Climb and Cruise RPM

AGB · Post by **AGB** » Thu Jul 29, 2004 11:24 am

Hello all,
Got a question for you, I think this question may have been discussed here many times before but i did a search on the forun and found almost nothing. The aircraft manual says something like “after take off reduce power as soon as practical’ but the good Cessna 170 International Association says something like ‘climb with full throttle because it provides more fuel to engine for better cooling’. I was thought to climb with 2450 rpm, so what’s the best? Will any harm be done climbing with 2450 but with the throttle closed about an inch? How about cruise rpm? Is 2450 too much for sea level? If you have to go to full throttle to get 2450 in cruise do you still lean the engine?
Well I suppose that’s a lot of questions for a first timer here, but will appreciate your comments.
Bons vÃ´os (good flights)
Donovan

Post by **Bruce Fenstermacher** » Thu Jul 29, 2004 3:41 pm

OK I'll take a stab at it.

First the operators manual at least for the B model on page 23 F. (6) says "Climb at full throttle, or power required for saftey" then on page 26 under Take-off for a land plane it (2) says "Advance throttle slowly to full throttle." It never says to reduce power.

For cruise on page 23 G. (1) "Recommended cruising r.p.m. 2450"

Here is what I do with my B model with a C-145 and a McCauly 1A170DM7554 prop (semicruise prop). I have had my tach checked and calibrated in fact I carry an optical electronic tack n the plane that I use to check the rpm in flight. I also have a manifold pressure gage which i use more than the tack when I'm setting power

Takeoff is full throttle. I only reduce power at level off to 22" manifold pressure and what ends up to be about 2550. I only lean so my plugs don't foul. I don't really care about saving a gallon of gas per hour.
I'm in PA at about 500 asl and rarily fly over 2000 ft asl. I only go to higher altitudes for smoother air or a big tail wind on a long trip.

What you should to exactly is hard to say. There are so many variables, prop pitch/condition and your altitude are a few.

BTW in the my signature photo below I'm cranking the rpm at 2600 with 21.5 inches of manifold pressure at 1500asl. The engines just coasting.

jcraver · Post by **jcraver** » Thu Jul 29, 2004 5:28 pm

N9149A wrote:OK I'll take a stab at it.

First the operators manual at least for the B model on page 23 F. (6) says "Climb at full throttle, or power required for saftey"

FWIW My '54 manual also says something like "after take off reduce power as soon as practical". It's a good question. I am still learning about my O-300. In my C-85 you would see a significant rise in cylinder head temps when you pulled back the throttle just a bit from full due to the enriching feature of the carb.
jc

Indopilot · Post by **Indopilot** » Thu Jul 29, 2004 9:44 pm

Just a couple of cents worth from Arizona. Looking in the Continental Model O-300 and C Seris Operators manual X-30015. Dated April 1977 FAA Approved. Under the T.O and Climb section, it says;
a) Open throttle to full speed stop.
b) RPM may not reach rated speed until craft is airborne. Maintain
rated rpm only until immediate obstacles are cleared; then reduce to
climb power setting.

Caution... Cylinder head temperature must not exceedd values listed
in specifications during climb.

Then in the specifications section on page 0ne it lists the max allowable CHT as 525 degrees F for the C145 and 0300. If you had a C125 you could go to 550deg.

As personal practice at our field elevation of 4200 msl, we give it everything its got and pray for more. Brian

mrpibb · Post by **mrpibb** » Fri Jul 30, 2004 12:11 am

I'm with Bruce, I lean to save the engine, not fuel. What prop do you have? I have a 76em50 which gives me plenty of rpm static and 2550 on climb. Once above pattern alt. I will lower the nose for a cruise climb keeping about 2550. If I stay local I cruise 2450 to 2500 rpm which gives me 95 to 105 mph and if I go longer a distance I'll run 2550 up at a higher altitude which gives me 110 mph (remember climb prop). With my current prop I can get up to 2700rpm level flight which yields 125 mph, and when I lean I lean using my egt gauge once in cruise. Last fall before the repitch my prop was a 53" and level flight full throttle was 2550 rpm at 130 ish mph and 115 mph at 2450. On my last trip from Hampton Airfield Back to Aeroflex I cruised at 4500 ft msl at 2550 rpm flew for 2.3 hrs and burned 18.4 gals, which came out to about 8 gals hr, I can live with that.

doug8082a · Post by **doug8082a** » Fri Jul 30, 2004 12:21 am

Vic, Hampton airfield? Next time you're in the neighborhood, give a shout. I'm at Mansfield, MA (1b9). Not too far out of the way. I'd be happy to meet you at Hampton sometime. Don't need much reason the fly up there... neat spot.

mrpibb · Post by **mrpibb** » Fri Jul 30, 2004 2:06 am

Bruce, My buddy lives in londonderry NH, He keeps his cub at Hampton and he also has a hanger at Skyhaven NH. I usually get up there a few times a month. I'm on Vacation next week and were heading to the lakes region but I will be driving, can't get the kayak in the 170

mabe my next plane will be a 207. But mid week I may drive down to Jersey to get the old gal. My routine is to fly up in the morning to Hampton and eat at the airfield cafe. Also thinking if I get the airplane up there is to go to Capecod for the opening of the airfield there, or go to the Vineyard and lay my lilly white butt on the beach and get some color.

mrpibb · Post by **mrpibb** » Fri Jul 30, 2004 2:10 am

Oh, how's the TFR

hope you dont work in Boston!! it's enough to make a Republican out of anyone

doug8082a · Post by **doug8082a** » Fri Jul 30, 2004 2:12 am

Well, hope to run into you someday soon. My plane won't be back in action for at least another 6 weeks. But by September and the beginning of leaf-peeping season, I should be good to go.

doug8082a · Post by **doug8082a** » Fri Jul 30, 2004 2:14 am

The TFR ain't botherin' me none with no plane to fly. The traffic situation is ridiculous. The DNC folks said that there would be no traffic problems in the city and they are right... because THEY are the ONLY ONES THERE! They move around great! Everyone else vacated the city for the week.

mrpibb · Post by **mrpibb** » Fri Jul 30, 2004 2:34 am

My buddy works at logan, They ask him if he wanted the week off WITHOUT pay. I told him to send Kerry his mortgage bill.

AGB · Post by **AGB** » Fri Jul 30, 2004 12:14 pm

Thanks for the reply,
I didn’t mention what airplane I have. It’s a 51 Model A, I don’t know for sure now what prop, but since it used to tow banners at the beach I suppose its not a ‘cruise’ prop. I get around 105 MPH with 2450 and 4000 ft. Static I only get around 2300 rpm. Full throttle in level flight gives around 2550, I suppose, because I don’t do that since there is a red line on the 2500. But I suppose my question remains: I don’t want to harm the engine so should I climb with full throttle (which gives around 2500) or reduce to 2400-2450.

Maybe I should explain better the reason I am so worried. On Monday I dropped my first parachute, its fun, and it’s another reason to fly. These days everybody wants to jump from turbine aircraft, but sometimes, as I was told, its fun go in a 170. The trip to 4000 ft agl and back took about 20 minutes, maintaining about 2000 rpm on the way back for cooling reasons.

Bons VÃ´os,
Donovan

Post by **Bruce Fenstermacher** » Fri Jul 30, 2004 3:29 pm

With a stock 170 of any model you should not have a red line at 2500, it's 2700. Get your tach checked to make sure it's working properly. Perhaps someone did check the tack and found it was indicating 200 rpm low then instead of fixing it just moved the red line down 200rpm.

If your tach is reading correctly then it should be no problem running the engine full throttle at 2550 in a climb as long as oil ane cylinder head tempature limits are not exceeded.

Rivas · Post by **Rivas** » Wed Aug 11, 2004 1:48 am

I live in Washington State where we rarely have really high temperatures. My '54 has a climb prop. When I'm solo or even with another person I don't always use full power for take off. Full power climb is close to 1,000 fpm in cool weather.

I have always cruised at 2350 rpm I suppose to conserve the engine. It must work as the engine has lasted 50 years so far without a top job. My cruise fuel consumption is right around 6.1 gph. On one occasion we flew 5 hrs on 33 gallons which included climbing to 12,000 ft in hot weather at full gross weight.

We tried out a GPS recently and found that we were seeing a ground speed of 118 mph in either still air or with a touch of headwind.

blueldr · Post by **blueldr** » Thu Aug 12, 2004 4:54 pm

If you have a C-170 with a 300 cu. in. engine and a fixed pitch prop that will give you a 1000 ft./min. climb, a 118 mph cruise at 6.1 gph., you better have it gold plated and sent to the new Smithsonian museum.