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I have only 8 hours left until I hit 40 hours on my Sonex and I am now working on gross weight testing. In a few old posts from the yahoo group I have seen mention of people taking off with one notch of flaps to lower lift off speed and/or increase climb rate. Before I go out and do some testing to see the what the actual affect is I was wondering if others have tried it and what they found.

Keith
#554

I have always added one notch of flaps when taking off of grass and when I am near gross weight. At gross weight it seems to help when raising the tail for better acceleration and climb out. Once I have climbed to safe altitude I will raise them and climb at normal climb rate.

I always use 1 notch regardless of weight, except when I forget ha ha
My foggy memory seems to think it was documented in the flight manual to always use 1 notch for takeoff?

Hi, Keith:

I've done a lot of takeoffs with and without. If I'm trying to get off the ground quickly or at gross, I've been doing a wheel take-off (2-point; tail wheel off the ground) with a notch of flaps. Seems to work well. Lately I've been going back and trying 3 point take-offs (not at gross) with no flaps, and it gets off the ground pretty fast. So I actually have on my to-do list to do some distance testing. I plan to put some markers on the side of the runway and try some multiple take-offs.

There's no reason not to try a notch of flaps on some take-offs. Just do what you learned in flight training and smoothly take out the flaps once you are at a safe altitude above obstacles.

This is something that I've been wanting to understand better about the Sonex.

There are many references that say "The best rate-of-climb and angle-of-climb is always reached with flaps up." I personally am uneasy about claiming this statement is always true, but it seems to have always been true for everything I have flown in my limited experience.

When you have more power than required for your airspeed (and hold airspeed constant by controlling pitch), the extra power is converted into gravitation potential energy (altitude). Adding flaps increases the drag, so more power is required for a given airspeed and you climb slower than you would without the use of flaps.

Since flaps reduce your stall speed, they allow you to begin climbing sooner in the takeoff roll than otherwise. From that point, there is a range where you are higher above the ground than you would have been using 0 flaps. There is a crossover point further away where the identical airplane without the use of flaps will outclimb you. I think knowing where this crossover point is would really help in making the decision between 0 and 10 degrees of flaps. I am curious about how precise I have to fly if I want to significantly benefit from the use of 10 degrees of flaps in the Sonex.

nwawingman wrote:I have always added one notch of flaps when taking off of grass and when I am near gross weight. At gross weight it seems to help when raising the tail for better acceleration and climb out. Once I have climbed to safe altitude I will raise them and climb at normal climb rate.

When I take off from grass, I notice that the airplane seems to accelerate significantly slower than from pavement, so in this case I would also use a notch of flaps (but switch back to 0 when I have enough speed and have cleared all obstacles). In general, on pavement, I don't use flaps at all, but would like to more precisely understand exactly what I could gain by doing so. I like to climb on the fast side of Vy to give myself a little extra time to react to engine trouble (and it helps in cooling).

Before I added the turbo on my AeroVee, I flew my Waiex for 130 hours and nearly every takeoff was with one notch of flaps. Since I've added the turbo I always takeoff flaps up. Ultimately I don't think it matters much, but I found that the Sonex is like most other airplanes: using one notch of flaps shortens your takeoff roll so you can get off the ground faster, but climb suffers a little bit. If you takeoff flaps up, you will roll a little longer, but your climb will be better since you already have the extra speed built up.

At this point I would use one notch of flaps if I'm taking off from a grass or rough field just to pop the airplane off a little earlier. Otherwise, flaps up works just fine!

The airplane is completely controllable either way, so try both methods and see what you're comfortable with.

gammaxy wrote:
Since flaps reduce your stall speed, they allow you to begin climbing sooner in the takeoff roll than otherwise. From that point, there is a range where you are higher above the ground than you would have been using 0 flaps. There is a crossover point further away where the identical airplane without the use of flaps will outclimb you. I think knowing where this crossover point is would really help in making the decision between 0 and 10 degrees of flaps. I am curious about how precise I have to fly if I want to significantly benefit from the use of 10 degrees of flaps in the Sonex.

This is a great discussion point on best angle of climb versus takeoff distance over 50' obstacle. Yes, best angle of climb will always happen with flaps up due to reduced drag, but the airspeed required for best angle of climb is higher with flaps up than with flaps extended. The big difference is the time/distance it takes to accelerate to that higher airspeed, and when you're trying to clear an obstacle on takeoff, you don't always have the distance to accelerate. Hence, takeoff with flaps extended to clear the obstacle.

But if you're, say, in cruise (i.e. already at high airspeed) and suddenly realize you need to climb to clear a mountaintop, your best bet is to climb at best angle speed with the flaps up.

The crossover point would be an interesting mystery to solve, but could be done with some experimentation. You could do test runs of 0 and 10 degree flap takeoffs and see which one gets you to, say, 50,100, 500 and 1000 feet in the least amount of distance traveled (use ground reference points or GPS to accurately measure distance from start of takeoff roll.) Eventually, flaps up should outperform flaps extended. Obviously wind and weather would be a factor.

The factory Waiex jumped off the ground much quicker with a notch of flaps. This was near gross with me and Joe in it. I didn't want to climb any quicker but it certainly got into ground effect nicely. Think that 1st notch would be great for soft fields in particular.

Thanks for all the advice and discussion. It looks like I will have to give it a try with flaps this weekend and see how it goes.

Keith
#54

I went and tried a number of takeoffs with one notch of flaps last night. What a difference. The takeoff was much smoother and it was way easier to raise the tail. Without them it always felt like the plane would gain alot of speed in the three point attitude and want to try to jump off the runway at too slow of a speed before I could raise the tail. With the flaps it was almost effortless to raise the tail after adding power for the takeoff roll. Once the tail was up it became a much more controlled process of deciding when to lift off. I wish I knew to try this earlier.

Keith
#554
40.4 hours and out of phase 1