Altitude hold vs. hand fly for speed

[Bob Axsom]

My ALTRAK is a wonderful piece of hardware and when I punch the ALT button it probably holds altitude within + 20 feet. I see the vertical speed needle vary up and down around "0" when flying in this mode which is a digital reaction to pressure deviations I'm sure. The question is, is the distance from point A to point B actually longer in this mode than a hand flying mode where the plane is allowed to "go with the flow."

Bob Axsom

[Kevin Horton]

How much elevator movement is there as the autopilot holds altitude? If it is too active on the elevator, it might be slowing the aircraft down a tiny, tiny bit.

But, I would think that the lower workload of flying on autopilot would have some advantages. It would allow you to use more brain power to manage the race (manage the mixture, fuel burn, wind vs altitude, etc), so you might run a smarter race if you take advantage of the autopilot.

[N916K]

Originally Posted by Bob Axsom

The question is, is the distance from point A to point B actually longer in this mode than a hand flying mode where the plane is allowed to "go with the flow."

Bob Axsom

Bob

You can change the response of the Tru Trak altitude hold. I slowed mine down one step and the plane flies very smooth with very little corrections. One thing I do is turn the hold off after I've settled in at cruise, to make sure it's not fighting the trim tab.

[Bob Axsom]

The Altrak is so smooth that I have too much time on my hands probably. Typically when I made the speed checks after a mod I would do everything I could think of to have a perfectly flat flight line (trim for hands off level before hitting the "ALT" button etc). Then as I'm cruising along reading off the GPS speeds every twenty seconds I notice the vertical speed above or below "0". My mind says even though the autopilot is doing a great job of holding the altitude it is having to work at it (not unusual over the hills around here) and I can't be acheiving maximum speed. I have thought up until now that the autopilot is the best way to fly the shortest distance between two points (and I think I still do) but the observation did start me to thinking about it.

Bob Axsom

[ddurakovich]

Originally Posted by Bob Axsom

The question is, is the distance from point A to point B actually longer in this mode than a hand flying mode where the plane is allowed to "go with the flow."
Bob Axsom

That assumes, of course, that you experience equal lift and sink, requiring no use of power to maintain altitude. Or, continual lift, where you have excess power that you can take advantage of.

In the absence of that information, you may still have to make considerable adjustments to maintain a specific altitude. I'm not sure doing anything beside accurate control of altitude would be beneficial.

However, in the event you have a 100% ACCURATE method of predicting lift and sink, I know some competition sailplane types that would pay good money for the knowledge

[n5lp]

Originally Posted by Bob Axsom

...The question is, is the distance from point A to point B actually longer in this mode than a hand flying mode where the plane is allowed to "go with the flow."

Bob Axsom

If there is significant vertical air movement, holding altitude is not the most efficient. Best is to slow down in lift and speed up in sink (dolphin flying). High performance gliders can often maintain an average altitude or even climb, just by doing this. Pretty compelling proof, huh?

This is easier to do in slower aircraft and at higher altitudes. The areas of lift and sink get pretty small at 1,000 AGL.