My Lidl RC conversion the 'Stumpy', finally ends up in the bin, but why?

[Bonzo Moon]

My Lidl Stumpy RC conversion had yet another redesign after a few too many fails. Here's the story and why it has gone to the great RC plane graveyard in the sky.

[SIMON CRAGG]

Well done Bonzo.......always enjoy your stories!

[Bonzo Moon]

2 hours ago, SIMON CRAGG said:

Well done Bonzo.......always enjoy your stories!

Thanks mate.   I found it quite interesting and maybe useful to share my learning experience! 

[SIMON CRAGG]

Thought this might appeal to you.

 

Thunderbob.

 

The original plan was for a 70cm Depron model.

 

 I turned it into a 1100mm span Foamboard cartoon scale job, three sheets of board = £15.00.

 

Interesting laminated three piece wing, resulting in a wing "section".

 

AUW LB4.

[MattyB]

22 hours ago, Bonzo Moon said:

My Lidl Stumpy RC conversion had yet another redesign after a few too many fails. Here's the story and why it has gone to the great RC plane graveyard in the sky.

 

 

In the section of the video where investigate the CG position, you talk about plank and swept flying wings interchangeably. They are aerodynamically very different, so I wouldn't put much weight behind the calculation from the swept flying wing calculator. This may be of interest, though there is quite a lot of maths involved!

 

https://www.mh-aerotools.de/airfoils/flywing1.htm

 

What you have there is very definitely a plank - there is almost no sweep at the mean chord point, and based on your build video you did not put any twist into the tips. Based on that you should probably seek to stabilise it with a more forward CG and reflex (assuming you are not using the elevator any more - I could not tell whether your flight videos were with or without that operating, sorry). Even then, I suggest you investigate whether you have some wash-in that was introduced by the "cut and shut" when you removed the dihedral during the build.

[Bonzo Moon]

11 hours ago, SIMON CRAGG said:

Thought this might appeal to you.

 

Thunderbob.

 

The original plan was for a 70cm Depron model.

 

 I turned it into a 1100mm span Foamboard cartoon scale job, three sheets of board = £15.00.

 

Interesting laminated three piece wing, resulting in a wing "section".

 

AUW LB4.

 Nice one Simon, thanks.  Any pics of your creation?

PS  I love foamboard! Cheap building fun.

[Bonzo Moon]

1 hour ago, MattyB said:

 

In the section of the video where investigate the CG position, you talk about plank and swept flying wings interchangeably. They are aerodynamically very different, so I wouldn't put much weight behind the calculation from the swept flying wing calculator. This may be of interest, though there is quite a lot of maths involved!

 

https://www.mh-aerotools.de/airfoils/flywing1.htm

 

What you have there is very definitely a plank - there is almost no sweep at the mean chord point, and based on your build video you did not put any twist into the tips. Based on that you should probably seek to stabilise it with a more forward CG and reflex (assuming you are not using the elevator any more - I could not tell whether your flight videos were with or without that operating, sorry). Even then, I suggest you investigate whether you have some wash-in that was introduced by the "cut and shut" when you removed the dihedral during the build.

Very interesting article you linked, thanks.  Reflex was mentioned by the guy I met at the strip. Definitely a combination of factors were preventing a successful flight for that creation. It's all a good learning process! 

[SIMON CRAGG]

Here we are Bonzo...........

[Andy J]

What a nice looking build Simon. Can you share how you obtained the finish on the model. Also the aileron servo looks an interesting arrangement.

[Bonzo Moon]

2 hours ago, SIMON CRAGG said:

Here we are Bonzo...........

 

 

Well done, that's amazing.  I'm going to have a go at a simplified version in foamboard. 

[SIMON CRAGG]

2 hours ago, Andy J said:

What a nice looking build Simon. Can you share how you obtained the finish on the model. Also the aileron servo looks an interesting arrangement.

The original Thunderbob was a 70cm Depron lightweight model.

http://rc-plans.com/catalog/item432.html

I increased the plan to 1100mm wingspan, and constructed it out of 5 and 10mm foamboard from Amazon.(£25 for 5 sheets delivered).

All edges shaped, filled and rubbed down.

Used a 240v and 3s Lipo powered glue gun throughout.

It was painted by hand in Farrow and Ball green emulsion I got from the local dump (where most of my modelling paint comes from).

One coat of hand applied, water based satin polyurethane varnish (again from the dump).

The Ailerons are controlled by two new mg 17g servos, with plastic spoons cut in half and painted black to provide suitable covers.

Control surfaces are hinged at the top only by wide reinforced tape.

4s powered, weight circa Lb4.

It could be constructed in a week, but as I was enjoying it so much.............took a month!

 

[Andy J]

Thanks Simon, love the idea of using plastic spoons for servo covers.  That rc-plans site that the original plan came from is also very interesting so will will have a good browse of its content today.