Mountain Flying in a 170B?

[CraigH]

Over the past couple of years I've started an annual tradition of flying up to the Arkansas River valley of Colorado to go river rafting with a buddy. The trip revolves around the 4th of July weekend, and the usual routine is to fly into Canon City / Freemont County, then early the next morning head up to either Buena Vista or Leadville. Previously I've made the trip in a 150hp Citabria and a 118hp Taylorcraft and am now wondering how the 170B will fare at such elevations.

Canon City (1V6) sits at 5400ft elevation and this year temp was at 98F when we arrived mid afternoon. The trips up to Buena Vista (7V1 / 7900ft) and Leadville (LXV / 9900ft) are usually made very early in the morning when temps are cooler but with enroute density altitudes up to 14000ft. At my home airport (elevation 1100ft) the climb is very lackluster compared to my previous aircraft so I'm wondering if the plane is capable of safely making it all the way loaded to within 200lbs of gross weight?

I'd sure like to hear from any of you who've flown your 170's in similar conditions. Highest I've had mine so far is 4500msl.

[AR Dave]

We live on the Arkansas River and have been thinking of following the river all the way to Colo.. Wife's family lives up there!
Hey, you need an 8043 prop.. I'd almost be curious to trade your speed prop (if that's what you've got, 7453) for my climb prop, while your on the trip. You'd only cruise at about 100 mph, but you'll climb 750 - 1000 fpm.. I just couldn't live with less than that! I know someone that changes props for different needs.
Will you be at Reklaw?

[CraigH]

I've got to look at my prop log and see which one I've got (the logs are at my A&P's office being updated). Since my top cruise is around 105mph I'm guessing I might have a climb prop - I hope.

I'll definitely be at Reklaw and am planning on an arrival around 2-3pm on Friday. Look me up as I'm looking forward to meeting some other 170 owners.

[GAHorn]

Uh, Dave, perhaps you made a typo? The standard prop for most 170's is a McCauley DM or MDM 7653. The 76 in 7653 represents the minimum diameter allowable. A 7453 would be too short.

[AR Dave]

Yep I meant 7653! Actually I was just meaning anything that's considered cruise. 105 mph ain't considered cruise though.
Craig I'm guessing yours is 76". Two reason's - First, since pilots notice the 80" and ask about it so much, you have to find out pretty quick after taking ownership. Second, 105 is not happening with an 80". When I say 100 mph, that's on a good day. Possibly even stretched a lil bit then.
Now I do have the 8.50 tires however, maybe that's the hold back.

[CraigH]

Mine is a DM 7653, which I believe is the standard prop?

[AR Dave]

Well then, you have a choice to make. Climb or Speed.
Either put an 8043 prop on or take the Red paint off!

[ron74887]

hey hey hey--- finially got George, and get top pick on him a little (all in fun) the 76 is the Max length (not min) allowable not under 74.5" in length
with the McCauley and only 71.5" min. length for the sensenich prop. George the DEVIL made me do it. gotta love it. if I only knew how to put in the faces Ron

(You mean like THIS? )

[GAHorn]

Coorreccctttt-o-Mundo!, Ron! (Goes to show you how you should proof-read before hitting the Submit button,....especially as old-age creeps up. The word should have read "maximum" not "minimum". The 7453 statement is still correct. It would be too short.)
BTW, Ron, ...careful how you dish it out. Paybacks can be H---! (The minimum length for the Sensenich M74DR metal prop is 72".... ...not 71.5.
The wood prop is allowed to be 71.5, but doubt if anyone operates a wood prop on a 170.)

The McCauley 7653 prop designates a MAX length (dia) of 76" and an original pitch of 53". Repair schemes of the prop can shorten the blades down to a dia/length of 74.5" and still be legal on a 170.
The 8043 prop is a compromise. It trades longer blades (80") for lower pitch (40"). Similar results can be had with a 7648 prop and avoid high tip speeds at the slight expense of acceleration. (But as in all cases of switching to lower/finer pitched props, cruise speeds will be traded for climb capability. If you operate out of short strips however, it's probably worth it.)
The problem becomes one of horsepower generation versus rpm limitations. Our original C145/O300 engines only generate 145 hp if they are turning 2700 RPM. If you don't turn that high rpm, then you are producing LESS horsepower. The typical 7653 prop only turns 2230 to 2330 on takeoff, and that only equals about 118-120 horsepower at the beginning of the takeoff.
If a finer/lower pitch prop such as being discussed here is used, then higher rpms and therefore higher horsepower is generated for takeoff and the takeoff roll/initial climb is increased. At altitude however, that finer-pitched prop may become rpm limiting as it may require a throttle reduction to prevent overspeeding, and the higher than normal rpms will also result in higher fuel consumption per mile. (The cruise props such as my 7655 may result in higher cruise speeds and reduce fuel consumption at cruise some, but the trade-off is longer takeoff runs and lower climb performance. But, I have had my gross-wt takeoff, make a cruise at 13,500 for a short period to get over the Rockies into Salt Lake City on the way to Tehachapi last year. It was two hours after takeoff before I attempted the altitude, however. That cruise prop doesn't like to climb up that high.)

[flyguy]

Almost all the airstrips/airports in high altitudes are long enough to assure that you can get to flying speed within the first half of the runway if your numbers are correct. In my experience the lower pitch prop will not necessarily reach that indicated air speed at that point any better that standard pitch (76/53) or higher pitch(76/55). Horsepower and lift factors deteriorate markedly as the density altitude increases. That is the thing you must watch like a hawk. No stock 170 regardless of prop pitch will be able to take-off safely at an airport with a density altitude of 12000' msl.

I have had my 170 to 18000' out of Taos, NM. Field elevation for take-off there is 7088' msl. Take-off to the south-west is recomended as there is a 40' downslope taking off that direction. 9000' DAL isn't too bad under those conditions. Getting up to 18000' was achieved by using "ridge lift" and full power for the long climb. It took about an hour and the engine never got much above 2100RPM. As the "ridge lift" petered out I began to gradually lose altitude. If I had had a 76/48 screwed on the front the indicated airspeed would have been less and the altitude loss would have been more rapid.

Ona cool morning, density altitude of 5000', your 76/48 might accelerate to 70 indicated but your ground speed will only be 60. My 76/55 will accelerate a little slower but we will break ground at nearly the same point.

I have flown lots of hours in the southwest US. The only time I had to abort a take-off was mid-day at Flagstaff, AZ where the FSS reported DAL 11500'. I was slightly over gross but decided with 9000' of runway I could make it. Leaned out to achieve full power RPM, I started rolling. Used more than half the runway and indicating 80MPH she wouldn't fly! Maybe I could have gotten airborn but would I have been able to climb into cool air? I assumed I couldn't and didn't give continuing the take-off a second thought. After I shut her down I taxxied back to the terminal to wait for cooler air temps. I went into the FSS office talked to the fellows and found that the DA had gone about 500' higher since my initial contact 15min previous!

My FWI

[CraigH]

Thanks Flyguy. Kind of what I gathered from looking at the performance figures in the owner's manual. I'll probably forego the Leadville leg of the trip next year and just base out of Canon City. I'm not only worried about the take-off portion, but the rate of climb that can be expected once I get airborne. Anything less than about 400fpm would make me a little uneasy.

Both the Citabria and the Tcraft used less than half of what it appears the 170 would use on takeoff, and I like to have a nice margin of safety when flying up at those elevations when unfriendly terrain lies below.

[AR Dave]

http://www.fly-low.com/feat1005/indiansummer.html

[170C]

WHAT Can it be true------a '56 C-170 with a cruise of only 105 mph (or was it 105 kts)? Surely there isn't one that is slower than Ole Pokey

I seem to remember reading an article a few yrs ago about some fellow in an Aircoupe flying into and out of Leadville, CO. Got his certificate of having done so. If this was doable, wouldn't a lightly loaded 170 be able to do so?

[CraigH]

Probably would be doable in the early morning and lightly loaded. Problem is that I'll most likely have my wife, daughter and 3-4 days worth of luggage.

As far as the 105mph goes, I'll have to verify that once we get a calm day. So far, every time I've flown the plane so far the wind has been blowing pretty good so it's hard to get an accurate groundspeed. I'm not convinced that my ASI is reading just right as of yet - time will tell.

[GAHorn]

... If I had had a 76/48 screwed on the front the indicated airspeed would have been less and the altitude loss would have been more rapid. ...

Ona cool morning, density altitude of 5000', your 76/48 might accelerate to 70 indicated but your ground speed will only be 60.
...
My FWI

Uhmmn, Flyguy, ... respectfully.... I think you'd better cut the chickory outta your coffee. At higher altitudes your true airspeed (and therefore your no-wind groundspeed) would be higher than indicated....not lower.
And the climb prop (7648) would improve your climb because of the higher horsepower generated due to the higher rpm generated. It would not cause a higher loss of altitude simply due to a downdraft/loss of "ridge lift", because it would improve your ability to climb.