400% Green Toys plane

[Tench745]

I think it was about a year ago now I was visiting a friend who has children. His son has a toy airplane that is the perfect blending of classic and caricature. Most of you with kids probably already know the plane. It's made by Green Toys and is available in a couple different colors, with one version on floats.
As soon as I saw it I wanted to see if it would it fly. I've seen blue, red, and green versions but I found a purple one on Facebook Marketplace for $10 and I had to have it.
I took some 3-view pictures and a bevy of measurements then plugged them into CAD.

I decided to scale things up to a 36" wingspan. That gives me a wing area of about 305in². If I can keep the weight around 36oz, the wing loading will be reasonable.
Two things that didn't scale very well were the prop, and the wing.
Scaled up, the prop would be a 16" 3-blade, but it's difficult to get a small/light motor to spin a prop that big without a gearbox and I don't really want to get into that quite yet. So I'll be starting with a 12" 2-blade.

The wing on the toy is semi-symmetrical, incredibly thick and comically small. Each wing is only about 13-1/2" long with a root cord of about 10-1/2". If I scaled the toy exactly the wing would be 3" thick at the fuselage and almost 1-1/2" thick at the tip. To keep the drag down and make construction a little easier I opted for a much thinner, semi-symetrical wing, only 1-1/4" thick at the root.

The fuselage is pretty simple, a 4" box with round formers over it. This makes figuring out the skins pretty easy because every section of skin is just a cone.

Then it was just a matter of fitting tail surfaces, cutting the cockpit, and figuring out a wing-joiner.

The tail took two tries. On version one I didn't think about a way to join the elevator halves and accidentally installed it upside-down anyway. Of course, I didn't realize my mistake until everything was assembled. This was an unexpected advantage though, because I could figure out my servo installations on a part that wasn't precious.

Version two uses a piece of 3/32 music wire to join the elevator halves. The Vertical and Horizontal are notched to slide over one another with some de-papered DTFB on either side to catch the fuselage skins.


The wing spar is a simple C-channel. There is another C-channel that runs through the fuselage which accepts a third C-channel that acts as a wing joiner/reinforcement. I don't have a lot of confidence in the strength of this system, but if the wings get glued solidly to the fuselage skins, I think it will be okay for a while.
View attachment
I'm waiting on a motor to arrive before I can finish up the electronics install.
Now I'm trying to figure out the landing gear install. The tentative plane is to bend some wire and zip-tie it to a plywood plate attached to the fuselage's center box. Of course, this is difficult to do with the skins on, and even more difficult to install the skins around a set of landing gear wires. If anyone has ideas on how to put landing gear on this chonky boi I'd be happy to hear them.

Oh, and I'll be gifting the purple plane to another friend's kid when I'm done taking my measurements. Spread the aviation bug.

 

[FlyerInStyle]

I think it was about a year ago now I was visiting a friend who has children. His son has a toy airplane that is the perfect blending of classic and caricature. Most of you with kids probably already know the plane. It's made by Green Toys and is available in a couple different colors, with one version on floats.
As soon as I saw it I wanted to see if it would it fly. I've seen blue, red, and green versions but I found a purple one on Facebook Marketplace for $10 and I had to have it.
I took some 3-view pictures and a bevy of measurements then plugged them into CAD.
View attachment 233186 View attachment 233187 View attachment 233188 View attachment 233189
View attachment 233202
I decided to scale things up to a 36" wingspan. That gives me a wing area of about 305in². If I can keep the weight around 36oz, the wing loading will be reasonable.
Two things that didn't scale very well were the prop, and the wing.
Scaled up, the prop would be a 16" 3-blade, but it's difficult to get a small/light motor to spin a prop that big without a gearbox and I don't really want to get into that quite yet. So I'll be starting with a 12" 2-blade.

The wing on the toy is semi-symmetrical, incredibly thick and comically small. Each wing is only about 13-1/2" long with a root cord of about 10-1/2". If I scaled the toy exactly the wing would be 3" thick at the fuselage and almost 1-1/2" thick at the tip. To keep the drag down and make construction a little easier I opted for a much thinner, semi-symetrical wing, only 1-1/4" thick at the root.
View attachment 233203
The fuselage is pretty simple, a 4" box with round formers over it. This makes figuring out the skins pretty easy because every section of skin is just a cone.
View attachment 233190 View attachment 233191
Then it was just a matter of fitting tail surfaces, cutting the cockpit, and figuring out a wing-joiner.

The tail took two tries. On version one I didn't think about a way to join the elevator halves and accidentally installed it upside-down anyway. Of course, I didn't realize my mistake until everything was assembled. This was an unexpected advantage though, because I could figure out my servo installations on a part that wasn't precious.
View attachment 233198
Version two uses a piece of 3/32 music wire to join the elevator halves. The Vertical and Horizontal are notched to slide over one another with some de-papered DTFB on either side to catch the fuselage skins.
View attachment 233199 View attachment 233200

The wing spar is a simple C-channel. There is another C-channel that runs through the fuselage which accepts a third C-channel that acts as a wing joiner/reinforcement. I don't have a lot of confidence in the strength of this system, but if the wings get glued solidly to the fuselage skins, I think it will be okay for a while.
View attachment 233192 View attachment 233195 View attachment 233196 View attachment 233194 View attachment 233197 View attachment 233193
I'm waiting on a motor to arrive before I can finish up the electronics install.
Now I'm trying to figure out the landing gear install. The tentative plane is to bend some wire and zip-tie it to a plywood plate attached to the fuselage's center box. Of course, this is difficult to do with the skins on, and even more difficult to install the skins around a set of landing gear wires. If anyone has ideas on how to put landing gear on this chonky boi I'd be happy to hear them.

you may run into a similar problem to the p26, the propeller needs to be so big to overcome the large fuse, that it will produce a lot of torque, especially with stubby wings

 

[Tench745]

you may run into a similar problem to the p26, the propeller needs to be so big to overcome the large fuse, that it will produce a lot of torque, especially with stubby wings

Oh, almost definitely. This is part of why I want the landing gear, so I can get up enough speed for the controls to counteract that torque before I try and lift off.

 

[FlyerInStyle]

Oh, almost definitely. This is part of why I want the landing gear, so I can get up enough speed for the controls to counteract that torque before I try and lift off.

same thing I am doing with my p-26! great minds think alike

 

[Mr NCT]

Oh, almost definitely. This is part of why I want the landing gear, so I can get up enough speed for the controls to counteract that torque before I try and lift off.

What's the biggest diameter of the fuselage? My QED is 6" diameter and flies great with a 9" prop.

 

[FlyerInStyle]

What's the biggest diameter of the fuselage? My QED is 6" diameter and flies great with a 9" prop.

my p-26 has a fuse diameter of 12" with a 14" cowling if scale. I scaled it down to a 12" cowling and a 9" fuse diameter

 

[Tench745]

What's the biggest diameter of the fuselage? My QED is 6" diameter and flies great with a 9" prop.

9" Fuselage on this one. The front of the cowling is only about 7"

 

[Mr NCT]

9" Fuselage on this one. The front of the cowling is only about 7"

I am humbled at a mere 6", kinda the story of my life...

 

[Piotrsko]

Just because he has a 9" and yours is only 6", no reason to be humble. Not the isze of the tool that matters it's how you use it, or at least THAT'S what she said..... Myself, I am better with my 20 oz than with the 32.

 

[Tench745]

Got my no-name 5010, 750kv motor in the mail yesterday, built a firewall, and installed everything. My local hobby shop had a 12x7 APC sport prop. Hooked up the watt meter today with a storage-charged battery. The meter showed 11.2V at rest and 10.3V at full throttle with a 15A draw. That's about 150watts of power for a plane with an estimated flying weight of about 2.25lbs, giving me a power/weight of 67watts/lb.
That will go up a little with a fully charged battery, but not a lot.

 

[Mr NCT]

View attachment 233254
Got my no-name 5010, 750kv motor in the mail yesterday, built a firewall, and installed everything. My local hobby shop had a 12x7 APC sport prop. Hooked up the watt meter today with a storage-charged battery. The meter showed 11.2V at rest and 10.3V at full throttle with a 15A draw. That's about 150watts of power for a plane with an estimated flying weight of about 2.25lbs, giving me a power/weight of 67watts/lb.
That will go up a little with a fully charged battery, but not a lot.

Looking good, can't wait for the flight video.

 

[Tench745]

It gets better. I think I have a landing gear figured out. Gear is 1/8" piano wire sandwiched in 4 layers of foam. A slot is cut in the lower skin and the foam sandwich glues to the bottom of the central box and the lower skin. Version 2 may need heavier wire and/or a socket of some sort inside to hold the foam sandwich. The wire legs outside the fuselage are then sandwiched between the two pieces of foam that make up the spats. These spats should help keep the gear from buckling backwards under normal landing loads.
Should.
Taxi and flight tests will tell whether it's actually strong enough. I took extra care to get the spats aligned with the plane's centerline so they won't hurt stability as much.

I still need to figure out where the battery goes, and then all that's left is aesthetics. I'll be patterning out a windshield tonight.

 

[FlyingTyger]

I can't help but smile and giggle every time I see an update on this. Looking good @Tench745 !

 

[CappyAmeric]

It gets better. I think I have a landing gear figured out. Gear is 1/8" piano wire sandwiched in 4 layers of foam. A slot is cut in the lower skin and the foam sandwich glues to the bottom of the central box and the lower skin. Version 2 may need heavier wire and/or a socket of some sort inside to hold the foam sandwich. The wire legs outside the fuselage are then sandwiched between the two pieces of foam that make up the spats. These spats should help keep the gear from buckling backwards under normal landing loads.
Should.
Taxi and flight tests will tell whether it's actually strong enough. I took extra care to get the spats aligned with the plane's centerline so they won't hurt stability as much.
View attachment 233286 View attachment 233287 View attachment 233288 View attachment 233289
I still need to figure out where the battery goes, and then all that's left is aesthetics. I'll be patterning out a windshield tonight.

So cool looking. I can't help but wonder about the prop size with that huge cowling. I know the MS P-47 it is an issue at launch because there is only a little prop blast over the elevator and rudder.

 

[Piotrsko]

Taking off will be a real joy. It'll want to torque turn like the devil because all the P Force from the prop. Probably have to start out 90 degrees to the eventual flight direction. Brings back memories......

 

[Tench745]

So cool looking. I can't help but wonder about the prop size with that huge cowling. I know the MS P-47 it is an issue at launch because there is only a little prop blast over the elevator and rudder.

I think that will be the biggest hurdle in whether or not this will be a flyable aircraft. I was a little concerned that the wheels are too far forward and it would have trouble lifting the tail, but after some quick testing in the living room I don't think that will be a problem.

I did a simple thrust test with a fish scale tied to the tail. Using a storage-charged battery I measured about a pound of thrust. Right now it balances with a 2200mah 3s battery in the nose and comes in at 35.7oz.
So thrust-to-weight of .44:1
When it's not 5 degrees out and blowing 30, I'll see about some taxi testing. The power system can take twice what it is now, so I can up-size the prop if I need to. More battery will probably be necessary if I do that.

 

[Piotrsko]

No monster turn at throttle up? Using a bigger prop, less pitch because the tips are going faster.

 

[Tench745]

I got impatient on Tuesday and decided to spray paint. The garage was too cold and I sprayed a little heavily so the paper wrinkled and lifted badly in a few places. I ironed what I could back on and I think it will be okay for a prototype, but I was quite mad at myself for it.

I got out to do a little taxi testing today. The wind was still blowing pretty well here, maybe 15mph, but it was low enough to get a sense of ground handling.
I started with some low speed taxis out and back. The plane tracked well enough going straight, but had a tendency to swap ends if I turned too hard or too fast, typical tail-dragger stuff. The wind may have contributed to this. I managed to scrub the tail skid off in a ground loop, so I didn't get to play as long as I would have liked. It's being re-glued with a BBQ skewer reinforcement as I write this.

On faster taxis I was able to get the tail up at about half throttle with no significant tendencies to swing the tail around.

I bought a 12x7x3 prop and a 14x7 in case I want more thrust than the 12x7 I have on there now can provide. I doubled up batteries to give me a 4400mah 3s so the voltage sag isn't as bad and redid my static tests with the new props.

The 12x7 drew 15.4A with voltage sagging to 10.7 (165 Watts) and it gave around 1.1lbs of thrust.
The 3-blade 12x7 drew 17A with voltage sagging to 10.6 (180 Watts) and it gave around 1.2lbs of thrust.
The 14x7 drew 19A with voltage sagging to 10.6 (200 Watts) and it gave around 1.7lbs of thrust.

 

[Tench745]

First maiden attempt happened today.

It felt pretty stable, responding to elevator reasonably well, but then it pitched suddenly for the ground, skimmed off, resumed flying, then dove for the ground again. I don't know what happened exactly. Maybe airspeed was too low and it stalled, or rates were wrong, or something.

Damage was pretty minor. The landing gear wire bent a bit, the right spat was ripped off, and the top of the tail got crushed. It's all glued back together now. I noticed two things during repairs. One was that I never reinforced the rudder and elevator hinges with hot glue when I built the tail. The other thing I noticed was some slop in the elevator linkage, the z-bends weren't straight and the elevator had some freedom to deflect down a not-insignificant amount. I have now remedied both these issues.
I suspect that as the plane leveled out, the elevator deflected downward, commanding the extreme nose-down attitude. I hauled back on the elevator enough to get rid of the slop and get back into the air, but it happened again as soon as the plane began to level out.

Hopefully the weather cooperates tomorrow and I can try again.

 

[Off-topic jes]

First maiden attempt happened today.

It felt pretty stable, responding to elevator reasonably well, but then it pitched suddenly for the ground, skimmed off, resumed flying, then dove for the ground again. I don't know what happened exactly. Maybe airspeed was too low and it stalled, or rates were wrong, or something.

Damage was pretty minor. The landing gear wire bent a bit, the right spat was ripped off, and the top of the tail got crushed. It's all glued back together now. I noticed two things during repairs. One was that I never reinforced the rudder and elevator hinges with hot glue when I built the tail. The other thing I noticed was some slop in the elevator linkage, the z-bends weren't straight and the elevator had some freedom to deflect down a not-insignificant amount. I have now remedied both these issues.
I suspect that as the plane leveled out, the elevator deflected downward, commanding the extreme nose-down attitude. I hauled back on the elevator enough to get rid of the slop and get back into the air, but it happened again as soon as the plane began to level out.

Hopefully the weather cooperates tomorrow and I can try again.

I got impatient on Tuesday and decided to spray paint. The garage was too cold and I sprayed a little heavily so the paper wrinkled and lifted badly in a few places. I ironed what I could back on and I think it will be okay for a prototype, but I was quite mad at myself for it.
View attachment 233352

I got out to do a little taxi testing today. The wind was still blowing pretty well here, maybe 15mph, but it was low enough to get a sense of ground handling.
I started with some low speed taxis out and back. The plane tracked well enough going straight, but had a tendency to swap ends if I turned too hard or too fast, typical tail-dragger stuff. The wind may have contributed to this. I managed to scrub the tail skid off in a ground loop, so I didn't get to play as long as I would have liked. It's being re-glued with a BBQ skewer reinforcement as I write this.

On faster taxis I was able to get the tail up at about half throttle with no significant tendencies to swing the tail around.

I bought a 12x7x3 prop and a 14x7 in case I want more thrust than the 12x7 I have on there now can provide. I doubled up batteries to give me a 4400mah 3s so the voltage sag isn't as bad and redid my static tests with the new props.

The 12x7 drew 15.4A with voltage sagging to 10.7 (165 Watts) and it gave around 1.1lbs of thrust.
The 3-blade 12x7 drew 17A with voltage sagging to 10.6 (180 Watts) and it gave around 1.2lbs of thrust.
The 14x7 drew 19A with voltage sagging to 10.6 (200 Watts) and it gave around 1.7lbs of thrust.

I remember playing with this is a little kid!