Extended wing tips

[z987k]

The 182 I fly has the Madras extended droop tips installed (STC # 1938WE). It lists the changes it makes to Vne, Vno and Va. The thing is, that's not what they are really for. They are there to increase the amount of lift the wing produces so we can climb faster(Am I right in that line of thought?). So I would like to know what Vy and Vx is and be able to calculate the Vy drop with the increase of altitude. I have a feeling this isn't possible with the lack of information in the STC.
The POH states that Vy is 76kts and Vx is 61kts(stock). Real world performance with the tips shows that Vy is really at around 70kts and drops to 65kts by about 10,000ft. Obviously I have been able to basically figure out what it is just by flying the airplane but I wouldn't mind being able to see it on paper I guess and confirm what I see. So if anyone knows anything about these tips or where/how I would go about getting that information, I'd appreciate it.

 

[tgrayson]

They are there to increase the amount of lift the wing produces so we can climb faster(Am I right in that line of thought?).

No, sorry. Airplanes don't climb due to having extra lift, they climb due to having extra thrust. Lift in any climb is just about equal to weight, and actually a little bit smaller when you work the math (thrust supports a slight amount of weight).

The wingtips reduce the amount of induced drag, hence their effect on Vx and Vy. A reduction in induced drag should reduce Vx and Vy, so your experience makes sense, although you'd have to take into account what your gross weight was.

 

[z987k]

No, sorry. Airplanes don't climb due to having extra lift, they climb due to having extra thrust. Lift in any climb is just about equal to weight, and actually a little bit smaller when you work the math (thrust supports a slight amount of weight).

The wingtips reduce the amount of induced drag, hence their effect on Vx and Vy. A reduction in induced drag should reduce Vx and Vy, so your experience makes sense, although you'd have to take into account what your gross weight was.

Yeah that makes more sense. I was rather sure I was wrong on that, hence the question in there.

 

[mshunter]

The 182 I fly has the Madras extended droop tips installed (STC # 1938WE). It lists the changes it makes to Vne, Vno and Va. The thing is, that's not what they are really for. They are there to increase the amount of lift the wing produces so we can climb faster(Am I right in that line of thought?). So I would like to know what Vy and Vx is and be able to calculate the Vy drop with the increase of altitude. I have a feeling this isn't possible with the lack of information in the STC.
The POH states that Vy is 76kts and Vx is 61kts(stock). Real world performance with the tips shows that Vy is really at around 70kts and drops to 65kts by about 10,000ft. Obviously I have been able to basically figure out what it is just by flying the airplane but I wouldn't mind being able to see it on paper I guess and confirm what I see. So if anyone knows anything about these tips or where/how I would go about getting that information, I'd appreciate it.

No, sorry. Airplanes don't climb due to having extra lift, they climb due to having extra thrust. Lift in any climb is just about equal to weight, and actually a little bit smaller when you work the math (thrust supports a slight amount of weight).

The wingtips reduce the amount of induced drag, hence their effect on Vx and Vy. A reduction in induced drag should reduce Vx and Vy, so your experience makes sense, although you'd have to take into account what your gross weight was.

You got a Vx/Vy chart that shows what happens to angle of climb with more lift? I understand that the STC is to decrease stall speed, but I could swear I read something somewhere that a larger wingarea will net you a better climb in either Vx or Vy. But it could be from getting home last night at 1am, then wakeing up at 3:50 to go fishing with my pop. (serious though, do you have a chart?)

 

[z987k]

You got a Vx/Vy chart that shows what happens to angle of climb with more lift? I understand that the STC is to decrease stall speed, but I could swear I read something somewhere that a larger wingarea will net you a better climb in either Vx or Vy. But it could be from getting home last night at 1am, then wakeing up at 3:50 to go fishing with my pop. (serious though, do you have a chart?)

No, but I'll look around the internet for one.

 

[ProudPilot]

Could always just go up flying and note rate of climb at given altitude and speed. Make a chart, experiment, then go with that.

 

[tgrayson]

You got a Vx/Vy chart that shows what happens to angle of climb with more lift?

It would be a boring chart, since lift is constant in unaccelerated climbs.

It may not be what you're talking about, but if you yank back on the yoke, you have accelerated flight (load factor > 1), which can greatly magnify the climb rate/angle as the airspeed is converted to altitude. But that isn't how must of us do climbs.

a larger wingarea will net you a better climb in either Vx or Vy.

That's certainly true, but it isn't due to more lift. A larger wing just carries a smaller AoA in order to make lift = weight. The reduction in AoA means that induced drag is lower and creates more excess thrust/power.

 

[z987k]

Could always just go up flying and note rate of climb at given altitude and speed. Make a chart, experiment, then go with that.

Yeah, I've essentially done that but like I said I was hoping there would be a way to do this with math... if nothing else just to have something fun to do.

 

[hook_dupin]

Yeah, I've essentially done that but like I said I was hoping there would be a way to do this with math... if nothing else just to have something fun to do.

There's actually a couple different ways to figure out Vy in a simple way. The two methods are the constant velocity climb (sometimes called a sawtooth climb as many of these data points were done back to back) and the level acceleration. Both use the concept of specific excess power. The climb thing is basically what other people said above with some math added, so I won't talk about it.

Specific excess power is the change in total energy normalized for weight. Here's its equation below:

Ps = dh/dt + (V/g)(dV/dt)

where dh/dt is the rate of change of height
dV/dt is the rate of change of true airspeed
V is the true airspeed and
g is the gravitational acceleration

The level acceleration technique is my favorite as it provides a continuum of data for each altitude band you pick and its kind of neat to show that you can predict climb performance in a level maneuver. You'll need a friend with a video recorder that has a clock built in to execute the test.

The idea of the level acceleration is that by maintaining a constant altitude, you are making the dh/dt term be 0. The equation then is just Ps = (V/g)*(dV/dt). Pick an altitude you're interested in (using 29.92 for a pressure altitude is common in flight test, but I don't imagine anyone here cares to hear about the joys of correcting flight data back to a standard day), and start in slow-flight. When you say "Go," have your friend record your pitot-static instruments while you go full throttle. Maintain your fixed altitude as best you can. You can stop the maneuver when you can only accerlate a knot or two every five to ten seconds. The data on that fast end tends to get really sideways because your small changes in height are large compared to the uber-small changes in velocity. When you get on the ground, do a video review and record the indicated airspeed every second or two and enter that into Excel. You can approximate the dV/dt term for your change in velocity from one data point to the next divided by the time interval you chose. Calculate Ps as described above for each data point and plot that out with your airspeed as the x-axis and Ps on the Y axis. The point where Ps is the highest is the Vy for that altitude. This isn't a perfect model as you didn't go back and convert your inticated airspeed back to true and we just assumed you were a rockin' golden arm test pilot and kept your altitude constant and the VSI nuts on zero the whole time, but it should be close enough. And it should give you something to do on your way to your next $100 hamburger.

Feel free to PM me if you care to know more or want a source document for all this.