertised 50 ROP, I can get more speed but I refuse to run my engine at the worst settings so I will be happy with deep ROP.

I'm finding this very interesting. Thanks for the additional data points. Although, your speeds still seem quite low. Is there something different about your aircraft? A large number of external antennas or tundra tires (just a little joke) , something creating additional drag. 80% power should produce around 170Kts from what I understand. 

[231LV]

Other than a tired engine (1700 since TBO) it is a standard 231. I will continue to play with the settings and see what they may yield. The experiment wasn't perfect because I had been battling headwinds but when the CAS agreed with the GS, I figured I was in a no wind condition. I didn't calculate how deep to the ROP side I was other than the readout on the JPI (80%). Next time I will try to be more exact in determining exactly where I was from peak EGT.....the point of comparison would be 5500 ft at 200 kts which is what a Rocket is claimed to do. I'm not sure what the fuel burn would be but I'm guessing close to 20 gph.

[cliffy]

If the airframes are the same (J-K-M-etc), the flat plate drag figure is the same (we're talking generalities here) therefore speed is directly proportional to energy expended at the prop for thrust.

BUT you can't double the fuel and get double the speed. Drag is a logarithmic function.

If you want to go fast(er) you gotta burn the fuel at what ever altitude you are comparing at.

How fast and at what cost is up to you.

As an example, on a 727-200 I'd do .78-.79 MACH at 9,000 lbs/hr. If I wanted to do .88 it was 12,000 lbs/hr. a 33% increase for 13% more speed. A 737 is even worse above best speed/fuel.

[BobAustin]

Have a Missile and it performs well at non-oxygen altitudes yet will quickly go to the teens if you want to.  Most of our flights are 10.5 to 13.5 at 180k and 11.5 to 13.5 gph.  Carry portable O2 and use O2D2 and use it sparely...ie 3 trips of 650nm per tank.

 

I have 3000+ hrs in J models and takeoff performance in Pagosa Springs CO (KPSO) at 7600' elevation

Is fine with 300 hp but not to relaxing with 200 hp.  Usual loading is 320 lb crew, 92 gal and 100 lbs junk (about 40 lbs below gross).This allows landing with 2+ hours of fuel in reserve.  650 nm trip.

 

See Scotts post above...he has it spelled out.

 

No too many Missiles around but worth considering.