climb performance

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  • #83534

    I’m currious of what others see in terms of climb performance with there pressurized twin cessna’s. I have a Ram7 340 with vg’s. I have to admit I’m a bit disappointed in the rate of climb with this airplane. With above average outside temps recently I expect climb performance to be less, but my airplane just seems to be a dog in the climb regardless. After takeoff and when the after take off checks are complete, I set climb power at 33″mp, and 2500 rpm. With 120kts indicated I will only see approx 800 fpm vertical speed. On cool day maybe I will see 1000 fpm. My usual weights are under gross by around 200lbs with Mains full, Aux’s about 20gls per side, and 2-3 average adults in the cabin.

    comments?

    Brent

    #94897

    I fly a 340A RAM IV with AA intercoolers. My chart indicates 2500 rpm and 33 inches with this setup, however, when the ISA plus temps are considered, I usually set in 34 inches which yields somewhere around 1000 fpm climb at 135 kts indicated. My weights are similar to yours and with my setup I believe the power produced at the same mp and rpm settings is very close to the same. So, you may want to time your climb to determine the exact rate, your rate needle may be in error or carefully check your power charts, the high temps may be robbing to much power.
    I think I shall go to flightaware and check my climb rates, could be that I’m not doing as well as I thought.

    #94898

    Looked at flightaware and oops, 800 fpm looks closer than 1000 fpm. So, looks like you’re in the ball park, have you tried climbing at 135 kts indicated? Seems like 800 fpm at 120 kts is a little slow, however, I can’t comment as I climb a little faster and don’t have a feel for the difference, if any, in climb rate.

    #94900
    rwelsh
    Participant

      My 340 only has 310 HP engines with AA intercoolers, but I get 1100 FPM climb down low and 1000 FPM above 5000 feet and tapering down to 500 FPM above FL210. I use 32″ and 2600RPM burning 29 GPH in climb. As I have an AOA indicator, sometimes when I want to get to altitude fast to satisfy departure ATC, I climb at 100 IAS and middle needle on the AOA. I can see 1200 FPM at this attitude up to around 4000 feet.

      It is possible your airspeed indicator, tachs or MP gauges are wrong which is not unusual with these old planes– have them checked. If you really want to climb, use 2700 RPM and 35 inches. The higher RPM is also helpful above FL200 when the turbos will run out of boost at lower RPMs. The engines are rated for max HP all day long, but make sure you have at least 37 GPH fuel flow to keep the engines cool. The faster you get to cruise altitude, the quicker the fuel burn gets to the 30 to 32 GPH range; this is especially so if you are climbing into a stiff tailwind eastbound. If your turbos bootstrap up high, just run the RPMs up at 2500 or 2550 to increase the mass airflow through the turbos, and you will have plenty of boost even LOP–it is a little more noisy but you can maintain your normal cruise power and speed even on high IAS temp days.

      I think 135 IAS is too fast to climb at as it takes forever to get to FL230 or FL250. I can get to FL250 when heavy in 28 or 29 minutes from a below sea level airport, KTRM. If you need that kind of speed to keep the engines cool, you have other problems, most likely a crummy baffle setup or too low of fuel flow in climb. Most mechanics seem to have heartburn with climb fuel flows above book numbers, but remember TCM doesn’t care if you engines need top overhauls at 600 hours. They put down what they tested back 40 years ago for the first 340. Cool engines are your friends!

      #94940

      I have a 340 with Ram VI and see pretty much the same numbers. My limiting factor seems to be 2 particular cylinders (3and 4 i think) on the right engine which show CHT close to 400 if i aim for much more climb. I’m going to have the probes and baffling inspected at annual as all other cylinders seem well below these levels and maybe i can squeeze a few more fpm with better cooling. Once i get a little altitude out of the heat i seem to be able to coax a little more climb rate out of her if i really want but by them im usually just content to stay dialed in on the A/P at a cruise climb of 800fpm.

      #94943

      Brent

      When I first bought the plane I used to climb at 2450 RPM and 31 MP and was seeing at the most 500-600fpm at gross weight 6290lbs (Vg’s) in ISA plus 15-20 deg C. (92F) which I though was on the low side….I would maintain this rate of climb all the way up to FL200 or so…..38 min later….burning 28GPH per side to get to altitude. All the while flying 120kts indicated. I talked to a few other 340 operators who mentioned trying a higher RPM in climb…..I found only slight improvement…..ie. 2500 to 2550 RPM again only seeing maybe 650 FPM under the same hot and heavy conditions….

      I then took the Advanced Pilot course offered online by the GAMI folks…. http://www.advancedpilot.com/

      Very interesting course by the way. Now I routinely climb at 2700 RPM and 34 MP ( Max continuous power setting ) and I see 800 FPM under the same conditions…..the difference is my fuel flows needed to be jacked up to keep my cylinders in the normal temp range in climb….ie. minimum 35GPH per side. Now you may think wow huge fuel burns but my time to climb is cut to more reasonable 25 min to FL 200 burning roughly 3-4 gals less in all. Yes it is louder to climb but it is faster with less total fuel burn and 2700 RPM is actually a healthy RPM in the climb phase….if you don’t believe me take the Advanced course.

      Now I really wish I had AA intercoolers because I think I’d be able to cut my fuel flows a bit and definetly get some more power out of my 310hp engines flying LOP…..but at $25K for the mod that pays for a lot of gas…..so I fly a bit slower at LOP in cruise but I make fuel there very easily to be able to get the range I need.

      I hope this helps.

      #94948

      Thanks Derek! Mine is the Ram7 with intercoolers, and I see those kind of numbers if I run the RPM at 2500 and 33″

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