# Using Level Accelerations to Determine Climb Performance

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#### Pops

##### Well-Known Member
Supporting Member
Not at all. I had done numerous climbs (and descents) in my RV-4 testing trying to determine Vx and Vy over many, many flights. Terrible results.

In less than an hour during one flight I had numbers for 1,200', 2000', 3000', 4000', 5000' and 6000'.
Not terribly accurate because I had a hard time keeping the altitude as the plane accelerated from near stall to max speed.
But that's a pilot issue.
I had a conversation with Nigel (I wondered about the need to start at 500' below desired test altitude). Turns out the method was developed for jets (taking a long time to spool up to full power). In my RV-4 it worked much better for me to slow down to near stall at desired test altitude and then advance to full throttle keeping my eyes glued to VSI. Discounting any prop stall, it's up to full power in a second or two. A factor is that RPM increases as airspeed increases, but apparently that's not an issue. Someone here may be able to explain that?

This method does require data logging. Having an Dynon 100 EFIS (10A is fine to), that is taken care of.

After a flight I download the data log, copy and paste airspeed, altitude and OAT columns into a spreadsheet (I use Excel 97). Identify the rows containing the acceleration, chart the airspeed column for those rows. Right-click on the curve and Add trend line. Select option to show equation for trend line. Right-click on the equation, Format Data Labels..., Number, Number, increase to 10 or more digits. Click on displayed equation, starting with the "+". copy equation into Notepad. Replace All "x" with "*B2^" (remove last "^"). Copy and paste the result into cell B2 in a new sheet for that test altitude. Click on cell B2 and drag down 30 or so rows. (When you click or select a cell or cells you'll see a solid black square in the lower right hand corner. Simply grab that square with your mouse pointer and drag that down.) Enter 0 in A2, 1 in A3. Select A2 and A3 and drag down 30 or so rows. (Column A is your time column in one-second increments.)

When you have a sheet for one altitude, you can copy that sheet. In the copy you just need to paste the equation for the next test altitude in cell B2 and drag down.

The attached needs do be redone with data from flights where acceleration is flown more accurately.

By displaying the climb vs airspeed columns as a XY (scatter) chart, you can hold up a ruler to the screen from 0,0 to where the ruler touches the curve and see Vx. Vy is of course the top of the curve.

Perhaps I should make a video on how to do this in Excel if anyone are serious about using the method.

Finn
I don't complain about flying. Just a good excuse to fly. Its sort of a let down when all the test flying is over. Now what? sharpen up my lazy eights, Chandelles, pylon eights, spins, etc.

#### Toobuilder

##### Well-Known Member
Supporting Member
The reason to start at 500 feet below target is to allow the engine to stabilize before collecting data.

#### Pops

##### Well-Known Member
Supporting Member
I always start at 500' to get stabilized when getting to the target . Just a lot of fun flying. The hardest part is finding the smooth air. Short time in the morning and evening. Glad I don't have a long drive to the airport.

#### FinnFlyer

##### Well-Known Member
I always start at 500' to get stabilized when getting to the target . Just a lot of fun flying. The hardest part is finding the smooth air. Short time in the morning and evening. Glad I don't have a long drive to the airport.

Yes that is the problem. Have to get up before sunrise and don't want to wake up the neighbors. With the Acceleration method you can get the needed numbers in one flight without having to land to refuel, then wait for identical conditions for the climb at the next higher airspeed and so on. In addition I have a cooling limitation at steep extended full power climbs.

I'm just uncomfortable with the high deck angle at near stall needed to maintain low and constant airspeed in traditional climb testing.

Finn

#### FinnFlyer

##### Well-Known Member
The reason to start at 500 feet below target is to allow the engine to stabilize before collecting data.

How much stabilizing do you need? I seem to be at full power in a second or two. Also I found it hard to keep the airspeed near stall while climbing the 500' and then to transition to level flight.

Comes down to pilot skill. I just find it easier to learn to maintain altitude as I increase power and speed comes up.

Finn

#### Pops

##### Well-Known Member
Supporting Member
You do it your way and I will do it my way.

#### wsimpso1

##### Super Moderator
Staff member
How much stabilizing do you need? I seem to be at full power in a second or two. Also I found it hard to keep the airspeed near stall while climbing the 500' and then to transition to level flight.

Comes down to pilot skill. I just find it easier to learn to maintain altitude as I increase power and speed comes up.

Finn

Pistons, Intake Manifold, and Cylinders do have different equilibrium temperatures at different power settings and airspeeds, and they matter to power produced. Power will change enough to throw noise into the data during time-to-climb or sawtooth sessions. Starting the climb 500 feet below intended start lets it get a lot closer to steady state output. If I was doing runs down near stall, I suppose I would start a lot closer to test start altitude in order to avoid overheating during the run.

Doing level acceleration runs, I would think that we would also want the engine close to steady-state temps during the run. To neither overheat nor start cool, I would think we would slow the airplane below the altitude for the test, open the throttle and hold speed while it climbs to test altitude, then level off and hold altitude while it accelerates at test altitude. I think I would experiment with just how many feet below my test altitude I would open the throttle to make sure I do not overheat during the short climb, using CHT as my guide.

Billski

##### Well-Known Member
Supporting Member
Which means I'm not looking outside the aircraft during a climb. Somewhat scary
We do alot of it in the flight test world!

##### Well-Known Member
Supporting Member
To be honest, the construct of the equations would have gone right over my head even if I took the full course
I could not agree any more. My going through USNTPS was tantamount to plugging a Li-Po battery directly into the wall. Someway, somehow I survived it!

#### Toobuilder

##### Well-Known Member
Supporting Member
How much stabilizing do you need? I seem to be at full power in a second or two. Also I found it hard to keep the airspeed near stall while climbing the 500' and then to transition to level flight.

Comes down to pilot skill. I just find it easier to learn to maintain altitude as I increase power and speed comes up.

Finn

Airbus requires 8 MINUTES of stabilization of the big turbofan engines. Touch the throttles during test and its a "do over".

Bottom line - Flight test is hard.

#### gtae07

##### Well-Known Member
actually find it pretty easy to explain the concept of an integral to the average person, if they can understand the idea of limits and infinity.
Lots of subjects (even complex ones, and the traditionally "scary" ones like calculus) can actually be explained in simple terms such that most people can understand them.
The problem is that the way our academic system traditionally teaches them. Usually it's extremely painful, with lots of proofs and rigor and "it can be shown that". Teachers and professors always start calculus with all this talk of limits and having you work it out painfully; engineering classes do a bunch of derivation and abstraction consideration of arbitrary bodies with generalized forces. Only after pounding your head and suffering through it all do they come back and say "but nobody really does it that way. Here's what we're actually doing when we do all that stuff, and how everyone actually does it, and here's what it means in the real world..."

#### wsimpso1

##### Super Moderator
Staff member
I could not agree any more. My going through USNTPS was tantamount to plugging a Li-Po battery directly into the wall. Someway, somehow I survived it!
Most engineering is taught so the student could formulate the math to make estimates about some real world problem. Then the vast majority of the time, the working engineer that comes out of the training simply applies the method straight up without thinking about the derivation.

When the time comes, you just go back to the methods and turn the crank...

Billski

#### Pops

##### Well-Known Member
Supporting Member
A good math teacher can make any math so much easier. Just not enough good teachers.

##### Well-Known Member
Supporting Member
Then the vast majority of the time, the working engineer that comes out of the training simply applies the method straight up without thinking about the derivation.
I cannot agree any more. Even though I know how to do the math, I just wiggle the sticks, doing exactly what the FTE wants me to do, when he/she wants me to do it. Aero & Perf stuff, I completely understand it, which makes it easy to plan tests with our engineering team. Aeroservoelastic (ASE) stuff? So far over my head that I'm just a bobblehead doll at planning meetings

#### Saville

##### Well-Known Member
A good math teacher can make any math so much easier. Just not enough good teachers.

Sometimes it's not good students. When I went to college I did not know how I learned things, nor how TO learn things.

20 years later I had learned how to read in order to extract the idea, learned how *I* personally learned stuff. Learning became much easier.
Calculus class now would be a snap as compared to when I took it in college because I've changed. In fact I've mulled over the idea of taking a calculus class (just integration and differentiation) at a community college when I retire. Just to prove I can ace it.

#### Vigilant1

##### Well-Known Member
Supporting Member
Sometimes it's not good students. When I went to college I did not know how I learned things, nor how TO learn things.
In most of my subjects my learning style was a good match for the typical instruction method (lecture), but chalkboard math derivations/explanations didn't suit me well. It's pretty linear and sequential (gotta be), and if the student misses something then the trail is lost. That was me. So, mostly I went home and worked slowly through any explanatory text and (hopefully, most important) good published examples. I might as well have been taking a correspondence course.

#### Hot Wings

##### Grumpy Cynic
Supporting Member
at a community college when I retire. Just to prove I can ace it.

Better learn how to use a Ti-89, if you don't already know how. Seems modern calculus can't be taught without that crutch. IMHO it actually slows down the process.
There was one student in my high school calculus class with a calculator - an Hp-35. Cost two months of my fathers wages. The rest of us had little bamboo devices.

I might as well have been taking a correspondence course.

Been there, done that - got the grade to prove it.
More instructors need to learn how to teach well:
How engineering students learn

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#### Pops

##### Well-Known Member
Supporting Member
In most of my subjects my learning style was a good match for the typical instruction method (lecture), but chalkboard math derivations/explanations didn't suit me well. It's pretty linear and sequential (gotta be), and if the student misses something then the trail is lost. That was me. So, mostly I went home and worked slowly through any explanatory text and (hopefully, most important) good published examples. I might as well have been taking a correspondence course.
I must be somewhat like you, I learned more by studying at home. Good published examples are great. I did some tutoring of other students in HS in their math but also had a couple nice looking girls tutoring me in English. Hate foreign Languages but their woman are nice.
I'm not the greatest at math, but I get along . My youngest son ( computer design engineer) and grandsons ( computer network engineer , mechanical engineer, and electrical engineer are very Good.

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#### gtae07

##### Well-Known Member
Most engineering is taught so the student could formulate the math to make estimates about some real world problem. Then the vast majority of the time, the working engineer that comes out of the training simply applies the method straight up without thinking about the derivation.

When the time comes, you just go back to the methods and turn the crank...

Heck, most of that phase of instruction seemed to be professors geeking out to the math, and many of the homework and exam questions seemed geared more towards testing your knowledge of obscure calculus functions and differential equations, or your ability to do lots of algebra without goofing it up, rather than actually testing your knowledge and understanding of the actual subject of the class.

My skills in such matters are now horribly atrophied; I was working a problem for my dad the other day (time-on-target calculations for formation flyovers given winds etc.) and at one point worked the algebra down to 0=5 Though the beers might have had something to do with that too...

#### Saville

##### Well-Known Member
Better learn how to use a Ti-89, if you don't already know how. Seems modern calculus can't be taught without that crutch. IMHO it actually slows down the process.
There was one student in my high school calculus class with a calculator - an Hp-35. Cost two months of my fathers wages. The rest of us had little bamboo devices.

Been there, done that - got the grade to prove it.
More instructors need to learn how to teach well:
How engineering students learn

I had an HP-35 back in '75 so I think I might be able to manage using a calculator in a modern calculus class....if that's really necessary. Don't see why it would be.