The International Cessna^® 170 Association

Folks,
What is the IAS for the best angle of climb for a 170A. Lets say 6000' DA. POH only talks best rate. Thanks.
Pete Smith
Lewistown, MT

Pete
I did some quick and dirty testing in my B model and found 62 IAS to work about right for Vx. Keeping in mind that at that AOA the diff between IAS and CAS is likely significant. I would have thought it would be a couple mph slower but thats what it worked out to. That "test" was at standard condition with a denalt of about 2000'. ROC by the way was in the area of 700fpm with 2 bodies and full fuel. I used runway markings/lights for distance over ground references.

I parked next to your 170A at LWT on the ramp last week (I was in N705) but had a quick turn before CBs started to build.

Ray

I believe the best angle of climb speed would be the same as at the best lift to drag ratio (or coefficient of lift) speed, which can be determined by finding the speed at which altitude can be maintained with the least amount of power. That speed should also be the best angle of climb speed. (Or is it the best rate of climb speed?)
Not being an engineer I stand to be corrected-
Rudy

I'm going to go out on a limb and propose that the best ANGLE of climb (at sea level, standard day, zero flaps) is 67 mph TIAS, and the best RATE of climb under the same conditions is 88 mph TIAS. I base my opinion on the performance data published thru the Owner's Manual and duplicated in the AFM.
The Owner's Manual (for both the A/B models, within one mph) is actually stated to be 88 mph. The best obstacle clearance speed (equating therefore to Vx) is 67 with the average recommendation range being 62-75 depending upon where you read the data and at what flap setting is selected.
Therefore, I am comfortable recommending Vx (best angle) to be 67 mph (actual range 62-75 depending upon weight/temp/altitude) and Vy (best rate) being 88 mph (decreasing with altitude) under zero flap, standard conditions. Standing by for incoming (and this being worth every penny you paid for it.)

Maybe a more important question is: what's the best glide speed? (just ask Miles after his engine sucked a valve. I've been there too).
Is it the same as best angle, or best rate, or some airspeed completely unrelated to either?

Eric

I honestly can't remember what I speed I used.

All I remember is that the incident occured at 7500 feet, and I arrived over Desert Center airport 12nm away at 6000 feet. The engine was still running making around 2000 - 2200 rpm. Whatever I did, it was sufficient.

Miles

I'd say I agree with George here, the owners handbook wasn't made like the newer ones are, but it's got pretty much everything in there. If the test pilots over half a century ago arrived at 67mph as the best speed for clearing a fifty foot obstacle then that's probably real close to Vx (when you're at gross weight). However, with a lighter pitch prop Vx would be a little less, and at a lighter weight it would be less as well.

Hmmmm well I tried (in my quick and dirty test) 67 IAS and noted much more ground distance traveled/altitude gained than using a slower IAS. I was under the notion that Vx was max alt in min distance. I will repeat though that it WAS quick (no replications or varible in conditions) and dirty (used IAS instead of CAS and a very crude method of measuring ground distance). What I DID notice for sure was that one should not expect stellar preformance from a 145hp(on a good day) engine. Out here trees grow nasty tall and going around them rather than over the top usually has a better outcome.

The Owner's Manual and the AFM are the only reliable data we have. It's easy to forget what info is available there unless we occasionally review it.
The stated, recommended best glide speed in all models is 70-75 mph. The straight 170 ("rag-wing") states a 1 mph difference in the best rate of climb (89 mph), and it also recommends a different obstacle clearance speed (Vx) of 76 mph (as opposed to the 67 mph recommended for the A and B models.)
For those curious as to why the A and B models share the same speeds....it's because both are stated to be zero flaps. (The major difference between the two's performance figures are not in speed, but in take-off and landing distances...due to the B model's slightly better flap performance.)

The Owner's Manual and the AFM are the only reliable data we have. It's easy to forget what info is available there unless we occasionally review it.
The stated, recommended best glide speed in all models is 70-75 mph. The straight 170 ("rag-wing") states a 1 mph difference in the best rate of climb (89 mph), and it also recommends a different obstacle clearance speed (Vx) of 76 mph (as opposed to the 67 mph recommended for the A and B models.)
For those curious as to why the A and B models share the same speeds....it's because both are stated to be zero flaps, and of course, they actually have the same airfoil other than flaps. (The difference between the two's performance figures are not in speed, but in take-off and landing distances and stall speeds...due to the B model's slightly better flap performance.)
Anyone attempting to verify these speeds with their own aircraft should keep in mind several important points: 1. Your airspeed indicator may/may not be accurate. When was the last time it was bench-checked, re-certified, and your pitot-static system leak-checked and re-certified? 2. Does your pitot tube match that shown in the Service Manual as regards shape, length, and position to relative wind? 3. Is your test flight being conducted on a standard day (or compensations made for non-standard atmosphere) at gross weight? 4. Did you actually, physically measure the distances and heights of runways and obstacles? (And did you actually attempt this with an actual obstacle? Or did you have observers down-field with accurate instrumentation to measure height gained over distance? Were the tests performed in zero-wind? If you used your VSI/ALT to measure rate of climb....were they also recently calibrated/recertified?)
In short, it's probably a good idea to have your airspeed indicator and pitot/static system recertified if you truly wish to fly your aircraft as accurately as the published data (if any of this discussion actually interests you.) You might also wish to consider the age, condition, profile, and pitch of your 50+ year old propeller (with gosh knows how many mechanics who have filed, repaired, ground the nicks and gouges out of it, and the airfoil thinning which takes place every time it's repaired/overhauled/polished/etc.) and the rigging and condition of your airframe. Then there's the accuracy of your tachometer in order to determine if your engine is actually making rated power (something considerably less than 145 hp at takeoff, by the way.) I hope the point I'm attempting to make is making the cyber-space leap.....namely that all the anecdotal experimentation and ad-hoc "test pilot" techniques in the world is not going to change a single mph of data which Cessna spent a considerable amount of time and money on. IF your airplane conforms to the type certificate, ...and IF your airplane has no appreciable loss of performance, ...and IF your pilot technique is as good as the professional test pilots with thousands of test-pilot-hours in dozens of different aircraft, ...and IF your instrumentation is accurate,...etc. etc. etc.,.....then your airplane will meet the published performance in the Owner's Manual and AFM.
I'm glad to see the interest in maintenance, performance and pilot skills that this discussion brings.

All good and vailid points. I am no test pilot but have a question sort of related that maybe George can answer regarding the pitot tube angle/position. Mine has been "altered" a few times. Once via a ladder and once via my head with the tail jacked up. I more or less positioned it back to spec(diagram) but am wondering about metal fatigue with much more bending. I have left it as is for fear of a fracture and accepted what may indeed be airpseed errors. The question which may be a dumb one is, how resilient to flex and resitant to fatigue is the pitot tube material? I will bet that in the future more "adjustments" will be made to the tube angle using body parts other than those most suited for adusting.

It's not likely you'll break it by bending it unless you do so over a small radius repeatedy. The tubing is "SO" temper, meaning it's fairly soft and pliable. In any case, it's also easily replaceable, as it has it's first connection in the leading edge, just above/aft of the nearby inspection plate.

I didn't mean to imply that it takes a "test pilot" to achieve published performance in our airplanes. The skill of a genuine/professional "test pilot" is primarily in his/her ability to repeatedly and consistently perform specified manuevers-performance and in the ability to document and describe the performance/handling issues being investigated. Average pilot skills, smoothly and consistently applied, utilizing Owner's Manual specified techniques with a properly maintained airplane will achieve similar performance the factory intended to document. You/We can do this.

Airspeed, shmearspeed... who needs it ?
Rudy

One of the pilots 10 commandments:

"Maintain thy airspeed lest the Earth arise and smite thee."

Does anyone know the actual angle at the best angle of climb speed? And how this might vary with altitude?