40% Turbo Laser (scratch built)

[forgues research]

	Quote: Originally Posted by danielgpr
	Ok, cool. There are small enough cameras out there to mount on flight surfaces that wont damage plane and could show it in action though. Dan

comon, I will not do this, its not important to me if anybody beleives it or not.

Do yourself a favor, go into a cesna 172, crank up all the trim and see what happens when you try to take off, and this is at slow speed.

Enough said on the subject on this thread, you guys had your chance on the other thread,

Now where was I on the 40 % laser, oh yes, waiting for the wing tubes from aircraft spruce.

For those of you who have not seen how the socket is made, I will show you in every detail and this is from Jack's instructions by the way.

Roger

[Cracky]

	Quote: Originally Posted by jack strickland
	As I understand it, the airflow over the surfaces is more or less at any given airspeed, so I do not understand what a little 10% tab is going to make a large difference at low speeds. Please explain in more detail. thanks

With low airspeed (stalled condition) is the tab going to have a large enough effect to be able to move the surface effectively with low powered servos. This is the reason why IMAC guys only need 12 degrees of deflection because they are flying in the upper speed ranges of the model. The 3D guys need 30-45 degrees because of the reduced airflow.

[jack strickland]

	Quote: Originally Posted by Cracky
	With low airspeed (stalled condition) is the tab going to have a large enough effect to be able to move the surface effectively with low powered servos. This is the reason why IMAC guys only need 12 degrees of deflection because they are flying in the upper speed ranges of the model. The 3D guys need 30-45 degrees because of the reduced airflow.

The way I see it is the tabs influence will be DIRECTLY PROPORTIONAL TO THE AMOUNT OF AIR OVER IT. Does this make any sence?

[danielgpr]

	Quote: Originally Posted by forgues research
	comon, I will not do this, its not important to me if anybody beleives it or not. Roger

That quote says it all, now it crystal clear to me.
Dan

[jack strickland]

	Quote: Originally Posted by danielgpr
	Ok, cool. There are small enough cameras out there to mount on flight surfaces that wont damage plane and could show it in action though. Dan

Good grief, give it a rest wont you? Ask for planes is going to go to a wind tunnel at Virginia Tech when he goes back to school and show all you uninformed souls just exactly how boost tabs work. Will all you doubters then apoligize to Roger for your rudeness, somehow I think not.

[jack strickland]

	Quote: Originally Posted by danielgpr
	That quote says it all, now it crystal clear to me. Dan

Dan, Please explain what is crystal clear to you. thanks

[danielgpr]

	Quote: Originally Posted by jack strickland
	Good grief, give it a rest wont you? Ask for planes is going to go to a wind tunnel at Virginia Tech when he goes back to school and show all you uninformed souls just exactly how boost tabs work. Will all you doubters then apoligize to Roger for your rudeness, somehow I think not.

At least we can see it then, no apoligizes since smeone that didn't start thead is going to the wind tunnel test.

Way to go 'Ask For Planes', let us know how they work out!
Dan

[BTerry]

At low speed the free airstream force on the surface is greatly diminished, so it isn't as big of an issue. Force isn't linear, it is closer to squared (increases with the airspeed increase squared) - as long as the flow is somewhat adhered. When it goes into the turbulent range all bets are off and drag approaches the cube of the speed.

I have a little program I downloaded called "Servo Torque Calculator" somewhere that calculates the servo torque required to move a control surface of a certain dimension to a certain angle at a certain speed. Plugging in some values I get the following results:

control surface size: 40" long x 4" wide

airspeed: 20 mph
angle: 15*
torque required: 4.181in*oz

speed: 40 mph
angle: 15*
torque: 16.72

speed: 100 mph
angle: 15*
torque: 104.5

So for 15*, increasing the speed by a factor of 5 from 20mph to 100 mph shows a 25-fold increase in torque required, or the airspeed increase (5 times faster) squared. (5^2 = 25).

Now for the fun stuff.

airspeed: 20mph
angle: 45*
torque: 25.07

double the speed and watch the torque requirement jump (it should about 4 times higher):

speed: 40 mph
angle: 45*
torque: 100.3

now for the rip-the-wings-off maneuver:

speed: 100 mph
angle: 45*
torque: 627.2

five times the original airspeed needs 25 times the torque.

[danielgpr]

	Quote: Originally Posted by jack strickland
	Dan, Please explain what is crystal clear to you. thanks

He doesn't care if anyone believes or not, so does he really? Shows alot about a person when one uses copouts to get attention off of them.

Like you posted a few minutes ago, i guess we'll see what 'ask for planes' comes up with.

I promise until then,
I'm out and have a nice day
Dan

[danielgpr]

	Quote: Originally Posted by BTerry
	At low speed the free airstream force on the surface is greatly diminished, so it isn't as big of an issue. Force isn't linear, it is closer to squared (increases with the airspeed increase squared) - as long as the flow is somewhat adhered. When it goes into the turbulent range all bets are off and drag approaches the cube of the speed. I have a little program I downloaded called "Servo Torque Calculator" somewhere that calculates the servo torque required to move a control surface of a certain dimension to a certain angle at a certain speed. Plugging in some values I get the following results: control surface size: 40" long x 4" wide airspeed: 20 mph angle: 15* torque required: 6.272 in*oz speed: 40 mph angle: 15* torque: 25.088 speed: 100 mph angle: 15* torque: 156.8 So for 15*, increasing the speed by a factor of 5 from 20mph to 100 mph shows a 25-fold increase in torque required, or the airspeed increase (5 times faster) squared. (5^2 = 25). Now for the fun stuff. airspeed: 20mph angle: 45* torque: 37.6 double the speed and watch the torque requirement jump (it should about 4 times higher): speed: 40 mph angle: 45* torque: 150.5 now for the rip-the-wings-off maneuver: speed: 100 mph angle: 45* torque: 940.8 five times the original airspeed needs 25 times the torque.

Cool info, what program is it?
Dan

[jack strickland]

	Quote: Originally Posted by BTerry
	At low speed the free airstream force on the surface is greatly diminished, so it isn't as big of an issue. Force isn't linear, it is closer to squared (increases with the airspeed increase squared) - as long as the flow is somewhat adhered. When it goes into the turbulent range all bets are off and drag approaches the cube of the speed. I have a little program I downloaded called "Servo Torque Calculator" somewhere that calculates the servo torque required to move a control surface of a certain dimension to a certain angle at a certain speed. Plugging in some values I get the following results: control surface size: 40" long x 4" wide airspeed: 20 mph angle: 15* torque required: 6.272 in*oz speed: 40 mph angle: 15* torque: 25.088 speed: 100 mph angle: 15* torque: 156.8 So for 15*, increasing the speed by a factor of 5 from 20mph to 100 mph shows a 25-fold increase in torque required, or the airspeed increase (5 times faster) squared. (5^2 = 25). Now for the fun stuff. airspeed: 20mph angle: 45* torque: 37.6 double the speed and watch the torque requirement jump (it should about 4 times higher): speed: 40 mph angle: 45* torque: 150.5 now for the rip-the-wings-off maneuver: speed: 100 mph angle: 45* torque: 940.8 five times the original airspeed needs 25 times the torque.

Hi Brett Did you read the dimentions of the 40% Laser that you asked for/ Interesting stuff you just posted, one question, the last formula "100 mph- 45 * 940 in. oz. (I assume) How much torque does it take to hold the surface at 45 degrees? The 3d stuff Ive seen approach those perameters without 900 in oz servos. There may be a little more involved here. Not trying to be negative, just want to learn.

[BTerry]

Jack, unfortunately not everybody can look at a diagram or plan and visualize it in his mind in 3 dimensions. This isn't a criticism of anybody, but people have different abilities.

back to the numbers: To take a control surface and deflect it requires a certain amount of torque (torque = force x lever arm radius). The surface requires a set rotational force be applied to it. however the surface doesn't CARE what is generating this force. Period, end of story.
If we take a certain percentage of said control surface and deflect it BACK into the freestream airflow it will create an additional "force", however this force will work IN THE OPPOSITE DIRECTION of the force working against the control surface AND will have a LONGER radius of rotation.

Sized properly this section of the control surface (which is tied to the airframe and moves automatically when the servo deflects the control surface) will generate a ROTATIONAL FORCE or a MOMENT that will add to the torque provided by the servo.

Does this help anybody? Those of us who understand the concept are baffled by those who can't grasp it, and are astonished at the attitude being thrown around. Please let me know if this makes sense!

If anybody REALLY needs a video, box up your camera and send it to Roger. I am sure he will take a vid for you and post it.

[BTerry]

	Quote: Originally Posted by jack strickland
	Hi Brett Did you read the dimentions of the 40% Laser that you asked for/ Interesting stuff you just posted, one question, the last formula "100 mph- 45 * 940 in. oz. (I assume) How much torque does it take to hold the surface at 45 degrees? The 3d stuff Ive seen approach those perameters without 900 in oz servos. There may be a little more involved here. Not trying to be negative, just want to learn.

Yes I saw the dimensions, thank you very much!.

That torque is the holding force, and includes a 50% safety factor (I didn't realize that when I first ran the numbers). Also no large 3D plane is going to deflect a control surface to 45* when moving at 100 mph, most of the stuff with the huge deflections occurs down under 20 - 40 mph range. I would expect throws under 20* at 100 mph, which on that surface would require 260 in*oz (much more manageable!).

My point was just to illustrate that we typically DO NOT require the full torque of the servo in relatively slow-speed 3D maneuvers. Below are more typical numbers:

speed: 100 mph
angle: 12*
torque: 107

speed: 50 mph
angle: 45*
torque: 235 oz*in

Danielgr, I don't know where I got the program, it was on one of the forums several years ago. Do a google search for "servo torque calculator".

Here is a good one: http://www.geistware.com/rcmodeling/...calculator.xls

[forgues research]

	Quote: Originally Posted by BTerry
	Yes I saw the dimensions, thank you very much!. That torque is the holding force, and includes a 50% safety factor (I didn't realize that when I first ran the numbers). Also no large 3D plane is going to deflect a control surface to 45* when moving at 100 mph, most of the stuff with the huge deflections occurs down under 20 - 40 mph range. I would expect throws under 20* at 100 mph, which on that surface would require 260 in*oz (much more manageable!). Danielgr, I don't know where I got the program, it was on one of the forums several years ago. Do a search for "servo torque calculator".

Brett, another thing to think about when considering holding power on servos, the digitals have tremandous holding power, but with the use of boost tabs, they are the holding power and don't even need digital servos.

I am installing 180 oz analogue servos with metal gears and ball bearings on my 40%. one per surface.

When I was doing knife edge passes at full power with my 35% yak, the rudder was controlled by the boost tab only which had a hitec HS 81 servos controlling the boost tab. No other servo input on the rudder .

Roger

[BTerry]

In summary boost tabs just add an additional ROTATIONAL force to the control surface IN THE SAME DIRECTION AS THE SERVO FORCE. This reduces the force requried of the servo. Good thing, n'est pas?

Canwe please put this to bed and get back to the Laser build without distractions?

Thank you again Roger for an insightful build. plus ca change, plus c'est la meme chose.