Hi all,
As I experiment a little more with APM in my Skyfun, I wonder if there's a suite of attributes we could use to compare airframes and get a good idea of where one airframe performs better over another. Just for starters, example attributes could be:
Performance
Stall speed
Max level speed
Max climb rate at flight-ready weight
Max climb rate at maximum weight
Efficiency
Max power draw
Power draw at optimum speed
Endurance at maximum speed and weight
Endurance at optimum speed and flight-ready weight
Physical
Dimensions
Dry weight
Flight-ready weight
Max payload
Avionics bay dimensions
Number of control axes
CoG thresholds (balance limits)
Each of the outputs of the above is then weighted based on a bias of vehicle requirements (eg: Speed vs Endurance vs Payload) and you end up with a rank for each airframe.
These quantitative attributes could be supplemented with qualitative data from users (eg: Beware tip-stall...! or Suitable for belly-mounted camera).
I'm not sure how to implement this - Perhaps an Excel or something, but am interested in people's thoughts...
Replies
[quote]
Performance
Stall speed
Max level speed
Max climb rate at flight-ready weight
Max climb rate at maximum weight
Efficiency
Max power draw
Power draw at optimum speed
Endurance at maximum speed and weight
Endurance at optimum speed and flight-ready weight
Physical
Dimensions
Dry weight
Flight-ready weight
Max payload
Avionics bay dimensions
Number of control axes
CoG thresholds (balance limits)
[/quote]
Instead of stall speed you could have stall constant and it be understood the actual stall speed is its weight * stall constant.
Instead of max speed there could be a max speed constant that can be used in a simple formulat with motor thrust to give max speed.
Continue doing the rest for the other stats.
I have already done a physical airframe spreadsheet that I update when people post up information or an airframe they are interested in. That way all the data can be verified and proven with manufacturers specifications not peoples choices of servos, motors etc thereby making the effectiveness skewed.
As efficiency and performance is dependent upon personal preferences you would end up with an enormous spreadsheet just for an Easystar let alone anything else.
Rupert, As part of my mission to (possibly) use the Skyfun as a high-altitude glider, I'm doing some relatively simple math modelling of the airframe at high density altitudes to see at what altitude it will begin to fly, what the terminal speed might be etc. At the moment I'm using assumed values for stall speed, mass, Cd/Cl etc, but if you already have some data from your Skyfun that you're prepared to share, I'd really appreciate it!
Andrew
Some if not most of the attributes you listed do not have to do with the "airframe" or which type you choose in general. There are a lot of different combinations of airframes that will fulfill the needs that you probably want. Two things that would affect most of your attributes is the airfoil that is chosen and the prop/motor combo that you choose. Besides that the airframe that you choose will mostly just affect the drag and handling of the airplane. Of course though, CoG would have to be worked out as you are designing it I would expect.
There are some more criteria that do not refer just to the airframe as well, such as dry weight, that would depend on building materials. I will give it to you though some airframes do need to use more material than others so that would make a difference, but construction materials does change the weight. ie. balsa construction vs foam.
- Jeff
Some sort of visual database like this would be of infinite use, especially to newbies like me. I've just spent a few hours looking over many blog posts and questions, before stumbling upon this. I can confidently say that a lot of questions could easily be answered with a resource indexing platforms and their characteristics.
Perhaps using something like Open Flash Chart (http://teethgrinder.co.uk/open-flash-chart/) to visualise the database (built by community-input content) and compare models could be a way forwared?