Introduction to RC flight through unplanned landings

[veloxsouth]

Holy Crap what is the wingspan on that thing, almost Kraken size?! They look like 5g given the perspective of the picture. Is it carrying a 9" prop on there? I has to be big. The Spear is a 41" wingspan, the Arrow is like 30" give or take a couple inches. Maybe try to downsize a bit and get it to fly good at a smaller size.

I know exactly what you are sayin about getting the splines to line up in opposite directions, pretty common with all the servos I have dealt with, actually I have never seen them line up. It doesn't really make a difference though. You do have a lot to work with in this wing given the info you have so far. To what lengths are you planning on taking this specific build? Have you built a FT wing stock to spec and flown it yet?

Thanks for reassuring me that the servo direction doesn't really make a difference. I won't concern myself with it anymore.
To answer your questions, it's a 50" wingspan with a 9" prop, and I haven't built a stock FT wing yet. My first ever RC plane was the FT Explorer in the opening post, which I quickly and completely destroyed.

It flew amazingly well on that last run...until it didn't. I was extremely happy with its handling and tracking where I point it right up until the servo simply came unplugged from its wiring extension during its flight, or at least I'm convinced that's what happened. So the only things I would like to change so far are hot gluing the wiring down since those extension wires were really loose, and swapping out the foam spar for a wooden one, and giving the control horns on the elevons more surface to work against.

The specs were
50" wingspan
912g All up weight
4.5 sq feet of wing area
cubic wing loading of 3.4
35 degree sweep
aspect ratio of 3.9
The linkage rods were 0.055" 'music wire' so the coffee stirrers and zip ties were a little superfluous for the length I was dealing with.
2 parallel 3S 2200mAh batteries
installed a 9x6 prop but I originally designed for a 10x4.5 prop.
ecalc link here

 

[veloxsouth]

Crash video is posted.

 

[The Hangar]

Crash video is posted.

It looked like you were flying it nicely and that was great considering it is your first flying wing and you designed it. I would definitely call that success. It also looked a bit tail heavy. How was the damage? Will you repair it or build another?

 

[BATTLEAXE]

Crash video is posted.

That was definitely a success considering you are new to flying and you flew a self designed wing. Even your launch buddy was surprised lol! fantastic work man. Your crash was definitely due to electrical failure for sure. At least taping the wire plugs together is definitely a must, you could glue them down too, but taping them together would be more beneficial.

With 2 2200mah 3s paralleled would give you a 12-15 minute flight time, even more. @The Hangar called it on the tail heavy side as well. Since you have to fix the nose you could extend it by a couple inches to get extra battery weight forward to help balance it out. Make sure you cut the throttle next nose dive to help with damage prevention.

Keep the vids coming though, they are entertaining if anything. The only thing that's important is that you are having fun

 

[veloxsouth]

It looked like you were flying it nicely and that was great considering it is your first flying wing and you designed it. I would definitely call that success. It also looked a bit tail heavy. How was the damage? Will you repair it or build another?

The two C-folded layers of foamboard I used as a spar broke in half and the left wing was just held on by the tape I applied to the leading edge. I could try fixing it but I'll take this as an opportunity to make some changes.

I balanced the CG at the 15% line with two batteries in it based on the ecalc link I showed earlier. After adding the wingtips, just having one battery in the front left it out of the 10-15% range I wanted. It seemed to track well to me, so I'm a little confused about the tail heavy observations. How can I tell if my plane is tail heavy when it's not doing back flips?

Thanks @BATTLEAXE and @The Hangar for your suggestions.

 

[BATTLEAXE]

The two C-folded layers of foamboard I used as a spar broke in half and the left wing was just held on by the tape I applied to the leading edge. I could try fixing it but I'll take this as an opportunity to make some changes.

I balanced the CG at the 15% line with two batteries in it based on the ecalc link I showed earlier. After adding the wingtips, just having one battery in the front left it out of the 10-15% range I wanted. It seemed to track well to me, so I'm a little confused about the tail heavy observations. How can I tell if my plane is tail heavy when it's not doing back flips? View attachment 147733

Thanks @BATTLEAXE and @The Hangar for your suggestions.

It's doing back flips because it I tail heavy. Wings are really sensitive to being tail heavy and are way more noticeable due to the fact that there is no fuselage with a tail to compensate using control surfaces to hide it. You want the plane to balance on the nose heavy side slightly. Your balance point should be around 25-30% of the wing chord back from the leading edge, and a wing sweep will move that back some from there. The center of gravity and center of pressure need to even out for the wing to fly level. Center of pressure is the balance point of lift applied to the wing in flight, thus creates your center of gravity. Just like how gravity at a static position will pull the plane down, lift will push the plane up and the center of pressure is the balance point from the top of the wing when flying. Funny thing is that center of pressure will move around as the angle of attack and speed to a certain point changes. There are vids on YouTube describing this effect.

 

[veloxsouth]

It's doing back flips because it I tail heavy. Wings are really sensitive to being tail heavy and are way more noticeable due to the fact that there is no fuselage with a tail to compensate using control surfaces to hide it. You want the plane to balance on the nose heavy side slightly. Your balance point should be around 25-30% of the wing chord back from the leading edge, and a wing sweep will move that back some from there. The center of gravity and center of pressure need to even out for the wing to fly level. Center of pressure is the balance point of lift applied to the wing in flight, thus creates your center of gravity. Just like how gravity at a static position will pull the plane down, lift will push the plane up and the center of pressure is the balance point from the top of the wing when flying. Funny thing is that center of pressure will move around as the angle of attack and speed to a certain point changes. There are vids on YouTube describing this effect.

I'm more confused about your reply.
You said that my balance point should be 25-30% of the wing chord but my balance point was far forward of that at 15% of the mean aerodynamic chord as calculated in this calculator.

 

[BATTLEAXE]

I'm more confused about your reply.
You said that my balance point should be 25-30% of the wing chord but my balance point was far forward of that at 15% of the mean aerodynamic chord as calculated in this calculator.

Rule of thumb is 1/4 to 1/3 of the wing chord on any wing whether a traditional airframe or a flying wing. 15% will be tail heavy. A glide test will tell you the same on a physical sense as well. If you chuck glide any plane it should fly level, tail heavy it will pitch up and stall, nose heavy it will fall nose first with no glide characteristics. You may have seen this with paper planes. 15% is way to far forward.

 

[veloxsouth]

Rule of thumb is 1/4 to 1/3 of the wing chord on any wing whether a traditional airframe or a flying wing. 15% will be tail heavy. A glide test will tell you the same on a physical sense as well. If you chuck glide any plane it should fly level, tail heavy it will pitch up and stall, nose heavy it will fall nose first with no glide characteristics. You may have seen this with paper planes. 15% is way to far forward.

I hate to keep going back over this but if my center of gravity is at 15% from the leading edge, with half the weight being in the forward 15% and the other half of the weight being in the remaining 85% to the tail, how can it be described as tail heavy?

 

[Vimana89]

I think the confusion might be stemming from which side you guys are measuring in from. If your CG is at 15% back from leading edge as you describe, it can't be CG related. Three things that most often mess up a maiden, especially a custom design, are CG(eliminated), thrust angle, and weight related issues(wing loading, thrust to weight ratio, etc.) This last one's kinda doubtful to cause your issue. I read the above post again and sounds like you think it was a mechanical failure of the servo coming unplugged? That will definitely be the fourth biggest issue. A servo coming unglued or unplugged, or perhaps an arm wasn't screwed in right. Those sorts of things have lead to quite a few crashes for me already! Anyway, awesome wing, I'm sure you will nail it on the rebuild

This being said, 15% is way too far forward on CG, I agree with @BATTLEAXE. It's good to err on the side of being nose heavy, but too much will still cause some pitch instability. 25% back from leading edge is the general rule of thumb for most planes if you want it to be just slightly to moderately nose heavy.

 

[Piotrsko]

@BATTLEAXE youre the only other person here that I have heard talking actual aerodynamics. Wow.

I'm gonna say you had a LOS because I didn't see the detached servo.

I have recently become enamored in the @Hai-Lee method of fine tuning wings: get high, chop power, full up. If it nose bobbles up & down, it's nose heavy, if it rocks its wings it is tail heavy. If it mushes down stable in a high alpha mode it is correct.

 

[Vimana89]

@BATTLEAXE youre the only other person here that I have heard talking actual aerodynamics. Wow.

I have recently become enamored in the @Hai-Lee method of fine tuning wings: get high, chop power, full up. If it nose bobbles up & down, it's nose heavy, if it rocks its wings it is tail heavy. If it mushes down stable in a high alpha mode it is correct.

I've seen him describe that method before. Sounds like it could work for deltas too

 

[BATTLEAXE]

I hate to keep going back over this but if my center of gravity is at 15% from the leading edge, with half the weight being in the forward 15% and the other half of the weight being in the remaining 85% to the tail, how can it be described as tail heavy?

Its a good question. Its about balace in nature. Nature likes balance. By thrusting an airfoil through the air we are essentially manipulating nature to get a desired result. Gravity being a part of nature will pull the wing down on whatever balance point you create, but nature creates the center of pressure based on the airfoil design.

If you were to have a stick on a horizontal position and with nothing but gravity acting upon it, like being static, it should balance in the center. If we place weight on one end, we can manipulate were the stick balances to level, correct.

Now think of the airfoil as the stick, but in forward motion and because it is an airfoil, Newtonian and Bernoulli principles apply given the effects of nature playing on the stick, or airfoil. This dictates center of pressure which is the opposite effect of center of gravity, which we have no control over. So we compensate by moving the center of gravity to match the center of pressure.

You know how you balance a plane by placing your fingers under the wing ata certain location, center of pressure is the same thing but in the opposite direction. As lift is created to force the wing up, it is like a balance point created by that lift striving to keep the wing level and will be 25-30% of the wing chord from the leading edge. Imagingine being able to be over top of the plane while in flight and trying to balance it from the top while the wing creates lift in motion, you will find that the balance of upward pressure on your fingers to maintain level flight is the magic 25-30% from that leading edge. Its akin to saying everyaction has an ewual and opposite reaction.

 

[BATTLEAXE]

Sorry for the spelling errors, i am texting on my phone and not at the computer lol

 

[BATTLEAXE]

I've seen him describe that method before. Sounds like it could work for deltas too

Works for all aero and hydrodynamics. Whether it creates lift or downforce its the same.

 

[veloxsouth]

Its a good question. Its about balace in nature. Nature likes balance. By thrusting an airfoil through the air we are essentially manipulating nature to get a desired result. Gravity being a part of nature will pull the wing down on whatever balance point you create, but nature creates the center of pressure based on the airfoil design.

If you were to have a stick on a horizontal position and with nothing but gravity acting upon it, like being static, it should balance in the center. If we place weight on one end, we can manipulate were the stick balances to level, correct.

Now think of the airfoil as the stick, but in forward motion and because it is an airfoil, Newtonian and Bernoulli principles apply given the effects of nature playing on the stick, or airfoil. This dictates center of pressure which is the opposite effect of center of gravity, which we have no control over. So we compensate by moving the center of gravity to match the center of pressure.

You know how you balance a plane by placing your fingers under the wing ata certain location, center of pressure is the same thing but in the opposite direction. As lift is created to force the wing up, it is like a balance point created by that lift striving to keep the wing level and will be 25-30% of the wing chord from the leading edge. Imagingine being able to be over top of the plane while in flight and trying to balance it from the top while the wing creates lift in motion, you will find that the balance of upward pressure on your fingers to maintain level flight is the magic 25-30% from that leading edge. Its akin to saying everyaction has an ewual and opposite reaction.

You don't need to explain aerodynamics like I'm five years old. I think you just aren't reading what I'm posting.

 

[BATTLEAXE]

I hate to keep going back over this but if my center of gravity is at 15% from the leading edge, with half the weight being in the forward 15% and the other half of the weight being in the remaining 85% to the tail, how can it be described as tail heavy?

I have read your posts and i dont mean to explain it like you are 5 years old. Not my intention. The common denominator is that you keep going to the 15% theory and nature dictates that it isn't 15%, its 25-30%, and on a wing its better at 30%. That the nature of it and cant be varied as far as center of pressure. Center of gravity needs to match or it just wont work, no matter what i or anyone else says.

I am just trying to help you, not insult your intelligence. Anyone else as you have seen will tell you the same thing. Sorry you feel that way but like i said all this information is out there on the university of youtube, thats where i got this info recently as i was researching flying wings specifically. Bruce Simpson of RCModelReveiws, and also known as Xjet has more in depth explanations of it. Check it out for youself.

I do have other suggestions to help you out with your wing but i am afraid to insult you further. Have fun and good luck

 

[The Hangar]

so I just want to add something short. EVERY model will have a slightly different cg, and EVERY pilot will have a different preference. You had a decent cg, but as I saw it seemed to be pitching up a bit, I personally would shift it an inch or half an inch away from the leading edge of the wing to make it fly a little better and easier for lack of a better word. If you like it where it is, go for it! It’s your plane, and you are the pilot, so find something you like and don’t let us make you change it. I was just trying to suggest something that would make it fly a little better and easier.
Good luck and have fun!

 

[veloxsouth]

I have read your posts and i dont mean to explain it like you are 5 years old. Not my intention. The common denominator is that you keep going to the 15% theory and nature dictates that it isn't 15%, its 25-30%, and on a wing its better at 30%. That the nature of it and cant be varied as far as center of pressure. Center of gravity needs to match or it just wont work, no matter what i or anyone else says.

I am just trying to help you, not insult your intelligence. Anyone else as you have seen will tell you the same thing. Sorry you feel that way but like i said all this information is out there on the university of youtube, thats where i got this info recently as i was researching flying wings specifically. Bruce Simpson of RCModelReveiws, and also known as Xjet has more in depth explanations of it. Check it out for youself.

I do have other suggestions to help you out with your wing but i am afraid to insult you further. Have fun and good luck

It's all beside the point. You said it was tail heavy which implies that the CG is closer to the trailing edge than it should be and should be moved forward to the 25 to 30% region. I'm not saying it should be at 15%. I'm saying it currently is at 15%, which is in front of that region, not behind. Therefore it is not tail heavy. If anything the CG is too nose heavy based on your own suggestions. @Vimana89 also tried to point this out to you. There was no need to go on a four paragraph lecture anthropomorphizing nature and literally using the word "magic" when that doesn't address the contradiction, then suggest that I'm going to miss out on your suggestions when I point this out.

 

[BATTLEAXE]

It's all beside the point. You said it was tail heavy which implies that the CG is closer to the trailing edge than it should be and should be moved forward to the 25 to 30% region. I'm not saying it should be at 15%. I'm saying it currently is at 15%, which is in front of that region, not behind. Therefore it is not tail heavy. If anything the CG is too nose heavy based on your own suggestions. @Vimana89 also tried to point this out to you. There was no need to go on a four paragraph lecture anthropomorphizing nature and literally using the word "magic" when that doesn't address the contradiction, then suggest that I'm going to miss out on your suggestions when I point this out.

I get what you are trying to say. If you have it balanced at 15% level, moving your fingers back to 25% should make it nose heavy. And you are not wrong. You are absolutely right. And you are probably holding your plane at level balance at the 15%, then move your fingers back to 25% and the plane pitches nose down into your lap. Makes sense if at static gravity is the only force acting on it. Think of it this way. You balance level at 15% holding the plane up acting against gravity. Now hold a finger over top of the wing at 25% and push down. What happens? The wing will pitch up or down? That is what center of pressure is doing to your plane in flight. Thats what needs to balance. CG and center of pressure need to cancel each other out for it to work.

I don't mean to confuse the situation. Trust me it took me a few times to wrap my head around it.