Taylorcraft air speed

[N96290]

Re: Taylorcraft air speed

One problem with average airspeed calculations is they tend to mess up a lot of good stories. We all have a brother in law who gets 30 miles per gallon with his full size pickup, loaded, pulling a trailer, and upgrade. I did have a BC12D that would fly over 100 miles per hour, climb like a homesick angel and handle any crosswind known to man. I would take you nor a ride and show you but I sold it to my brother in law.

[jstall]

Re: Taylorcraft air speed

One problem with average airspeed calculations is they tend to mess up a lot of good stories. We all have a brother in law who gets 30 miles per gallon with his full size pickup, loaded, pulling a trailer, and upgrade. I did have a BC12D that would fly over 100 miles per hour, climb like a homesick angel and handle any crosswind known to man. I would take you nor a ride and show you but I sold it to my brother in law.

So then my friends? How fast are we?? I'd say about 80 Kts TAS pretty well takes it

Whatchathink??

JS

[Guest]

Re: Taylorcraft air speed

So then my friends? How fast are we?? I'd say about 80 Kts TAS pretty well takes it

Whatchathink??

JS

LOL at myself!

I don't know, maybe don't care, having too much fun revisiting vector math and figuring out ways to calculate it!

LOL

Dave R

[PA1195]

Re: Taylorcraft air speed

Here's an interesting article on determining TAS from GPS:

Gary

[Scott]

Re: Taylorcraft air speed

Hi Scott,

I don't think this part is correct.

In Tom's example the airplane ground speed is 30 out and 90 back.

The simple average is 60 same as TAS in his example.

That's not a coincidence, if you write the two equations and solve for TAS it comes out equal to the simple average of the two ground speeds.

Looks like you are doing a weighted average.

Dave R

p.s. ahhh... I think I see the confusion that is taking place. That part is just different than what I was thinking about there is nothing wrong with it. It's in what we each mean by "average ground speed" I mean only the average of the two speeds (out and back). The out speed is distance traveled out divided by flight time out or by GPS, similar for return. Average of those two is TAS always.

The other way to do "average ground speed is round trip miles (180) divided by total time (4), I don't mean that one but I see what you guys are saying now.

I should have said something like "the average of the ground speed calculated to the destination and the grounds speed calculated from the the destination" instead of just the average ground speed. My bad.

The point is the statement that the headwind effect is greater than the tailwind effect is incorrect when talking TAS & GS, but I can see the confusion when we start to intermingle distance and time in the discussion (which really has no impact on calculating TAS from ground speed).

In the practical GPS exercise, we're going to fly outbound (on whatever heading), doesn't make any difference how long except that we want a representative stable flight GS which will be +/- a knot or two. Make a 180 and repeat. The average of the two GS from the GPS is a reasonably close approximation of TAS. You may well end up a couple of extra miles downwind, or your upwind and downwind legs could have been different duration, but it makes no difference to the TAS calculation (as long as you haven't flown into a different winds aloft area).
S

[Guest]

Re: Taylorcraft air speed

The point is the statement that the headwind effect is greater than the tailwind effect is incorrect when talking TAS & GS, but I can see the confusion when we start to intermingle distance and time in the discussion (which really has no impact on calculating TAS from ground speed).

In the practical GPS exercise, we're going to fly outbound (on whatever heading), doesn't make any difference how long except that we want a representative stable flight GS which will be +/- a knot or two. Make a 180 and repeat. The average of the two GS from the GPS is a reasonably close approximation of TAS. You may well end up a couple of extra miles downwind, or your upwind and downwind legs could have been different duration, but it makes no difference to the TAS calculation (as long as you haven't flown into a different winds aloft area).
S

Agree on point #1.

Mostly agree on point #2 but I am unclear about the degree of error introduced as a function of the difference in the heading angle and the wind angle.

At a zero degree diff the error is zero.

At 5 degrees also small but what about at 90 degree diff?

I want to sit down with a paper and pencil and calculate that impact (if any). Have you done that?

Dave R

[3Dreaming]

Re: Taylorcraft air speed

Agree on point #1.

Mostly agree on point #2 but I am unclear about the degree of error introduced as a function of the difference in the heading angle and the wind angle.

At a zero degree diff the error is zero.

At 5 degrees also small but what about at 90 degree diff?

I want to sit down with a paper and pencil and calculate that impact (if any). Have you done that?

Dave R

There is an Advisory circular AC23-8C. In appendix 9 they show a method of calibrating an airspeed indicator using a GPS. They want 3 legs with a change in heading of between 60 and 120 degrees, then average the 3.

[Guest]

Re: Taylorcraft air speed

There is an Advisory circular AC23-8C. In appendix 9 they show a method of calibrating an airspeed indicator using a GPS. They want 3 legs with a change in heading of between 60 and 120 degrees, then average the 3.

Hi Tom,

Thanks!

Question, where do you see it says average the 3 ground speeds?

I don't see that, I see => True Airspeed =SQRT((B7-B17)^2+(B8-B18)^2)=184.4 on page A9-14 at the bottom of the table.

The average comes out to a smaller number.

Dave R

[Mark Bowden]

Re: Taylorcraft air speed

Hi

The reason for a multi leg, multi heading flight is so you can use your ground speed simply as a tool to get you close to True Airspeed. Because you can just never find a still air mass when you need one.

Unless Hank has a surplus NASA calibrated pitot boom we could use, were stuck with more than 2 leg testing.

That’s a good paper Gary. Also attached 2 papers on the theory I got from one of my engineering betters of which there are many. The papers show the math and a bit of why explanation.

Also a link to the EAA chapter 62 TAS calculator based on a 3 leg course & cited in one of the papers.

http://www.eaa62.org/technotes/speed.htm

You cannot do an out and back course into a headwind and with a tailwind to determine TAS from the GS. You spend too much time in the headwind and it reduces the average GS to become a lot less than TAS.

Scott this is what you stated earlier, but too much time going slow is the reason we cannot. It is why I said the headwind effect is greater.

Here is example: (and hoping for good math in forum post, lol)
TAS = 85, fuel burn 4.0 gph, Fuel total 18 gal, 30 min VFR reserve
Out and back legs =170 miles

Calm wind legs out & back 170/85 = 2.0 hrs. each. Total flight time 4.0 hrs. 30 min fuel reserve met.
TAS = GS, 85

Wind day, 30 mph headwind on the nose, 30 mph tailwind, on the tail.

Headwind out leg: 170/(85-30) = 3.1 hours
Tailwind back leg: 170/(85+30) = 1.5 hours

4.6 hours total. GS = 73.9

Ground speed is 13+% slower than TAS
Run out of fuel before destination.

Now we need to go fly some test courses.
Great discussion, Mark

[Mark Bowden]

Re: Taylorcraft air speed

Tom, it is interesting that the AC data reduction table is the same as that in Mr. Gray's 1998 paper. Wonder who did it first?

[Guest]

Re: Taylorcraft air speed

Hi

The reason for a multi leg, multi heading flight is so you can use your ground speed simply as a tool to get you close to True Airspeed. Because you can just never find a still air mass when you need one.

Unless Hank has a surplus NASA calibrated pitot boom we could use, were stuck with more than 2 leg testing.

That’s a good paper Gary. Also attached 2 papers on the theory I got from one of my engineering betters of which there are many. The papers show the math and a bit of why explanation.

Also a link to the EAA chapter 62 TAS calculator based on a 3 leg course & cited in one of the papers.

http://www.eaa62.org/technotes/speed.htm

You cannot do an out and back course into a headwind and with a tailwind to determine TAS from the GS. You spend too much time in the headwind and it reduces the average GS to become a lot less than TAS.

Scott this is what you stated earlier, but too much time going slow is the reason we cannot. It is why I said the headwind effect is greater.

Here is example: (and hoping for good math in forum post, lol)
TAS = 85, fuel burn 4.0 gph, Fuel total 18 gal, 30 min VFR reserve
Out and back legs =170 miles

Calm wind legs out & back 170/85 = 2.0 hrs. each. Total flight time 4.0 hrs. 30 min fuel reserve met.
TAS = GS, 85

Wind day, 30 mph headwind on the nose, 30 mph tailwind, on the tail.

Headwind out leg: 170/(85-30) = 3.1 hours
Tailwind back leg: 170/(85+30) = 1.5 hours

4.6 hours total. GS = 73.9

Ground speed is 13+% slower than TAS
Run out of fuel before destination.

Now we need to go fly some test courses.
Great discussion, Mark

Hi Mark,

You are not calculating what I and some others are trying to describe.

It's confusion over what average we are defining.

You are calculating the average ground speed. I and perhaps others have used that term when we really meant the average of the ground speed calculated on the upwind leg and the ground speed calculated on the downwind leg.

I mean only the average of the two speeds (out and back).

The out speed is distance traveled out divided by flight time out or by GPS, similar for return.

Average of those two is TAS always (well AS maybe).

I should have said something like "the average of the ground speed calculated to the destination and the ground speed calculated from the the destination" instead of just the average ground speed.

Dave R

[Guest]

Re: Taylorcraft air speed

Tom, it is interesting that the AC data reduction table is the same as that in Mr. Gray's 1998 paper. Wonder who did it first?

Gray's name does nor even appear in the AC.

[PA1195]

Re: Taylorcraft air speed

When you guys figure this out maybe we can work on CG and weight as factors influencing TAS in a Taylorcraft.

Gary

[Scott]

Re: Taylorcraft air speed

Agree on point #1.

Mostly agree on point #2 but I am unclear about the degree of error introduced as a function of the difference in the heading angle and the wind angle.

At a zero degree diff the error is zero.

At 5 degrees also small but what about at 90 degree diff?

I want to sit down with a paper and pencil and calculate that impact (if any). Have you done that?

Dave R

Yes, I do it or a version of it once every 2 years when I do my instrument check ride! I'm sure you've done it too ie plot the winds aloft, TAS, magnetic variation, compass correction, on the back of your flight computer to obtain your magnet heading and ground speed for flight and fuel planning.

I used to do it dead-reckoning in my sailboat too. Basically we separate the wind into two component forces relative to desired track... cross-track component and headwind/tailwind component. TAS plus or minus the tailwind/headwind component yields ground speed. Pick any two headings 180 degrees apart and the headwind/tailwind component will be equal and opposite for a given wind speed and direction. Use three or more headings to lessen the magnetic and other potential heading variations.

It does not matter how far you go or for how long, speed is speed. Whether you have a tailwind, headwind or whatever wind, ground speed will be TAS plus or minus the tailwind or headwind component respectively. Conversely TAS will be GS plus or minus the tail wind or head wind component respectively.

Remember, we're given ground speed from the GPS, there is no need to measure/calculate time and distance and in fact they are irrelevant to the exercise.

[PA1195]

Re: Taylorcraft air speed

And ultimately ground speed and track gets us from A to B and fuel burn versus available keeps us aloft. Flying isn't complicated.

Gary