Own Design Aerobatic Aeroplane

[Concorde Speedbird]

Good afternoon,

I have always wanted to design my own aeroplane so I have done so. It's a low wing aerobatic aeroplane (Extra- Edge sort of thing) that is 45" span. The plans are drawn and keeping it light has been the main priority. It has not yet got a name.

Initial progress will be slow due to exams but I'll try and get a bit done here and there. It is mostly cutting stuff out initially. Here are the fuselage sides and yes, the lower rear is inspired by the Chris Foss aeroplanes.

It is worth noting that Peter Miller's book about designing model aeroplanes is superb and has been of great use to me in designing this one.

I have not forgotten about the Spitfire, that needs some more painting which is time consuming so I will probably finish that after exams.

CS

[FastFlyer Smyth]

It's refreshing to see a new design/build blog CS. I hope you can find the time to keep us up to date.

[IanN]

Sounds like a good project. Agreed re P.M.'s book.

Watching with interest

[Peter Miller]

Great to see that Concorde Speedbird, Keep at it.

Oh and thanks for the kind words.

[kc]

I think this is the book CS recommends. As you can see one of the copies is on sale for 999.11 pounds!  I expect you could buy Peter's personal copy for that and he would autograph it too !   For anyone with slightly less to spend you can buy it from Traplet for a modest 7.99 pounds. You might consider buying Peter's other titles from Traplet too

Edited By kc on 10/05/2015 19:52:41

[Geoff S]

I'm prepared to sell my copy for a mere £500 post free. That's a 50% discount, you know Like the model plane and perished rubber motor for sale at 4,500 euros Peter himself drew our attention to it's amazing what prices people ask. I assume none sell at that!

It is a very useful book and I, too, recommend it. I find it a useful reference even for mods I make to kits.

Interesting o see how Concorde S's design progresses. I sympathise over exams. I'm pleased to say, mine are half a century in the past

Geoff

[Tim Hooper]

CSB,

Good for you! It's always great to see somebody having a bash at an own design.

tim

[Concorde Speedbird]

Thank you. Peter's book is worth £999!

The last few kits I have built I have made lots of modifications to improve them (in my view). So I thought 'why not start from the ground up?' So I did, a set of plans were drawn, which I then proceeded to keep modifying!

On paper, I think it looks all right. It will be interesting to see the shape in full form once it is done, and of course the flying performance. I'll keep cutting bits out in between revision.

CS

[cymaz]

Amazon sell it for £7.99 plus postage as well as advertising it for £999 !

[Paul Jefferies]

FWIW a couple of tips....... I don't know what you have in mind to go in front of those fuselage sides but it looks as though your model is going to have quite a short nose. A short nose often means that the model ends up tail heavy and you have to add weight to the nose to achieve the correct Centre of Gravity. Be careful that you are not designing in a CG problem, don't be afraid to add an inch or so to the nose...... it can be considered as "adding lightness"!

For all models, and particularly aerobatic models, do ensure that the tailplane is big enough. For aerobatics you will probably want a fairly rearward CG which will tend to make it a bit sensitive in Pitch. Therefore the tailplane needs to be big enough to have "authority" over pitch. Also, if you look at an arrow or a dart with their flights at the back, a bit of extra drag at the back only helps to keep it flying it the direction it is pointed....... I have designed many aerobatic models and I go for a tailplane area of about 26% of the wing area.

Paul

[Peter Miller]

And just to confuse the poor lad. These day I use a CG position at 25% chord and a tailplane area down nearer 15%. That seems to work very well.

This does mean that alonger nose is needed,

[Paul Jefferies]

Peter, I think it may depend on what kind of aerobatics we are talking about. More or less anything can be made to fly but when you DESIGN a model you try to design in certain characteristics........ For general club type "chuck about" aerobatics...... a loop here, a roll there and sometimes even turning it upside down (), you can get away with all sorts of things and as long as it flies that is all that many people want. However if you set out to design a model to do a particular job and fly in a particular way then that is when you have to consider how you want to achieve that and you design in certain features that will give the model the characteristics that you want. If it isn't quite right then you alter the next one...... May I refer you to a thread in the UKCAA section of this forum which features many aerobatic designs and my own contribution to that thread which shows the "development" of some of my designs........http://www.modelflying.co.uk/forums/postings.asp?th=78824&p=11

Admittedly that was all quite a few years ago but the principle has not changed........ I guess it depends on what you want the model to do and how you want it to respond to your commands. Personally I want a model that is smooth but responsive and so I can fly it fast or slow and it remains predictable. Sometimes you get it right and sometimes there is room for improvement.......

Paul

[Peter Miller]

True.

What I want from a design is a model that will be steady in flight and yet will do all the aerobatics that I want, the normal loops and rolls and inverted. Plus my favorites such as four point rolls, avalalanches , flick rolls and spins without ever turning round and biting one.

So yes, a really nice club flyer that will do averything that the average modeller wants but perhaps not a precision aerobatic model.

It is interesting that all my club mates like flying my models and they don'tmince words when I do get it wrong. From what I read a lot of other people seem to like my plans. So maybe I have the right formula for what the average modeller likes.

AS you say, it depends on what you want.

[Concorde Speedbird]

Thank you all for the input. I have been cutting out the parts for the frame of the tailplane and fin, there is not much to show so I didn't take any pictures. These components are built up and sheeted in thin balsa.

The aeroplane's layout is based around the Extra 300, which generally fly pretty well at RC size. It is a true low winger in that there is no fuselage running beneath the wing (like an Acro Wot) for simplicity. The nose is quite short to the engine bulkhead, but I am using a four stroke which makes the nose a fair amount longer.The battery can be stored in front of the wing if necessary, something I considered in the design phase. Behind the centre of gravity (and in front!) the structure has been designed with lightness in mind.

The wing is tapered with a straight leading edge, like an Edge 540 or Acro Wot, but not too much taper to try and reduce tip stall tendencies. The aerofoil section is a scaled down Wot 4 wing section because it gives good upside down performance and safe slow speed handling, hopefully Mr Foss doesn't mind since I won''t be selling the design. All control surfaces are large, the elevator and rudder with aerodynamic balance tabs. Suitable servos will be used. The tailplane (+ elevator) area is generous, again based on the size of the Extra's tailplane.

It won't be the most precise aerobatic aeroplane but I am hoping for good spin, flick roll and tumbling manoeuvre performance. Of course, being a design we will only find out if my ideas work when I fly it. It is quite exciting seeing something I have drawn come into fruition, and if it flies well then that will be quite an achievement!

CS

[Peter Miller]

Sounds very good.

IT is what design is all about. You design what YOU like. That is what matters.

Remember the old saying, if it looks right it will fly right...usually!

[Concorde Speedbird]

Thank you very much! I really enjoyed drawing the plans and the build is exciting. This is definitely something I am going to do more of.

CS

[Simon Chaddock]

CS

Just a small point but a straight leading edge and tapered tapered trailing edge does mean in effect your centre of pressure along the wing moves forward towards the tip. In effect the wing has a slight forward sweep.

Not usually a problem unless you load the wing sufficiently for it to flex significantly then there is a danger that the tips will increase their incidence slightly. Wash in when under load is not something you normally want.

On the other hand a tapered wing with a straight trailing edge has a slight aerodynamic sweep back which tends to wash out (and so 'unload' the tips) when it bends under load.

Designing wings is not only fun it is also very interesting.

Keep going!

[Peter Miller]

If using a "D" box with sheeting top and bottom and a spar web you will never twist the wing however hard you try. Even without the web it will still be quite stiff enough to avod any twisting.

[Concorde Speedbird]

Thank you again. Wing design is fascinating and something I am really interested in. I chose a straight leading edge partially for aesthetics and because the Edge 540 has it, one of my favourite aerobatic aeroplanes. The aerodynamic consequences will be discovered in test flights. It is almost tempting to do an Extra style wing as well!

Peter is right about the built up wing, but for this design I am going to hot wire cut a foam wing. I know some people don't like foam wings but hear me out! It is partially because it is cheap and my Dad has a hot wire cutter. I am not going to cover it in veneer or balsa but brown paper, with a GRP bandage in the middle (tapered off at the edges). We have a Wot 4 with a wing like this that my Dad cut and it is very stiff and very light, so I thought I would try it again for this design. The ailerons will be controlled by a centrally mounted servo and torque rods to reduce the weight out on the wing.

This is an interesting diagram. My wing does not have as much taper as the Edge wing.

Thanks for all of your input, I'll try and get the tailplane and fin constructed when I am not revising!

CS

[David Hardaker]

CS

Looks good so far. The Extra wing planform is the way to go.

I note you suggest using a centrally mounted aileron servo... For me, I'd go for a servo in each wing, especially if the ailerons are on the large side. No worries about installing torque rods which can be a faff. Also the linkages will be more rigid.

Keep going !

D

[Stefan Hafner]

Looks good CS, I'd agree with David, 2 servos are the way to go if you want to go for aerobatics, it'll give you the freedom to add differential and other mixes too.

You'll find the Edge style wing will be less prone to tip stalling as it is effectively a forward swept wing, but if you're not using too much of a taper that won;t cause any major issues anyway.

[kc]

The wing materials are unusual and using 2 servos might mean weakening the wing if they are mounted outboard. Mounting 2 servos in the middle might solve the problem though

There is at least one wing of similar foam covered in brown paper construction amongst.RCME designs -Tercel - and this used a shaped hardwood ( DIY shop moulding) leading edge as a wing brace. Only works for wings without dihedral though.

CS. Have you thought about doing some testing to destruction of a 'sample' wing to determine the load your wing design might cope with. Gradually loading the wing until it fails might produce useful data if done as scientifically as possible.

[Peter Miller]

I like the servo in the middle of the wing, this keeps the weight in the middle. Weight out towards the tips makes stopping ad starting rolls less precise.

However with a foam wing this is not so practical. On the other hand I do like to connect the pushrod well out on the aileron as this reduces any possibility of the ailerons twisting which reduces the throw out at the tips.

This does apply to strip ailerons especially.

[Concorde Speedbird]

Thank you all for the informative comments!

The problem with putting a servo in each wing is that I have to cut into the brown paper skin, and that is where the strength is in this wing design. Putting a servo in the middle means I can cut less out and that is where the GRP supports it too. The servo I will use has good torque, one operates 4 ailerons in one aeroplane I have done! The strength of this wing design has been proven by the Wot 4 we have done so I am not too worried about that. It is quite thick which will help. I will check when the wing is covered in brown paper though to make sure that it is sound.

Straight leading edge is still the favourite. From the top view it is not too dissimilar to an Acro Wot wing, maybe slightly more taper and bigger ailerons.

I have constructed the tailplane frame. The elevator balance tabs go around the ends of the tailplane which is why they are so square. This will be sheeted in balsa, which will obviously increase the strength a lot.

CS

[Simon Chaddock]

CS

"The problem with putting a servo in each wing is that I have to cut into the brown paper skin"

The answer is simple put the servo in before you skin it.

I know this always meets with shock horror "how do you replace the servo?" but I have had to only replace one 'in situ' out of the 72 I have in current use and some have been in for several years.

The other aspect is short direct linkage to a single aileron is much kinder to the servo, it does not have to work so hard and as a consequence it is much less likely to fail in the first place.

Just my two penny'oth.