Suggestions for a very simple aircraft design to swing out of an arm rotating on top of a pole

[Transisto]

I'm helping run a STEM (science, technology, engineering and maths) expo for school children in both primary and secondary schools in my neighbourhood. We have plenty of tabletop displays but the hotel balloom has a very high ceiling and it seems such a shame to waste all that space. 😉

I have some window winder motor gearbox units that run at 30 RPM and I thought it would be nice to mount these on top of poles and have some simple models swinging around - see the simple sketch. I have the system working just using a washer on the end of a string and it has potential.

Could someone post a sketch of a simple aircraft - preferrably made of flat card or similar. I have a laser cutter so I can do complex 2D designs but that also means that I could do inner structures for the wings and put a good profile on it.

I'd accept any tips on where to attach the string and adding a little weight if required. What would be a good "string" to use to minimise wrapping around the pole or general tanglement?

 

Many thanks.

Edited January 24, 2023 by Transisto
Typo.

[Simon Chaddock]

It depends on how much time you have but have you considered powered RTP (Round The Pole) flying.

A simple plane with a small brushed motor. The power is fed to it through two fairly thin wires using a simple Scalextric type hand controller.

The planes is truly flying so it has to take into account the basic laws of aerodynamics.

This video from the University Bristol demonstrates the principle.

If you search Google there are several companies that can supply all you need.

Just a thought.

[Transisto]

Hi, Simon.
Yes I had found that on my research but I'm trying to keep it simple and use stuff that might inspire young engineers of the future. I'm an electrical engineer so that part of it wouldn't scare me but would add expense that the kids might not be able to afford. So far the only specialty item is the motor-gearbox and they're readily available from a breaker's yard.

Is there any reason what I'm proposing is a non-flyer?

[Robin Colbourne]

When I was at college, our lecturers used to impress on us RTFQ - Read the _ Question. 
Reading the  question here, it is requesting a design for a simple model which will reliably fly like a whip controlled model.  I.e. no motor or elevator control, just dragged around by the arm on the rotating pylon.
To achieve this reliably the model needs to be:

1. Stable
2. Robust

Stability comes from having a small amount of longitudinal stability, AKA a wing positive incidence and a bit of negative incidence on the tailplane.  The model also needs to not dive into the circle.  To achieve this, have a small weight on the outboard wing tip to offset the drag of the line, and a line attachment on the inboard wing far enough back that the nose of the model points slightly out of the circle.

Robustness comes from having depth in the middle, tapering off towards the extremities.  Something like a profile Grumman Panther would fit the bill (have the wheels up).  For extra strength at the front, the fuselage could be given both depth and width as seen on indoor radio controlled shock flyer models.  The tiptanks will give a bit of strength to the wingtips and also act as skids :

[Transisto]

Thanks, @Robin. Your understanding is correct and "whip-controlled" may be the search term I'm looking for. A quick search has shown up Whip-power P-84. Am I on the right track?

This one seems to have elevator control so that stunts can be performed. How would I trim this for fairly level flight?

 

 

[Brian Cooper]

Attach the model with a piece of thin piano wire. . That will stop it from wrapping itself around the pole. 

[Transisto]

I wonder if I fastened the control wires to my swing arm in a vertical fashion could I get it to self-regulate? If the plane goes down the bottom wire would go slack and the top wire would turn the elevators up. As the plane comes up the top wire would go slack ...

[Trevor]

That could work. We used to teach control line flyers by saying 'point the handle where you want the model to fly'. With the model suitably trimmed, it would adjust its altitude to equalise the length of the two lines. It always amused me that the best 'grown up' C/L pilot in my schooldays flew with the handle the other way up (down line attached to the top). When asked why, he would simply say that that was the way the lines were when he picked the handle up for his first flight. 

[Denis Watkins]

All good suggestions here above. In my last life I was a school teacher and we evolved to the powered pole from free flight.

Like the flat based gliders from the BMFA today, we 1st designed, trimmed and flew low cost gliders from hand launch.

They were then stabilised by 2 strings from 2 points from the powered pole, with small outer wing tip weight as suggested.

Most of the models actually flew well as opposed to some being dragged around the pole.

 

[Robin Colbourne]

5 hours ago, Transisto said:

Thanks, @Robin. Your understanding is correct and "whip-controlled" may be the search term I'm looking for. A quick search has shown up Whip-power P-84. Am I on the right track?

This one seems to have elevator control so that stunts can be performed. How would I trim this for fairly level flight?

 

 

Transisto, That P-84 looks ideal. 
Having a working elevator will add complexity and unreliability.  Simply have the leading edge of the wing about 1/16" higher than the trailing edge, (or the opposite way round with the tailplane) and  make one elevator a trim tab, adjustable on the ground.  The thicker aluminum takeaway trays or metal cut from the top of an aluminium fizzy drink can is ok for the 'hinges'.  Thin enough to bend, thick enough to stay where you bend it to.  If you cut them in a very slight hourglass (egg timer) shape, they will bend between the surfaces rather than getting torn off.  Roughen them with emery, degrease with meths or rubbing alcohol and stick with epoxy or cyanoacrylate.

'The Control Line Aeromodeller' from page 12 in 'Trimming Procedures for Stunters', gives details on trimming control line models to fly straight and stay where you want them. Its aimed at advanced aerobatic flyers, but the info in the diagrams is in many cases equally applicable to a whip power model.  The Control Line Aeromodeller  

Edited January 25, 2023 by Robin Colbourne

[kc]

It might be worth asking if a local model flying club has anyone who can assist with this aspect as it's easy for experienced aeromodellers to get this right.   A list of clubs is on the British Model Flying Association website.   BMFA is also very keen to promote aeromodelling to youngsters so they have the BMFA Education Programme. .   They also sell simple kits for youngsters like the Centenary Dart at £3.50 or a capacitor powered free flight model called Centenary Rookie.

Edited January 25, 2023 by kc

[kc]

My thought is that todays youngsters would want something they could control by RC and so an electric plane running round the pole with it's own motor and inbuilt battery with simple RC would be better than something swung around by a pole mounted motor.  

[Transisto]

Quote

Thanks, @kc.

As explained in the original post the purpose is just a simple display at a science expo. I'm trying to get them interested in STEM rather than flying itself. I'm in the north-west corner of Ireland so I could find it a bit more difficult to find a local club!

Quote

 

 

 

[Transisto]

10 hours ago, Robin Colbourne said:

Having a working elevator will add complexity and unreliability ... 

... The Control Line Aeromodeller  

Thanks, @Robin Colbourne. The simpler approach is much more sensible for this application.

I cut a P-84 out of 4.5 mm "Foamex" equivelant (foam board clad with light plastic film). It caught fire on the second pass of the laser so I extinguished that and finished the cut by hand. I got enough informaton from the linked article to balance it up well enough to fly on my motorised whip arm. I've some further work to do but I'm off to a great start.

 

One question for now: the wings now have square leading and trailing edges. The leading edges are straight so I could glue on a drinking straw to reduce drag. Thoughts?

 

I'll report back over the weekend.

[Trevor]

9 hours ago, Transisto said:

One question for now: the wings now have square leading and trailing edges. The leading edges are straight so I could glue on a drinking straw to reduce drag. Thoughts?

Sounds like an excellent question to put to the kids! Time a few laps, add the straws and repeat.

[Transisto]

@Trevor, thanks, but there are two problems with that. 

1. I won't have time!

2. The speed is determined by the central motor. The planes are unpowered.

[MattyB]

12 hours ago, Transisto said:

@Trevor, thanks, but there are two problems with that. 

1. I won't have time!

2. The speed is determined by the central motor. The planes are unpowered.

 

The speed will not be determined by the parameters (Kv, input voltage etc) of the central motor alone. The load (in this case the drag of the aircraft) will have an effect too. A good related example would be changing the prop on an electric model - increase the diameter and/or pitch and keep all other variables the same, and RPM will dip even though the motor will be trying to turn at the same RPM as before. 

[MattyB]

On 25/01/2023 at 19:32, kc said:

My thought is that todays youngsters would want something they could control by RC and so an electric plane running round the pole with it's own motor and inbuilt battery with simple RC would be better than something swung around by a pole mounted motor.  

 

I think you'd probably have an entertaining session or maybe two doing this, but based on expereince with my Cubs, yes - if you want to sustain their interest, they will want to feel a degree of control over the aircraft. Anything less and they are likely to drift away pretty quickly...

[Transisto]

Guys, it's only a gimmicky display. It's 4 m up in the air so there is no oportunity to interact with it this year. I've also got to make a 60 cm diameter rotating Earth globe with geostationary satellite out at 2 m; a 150 mm moon to be positioned at relative scale about 18 m away; stands on refraction of light; polarisation (why do fishermen wear sunglasses but pilots don't), colour perception and the human eye; physics of sound with tubular bells, electric guitar, sine, square and triangle-wave generation and display on oscilloscope; and several other things. If I can get the planes to fly in a circle for two hours at a time in the morning and afternoon then it's a win!

 

Thanks for all the interest and suggestions. @Robin Colbourne gave me the correct terminology and a practical setup reference which saved me a lot of development time. For me, "pretty good" will be good enough.

[Steven S]

On 25/01/2023 at 17:20, Transisto said:

One question for now: the wings now have square leading and trailing edges. The leading edges are straight so I could glue on a drinking straw to reduce drag. Thoughts?

 

I'll report back over the weekend.

The Whip Power P-84 design calls for a rounded leading edge as per the last paragraph in the article:

 

Cut both the wing and tail surfaces from fairly soft light 1/8 balsa sheet. Sand all surfaces to a streamlined section.

 

 

[Robin Colbourne]

Transisto, good luck with the models.  If you do want to make the models more ding resistant, adding thin bamboo barbeque skewers to the perimeter would beef up the leading edges and around the nose of the fuselage.  They can be formed to curves over a candle and then glued on with PVA.  Taper the ends away to nothig, otherwise the sudden change in strength will create a stress point.

Please report back with some pictures and how it goes.  😀