Equations to Use?!?

[sligo565]

Hi all!

For my final year project/thesis I have to carry out an in-depth conceptual design study of a high-altitude (65,000ft), solar powered unmanned air vehicle.

The project includes a comprehensive survey of previously conducted research and emerging technologies that will impact future projects (e.g. light-weight solar panels, batteries).

The primary design parameters (i.e. size, weight, cruise speed, endurance, powerplant type, materials) also have to be determined. Please find attached a copy of my design.

I would greatly appreciate any help you can offer with setting of out the design parameters, such as primary data calculations etc. Below are calculations on how far i have gotten with the project:

Reynolds Number: 129,788
Wing Loading: 13.82 kg/m^2
Power Loading: 35 Kg/Kw
Aspect Ratio: 19.24
Taper Ratio: 0.45
MAC: 0.836
MGC: 1.196
Design Cl: 0.73

I have chosen the E423 of the eppler series due to its high lift properties.

Using software i found the following parameters:

CLmax: 2.253 @ 11 degrees
(L/D)max: 39.303 @ -2 degrees
V at (L/D)max: 18.45 m/s

My problem is that i dont know which equations to use for where!

I was going to attempt to find my Cd from the equation:

Cd= Cdo + K(CL^2)

where Cdo = 1/(pi A e)

But i found another equation showing:

Cd = Cdi + Cdo

and

Cd= Cmin + K(Cl-Clmindrag)^2

There was also another on how to figure out Cdo which im sure you all know...it contains Cfc and FFc etc...

I have also been having difficulty in finding the equations to calculate:

Cruise
Endurance
takeoff distance
max climb rate
cruise speed
endurance
range
Propeller Efficiency
Equation for Propeller Efficiency

Could anybody point me in the right direction on which equations to use? I have been having a huge amount of trouble finding Cdo

[Odysis]

G'day Sligo,

The range/endurance equation you're after is the Breguet range equation. It's not a simple, one line sort of thing; you must know your aircraft's drag polar, cruise altitude, prop efficiency etc.

How to estimate these factors should be covered by any aircraft design textbook. I've used Raymer in the past, but unfortunately sold my copy at the end of my degree. (Don't do that! You'll regret it later!)

Let us know how it goes.

[sligo565]

Thanks Odysis,

Ye i have basically all my values except for my drag polar...it is the pain in my arse!!

[sligo565]

Hi Fellas,

I came across what seems to be a brilliant software package to help calculate my L/D etc. It is called Javafoil.

I also got a lend of Anderson: Introduction to flight and on pg 388 and 390 he talks about the Cdo....the area on which i am stuck on!

Basically my question is this...on the attached graph is my Cdo equal to the blue line or the red line?!

[Odysis]

It would be the blue line, if that were the right graph to use.

Cdo is for the aircraft, not just an aerofoil or wing. HUGE difference. It appears you have a wing polar, which is a good start. It should a L/D of 33-35 though; probably not going to happen for the whole aircraft.

My memory is rusty, but the way Raymer estimates Cdo is by using a ratio of wetted to reference area, then comparing that to statistics of other similar aircraft. The details of all of this are lost to me in the annals of history.

[sligo565]

Thanks man,

Its been a constant thorn in my side for the past few days let me tell you!

I know how to figure out nearly all of the above equations now except for:

Endurance
Range

I think my problem is that seeing that im using Electric Aircraft what do i do with the SFC and Fuel Weight in these equations....do i make them constants (1)!?

[Odysis]

My initial thought would be yes.

If you use the differential form of the Bregeut eqn, you should be able to see a term that reads something like dFw/dt (fuel mass flow). Set that to zero. I think if you were to use any of the post-integral forms, you'd have to figure out which term is the one that determines mass flow rate; this can be a problem, as I've seen some which just has a "number" for jet fuel etc, and that's it.

What scale is this to be built at, and what lab equipment do you have access to? I'd expect as a final year thesis student, you should have the low speed wind tunnel? Even better would be a water tunnel with balance, but they're not as common...

[HugePanic]

we usedAAA (http://www.darcorp.com/Software/AAA/) to do some design and performance calculations.

the programm was weird to use, but basically very simple.
you put in all data you have, and it plots you every information (performance, size, weight...) what can be calculated with the given data.

maybe you could check this out....