High altitude t/o with stock 170

[buzzlatka]

Wondering what the wisdom is for a stock 170 takeoff at high density altitudes. I know the book says the distance is longer with 1 notch of flaps. I tend to disagree at least for my 5-6k strips around CA. I tend to get the airplane into ground effect and slowly retract the flaps. It seems to get me airborne the quickest. Thoughts?
I'll be heading over to Reno next week and it going to be hot and I'll be near gross. I'm going to do some testing.

[Robert Eilers]

Buzz,

My undertsanding of the takeoff performance figures reflected in the Owner's Manual are based on clearing a 50 ft obstacle. Although the first notche of flaps may get you off the ground sooner, it is your rate of climb that is most affected by the flap sitting. At Reno, with the possible exception of early morning, you will clearly be in the "Black" or "Starred" caution area of the Take-off Performance chart. Reno has plenty of runway, but is surrounded by higher terrain. IMHO I would adhere to the book recommendation regarding flap setting.

The performance figures are based on a typical 170 with a McCauley prop (no indication which McCauley), But I suspect it is most probably the 7653. A different prop, will of course produce different performance results.

Rate of climb, if takeoff is during hot temps, will be significantly less than 500 fpm - so pre-takeoff departure path planning and a consciousness of mountain wind effects are paramount. Be sure to cimb to a good terrain crossing altitude before heading back West across the mountain ridges and generally into the wind.

Probably more info than you need.

Good trip

[Robert Eilers]

Just one more thing Buzz - it's late and I'm bored. Departing Reno in the afternoon, i.e., 6000 MSL and 80 F+ will produce a Density altitude of close to 9000 ft. I couldn't find the service ceiling listed anywhere in the Owner's Manual, but I suspect it is most probably 14,500. So, if you begin with a ROC of 395 at 6,000 MSL (9000 DA), and must climb 4,000 feet (assuming climb to 10,000 MSL) then your ROC at 9,000 MSL (for example - assuming a non-standard summer lapse rate) will be approaximately 200 fpm. If winds aloft across the Sierras are 25 knts or more West to East, you may find you cannot out climb the down draft on the Reno side of the mountains. Just one more reason for an early morning departure and good departure path planning.

[canav8]

I will add .02 cents since it is early in the morning. Interesting enough the service ceiling is a theoretical altitude. It is the highest altitude at which the aircraft can maintain a climb of 100ft./min. In the 170 it is pretty low but it is also a function of load your carrying. Aircraft also have an absolute altitude. It is the altitude at which you have a 0 ft/min climb at Vy speed. It is also predicated upon weight and temperature.I will also offer this to. Under FAR part 23 some aircraft have an maximum Operating altitude. That is the max altitude at which the aircraft can climb due to structural requirements (ie pressurization system). The most important thing to remember in VFR flying is do I have the runway distance to take off?

Buzz, make sure you get off early. You may not even have the power to climb to pattern altitude if the temps are high. When I talk with students about density altitude I show them how much degradation there is in power output. If you take your 170 and takeoff at sea level you will be using 145hp. When you get up to 7500 feet your power output is about half. Picture you taking off out of Reno with a full boat. You know how well it performs full don't you? picture your airplane flying with a power output of 72 1/2 HP. Make sure the temps are cool. It would be ill advised to takeoff if the temp gets over 75 degrees at gross weight. I am being conservative but I have lost way to many friends to density altitude situations. They just forget about this when they are flying.
When I used to fly out of the Grand Canyon non turbo charged airplanes had to leave at first light or below 70 degrees. If they didnt you always found them in the trees at the end of a 9000 foot runway. It is serious business. If you get delayed out of Reno due to unforseen curcumstances delay the departure till the evening or next day early morning. Good Luck and hope you dont have a story for us requiring super natural piloting techniques. Doug

[buzzlatka]

I guessed I asked the question wrong. I am very experienced with high airports. I'm not looking for instruction. I am specifically wondering about getting the airplane off the ground quickly. I agree that the plane climbs clean better. What I find is that with one notch of flaps It seems that i get the plane off the ground quicker. When I tAke off clean I just feel like I roll on the runway forever. This is all just opinion. I am going to do some testing next week. I wS wondering if there are any other stock 170 guys out there who routinely operate high that have opinions. And by the way this is for long paved strips, not grass.

[canav8]

I guessed I asked the question wrong. I am very experienced with high airports. I'm not looking for instruction. I am specifically wondering about getting the airplane off the ground quickly. I agree that the plane climbs clean better. What I find is that with one notch of flaps It seems that i get the plane off the ground quicker. When I tAke off clean I just feel like I roll on the runway forever. This is all just opinion. I am going to do some testing next week. I wS wondering if there are any other stock 170 guys out there who routinely operate high that have opinions. And by the way this is for long paved strips, not grass.

Ok Buzz. The fastest way to get off the ground is to accelerate close to take off speed and then pull one notch of flaps. That is the graduate level technique. You will accelerate faster and then have an infusion of lift. Howz that! Its the best of both worlds.

[rhymes]

Buzz,
I'm a fairly new 170 driver, but most of my flying has been around Reno or our home 'port of Susanville, CA (KSVE), about 80 miles north of Reno.
I've tried both 0 flaps and 10 degrees for takeoff with our stock B model, freshly-overhauled stock engine and McCauley climb prop. Takeoffs at our elevation of 4,150msl, with density altitudes of 7K or more work better with no flaps on takeoff, as per our POH.
I develop more speed, and can maintain that airspeed on climbout better w/o flaps. I agree that it seems I'm rolling a loooong time!
I'll be at the Reno Air Races, on display in the Heritage Trophy Invitational area, so c'mon by and say howdy!
Hope this helps...

[GAHorn]

...Ok Buzz. The fastest way to get off the ground is to accelerate close to take off speed and then pull one notch of flaps. That is the graduate level technique. You will accelerate faster and then have an infusion of lift. Howz that! Its the best of both worlds.

I respectfully disagree with that ... I believe it is the WORST of both worlds. Not only does one experience the long takeoff roll using that technique....one also becomes airborne with the drag and climb-penalty of deployed flaps.

The factory got it correct: Zero flaps at higher density altitudes results in better takeoff field performance. Yes, of course (!) higher density altitudes require longer takeoff rolls and longer distances to obstacle-clearance heights. But the aircraft definitely performs better with no flaps under conditions above 4K, as described in the Owner's Manual.

One more thing, Doug... one does not acheive 145 hp at sea level in standard conditions using the stock C-145/O-300 engine and McCauley prop. If one consults the TCM Operator's Guide the charts will demonstrate that static rpm (as per the TCDS) achieved during takeoff is in the 2330 rpm range. This develops about 120 hp for takeoff.

[canav8]

...Ok Buzz. The fastest way to get off the ground is to accelerate close to take off speed and then pull one notch of flaps. That is the graduate level technique. You will accelerate faster and then have an infusion of lift. Howz that! Its the best of both worlds.

I respectfully disagree with that ... I believe it is the WORST of both worlds. Not only does one experience the long takeoff roll using that technique....one also becomes airborne with the drag and climb-penalty of deployed flaps.

The factory got it correct: Zero flaps at higher density altitudes results in better takeoff field performance. Yes, of course (!) higher density altitudes require longer takeoff rolls and longer distances to obstacle-clearance heights. But the aircraft definitely performs better with no flaps under conditions above 4K, as described in the Owner's Manual.

One more thing, Doug... one does not acheive 145 hp at sea level in standard conditions using the stock C-145/O-300 engine and McCauley prop. If one consults the TCM Operator's Guide the charts will demonstrate that static rpm (as per the TCDS) achieved during takeoff is in the 2330 rpm range. This develops about 120 hp for takeoff.

Lol, ok George, I will engage you. A couple things I commented on are correct and I should explain my conjecture. First thing. The question was how do I get off the ground in the shortest distance. Not a climb out!. The comment I made is in fact true. Flaps up will accelerate faster. Adding flaps will increase lift. In ground effect you can also fly the aircraft at a slower speed. Since VSO now is a player instead of VS. Since you ask, you should also quantify how many flap notches you have. As you know not all 170s are the same. The next thing is horsepower. Everything you state is absolutely correct. The only problem is take off does not stay in a static state it converts to a dynamic state. The rate at which it converts to a dynamic state is variable. The reason why engineers will give a static number is because it is a known number...FYI

[GAHorn]

If one consults the operational data contained in Section V of the 170B Owner's Manual, one will find takeoff distance data developed/documented by Cessna test pilots. Their recordings are far more objective than our/your subjective feelings on this matter.

This should be evident by the notations contained within the left box and the starred commentary.

The "No flap" data states that takeoff ROLL is approx. 40% of total takeoff distance.
The 20-degree flap data states that takeoff roll is approx 38% of total takeoff distance...which confirms the ordinary belief that the use of takeoff flaps shortens takeoff ROLL..... until higher density altitudes are confronted! (That is where the starred/bold data is applicable.)

Looking at the higher elevation, deployed-flaps data one will see that the DRAG of deployed flaps above 4,000' density altitudes increases the total takeoff distance over that of zero flaps...and that includes the approx. 38% of the total which equates to ground roll. (Example: Looking at the 60-degree data taken at 7000' elevation, the zero flap distance of 3500 multiplied by 40% equals 1400 feet of ground roll. However the same conditions with takeoff flaps deployed: distance of 3735 multiplied by 38% equals a greater distance of ground roll, 1419.3)

As for the static rpm portion of this discussion,... Do you imagine that the aircraft used to develop the takeoff data were somehow not subject to the same "dynamics" of acceleration as our aircraft in the fleet?
Regardless of the small increase in indicated rpm (less than 100 increase typically)...NONE of our standard fixed pitch installations EVER achieve 145 hp during takeoff. The only time 145 horsepower is ever developed in our standard engines/props is at sea level, standard conditions, 2700 RPM. This is only likely (or possible even) in level flight or, more likely, in a descent (which won't be for-long at sea level.)

When was the last time you ever observed that (2700 rpm), especially during a S.L. takeoff...??? (not to mention at Reno!)

[robw56]

Buzzlatka as you might know I used to live in Cheyenne where the field elevation is over 6000ft and the density altitude was pretty much always higher when I went flying, unless it was below about 37degrees F. I found that the plane will get off the ground quicker with one or two notches of flaps(10 or 20 degrees) but climb would suffer. I did a test doing several takeoffs using no flaps, first notch, and second notch and climbed to a specific point in the pattern. With no flaps it took a little longer to get off the runway but I was around 250ft higher in the pattern (if I remember correctly) than I was with 20 degrees of flaps. 10 degrees was somewhere in the middle. So I suggest to you if you have the runway length just do a no flap takeoff, or 10 degrees to get off the ground then retract the flaps in ground affect build up your speed and climb out. I usually only use flaps for take off at high altitudes when its grass/rough/soft, then I get the flaps retracted as soon as I can to climb out. I hope this helps.

-Rob

[Bruce Fenstermacher]

It has been alluded to but to be clear not all 170B models have a 20 degree flap indent allowing the flaps to be set at 20 degrees.

[GAHorn]

I believe Bruce meant to say TEN degrees. Early 170B models had only four flap-positions....zero, 20, 30 and 40 degree settings. Later models added a 10 degree setting. When Cessna ran out of 20-degree flap sector parts they approved the replacement of 4-position sectors with 5-position sectors. (Hint: Cutting a 10-degree setting into your sector requires a basis-of-approval*...but replacing it with a 5-position sector is a mere logbook entry.)

The sector replacement is incredibly simple....remove the long pivot bolt/bushing which holds the sector...and replace the sector and reinstall. Takes all of 15 mins. (A short slit cut in the carpet allows access to the bolt and the carpet is easily re-glued to be invisible.)

*See the MX Library http://www.cessna170.org/forums/viewtop ... =26&t=8901

[buzzlatka]

Thanks rob,
That is what I was looking for. I wish I had the 10degree flap setting but that is another thread. I have been using flaps at high altitude because I just don't like the feeling of extended takeoff rolls at high speeds. I'd rather get airborne quicker and accel in ground effect and climb. I go to bishop and south lake a lot and some of my more exiting takeoffs are when the gusty winds start to play with me towards the end of the takeoff roll. Lots of ground speed but the plane is still not ready to lift off.
I have never had time to do testing at high altitude airports because I am always going somewhere and don't want to waste the time.
Anyway thanks for the report. I know what the manual says but it is nice to get an actual report.

Have fun this weekend, I have to work. Delta will be mowed this weekend.

[robw56]

It has been alluded to but to be clear not all 170B models have a 20 degree flap indent allowing the flaps to be set at 20 degrees.

I understand that not all 170's have the 10 degree flap setting, that's why I clarified by stating "(10 or 20 degrees)". If I remember correctly the 10 degree setting wasn't standard until 1955 but a lot of earlier 170's, such as mine, have been modified to add the 10 degree notch.