climb speed

[8233]

I read the chart the same way that John does,

In my example I used 1st row and 4th column, so at 81 mph, sea level, and 60 Fahrenheit expect 640 fpm.

In John's example 1st row and 1st column, so at 81 mph, sea level, and 0 Fahrenheit expect 740 fpm,

I have noticed in my 140, in the conditions I wrote before, that if I increase the speed from 81 up, flying hand off on a calm wind day, I get best variometer readings. That makes me think that 81 mph is NOT the best rate of climb speed. For that reason I am convinced (with my 140) that Vy is higher than 81. That is coincident with Checkmate list, that gives Vy = 89.

For that reason I use 85 to 90 mph after clearing obstacles at 75 mph aprox.

Observation about the wording of the chart:

The chart (1947) says NORMAL RATE OF CLIMB. What means "NORMAL" ?
There are of course infinite possible climbs, but the two interesting and most used are "BEST ANGLE" and "BEST RATE".
For that reason, I think that we must interpret "BEST" where the chart says "NORMAL"
Am I right ?

Kind regards,

This is where I think things get a bit complicated. It really depends on your engine, your prop and your airspeed indicator. Based on my airplane and trying different airspeeds, I believe those numbers do produce Vy for me.

There is an article in the library that covers most of the 1946 models but can also apply depending on who worked on the airplane. What I found after reading that and talking to a few other members is that the static port placement is horrible on our airplanes and in my case, even after having everything checked, I always got a more accurate airspeed indication by venting to the cabin versus the static line. It's a real odd issue and I have gotten a wide range of opinions but at the end of the day and 2 airspeed indicators plus static system checks, that is how I got mine to finally read correctly.

Here is a link to the Neal Wright article:

viewtopic.php?f=10&t=133

[6643]

Each line of the chart is for a different altitude (or PA). The speed is the recommended climb airspeed for that altitude, and the remaining cells are for the expected climb rate for the individual temperatures. There is no correlation between the different lines other than as you go up in altitude your recommended climb speed decreases as does your climb performance.

I wouldn't count on "normal" climb being the same as Vy. I expect is more like "recommended," "suggested" or "average".

[6930]

Right or wrong (and I know I could very well be wrong), I have interpreted the operating booklet as meaning Vy = 81 mph at MGW and standard pressure/temperature (sea level, 60 deg f) and Vx = 73 mph. 81 comes from the performance table and 73 comes from the operating procedures on page 5 of the book.

The actual single sheet “manual” which is required to be kept in the plane shows what I believe is the same performance table as the operating booklet. The performance table is for a wooden Sensenich 74FK-49 which I certainly don’t have, and doubt many others do either. So, the reality seems to be that the numbers are all “kind of sort of general recommendations so do what you like” values.

After my overhaul with the O200 crank, I did a bunch of time to climb tests and found that the best rate of climb, or Vy, for my plane is 70 MPH. With that said, I would think that our aircraft with a standard healthy C85 would generally provide the best rate of climb between 75 and 80 mph at sea level and 60 deg F. Going up or down from that with temperature and altitude variations.

Mike

[a64pilot]

Each line of the chart is for a different altitude (or PA). The speed is the recommended climb airspeed for that altitude, and the remaining cells are for the expected climb rate for the individual temperatures. There is no correlation between the different lines other than as you go up in altitude your recommended climb speed decreases as does your climb performance.

I wouldn't count on "normal" climb being the same as Vy. I expect is more like "recommended," "suggested" or "average".

As the marketing dept gets involved with any performance charts, I’d expected recommended climb speed to be at Vy, reason is it gives the highest rate of climb numbers, and most everyone when shopping will compare numbers of the models of whatever they are looking at to buy, that’s led many marketing depts to simply lie, car stereos for example, they often claim power outputs that are simply impossible based on the fuse that is in the power wire.
The FAA has an allowable tolerance for indicated airspeed accuracy, manufacturers will often go to a lot of work to position the pitot tube etc to give an indicated airspeed that is within allowable error. but displays one that is higher than actual.
Get in one model of airplane that actually cruises at 120 kts, but it displays 117 and then get in another that displays 123, both are within tolerance, both cruise at identical air speeds, but almost every GA pilot out there gets the opinion that the one with a higher reading is a faster airplane, so it will sell better.

When I Certified the S2R-H80, the AS read low, within tolerance, but low, as do all Thrush aircraft. Air Tractors read high, so people think they are faster. I had a .030 step machined in the static port to increase low pressure on the H-80 and this raised indicated AS very close to actual. and people of course think it’s faster than other models, because the AS indicator says it is. I could have made that step .040 and gained a few MPH and stayed within allowable but left it at .030 as that’s more accurate.
But I can tell you what sales would have done if they knew about it.

[a64pilot]

I don’t think that an increase in power of an engine changes Vy by much, Vy is simply the airspeed at which the lowest power is required for the aircraft to fly,it’s also usually max endurance airspeed.
So as it’s the airspeed that requires the least power to fly, there is also the most excess power available, and that excess power can of course be used to climb.
So if you increase or decrease the HP of an engine Vy shouldn’t change much, the rate of climb will change of course, but the speed shouldn’t, or not by much anyway.

I haven’t read this, but at a glance it seems to be a good dissertation of aircraft performance
https://www.faa.gov/regulations_policie ... k_ch11.pdf

[6643]

Things were a little different in 1945...

[8233]

I don’t think that an increase in power of an engine changes Vy by much, Vy is simply the airspeed at which the lowest power is required for the aircraft to fly,it’s also usually max endurance airspeed.
So as it’s the airspeed that requires the least power to fly, there is also the most excess power available, and that excess power can of course be used to climb.
So if you increase or decrease the HP of an engine Vy shouldn’t change much, the rate of climb will change of course, but the speed shouldn’t, or not by much anyway.

I haven’t read this, but at a glance it seems to be a good dissertation of aircraft performance
https://www.faa.gov/regulations_policie ... k_ch11.pdf

Vy IAS lowers with increase in altitude. Vy TAS increases as you increase altitude. I believe that chart was trying to convey IAS. Agree that excess power will translate into rate of climb so as you gain altitude, less excess power, less rate of climb.

[a64pilot]

Vy IAS lowers with increase in altitude. Vy TAS increases as you increase altitude. I believe that chart was trying to convey IAS. Agree that excess power will translate into rate of climb so as you gain altitude, less excess power, less rate of climb.

I believe as density altitude increases Vx speed increases, and Vy speed is reduced,(Indicated airspeed), and they will converge at the absolute altitude, which is of course the highest altitude the aircraft can achieve, and it can only achieve that at one airspeed, the one that requires the least power to fly, any faster or slower and it will descend.

Sort of the coffin corner just without the coffin

[a64pilot]

Knowing what your Vy is can be important, as it’s the speed that requires the least power to fly, it’s likely the airspeed you should shoot for if for instance the engine isn’t running very well, or for whatever reason you really wanted to maximize the time you could stay in the air, waiting for ground fog to burn off for instance.

I was surprised to find out it was a lot higher than I had supposed it was, but apparently a C-152’s Vy is 67 kts, which is roughly about 77 MPH?
We aren’t 152’s but it would seem logical that our air speeds ought to be similar?

[8233]

Vy IAS lowers with increase in altitude. Vy TAS increases as you increase altitude. I believe that chart was trying to convey IAS. Agree that excess power will translate into rate of climb so as you gain altitude, less excess power, less rate of climb.

I believe as density altitude increases Vx speed increases, and Vy speed is reduced,(Indicated airspeed), and they will converge at the absolute altitude, which is of course the highest altitude the aircraft can achieve, and it can only achieve that at one airspeed, the one that requires the least power to fly, any faster or slower and it will descend.

Sort of the coffin corner just without the coffin

Yep, for indicated Vy will reduce and Vx will increase slightly. When you talk about TAS, that's another matter:

https://www.boldmethod.com/learn-to-fly ... they-meet/