Mini Gee Bee 3d Printed Modular Plane

[telnar1236]

I've had my version 3 of my modular Gee Bee sitting on my shelf for a few months and just been too scared to try and fly it, since this was the last chance before I gave up on the design. The good news is it flies! Unfortunately, that's also currently the best thing I can say about its flight characteristics. However, it now shows enough promise for me to keep working on it and get it flying a bit better.

The 30mm fuselage extension shifted the CG far enough forward to make it flyable. In fact on the first flight of the day (video is of the second flight and I flew it a third time a bit later) it was a bit too nose-heavy. I think the issues I experienced during today's flights come from three sources. First, it was pretty windy at 17 mph and this is a plane with a 20" wingspan. Second, a small mistake I made while modeling the channels for the push rods limited the throw I could achieve on the elevator and rudder. I think the CG I had on my first flight was actually probably closer to what I want since it was far more stable and I just couldn't get enough throw to compensate for it very well. Third, the wing loading is quite high. This makes it pretty fast, but landings are... interesting. Issue 2 should be fixable and issue 1 wasn't a problem with the plane, but issue 3 is something I'll have to live with. Adding some form of spring or TPU suspension to the gear should help a bit with making landings less bouncy.

Now for the good news. First-off the changes to make this work a fair bit better are easy to make and fairly minor. I expect to have the final version ready to fly in a week or two. Second, this plane is exceptionally easy to print and assembly. It's only a couple hundred grams of filament and can be assembled in an hour or two. While the motor mount needs to be ABS to deal with the heat of the motor (especially in Florida) everything else is standard PLA. The power system is also one of the cheapest ones available and sold under about a dozen different brand names. While very much not a trainer airplane, for someone with a ton of flying experience, it could be a good introduction to 3D printing RC planes if I can get all the kinks worked out.

Also, so far as my other modular planes, I haven't forgotten about them. The F-104 remains one of my go-to jets and I fly it pretty much every weekend. The modular jet trainer remains in development, I flew it again today and it's getting where I want it to be. Should have more updates on it soon. And finally, I am in the process of putting together CAD for a 6s thrust vectoring jet that will also use the modular system. As I add more designs to the library of modular aircraft, I'm starting to get to the point where I can start sticking random parts together and experimenting.

 

[Mr Man]

Just found this thread, What an awesome plane!

 

[L Edge]

@telnar1236
Read the section on landing especially 31-32.

https://carf-models.com/files/product/a1/d3/3d/carf_models_geebee_instructions.pdf

Some very good hints on what to do, especially about the rudder and how to use the elevator on landing. You did good on approach and remember what they say.
Our racing planes were the same way on landing. Remember, go fast and turn left for this is not a intermediate plane. You really need to get everything perfect to make that landing.
All you need is a little more practice.

 

[Piotrsko]

If I remember correctly, when Delmar Benjamin flew the latest incarnation, he flew it onto the ground tail high and technically didn't stall. Reportedly a handfull until it stopped. Not certain models exhibit different traits and you don't have brakes. Tail skid might help.

 

[Mr Man]

Definitely.

 

[telnar1236]

Just found this thread, What an awesome plane!

Thanks, unfortunately I never got it flying the way I wanted. The wing loading was just too high. I got it where it was reliably stable, but a 600-gram plane at this scale is just a little too much (and I like planes with high wing loading). The stall speed was about the same as my F-104 and the torque from the motor made it less predictable. The various redesigns I mentioned (redesigning the push rod channel, shifting the CG forwards, and increasing elevator throw) made it completely flyable and so long as the speed stays up it handles just fine. I also ended up designing in suspension into the main gear struts which helped a lot with the bouncy landings. I think the originals were just way too stiff which transmitted too much shock into the rest of the plane and catapulted it back into the air

Had I continued to develop the design, the gap would have been faired over. Another important change was going from a 1000 kv motor to a 1400 kv motor and down to an 8 inch prop from a 9 inch prop. It improved thrust while reducing the torque, and critically adding to the ground clearance. Plus, it looked more scale.

In it's current form it flies well and is totally controllable. Landings are fast but manageable and no longer bouncy. But it just isn't fun, in my opinion. While it is fully aerobatic, you need to watch out for the stall and the torque of the prop. In the end, I just like my fast jets better and when it did eventually crash again, due to some pretty bad turbulence and some careless flying on my part I didn't bother to rebuild it.

If anyone wants the STLs, it's an ok aircraft, and it looks at least as good as anything else I have built (in my opinion at least) but it is NOT an easy plane to fly.

 

[telnar1236]

@telnar1236
Read the section on landing especially 31-32.

https://carf-models.com/files/product/a1/d3/3d/carf_models_geebee_instructions.pdf

Some very good hints on what to do, especially about the rudder and how to use the elevator on landing. You did good on approach and remember what they say.
Our racing planes were the same way on landing. Remember, go fast and turn left for this is not a intermediate plane. You really need to get everything perfect to make that landing.
All you need is a little more practice.

Interesting. I ended up liking the 3 point landings better for this particular design. Might just be the limits of my skills as a pilot, but I found I was less likely to bounce or strike the prop doing that. But everything else in that manual seems completely correct. The fairly extreme right thrust in my design meant I didn't need the throttle to rudder mix, but even with that thrust angle the torque and p factor were very noticeable. I find it interesting that they mention the plane can rotate as soon as the tail lifts off because I had the same experience, somewhat to my surprise. If anything, keeping it on the ground longer than necessary made it harder to handle. Might just be a feature of the design.

 

[Mr Man]

If anyone wants the STLs, it's an ok aircraft, and it looks at least as good as anything else I have built (in my opinion at least) but it is NOT an easy plane to fly.

YES WE DO!!😃

 

[telnar1236]

YES WE DO!!😃

I'll put them together and post them then. I think I kept good enough control of my files on this one that I should be able to get them together pretty quick without needing to sort through and find what fits with what version and the Fusion 360 files are pretty simple to modify if anyone wants to keep developing it

 

[telnar1236]

YES WE DO!!😃

Here they are. Most parts are fully modeled and should be printed with 2 walls and 8% gyroid infill. The control surfaces should be printed with one wall and 5% cubic subdivision infill, and the control horns should be printed with 3 walls and 100% infill. The modular connector is common to all the modular planes I've designed (though the only other set of STLs I have released are for the F-104) and should be printed with 3 walls and at least 80% infill. See the F-104 PDF instructions for how they should be installed (https://forum.flitetest.com/index.php?resources/modular-f-104-70mm-edf-jet.428/). The infill and wall thickness of the dummy engine can be varied to achieve CG. I used two 40mm wheels with a 3mm hole for the main gear and some tiny little wheel I had sitting around on a paper clip for the tail wheel. Most of the air frame glues together and once everything is assembled, the rest goes together with a mix of M2x10mm and M3x10mm self-tapping screws (they should not have countersink heads). There are two sets of channels for control rods in the tail fuselage. The outer ones should be used since I never got around to deleting the inner ones.

This was the final power system I used with an 8x6 prop on 3s.

https://www.amazon.com/gp/product/B089YSW988/?tag=lstir-20

All the servos are the cheap blue plastic 9g servos available everywhere and they are hot glued in place in the wing and fuselage.

 

[Mr Man]

I’m a big fan of flash hobby motors

 

[Mr Man]

Even though I only own 1.

 

[L Edge]

Have you taken any flights of the G-Bee in calm air?

If you review video's of the pro's CARF version of the G-Bee you will see 2 different styles for takeoff and landings. Your style and the approach of a bipe. That is, a rolling takeoff where tail comes up, gathers speed and then lifts off (not full throttle) and where the landing is fly it to the ground till main wheel touch, it slows down and then you bring the tail down which eats up runway.
Then, some do it your way. By the way, you had cross winds and that caused your flip over. Nothing wrong with your style, some of the CARF representatives do the same if you review a number of videos. By the way, CARF planes are designed real well. I even have a CARF plane that was designed with Kevlar hinges.

I have reached a conclusion that your G-Bee bird doesn't need any more mods. This plane is ready as is. As you stated, this design is for someone with has quite a number of hours of flying, understanding the use of rudder, low wing and throttle management.
The Granville brother's designed this as a racer, not everyone can fly this one. Ask me how I know. You can fly it.

 

[telnar1236]

Have you taken any flights of the G-Bee in calm air?

If you review video's of the pro's CARF version of the G-Bee you will see 2 different styles for takeoff and landings. Your style and the approach of a bipe. That is, a rolling takeoff where tail comes up, gathers speed and then lifts off (not full throttle) and where the landing is fly it to the ground till main wheel touch, it slows down and then you bring the tail down which eats up runway.
Then, some do it your way. By the way, you had cross winds and that caused your flip over. Nothing wrong with your style, some of the CARF representatives do the same if you review a number of videos. By the way, CARF planes are designed real well. I even have a CARF plane that was designed with Kevlar hinges.

I have reached a conclusion that your G-Bee bird doesn't need any more mods. This plane is ready as is. As you stated, this design is for someone with has quite a number of hours of flying, understanding the use of rudder, low wing and throttle management.
The Granville brother's designed this as a racer, not everyone can fly this one. Ask me how I know. You can fly it.

Pretty much agree. I just want to reiterate how highly loaded it is though. 600 g with a 20 inch wingspan is scary

 

[Mr Man]

Yep.
Just wondering, what size build plate would I need to print this?

 

[telnar1236]

Yep.
Just wondering, what size build plate would I need to print this?

This will print on most printers including an Ender 3. I printed it on one with a 220x220x280 print bed, but you can definitely go a bit smaller. The smallest print bed I think would be possible without splitting some of the parts is 170mm W x 170 mm L x 240 mm H, but only the 2 wings, core fuselage, and tail fuselage come close to that size. Everything else will fit in a 120 mm W x 120 mm L x 120 mm H printer or smaller.

 

[Mr Man]

Thanks!

 

[L Edge]

Pretty much agree. I just want to reiterate how highly loaded it is though. 600 g with a 20 inch wingspan is scary

I am going to let you in on a secret. Bob G. of the Gee-Bee Brothers was a co-worker of mine and guess what? he was one of my 2 flight instructors as well for my 6 year old son. It is very interesting when he talked about those days of development of those planes.

Again, this plane requires a pilot who can bring it in fast, land at a high speed until the main wheels touch, and then bring the tail down to prevent bouncing. So, this isn't a plane to fly for everyone. You should note that in the plans.

 

[Mr Man]

Very cool!

 

[Mr NCT]

Bob G. of the Gee-Bee Brothers was a co-worker of mine and guess what? he was one of my 2 flight instructors as well for my 6 year old son.

Wow! How cool! It has always eaten at me that I lived just a few miles from Roscoe Turner and never got to meet him.