Thank so much for your response! I would love to see a diagram, but it`s more clear to me now. Aloso, what is the angle of incidence?
Help! Designing my first rc airplane. Need some help:)
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Tench745
Master member
Okay, so here's a quick set of diagrams showing what I was saying.
The angle of incidence is the angle between the chord line of the wing and the longitudinal axis of the aircraft. (Figure 1)
Figure 2 shows a plane with no incidence to the wing or tail. This can work, but most airfoils perform better with a little incidence.
A thing I did not note on the drawing: the difference between the angle of incidence of the wing and the angle if incidence of the H-stab is called "decalage". The wing and the H-stab here have no decalage.
Figure 3 is shows a highly exaggerated incidence on the wing and no incidence on the tail. This plane has 9 degrees of wing incidence and -9 degrees of decalage. Looking at the picture it should be pretty obvious that the the tail would always be forcing the wing to a high angle of attack in this configuration.
Figure 4 is a plane with the same 9 degrees of wing incidence but now it has the same 9 degrees of incidence on the horizontal stabilizer. That means it has 0 degrees of decalage and the wing/tail together would behave like the plane in Figure 2.
BUT, the plane would look like Figure 5 when flying straight and level. You can see how confusing it would be to have the fuselage pointing downward like that while the plane is flying straight and level.
The angle of incidence is the angle between the chord line of the wing and the longitudinal axis of the aircraft. (Figure 1)
Figure 2 shows a plane with no incidence to the wing or tail. This can work, but most airfoils perform better with a little incidence.
A thing I did not note on the drawing: the difference between the angle of incidence of the wing and the angle if incidence of the H-stab is called "decalage". The wing and the H-stab here have no decalage.
Figure 3 is shows a highly exaggerated incidence on the wing and no incidence on the tail. This plane has 9 degrees of wing incidence and -9 degrees of decalage. Looking at the picture it should be pretty obvious that the the tail would always be forcing the wing to a high angle of attack in this configuration.
Figure 4 is a plane with the same 9 degrees of wing incidence but now it has the same 9 degrees of incidence on the horizontal stabilizer. That means it has 0 degrees of decalage and the wing/tail together would behave like the plane in Figure 2.
BUT, the plane would look like Figure 5 when flying straight and level. You can see how confusing it would be to have the fuselage pointing downward like that while the plane is flying straight and level.
Thanks so much for zour detailed response! I still have a question: in the figure 3 you said that with -9 degree decalage, the plane is hoing to have a tendence to pitch up. Is it because when the plain will be flying straight the H. stab is gonna be on an ange to incoming air?
Also, how do i calculate/meaure decalage? I assume it is angle of the H stab - angle of the wing.
And, the last one, after all, what decalage is the best to have, and i know you said incidence doesn`t matterm but still if there is any recommended? BTW, what is the definition of the longtitudal axis?
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Tench745
Master member
The short answer is, yes. The H-stab will constantly be trying to force the wing into a high angle of attack similar to what I have drawn. You would need to hold down elevator constantly to keep the wing at an angle of attack where it will fly level.
I have seen different sources refer to decalage differently. Some people would call what I have shown in Figure 3 "+9 degrees of declage."
So, either h-stab incidence minus wing incidence, or wing minus h-stab could be considered correct depending on who you talk to.
The longitudinal axis is basically an imaginary line drawn from the nose of the plane to the tail. Usually, the longitudinal axis is horizontal in during level flight.
The best decalage depends on a lot of factors. You can get into all the variables involved as you learn more. But for now, for the FT style planes, this is my basic rule of thumb:
Set the angle of incidence of the horizontal stabilizer parallel to whatever angle you want the fuselage to have in level flight. Give the wing a little positive incidence; something between 0 and 1 degrees.
When designing your own plane, it's worth looking at other similar planes to see what they did.
For instance, if you look at the plans for the FT Sportster you'll see that the H-stab and the bottom surface of the wing are parallel. Similarly the FT Cub has the H-stab and bottom surface of the wing parallel to one another.
Hello! I’m not sure what do you mean by the H-stab angle being parallel to the fuselage angle. Do you mean i should set it depending on gow i want the plane to look? Also now thinking about it, what is the H-stab for anyways? Is it like because the center of lift without it would be too far ahead the center of mass? Also, does the H stab need to be an airfoil?
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L Edge
Master member
For your first design, you have taken on a complicated setup. This design is used on STOL. Here is a video just varying the wing. Watch what happens not only fixed wing and elevator, but climbing and diving. Especially where I start to flare.
Tench745
Master member
It sound like you get the concept, yeah. Just align the h-stab. with the direction of flight like in figure 2 and 3.
The horizontal stabilizer does exactly what its name implies. It stabilizes the airplane. Wings have a tendency to pitch up or down as they fly faster or slower, and the horizontal stabilizer, together with the elevator, helps control that.
The h-stab does not need to be an airfoil. If you look at the various FT planes, they all use a single sheet of foamboard for the tail surfaces. Even some full-size airplanes like the Piper Cub have flat tail surfaces.
Ok. Guys. Thanks so much! That really helps!
Hello everyone! I know that i need to by a battery checker. I just stumbled onto this thing. It says it can measure voltage of the cells and the whole battery up to 8S, and seems to be pretty cheap. Is it a good alternative to buying a more expensive battery checker? I’m kinda on a budget
Attachments
Shurik-1960
Well-known member
I haven't soldered the connectors to the motor and regulator for a long time. There have been many accidents in 15 years due to the oxidation of connectors. I recommend soldering the motor directly with the regulator, not forgetting to check for the correct rotation of the motor. It's very reliable.
Hello everyone! Finished soldering the connectors with my dad. The XT-60 was the hardest one - but we got it done. I put all the elrctronics together to test them. I have 2 questions:
1. Is it normal, that my SG-90 servos are greesy on the sides?
2. My Y-type servo extender, which is supposed to reverse the rotation of one of the servos, does not. Is that a problem with the extender or did i just do something wrong? (servos work on the extender, just spin the same way)
1. Is it normal, that my SG-90 servos are greesy on the sides?
2. My Y-type servo extender, which is supposed to reverse the rotation of one of the servos, does not. Is that a problem with the extender or did i just do something wrong? (servos work on the extender, just spin the same way)
Tench745
Master member
1) it's not too uncommon for a little of the grease inside to have gotten out in shipping. Just wipe the sides clean with some type of degreaser so that the glue can stick.
2) Sounds like you got a regular Y harness not a reversing Y.
Flying Monkey fab
Elite member
Those are designed to be left in the plane but would be a lot better than nothing.
You can buy a good field battery checker for very little though. I'd skip few sodas and get this :
Digital Battery Capacity Tester, Battery Capacity Voltage Checker Controller Tester with LCD for LiPo Life Li-ion NiMH Battery https://www.amazon.com/dp/B07RNPHJN6/?tag=lstir-20
I dont know man, I specifically asked the guy in the gobby shop for it to inverse servos…
Tench745
Master member
Don't know what to tell you. If it's not reversing one servo, it's probably not a reversing y. Reversing Ys have some kind of circuit board with a microchip to invert the signal going to the servo, typically located where the Y splits off . Non-reversing Ys will usually just have a chunk of black plastic or heat shrink. What does yours look like?
As a follow up question, are you sure you need a reversing y? I've built probably two dozen planes over the years and have never needed a reversing y.
leaded50
Legendary member
if your aileron servos dont function as one reversed with the Y-wires, are you shure your servos are mounted in correct ways, as on my scetch? ( whatever version as the bigger one, or the ones on the right side) There you will see that the servos are mounted different (as in a mirror) depending on which side its used on.
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synjin
Elite member
You may be beyond CG at this point, but I run my designs through this calculator and it works well: https://rcplanes.online/cg_calc.htm
