Long takeoff with flaperons

[Gabe]

Ok guys, I need your expertise. I kicked up the flaperons to 100% deflection to experiment with a real short takeoff on the habu. I was previously using about 60%.

Well, she took almost the entire field to get off the ground. It was so much that I cut the throttle thinking she was gonna run off the runway into the trees. As I killed it, she got lift for some reason, bounced once, and I gave her full throttle into an awesome, high alpha climb.

So why the heck did it take so long to get off the ground? I turned off the flaperons and paid close attention - she gets lift sooner without them (even at 60%) deflection.

[19000rpm]

I think this is a problem with some EDF's. The roll out out was longer due to the fact that the flapperons are not allowing it to speed up fast enough and achieve lift in as short a distance as without them. Once you get sufficient speed then the flapperons provide the lift and climb.

[Gabe]

Interesting. I guess that would explain why they work great on my T-28. Lift is provided almost instantly from the washout effect of the prop.

I wonder if I tried WOT with no flaperons to get the jet rolling, and then kicked them on once some speed had developed.

[akent]

It makes some sense to me that they would create a lot of drag. And since they cause the plane to nose over, you would need a lot more elevator to compensate, creating yet more drag and less ability to rocker over to take off.

I think less of a flap might be better, or it might be worth a try to let it get some speed and then give it flap.

It will be interesting to hear what works best!

This is all interesting as someday I want to get a nice EDF!
Kent

[19000rpm]

Apr 30, 2010 9:53:06 GMT -6 Gabe said:

Interesting. I guess that would explain why they work great on my T-28. Lift is provided almost instantly from the washout effect of the prop.

I wonder if I tried WOT with no flaperons to get the jet rolling, and then kicked them on once some speed had developed.

That might work, but I'd be concerned that your nose would want to go down immediately when you applied the flapperons. There might not be enough elevator effect to pull the nose up fast enough.

I think flapperons on an EDF will only work if you have an abundance of thrust to counteract the the drag from the flaps and the elevator...Kind of like with your T-28 which has an insane thrust to weight proportion and lots of wing area to aid in lift.

[Gabe]

Point taken. Now, I'm wondering what spoilerons would do on takeoff.

[akent]

Since spoilerons actually reduce lift and make the nose point up, I would think on a jet that it would be a bad idea.

That's just my own uncommon sense thinking...

I flew my Yak this afternoon in some fairly high wind. When I tried to hover with the spoilerons it just didn't work. Those are great for high alpha, but are bad for hovering!
Hey, I'm actually trying to learn to hover a plane now! It's far different than high alpha, that's for sure!

Anyway, I love these spoilerons when popping into high alpha from forward flight. I turn them off for everything else.

Of course, I'm still learning this stuff!

What do you think?
Kent

[19000rpm]

Apr 30, 2010 20:36:33 GMT -6 akent said:

Since spoilerons actually reduce lift and make the nose point up, I would think on a jet that it would be a bad idea.

That's just my own uncommon sense thinking...

I flew my Yak this afternoon in some fairly high wind. When I tried to hover with the spoilerons it just didn't work. Those are great for high alpha, but are bad for hovering!
Hey, I'm actually trying to learn to hover a plane now! It's far different than high alpha, that's for sure!

Anyway, I love these spoilerons when popping into high alpha from forward flight. I turn them off for everything else.

Of course, I'm still learning this stuff!

What do you think?
Kent

I'd agree that spoilerons are going to slow it down and not add the extra lift that you're looking for in a short takeoff. Spoilerons should help slow it down on landings.

[Gabe]

Points well taken boys.

Interesting thoughts on the spoilerons for high alpha vs hovering. I've been experimenting with hovering my T-28 and I've always used spoilerons. I'm gonna give it a whirl withou them when I get back from the road next week.

[Gabe]

I did some more experimenting the other day with the Habu and flaperons. I backed the mix off to about 60% of the available throw for the flaperons and gave it a whirl. This time, the Habu took off in about half to 2/3 the distance it would without flaperons.

I believe from my little experiments that there is a relationship between the drag and the lift produced when flaperons are active; and that this relationship has it's peak performance around the 60% throw mark. I'm going to try some tests soon and use the markings on the soccer field as a guide. My plan is to use:
1. No flaperons
2. 30% flaperons
3. 60% flaperons
4. 90% flaperons

-and record the approximate takeoff locations. I'm also thinking that, since my buddy who is a super rc whiz and pilot, was big on flaperons for STOL in a super small parking lot, the additional friction produced by the grass and uneven surface of the soccer field may play a part in the long takeoff at 100% deflection of the flaperons. I will need to find a suitable runway though to test this theory.

[Gabe]

Ok the results are in:

There was approximately 10mph winds today. All takeoffs were against the wind. From a measurement on Google Maps, the field is about 100 yards long.

1. No flaperons: No test performed due to time constraints and a Sheriff lingering around. Muni code prohibits rc planes in public parks (but this is a private deed restricted community - still sketchy though).

2. 30% flaperons: Shortest takeoff. Approximately 20 yards or less.

3. 60% flaperons: Approximately 50 yards.

4. 90% flaperons Approximately 50 yards.

I REALLY wish I had gotten the data on the "No Flaperons" run. I'm thinking that the wind situation may have provided additional lift that would not typically be there in a no wind, or even a tail wind situation.

So perhaps the 30%deflection for the flaperons is the best setting for now.

I'll try again later this week when I get back from the road. I also found a spot in my complex where I can try a concrete/asphalt take off and landing. Kinda sketchy as the main flying area is over a huge pond/lake.

[19000rpm]

Nice testing Gabe

I think the results make sense. Flaps are supposed to add lift and shorten the takeoff and they do with the right amount of flap (a setting where the drag created by the flap is balanced with lift).

30% would seem to be the best combo of flap and thrust for the Habu. You won't see many full size planes using much more than 30% flaps for take off except the extreme bush type planes or other specialty types.

60%-90% is creating more drag than desireable. Too much drag is initially cancelling the ability to create enough speed for lift off.

It'll be interesting to see what the zero flap results are. I'm going to "guess" it's not that much different than 90% flaps where you're not getting the flap induced benefit of lift until you also have some speed built up. So it's a contest. i.e. Extreme drag, high flap setting, versus low drag, no additional drag, to achieve lift.

I definitely think that the runway surface will be a big factor also. Grass, another cause of drag, is slowing the plane down so lift should come quicker on smooth pavement.

A head wind is going to cause lift earlier too since whatever that wind speed is, it's going to be seen, at least partially, by the plane as additional airspeed.

[akent]

From my own uncommon sense thinking, I think that power and flaps work together. I wish I had a formula, but I'm willing to bet there is one, given the wing shape, the flap amount, the thrust, wing loading, etc. More power = more useable flap amounts, and vice versa, but it may not be a linear relationship at all.
Kent

[Gabe]

Yup, I'm guessing exponential- possibly cubic. I'll look into it.

[19000rpm]

Undoubtedly it is a formula that includes thrust/power and flap angle and area along with weight, wing loading etc. There must be in order for designers to create the best parameters for each type of plane. I don't know what it is either though.