I build, I crash. What am I doing wrong?!?

[navillus5]

Hi -

Big fan of the work done by the FliteTest crew. I've never flown an RC aircraft, so I decided to start with the FT Tiny trainer. I'm an engineer, so of course I needed to create CAD models to verify the CG and other things like that. The problem is that no matter what I do, I end up crashing almost immediately after launch. There is a small RC group near where I live but the time of year and Covid makes getting help problematic.

I have built and crashed the Tiny Trainer a couple of times. The pictures below are of my latest attempts. That I have tried to get into the sky. In both cases I am using a 3S pack with a Lumenier 2207/2450 kV motor and a 5" prop.

There are a couple of variations from the original design such as:

• the servo linkages are external
• the wing tips are shaped as a series of three angles instead of a smooth curve
• I added some 3D printed parts - the firewall, stops for the wing and an insert that is used to make sure that the rear stabilizer is properly centerer.
• The elevator is about an inch lower than the original design.
• I needed to add some putty in the front cavity to get the CG to be about 1/3 of the cord from the leading edge of the wing.

The Version 1 was able to fly, sort of. After hand launching, it rose and curved to the right and then went into a dive and crashed. I tried a couple of more times but it immediately crashed after launch. At this point I needed to replace the nose. I extended it by 1.25", this moved the CG to 30% of the cord and removed the need for the putty.
I also made a new firewall that angled the motor 2 degress to the right and 2 degrees down. The firewall was glued to a motor pod that fit tightly within the nose and was held in place with two skewers.

This Version 2 flew well when it was tossed a couple of times between my friend and I, so I was pretty hopeful. First launch, I forgot to check the motor direction and it crashed after launch. The firewall came loose, so I glued it back onto the pod and used duct tape to reinforce it.
When it was hand launched it immediately turned to the right nosed down and crashed. This happed three times and I finally gave up. This is a link to a low resolution slow motion video of what was happening - my friend will be emailing me a higer-res version which I will upload when I receive it. The launch happens at 00:24.
https://photos.app.goo.gl/AUABHaGCaqMpEMdH8

So...
Is this a design problem, a build problem, a pilot problem, or a combination of all three? Or is it just that Josh Bixler is an RC aircraft god, and I am simply not worthy??

Many thanks for any replies...

 

[Whit Armstrong]

Hi -

Big fan of the work done by the FliteTest crew. I've never flown an RC aircraft, so I decided to start with the FT Tiny trainer. I'm an engineer, so of course I needed to create CAD models to verify the CG and other things like that. The problem is that no matter what I do, I end up crashing almost immediately after launch. There is a small RC group near where I live but the time of year and Covid makes getting help problematic.

I have built and crashed the Tiny Trainer a couple of times. The pictures below are of my latest attempts. That I have tried to get into the sky. In both cases I am using a 3S pack with a Lumenier 2207/2450 kV motor and a 5" prop.

There are a couple of variations from the original design such as:

• the servo linkages are external
• the wing tips are shaped as a series of three angles instead of a smooth curve
• I added some 3D printed parts - the firewall, stops for the wing and an insert that is used to make sure that the rear stabilizer is properly centerer.
• The elevator is about an inch lower than the original design.
• I needed to add some putty in the front cavity to get the CG to be about 1/3 of the cord from the leading edge of the wing.

The Version 1 was able to fly, sort of. After hand launching, it rose and curved to the right and then went into a dive and crashed. I tried a couple of more times but it immediately crashed after launch. At this point I needed to replace the nose. I extended it by 1.25", this moved the CG to 30% of the cord and removed the need for the putty.
I also made a new firewall that angled the motor 2 degress to the right and 2 degrees down. The firewall was glued to a motor pod that fit tightly within the nose and was held in place with two skewers.

This Version 2 flew well when it was tossed a couple of times between my friend and I, so I was pretty hopeful. First launch, I forgot to check the motor direction and it crashed after launch. The firewall came loose, so I glued it back onto the pod and used duct tape to reinforce it.
When it was hand launched it immediately turned to the right nosed down and crashed. This happed three times and I finally gave up. This is a link to a low resolution slow motion video of what was happening - my friend will be emailing me a higer-res version which I will upload when I receive it. The launch happens at 00:24.
https://photos.app.goo.gl/AUABHaGCaqMpEMdH8

So...
Is this a design problem, a build problem, a pilot problem, or a combination of all three? Or is it just that Josh Bixler is an RC aircraft god, and I am simply not worthy??

Many thanks for any replies...



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Can you post a video of your attempts? (I couldn't open the one posted earlier)

 

[mackaiver]

nothing!
THIS IS THE WAY

 

[JasonK]

- not sure if it is perspective, but is the polyhedral symmetrical? (the photo makes it look like it would roll to the right)
- the video has so serious roll to the right, much worse thing any exception
- what was your thrust angle? down? right?
- were the numbers on the prop facing forward?

 

[Ketchup]

I was thinking it could be the launch. It looks like a really high angle of attack so it could just be stalling out.

 

[Ketchup]

Also make sure that your controls are going the right way.

 

[Paracodespoder]

As the others said, the launch is too high of an angle, and it seems to me you are applying throttle after launch and getting serious torque roll, could you post a video at regular speed?

 

[Paracodespoder]

And maybe move the cg forward a tad, seems a little far back.

 

[flyingkelpie]

Hi -

Big fan of the work done by the FliteTest crew. I've never flown an RC aircraft, so I decided to start with the FT Tiny trainer. I'm an engineer, so of course I needed to create CAD models to verify the CG and other things like that. The problem is that no matter what I do, I end up crashing almost immediately after launch. There is a small RC group near where I live but the time of year and Covid makes getting help problematic.

I have built and crashed the Tiny Trainer a couple of times. The pictures below are of my latest attempts. That I have tried to get into the sky. In both cases I am using a 3S pack with a Lumenier 2207/2450 kV motor and a 5" prop.

There are a couple of variations from the original design such as:

• the servo linkages are external
• the wing tips are shaped as a series of three angles instead of a smooth curve
• I added some 3D printed parts - the firewall, stops for the wing and an insert that is used to make sure that the rear stabilizer is properly centerer.
• The elevator is about an inch lower than the original design.
• I needed to add some putty in the front cavity to get the CG to be about 1/3 of the cord from the leading edge of the wing.

The Version 1 was able to fly, sort of. After hand launching, it rose and curved to the right and then went into a dive and crashed. I tried a couple of more times but it immediately crashed after launch. At this point I needed to replace the nose. I extended it by 1.25", this moved the CG to 30% of the cord and removed the need for the putty.
I also made a new firewall that angled the motor 2 degress to the right and 2 degrees down. The firewall was glued to a motor pod that fit tightly within the nose and was held in place with two skewers.

This Version 2 flew well when it was tossed a couple of times between my friend and I, so I was pretty hopeful. First launch, I forgot to check the motor direction and it crashed after launch. The firewall came loose, so I glued it back onto the pod and used duct tape to reinforce it.
When it was hand launched it immediately turned to the right nosed down and crashed. This happed three times and I finally gave up. This is a link to a low resolution slow motion video of what was happening - my friend will be emailing me a higer-res version which I will upload when I receive it. The launch happens at 00:24.
https://photos.app.goo.gl/AUABHaGCaqMpEMdH8

So...
Is this a design problem, a build problem, a pilot problem, or a combination of all three? Or is it just that Josh Bixler is an RC aircraft god, and I am simply not worthy??

Many thanks for any replies...



View attachment 189192
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View attachment 189194

Could you post a video of the crash? Or try to fly again and take a video?

 

[Ketchup]

Could you post a video of the crash? Or try to fly again and take a video?

There is a video. We just need one at full speed.

 

[Whit Armstrong]

Hi -

Big fan of the work done by the FliteTest crew. I've never flown an RC aircraft, so I decided to start with the FT Tiny trainer. I'm an engineer, so of course I needed to create CAD models to verify the CG and other things like that. The problem is that no matter what I do, I end up crashing almost immediately after launch. There is a small RC group near where I live but the time of year and Covid makes getting help problematic.

I have built and crashed the Tiny Trainer a couple of times. The pictures below are of my latest attempts. That I have tried to get into the sky. In both cases I am using a 3S pack with a Lumenier 2207/2450 kV motor and a 5" prop.

There are a couple of variations from the original design such as:

• the servo linkages are external
• the wing tips are shaped as a series of three angles instead of a smooth curve
• I added some 3D printed parts - the firewall, stops for the wing and an insert that is used to make sure that the rear stabilizer is properly centerer.
• The elevator is about an inch lower than the original design.
• I needed to add some putty in the front cavity to get the CG to be about 1/3 of the cord from the leading edge of the wing.

The Version 1 was able to fly, sort of. After hand launching, it rose and curved to the right and then went into a dive and crashed. I tried a couple of more times but it immediately crashed after launch. At this point I needed to replace the nose. I extended it by 1.25", this moved the CG to 30% of the cord and removed the need for the putty.
I also made a new firewall that angled the motor 2 degress to the right and 2 degrees down. The firewall was glued to a motor pod that fit tightly within the nose and was held in place with two skewers.

This Version 2 flew well when it was tossed a couple of times between my friend and I, so I was pretty hopeful. First launch, I forgot to check the motor direction and it crashed after launch. The firewall came loose, so I glued it back onto the pod and used duct tape to reinforce it.
When it was hand launched it immediately turned to the right nosed down and crashed. This happed three times and I finally gave up. This is a link to a low resolution slow motion video of what was happening - my friend will be emailing me a higer-res version which I will upload when I receive it. The launch happens at 00:24.
https://photos.app.goo.gl/AUABHaGCaqMpEMdH8

So...
Is this a design problem, a build problem, a pilot problem, or a combination of all three? Or is it just that Josh Bixler is an RC aircraft god, and I am simply not worthy??

Many thanks for any replies...



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View attachment 189194

It's probably the elevator. Moving it even an inch down could mess up the way it works.

 

[Ryan O.]

It's probably the elevator. Moving it even an inch down could mess up the way it works.

That and the long control rod, I'd recommend stiffening it with a bbq skewer

 

[JasonK]

That and the long control rod, I'd recommend stiffening it with a bbq skewer

your right, that elevator push rod is bowed, the servo isn't centered, but the surface is... I suspect there is very little to no good control on that surface.

 

[mdcerdan]

You should first do a test glide.
Center your links with the control surfaces neutral. The servo arm must be pointing up to have equal travel both ways. Simply unscrew the arm and position it looking up. Then adjust the elevator neutral with the linkage stopper.
Same for the rudder.

 

[Merv]

I agree with @Paracodespoder. Your CG is foo far aft.
Make the CG at 25% of the cord, 1.25 inches from the leading edge

 

[flyingkelpie]

One side of the airfoil is either not built properly, or over weighted. A video would help and yes also I think the cg might be off.

 

[Monte.C]

I agree with @Paracodespoder. Your CG is foo far aft.
Make the CG at 25% of the cord, 1.25 inches from the leading edge

For some strange reason my planes are wanting the CG further forward than that. Seems like every time. And to start with a good maiden flight don't you want to begin a bit forward anyway? I would think you would want to be on the safe side of 20%.

Or maybe my ruler's broke.

 

[Ketchup]

Also I did want to add in one more thing that you might have done wrong. You overcomplicated it. To find the CG you don't need to build a CAD model since FT supplies CG locations for you. Also for a first RC plane it is always best to go with how FT designed it. They have been doing it for years and they did everything on that plane for a reason.
Just remember that it is just a foam board plane. It doesn't need to be perfect, and often times trying to make it perfect does the opposite.

 

[Merv]

For some strange reason my planes are wanting the CG further forward than that. Seems like every time. And to start with a good maiden flight don't you want to begin a bit forward anyway? I would think you would want to be on the safe side of 20%.

Or maybe my ruler's broke.

Nothing wrong with CG at 20%, @navillus5 had CG at 30%, way to far aft for a beginner.

 

[navillus5]

Hi Everybody -

Wow! Thanks for all the replies and the advice. So to answer a couple of the questions that have been posed:

• Crap! The dihedral on wind is not symmetrical. I used a dihedral on both sides when I built the wing and at the root they both have an angle of 15 degrees. However, the left side is straight and has a vertical height of 1 7/8" at the tip, but the right side is bowed upward such that its vertical distance is 2 7/8". Its obvious as I look at it now...
  So that results in the left dihedral generating about 4% greater lift than the right.
• Thrust angle is 2 degrees right and 2 degrees down. At least that is the starting point. All bets are off once I crash.
• I probably did launch it at too high of an angle. I wanted my friend to take a video, so I launched it by myself.
• I didn't think that the elevator could make that much difference. BTW - the control surfaces were all trimmed to be level and I didn't even have time to adjust the stick.
• The control rod is shorted than the original design. I didn't notice the bent rod, but again the control sufaces were all level at launch.
• I did a test glide and it flew straight and level.
• The one issue that I have with the CG is that I always end up tail heavy. Is there a concern that adding putty as ballast would make the plane too heavy? This is the primary reason that I increased the length of the nose.
• And yes - I thing my tweaks are causing too many unknowns. Since I need to rebuild, I am going to follow the plans to the T. Also the CAD model is just an aside, I teach CAD to sophomore mechanical engineers, so creating a solid model is just 2nd nature.

So thanks again for all the help and advice. I will post again after I build the new plane. I think that I should do this BEFORE I go ahead and try to build the duct tape plane!