AcroWot Built up wing

[kc]

I think that Martyn's costings may have put people off cutting their own balsa ribs. Martyn said 40 pounds for laser cut compared to 8 sheets of balsa at 2 pounds. That makes 16 pounds. However having measured up I find that at least 8 ribs can be cut from a 4 inch by 36 balsa at 1.14 pounds. I am not sure the exact number of ribs used but i think it's around 20 so two and a half sheets would be needed. ( possibly less if the ribs are interleaved to make full use of the balsa )
So it's about 2.85 pounds if you cut them by hand from Balsa Cabin wood.
So dont be put off cutting ribs by hand - its quite quick even for a tapered wing. For a straight wing it's even quicker by bolting a pack of ribs together and planing to shape.
But did the built up wing turn out lighter than the foam? I dont think so if you compare it to the weights of my Acrowot wings! ( there are 3 servos in Martyns only 1 in mine )

[simpson j]

Hi

downloaded dx files for the ribs , when i tried to open the files all that happened i get a message saying 'error 21051 unknown product code' can anybody advise please?

[Martyn K]

sj - Just downloaded it here OK and the file opened OK in Draftsight.

kc - fair comments, I never said that it would be cheaper, I just needed something quick and convenient and strong - these ribs are definitely stronger than a balsa equivalent - although they are slightly heavier.

There are 20 ribs all in, ranging from 10" long down to 6.5" long, the thickest are just over an inch thick.

However, you would need additional ply ribs at the centre and additional reinforcement where the servos are mounted - this adds a bit of complexity but the wing is simplified because there is no undercarriage mounting to worry about.

Horses for courses - it is what suited me.

There is nothing to prevent anyone exporting the file to pdf and cutting ribs directly from this, they may save about 30 grams or so but this is not worth worrying unduly about for a model this size with a 61 at the front. They could even request the cuter to cut them from 3mm balsa, however the file would need to be redone to achieve this. It was something that I considered when I did the original export. Profili isn't especially efficient at saving wood, and this is compounded that the TE and sheeting need to be manually removed. Not a huge task and the ribs can be moved about if required.

Martyn

[Martyn K]

The 'How to Create a Use Once Plan" is here

Hope that's OK.

Martyn

[IanR]

I opened the ver 3 file in TurboCad. OK.

Ian

[kc]

Martyn, there is a growing trend especially amongst younger modellers to think that it is essential to have laser cut ribs to build a model. If the idea also got around that it was extremely expensive to cut them yourself with a scalpel then this might hinder potential builders. Hence my comments.
Clearly everyone does what suits them best trading off time for money or vice versa. And of course whatever process they enjoy most might affect the chosen method of CAD CAM, foam & fibreglass or scalpel into balsa. As you say its what suited you. For me it would be Profili then print onto paper and stick onto balsa and a relaxing hour with the scalpel.


Actually I think you meant " the thickest are TWO inches thick" and that's what I allowed for in my costing.

[Martyn K]

Good point. I write this stuff to encourage people, not put them off. Normally I would cut them but at the time i was wrapping up the flea fli and doing some essential maintenance on the astrohog. Me excuse and i am sticking to it.

[Martyn K]

Well - just 2 months after finishing the wing, I managed to get chance to try it.

Bear in mind that the same time I was testing the wing, I was also testing a new engine.

There were no significant trim change with the new wing, elevator trim settings were the same as they were before which is a good sign. With the flaps in the 'normal/level' position, the model behave much like an Acrowot although the new (SC61) engine was not pulling as well at the ST61 I originally had in there.

Putting the flaps into 'Snap' mode - ie coupled with the elevator made the corners in a square very very sharp, So sharp I was wondering what sort of load was being placed on the wing. However, it held together.

The combined Crow and landing flaps mode was a little inconclusive. I slowed down and switched them in at about 200 feet. There was quite a distinct pitch up, but nothing unmanageable. The model could be flown very slowly, but when it tip stalled it wasn't taking prisoners. I didn't try it for landing, I am going to reduce the throws slightly before trying again. I also want see how effective they are in a down line.

So.. they worked, nothing fell off and nothing got broken. I only managed to get two flights in and the first was interrupted when the silencer came loose but it is certainly worthwhile experimenting further.

BW

Martyn

[mark palmer]

I can see this is an old thread but dies anyone still have the dxf files and plan for the built up wing? Unfortunately the link provided doesn't work....

all the best

Mark

[Nigel R]

See here for pdf version:

 

https://outerzone.co.uk/plan_details.asp?ID=13085

[kc]

Mark, welcome to the forum.     The notes on the Outerzone KillerWatt files suggest some problems -  it might be better to send a Personal Message to Martyn K as his link does not work.  MartynK is a very helpful forum member and I reckon he will supply his wing data if it's still to hand.