Aerodynamics

[Gemma Jane]

Came across a useful web resource I hadn't seen before today:

AppliedAerodynamics

Enjoy!

[260 Flyer]

One of my favorite aerodynamics sites.

See How It Flies

[Erfolg]

Emma

I have had a look at the site, and it does seem that some technical, mathematical knowledge and interest is required.

 

An example is dimensionless groups, where Reynold Numbers and Mach numbers are presented.

 

A second example is Conservation laws, where continuity, momentum and energy are described in mathematical terms as intergrals.

 

Which are then combined/substituted to obtain further expressions.

 

It is a good site though, I will examine it further 

 

Erfolg

[Gemma Jane]

I should have sub titled it 'but put off buying a textbook' - unfortunately there is very litte aerodynamics without mathematics.

 

I was reading a model site last night where it was discussing aerofoil choice for models. The authors conclusion was simply stick to what you know works if you want to know more do an aeronautical degree. Funny thing is once one has one continues to stick with what one knows works. I thought some might find the site interesting though and be able to glean some things from it.

 

The Denker site is perhaps of more interest to those here, though any attempt to explain 'how it flys' tends to open an extremely large can of worms.

[Stefan Hafner]

Ah yes, differential and integral equations..........every aero students best friend 

 

I have to say, that sticking with what you know works won't always work.  As a project for uni we had to design a heavy lift model to lift as much as we could using and Irvine 40 for power.  If we'd just used what i know works from most models we would have struggled to compete, let alone get second place .  The setting angles that we had to use would have been laughed at by most modelers

 

 

 Odd looking plane i know

 

As it turns out we managed to lift a total weight of 10.5 kg using an Irvine 40

[Gemma Jane]

I know about that competition for the 'transport' model they run it in the States also, you did very well . There is always much room for better undestanding, I'm very new to what is and isn't known with models particularly regarding aerofoils and busy researching, for a particular applications such as lifting the maximum weight possible with a given power source, one can't avoid design. Seems like the whole sphere of knowlege surrounding low Reynolds numbers aerofoils is in its infancy, which is great for modellers as the potential for better aerofoils is vast. Yet from what I have found out so far apart from a advances in competition slope soarering models, there is only a handful of aerofoils in common use for models.

[Stefan Hafner]

What I've found is that a small amout of research was done for low reynolds number has been done, but the cost of doing accurate wind tunnel testing is very high and it's probably a case of not being able to justify the spending for most insitutions with access to wind tunnels.  The majority of data that I've found is from Universities, who will run it as projects for students I expect.

 

Trying to do calculations from basic theorems is theoretically possible but I wouldn't want to try it

[Pete Rieden]

Delft University have done quite a lot of work on low-Re aerodynamics, but one 6thing that comes out is that at the very low Re and Mach numbers the air is so "sticky"  that the difference between "usable" and "optimum" is much smaller than at higher numbers.

 

For this competition - were you allowed to gear the engine down to allow a usable prop to be driven with the engine nearer to its peak power? The stock Irvine 40 peaks on something like an 9-6 prop, which would be unsuited to the application, and a more suitable prop would see the engine producing probably no more than 60% of its peak output...

 

PDR

[Gemma Jane]

"Trying to do calculations from basic theorems is theoretically possible but I wouldn't want to try it "

 

Me either Stefan whenever I contemplate that I remind myself that Einstein failed with his 'high lift aerofoil' which was a total aerodynamic disaster.

 

What I'm interested in at the moment is flinging some foamies in the air with different aerofoils to see which I like and get a feel for them, a much more sensible approach 

 

Seems Illinois has a programme for student research on aerofoils for models, but I haven't found how to access much data as yet. Also found "Winfoil" which is an interesting shareware programme to aid model design, not sure what to make of it as yet but I've a 30 day trial to see if I can figure it out!

[Stefan Hafner]

Pete - we weren't allowed to use gearing so we ended up using a 10 x 5 prop, which was found to be the best from previous years in the competion.  This meant that a lot of people were running their engines lean and someone managed to damage their engine.

 

The low reynolds numbers were problem for us as we had to avoid any hysteresis efects, not ideal when flying low circuits with an underpowered 10kg plane.

 

Gemma, sounds like you'll be keeping youself entertained "researching" wing profiles

[Erfolg]

Now I have re-visited the site, I now think it is more useful than I originally thought. The concepts are explained quite well, although the formula and expressions provided are not simple, they do support the idea.

 

Regarding  aerofoil sections and reliable data, it is very useful to know that small variations can have profound effests on the sections performance. Knowing this encourages the search for the section that is least critical of fabrication errors. Rather than best lift/drag under particular conditions.

 

With respect to research, I think it is unlikely that there will be much undertaken at sections of less than say 200mm chord, until the milatary require devices to fly in this chord region, due to the tight funding criteria these days within universaties or private companies.  

 

As for the maths, I used to do this type of thing on my models, to keep me entertained/engaged at work, rather than suffering the tedium of just cranking the wheel. Of course, I never did anything remarkable, my models just looked much the same as all the other gliders.

 

Well done Gemma