Cruise Performance

Tom · #1 11-09-09, 10:06 AM

I have a normally aspirated 1965 337. I use 25/25 for climb, then let it accellerate at climb power at level off (3000-5000 ft) then slowly reduce power to 23/23. My GPS and LORAN usually indicate a GS of 130 kts.
(I know GS is dependent on winds) I true out at between 140-145 miles (ASI is in miles). Is this normal? The book says I should be getting somewhat better. The engine compressions are all over 70/80, fuel flow is about 10gph/eng. The plane seems to be in rig. The paint is not great but I've seen worse. I fly mostly XC between Chicago and northern FL. All things roughly being the same, the numbers are consistent. What do you fellows think?

rowekmr · #2 11-09-09, 12:24 PM

Are you able to go from Chicago to FL non stop? How much fuel does that trip typically take.

Ernie Martin · #3 11-09-09, 12:30 PM

I'm on my second 337, both normally aspirated. To me your numbers seem low. Ground speed is hard to correlate to airspeed without knowing both winds and altitude, but here are my numbers, about the same for both aircraft ('69D, '73G):

Cruise 5,500 ft, 23.5rpm/21mp, ground speed=140 kts, no wind.

Notice it's knots, so about 160 mph.

The low manifold pressure comes from "babying" my engines. At about 500 ft I go to 25/25 and I never touch the throttle again until the descent (when I get to cruise altitude I reduce rpm from 25 to 23.5). So mp is what it is. At 5,500 ft around 21, at 6,500 ft around 20, etc.

Ernie

cessna02337 · #4 11-09-09, 02:26 PM

I have a 1967 O-2A...at 1000 FT AGL, I reduce power to 25/25...take a pause, then "Gear Up and Flaps Up."

I cruise all day long top of the green (24 inches) SFC-5500 ft.....at higher altitudes above that, I have the power full forward to give me whatever it can provide within the limits of the Green range and 2400 on the Prop RPM.

I utilize a Shadin Air Data Digital fuel flow of 11.5 Gallons per hour, normal indicated airspeed around 135 - 145 knots (lots of drag with the O-2A), especially with the wing pods! As previous post indicates, ground speed is subjected to winds and direction of flight....Tom

Tom · #5 11-09-09, 03:50 PM

I might be able to go non stop, but typicaly I don't. I have the long range tanks (46 +18 per side). Old pilots and bold pilots... and the fuel is generally cheaper in TN and AL. I probably use 100gal for a 650nm flight. I fly light also, maybe 50 lb of baggage and only the front two seats installed. I try to load for a slightly aft CG also.

Thanks for the info. Glad I found this site.
T

John Hoffman · #6 11-09-09, 08:21 PM

I have a 1973 NA plane and usually fly 23x23 as high as I can, I expect to see 145K and burn a little less than 20gph. Since you are burning the fuel you must be making good power so my guess is somethings draging your speed down. I had some reriging done years ago after I bought the plane and believe it helped the speed. You might have someone take a closer look at the airframe for rig.

Skymaster337B · #7 11-09-09, 11:24 PM

Do you keep your cowl flaps open after reaching cruise?

tropical · #8 11-10-09, 12:53 AM

I have a 74 "G" and at 6000' running 23/2300 and 10gph/engine I average 155 to 160 KTS TAS.

Tom · #9 11-10-09, 07:38 AM

Yes, cowl flaps are closed, gear up and wing flaps retracted

edasmus · #10 11-10-09, 09:06 AM

I second "tropical." My 73G model (no turbo) does the same. I run 2300 RPM and whatever manifold pressure I can get depending on altitude. If I am low however, I will usually not run much more than 24 inches.

Roger · #11 11-10-09, 06:16 PM

I fly mine non-stop between ART - SGJ typically 890-900 NM, and my average block to block is 5:50 - 6:10, for an average of 6 hours, at 150 Knots, 10.2 gals per hour per end. 7000 feet average 2300 rpm with throttle to the wall. 80 - 337-H.

Skymaster337B · #12 11-10-09, 10:59 PM

Wow, isn't that pushing the gas....6.0 on a full tank?

JeffAxel · #13 11-11-09, 12:33 AM

Quote:

Originally Posted by Skymaster337B

Wow, isn't that pushing the gas....6.0 on a full tank?

I am guessing he has the long range 148gal capacity........

Roger · #14 11-11-09, 08:25 PM

Yes, I have the interconnected 148 gallons useable, so no worry about burning mains first, then Aux, then back to mains,etc.. Plus I only fly it nonstop when VFR, so my 45 - 60 min reserve is not an issue. But there is an inverse relationship between the amount of liguid in the tanks, to the amount in your bladder in the 900 NM range

billsheila · #15 11-14-09, 08:40 AM

I have a 65 337, serial #31, so likely the same rivet crew that built your bird. I typically get 148KT to 152KT (TAS) depending on aircraft loading, as top cruise speed. I have compared to book when I first got my machine and while off a little bit, it was pretty close as I recall the analysis.