Having trouble with scratchbuilds, most won't even glide properly

[Jessek1486]

Those videos are very helpful. Here's what I'm seeing:
You are throwing the plane with enough force for it to fly, so that's good.

The second video was close to what I would call a good glide, right until the end.
The third video looks like the plane may be on the verge of a stall: the nose stays high and the plane kind-of mushes towards the ground, then the nose begins to drop and the plane doesn't recover.

I think you're fighting a trim issue rather than a CG issue. Most wings need a little bit of a positive angle of attack to generate sufficient lift. In your pictures it looks like the one plane has a symmetrical airfoil. Symmetrical airfoils need slightly more angle of attack than a flat-bottomed airfoil to generate lift.

So here's what I think is happening: When you throw it, the plane is at a good angle of attack and starts to glide, but because the horizontal stabilizer is in line with the wing chord, it lets the nose drop, eliminating the AOA necessary to generate lift, and the plane begins to lawn-dart.

Here's my solution: Either add a shim under the leading edge of the wing to give the wing some incidence (I'd guess 1-2 layers of foamboard), or add in a little up-elevator trim until you get a predictable flight path. Once it flies predictably you can continue to tweak trim and CG to get a good glide.

Hey thank you for watching the videos and and all of that!!

So I was suspecting a trim issue, as I was reading up on that last night.

Bear in mind, I am not intending just to make a glider, but rather a powered aircraft so you're the first person to acknowledge that.

Would this still be considered a symmetrical airfoil? I think it might be the perspective of the original pics.

The tail wing is just a flat piece of foam, so maybe that is the issue?

 

[Jessek1486]

It's hard to tell from the video, it looks like you are not throwing it hard enough & the plane is stalling out, that is going too slow to produce lift. If you want a glide test, find a place with a lot more room & throw the plane a bit harder. Like you are trying to throw a baseball 10 yards or so.

If you have done the math, I would not bother with a glide test. I would go for a powered flight.

So, I have done that. I spent 30 minutes yesterday at the park doing precisely that. This was outlined in the initial post.

I have done the math, and even came up with the same results as you did, suggesting my plane should weigh around 16oz. and have done numerous powered flights, they end in disaster. As detailed in many posts.

This is what brings me here...

 

[Merv]

Sound like I need to reread everything from the beginning.

 

[Jessek1486]

Sound like I need to reread everything from the beginning.

I really respect you admitting that. It's okay, it's a lot of info, and this is a subset of a subset of a common issue, so a bit off the beaten path.

 

[Merv]

...(after crashing in <2secs of powered flight) ...

Is it possible had the elevator reversed when you attempted the powered flight?

 

[Tench745]

Hey thank you for watching the videos and and all of that!!

So I was suspecting a trim issue, as I was reading up on that last night.

Bear in mind, I am not intending just to make a glider, but rather a powered aircraft so you're the first person to acknowledge that.

Would this still be considered a symmetrical airfoil? I think it might be the perspective of the original pics.

The tail wing is just a flat piece of foam, so maybe that is the issue?

It was probably the angle of the picture. I'd consider this a semi-symmetrical airfoil, so it won't need as much AOA to generate lift as a fully symmetrical airfoil would.
I stand by my previous advice as a starting point; add some up-elevator trim or a shim under the wing and see what changes.

If we can get your plane to glide, it will fly.

Most, if not all FT planes have a flat piece of foam for the tail, so that shouldn't be an issue.

 

[Jessek1486]

Is it possible had the elevator reversed when you attempted the powered flight?

I really don't think so, no. I'm open minded to my own cause of error, however, if the thing won't even glide, it certainly explains the failure under powered flight.

It's really hard to get good video of a flight, but from what I can tell, it just stalls and then rolls left/right. Which is basically what it does in glides... So solving that issue is paramount.

 

[Jessek1486]

It was probably the angle of the picture. I'd consider this a semi-symmetrical airfoil, so it won't need as much AOA to generate lift as a fully symmetrical airfoil would.
I stand by my previous advice as a starting point; add some up-elevator trim or a shim under the wing and see what changes.

If we can get your plane to glide, it will fly.

Most, if not all FT planes have a flat piece of foam for the tail, so that shouldn't be an issue.

I'm playing around with this currently, since my wing is removable I can add a shim of foam under it.

I'm currently doing it with nothing on the plane, except enough weight to get the balance point near the 25%-33% lines.

I think it's better? it's hard to tell since it's dark outside.

I'm convinced if it can glide, it can at least have a powered flight until I wreck it using the controls(which at this point, I'd be really thrilled to do, vs it auto-wrecking itself by unstable aerodynamics at the controls. Then I can at least work on improving my flying skills!).

 

[Merv]

I really don't think so, no. I'm open minded to my own cause of error, however, if the thing won't even glide, it certainly explains the failure under powered flight.

It's really hard to get good video of a flight, but from what I can tell, it just stalls and then rolls left/right. Which is basically what it does in glides... So solving that issue is paramount.

Your glide test just don't look that bad to me. At least not bad enough to cause a immediate crash in powered flight. I'm thinking something else is the problem.

Let's check the controls just to be sure. Stand behind the plane with the nose away from you. When you pull back on the elevator stick, the elevator should go up. When you move the rudder stick right, the rudder should go to the right. When you move the aileron stick right, the right aileron should go up & the left one down. That is if you have ailerons.

 

[Jessek1486]

So I added 2 pieces of foam under the front edge of the wing, and I did get it to glide successfully.

However, it could just be I threw it harder since I was a bit annoyed. It definitely stalls/lawn darts at slower speeds.

 

[Jessek1486]

Your glide test just don't look that bad to me. At least not bad enough to cause a immediate crash in powered flight. I'm thinking something else is the problem.

Let's check the controls just to be sure. Stand behind the plane with the nose away from you. When you pull back on the elevator stick, the elevator should go up. When you move the rudder stick right, the rudder should go to the right. When you move the aileron stick right, the right aileron should go up & the left one down. That is if you have ailerons.

I mean, it bangs into the ground hard enough to produce an audible "bang" and throw components off. It often just stalls about 2-3 secs after I launch it with power, before I've had a chance to even input controls. That's normal behavior?

I really don't know if it is or isn't, I have no baseline to compare to or experience to really draw from. I just know that it has been incredibly hard to get it to do anything other than stall and eat dirt.

I also have checked my power, and my motor can peak at 180w with an 8x6 prop, so I doubt it's underpowered?

I appreciate the walkthrough on the controls, they are functioning as intended. I do not have ailerons.

 

[Merv]

... my motor can peak at 180w with an 8x6 prop, so I doubt it's underpowered?...

Is the prop on the right way around? The numbers on the prop need to be facing the direction of travel. If the prop is backwards, it will only produce 50% of the expected thrust.

 

[Jessek1486]

Is the prop on the right way around? The numbers on the prop need to be facing the direction of travel. If the prop is backwards, it will only produce 50% of the expected thrust.

It is. I always check to feel air flowing towards the tail of the plane. Plus I can feel it as I hand launch, and that the plane is pulling foward.

It's unfortunately not something so simple, I do believe it to be related to aerodynamics. Something in the way I am building. I'll have to figure out how to cut up parts for a known good plane, it's just a pain to cut all the parts to specific dimensions/angles for hours, only for the thing to crash in a second. That's why I've been avoiding using a FT simple cub or trainer or whatever.

 

[Shurik-1960]

1. I throw with my right hand (I am right-handed) and quickly take the control panel in both hands. When the model loses speed at the end of your video, you need to add a joystick to the elevator and the model will sit smoothly. 2. You have chosen a very small place to throw. We need a clearing of 30 meters x 20 meters... 3. It is ALWAYS necessary to throw models against the wind. 4. If you throw it from a hill, the model will fly a longer distance...

 

[Jessek1486]

1. I throw with my right hand (I am right-handed) and quickly take the control panel in both hands. When the model loses speed at the end of your video, you need to add a joystick to the elevator and the model will sit smoothly. 2. You have chosen a very small place to throw. We need a clearing of 30 meters x 20 meters... 3. It is ALWAYS necessary to throw models against the wind. 4. If you throw it from a hill, the model will fly a longer distance...

1. Right handed as well. But that seems valid,I will try that at a larger field. This is my yard.

3. Fair point. There wasn't much wind that I recall. Wind here is often extremely variable in direction too.

I don't think there are any hills in the entire state 😂 I envy those that can just walk to a hill to launch their plane from. I think I'd need to get a flight to find a hill.

 

[Merv]

...I'll have to figure out how to cut up parts for a known good plane,...

Did you follow Ed's dimensions for the NoobTube? Length of tail, size of control surfaces, ect.?

 

[L Edge]

Suggest to you another way to get it flying.

1) Take wing off and place on flat surface. Measure leading edge and trailing edge of each dihedral. Could be a twist which drives left wing down. If twisted, do it right.
2) Lift up prop shaft and rudder(centered) to check if plane wing rolls left or right. Add weight to wing tip so it is balanced.
3) Get CG at 25 % of wing chord and make sure prop size and twist is on leading edge of rotation.

4) Logic I use to maiden countless planes and not crash and video to prove how it's done.
a) take a day where there is a 5-10 mph wind(fairly even)--assume plane's wing flies at 20mph, so your have airflow across the wing and elevator just standing there.
b) for your radio- hold in left hand and thumb able to use the gimbal to increase/decrease throttle or shut it off.
c) now grab plane in right hand, into wind blowing, add throttle so there is good forward thrust(not full throttle) and bend over so plane is 1 ft above ground. (your plane's prop shouldn't hit ground being that high)
d) Now launch your plane straight forward, not up or down to induce direction of wing angle. If enough thrust from prop, plane moves forward starting off at 5-10 and your on your way. Not enough thrust, it will drop and slide. So launch again and add more thrust and sooner or later it moves forward.
e) Now it either goes nose up, sorta flies and drops, or go fast nose down.(cut power) That's tells you location of CG. Goes nose up, move battery forward. Go quickly nose down, battery back. Sorta flies nose up/nose down, your close.

So net result, you tested your location of the CG and being 1 foot off the ground into the wind, the nose or tail can't rotate much to do damage other than dings.

Now your close, move up to 2 ft launch and fine tune your CG by using the wind and throttle method. If your prop is turning and plane heading for earth, left thumb can handle that while right hand can handle roll and pitch.

It also applies to larger aircraft that need a runway. I used the gusty high wind to find the CG nose heavy. Wouldn't lift nose.

Moved battery aft to much. Knew I was close, so chucked it.

Fine tuned it and this is result. I forgot about the spline not entered in the calc program. for CG.

So maybe starting low(very little kinetic and potential energy) will prevent those high launches crumples and crashes.

 

[quorneng]

jessek1486
Watch your videos carefully. What direction is the plane going as it leaves your hand? I think you will agree answer is horizontal or even slightly nose up. This means the plane will slow down and stall which is what it does.

It may seem counter intuitive but a glide hand launch need to be pointing down at the angle the plane needs to glide and fly at.
Your plane is not particularly aerodynamically efficient compared to a true glider so the angle needs to be at say 15 degrees downward. This means gravity will now keep the plane flying at the launch speed.
What the plane does in the couple of seconds before it hits the ground tells you how the plane is trimmed. If you test glide over a smooth grass surface the plane will automatically slow down as it lands due to the aerodynamic ground effect.
That glider video demonstrated this effect beautifully but then it was a 'big wing' glider and it was in perfect trim.

I still say removing weight means your plane will glide slower giving you that bit longer to judge what the plane does. It also reduces the speed of impact when it doesn't glide properly! Find a big unobstructed open space (it reduces turbulence) and launch into the wind no matter how gentle it may feel.

Nearly all the planes I have are scratch builds. I fly from a rather rough field so I have to hand launch the majority including my EDFs!

 

[Jessek1486]

Wow, some great advice here. The tip about throwing it a bit down is exactly on point.

I did try changing the incidence of the wing, with 1 and 2 pieces of foam under the leading edge, but tbh, I did not notice a difference. It actually even fell off, and I hadn't noticed that it did, so I got a "blinded" test since I did not know it came off.

I think it glides great now, and I think I'm ready to start putting components back in to get it powered. My only concern is that the dang thing goes back to flying like a brick on a parachute.

Also I did realize I was throwing it wrong as a glider, so that makes me think perhaps part of my issue was that I was throwing it wrong as a powered plane too? I think I was throwing it in such a way, that caused it to start off unstable and since it wasn't able to climb yet, I had zero time to react and fix it. Whether the control surfaces would even have an effect at the slow speed, is another nail in the coffin.

 

[Jessek1486]

A lil update: I took her to the park, and she glided beautifully.