RE: Designing a new pattern model
 

This really impressed me, Keep up the great work!!!!!!

I know I am interested!


Ernie

RE: Designing a new pattern model
 

Yea I can't wait for the next post....

Oh yea.

I want one........!!!!!

RE: Designing a new pattern model
 

what aerofoil did you use?

RE: Designing a new pattern model
 

I used a NACA 64 A 012, which is a laminar airfoil. As far as i know, it is used on many pattern models these days. I'm not sure about the reasons why it was initially introduced, but i can take a guess why it is so popular.

If you look at the pressure distribution of a regular airfoil (like NACA 0012 for example), you will see that the pressure is very high close to the leading edge and drops quickly towards the trailing edge. This means that the resultant lift force is located closer to the leading edge and far away from the center of gravity, meaning that the stab needs to generate more lift to counter the moment created by the wing lift force.

For a laminar airfoil the pressure is more equally distributed along the chord, meaning that the resultant lift force will be placed closer to the center of gravity and the moment created by the wing will be smaller. This way the stab needs to generate less lift and can be set close to 0 deg. incidence; the model will behave more "neutral" and probably won't need too much trim over a large speed envelope.

RE: Designing a new pattern model
 

The lift center of a symmetric foil is always on 25 % of chord, with NACA 0012 and 64A012 too. The difference in pressure distribution affects on profil drag.

RE: Designing a new pattern model
 

The lift center position is not set in stone and it changes not only from one airfoil to another, but also with the angle of attack. I attached 2 images showing the pressure distribution for NACA 0012 and NACA 64012 and even if the difference is not as big as i remembered, obviously the position of the lift center is not identical.

Anyway, i could be right or i could be wrong about this - it doesn't matter too much. The airfoil has been used and it works well and according to other designers, the wing shape is a lot more important than the airfoil.

RE: Designing a new pattern model
 

Hi Alex

You do awesome job.
I agree with your choice about airfoil. Oxalys, Integral, mines and others have NACA64012
Regards

RE: Designing a new pattern model
 

Hi Alex,
I hope you are well and may I wish you a happy new year.
Looking good so far.
It's a lot of work isn't it.
What weight is the Fuz at this stage ?

Brian

RE: Designing a new pattern model
 

Am I right in thinking it is a wing root to wing tip ratio of between 2-1 and 3-1?

RE: Designing a new pattern model
 

The wing is 212mm wide at the tip (measured at the tip of the aileron) and 460mm at the root (measured along the side of the fuselage), which gives a ratio of 2.16.
I think 3:1 would probably be too much.

The weight of the fuselage including the rudder, canopy and cowling is 1250g. I know it's probably on the heavy side, but it's the best i could do with regular balsa sheets. The canopy and cowling are a little bit heavier than i expected (110 and 115g ) but i'm going to use them anyway. Since it's my first 2m model, i have no idea about the final weight at this stage. There are a lot of experienced builders here, so i'm looking forward to hear your opinions about this.

RE: Designing a new pattern model
 

I've heard on here that with an electric setup you need to aim for a fuselage and wing weight of under 2500grms, this should allow you enough room for batt's esc motor and radio gear.

I also read on another thread that wolfgang matt's Amethyst is over the weight limit with 5000mah batts so they have them for practicing and 4350 for competition

RE: Designing a new pattern model
 

The reason has nothing to do with the resultant lift force.

It's called laminar because the flow is laminar in most of its surface, upper and lower. The reason ,well the center of pressure is located backwards, so the point of maximun speed fo the air is backwards too, and the turbulent flow that is generated after de C of P affects the wing in a smaller area than the non laminar airfoils, where the turbulent flow is generated nearer to the leading edge.

RE: Designing a new pattern model
 

Hi Alex,
Yes getting on the heavy side.
1100 to 1250 glassed and painted would be good. My Oxai Ventura is 1120g painted inc the rudder.
You mentioned waiting for glass cloth @25g for finishing. That will take a lot of resin to fill.
I would sand & seal the balsa first, get 15g cloth and use lots of microballons. See BM3 threads here.
If that gets much heavier you will not have a model that reflects the potential in your design.
Also go to extremes to get light wings and tails to compensate some.

RE: Designing a new pattern model
 

Hi Brian,

Thanks for the advice. I'll do my best to keep the wings and tails as light as possible, but the fiberglass cloth is already ordered and 25g is the lightest i could find at a reasonable price. Anyway, it's meant to be a cheap model and competing with Oxai models regarding weight would be too much to ask.

RE: Designing a new pattern model
 

Hey Alex....

I just finished a [link=http://www.rcuniverse.com/forum/m_6875170/mpage_22/key_/tm.htm]SebArt AngelS 50[/link] and she has lightning holes in the fuselage. And an air dam located at the bulkhead near the trailing edge of the wing. Also 2 exit holes in the bottom.

http://i459.photobucket.com/albums/q...r/DSC00753.jpg

http://i459.photobucket.com/albums/q...r/DSC00754.jpg

http://i459.photobucket.com/albums/q...r/DSC00755.jpg

http://i459.photobucket.com/albums/q...r/DSC00757.jpg

RE: Designing a new pattern model
 

Lightening holes would only work for a film covered fuselage, not a glassed one. The air dam is already installed inside the fuselage and i think it's visible in some of the photos. I will cut the exit holes later.

RE: Designing a new pattern model
 

how much did the laser cutting cost?

RE: Designing a new pattern model
 

Hi Alex

Just to share with you my little experience.
On my wooden fuse (similar volume as your own), before putting glasscloth I put dope on balsa. Then I put 25 g glasscloth with resin. Weight with resin after sanding is about 100 g.
But to get good finishing it's need to put primer. So primer is a litlle heavy 60 g. Paint is 40 g and clear coat is 40 g. 240 g total weight of finishing.
I think to get lighter is to replace glasscloth and resin by "japan paper" with dope. It's less resistant but you 'll have no problem with electric motor because less vibrations than thermic motor.
In this link see pages 25 to 27, finishing with silk, talc and dope (very long to do) : http://translate.google.com/translate?u=http%3A%2F%2Ff3a.sakura.ne.jp%2Fradioc ontroll%2Fspecial%2Fmake%2Faddction%2Faddction_01. html&langpair=ja|en&hl=en&ie=UTF-8
Claude

RE: Designing a new pattern model
 

Thanks Claude.
It looks like the Addiction is about 125g lighter than my model at this stage. It's not too bad, but i have to consider the fact that the electric setup is heavier.
I put dope and talc on the rudder this morning to see how it goes and it turned out fine, but the mixture was a little too thick and sanding it took some time. What was the dope : talc ratio for your mixture? I don't know exactly what dope is, so i used nitro laquer instead. I would also like to know if i can use this mixture for things like canopy fitting, where the layer needs to be a little thicker or is it better to use epoxy+ microbaloons?
I will look for "japan paper" here, but if i won't be able to find it i'll have to use the 25g fiberglass cloth.
The approximate weights for each finishing step is very useful.

Foofydoo, the cost of laser cutting was about 200$.

RE: Designing a new pattern model
 

Hello Alex

Dope with talc is a mixture of "cellulosic liquid" with talc http://www.aeromodeles90.com/product...roducts_id=505
For getting thickness I use a very light mastic easy to sand like that
http://www.topmodel.fr/product_detail.php?id=7418
See pictures for example. I bought in "material shop" because it is cheaper

RE: Designing a new pattern model
 

Hi Claude

I found a similar light filler at a hobbyshop here in Romania: http://www.sierra.ro/Chit-bicomponen...ic-p2976p.html
My mixture of nitro laquer and talc seems to be working so i'll continue to use it.
Thanks again.

RE: Designing a new pattern model
 

I didn't know this airfoil was popular and successful.... I am s'prised to learn this.....
Usually, model airplane aerodynamics don't like full scale airfoils with persistant laminar flow....
has to do with adverse pressure gradiants being very aggressive and laminar bubbles persisting........

I would bet a $5.00 gift certificate to McDonalds, the surfaces of the wings on these moderls is rough enough that turbulant flow, (Transition), is instigated well ahead of the min Pressure/onset of the adverse pressure gradient.....

Have you calculated the max and min Reynolds number you will encounter with a pattern plane???

RE: Designing a new pattern model
 

The wing surface is actually very smooth, being either film covered or glassed and painted. Some experimented the use of turbulators, apparently with good results. There are a few posts about it in this thread: http://www.rcuniverse.com/forum/m_92...tm.htm#9224491

The speed is supposed to be constant in pattern flying, but i'm not sure how fast our models are. IIRC for a speed of 100 km/h, the Reynolds number is about 760 000 for the wingroot airfoil.

RE: Designing a new pattern model
 

I think that we can go up to Re 350.000 with no problem keeping the laminar properties; there are many foils that arrives even to 120.000 being still laminar (see Selig ones). Turbulator could help also but the real answer can be get only from a wind tunnel test...
I still don't have any answer the the question I made in http://www.rcuniverse.com/forum/m_92...tm.htm#9224491 so I'm going back to the university in order to give back my aernautical engineer laurea... what a pity.
But (now seriously again), I think that several thingamajigs (as the ones of Mr. Silvestri) contributes only to get the stall condition while snaping or other stalling maneuvers - so the helps to provoque the stall. The turbulator has another different scope which is to energize the boundary layer.
Regarding to the flight speed; there is a person in norway or sweeden that achieved several interesting experiments on F3A technologies; basically he mounted a lot of sensors on several planes in order to measure speed, servor torque and other issues. Now I don't remember who is he or how to find him but he has a pretty nice site in english too.

BTW Alex; can share me the engine model? I work with CATIA V5 so a *.stp or *.igs model goes well. Thanks on advance.
Guille

RE: Designing a new pattern model
 

I think it's Ola Fremming's website: http://www.ofremmi.info/index.htm
I found a lot of interesting servo tests but nothing regarding flight speed.

I sent you a PM regarding the YS 3D model.