# Aircraft efficiency, a tool and list of Equivalent Flat Plate Areas of various planes

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##### Well-Known Member
I've made a quick 'n dirty tool to calculate/estimate Flat Plate equivalent Area. It's a great variable to know, because it's the only way to define the drag of an aircraft, independent of anything else.

I picked various numbers, just from the internet. Others were more reliable and actually measured by an independent source.

A couple of things that really stood out:
*The White Lightning has an extremely low quoted number. To me that looks like pure marketing, the lowest-drag 4-ship has twice the (claimed) drag of the lightning.
*The rather low drag of the Mooney 201
*The extremely low drag of the ASH-30. While I already knew that gliders are much more efficient in terms of drag compared to even the most optimized powered aircraft, this is rather astonishing. The 85ft, 1900 lbs, two seat glider has almost exactly the same drag as the Arnold AR-5 which is very small inside and can only hold a single(small) person and limited payload. (The ASH-30 carries 622 lbs if the engine is installed, about 200lbs more without engine). The closest two-seater is the Nemesis NXT, with 50% more drag.

There's also a tab where you can calculate/estimate the FPEA. Either fill in the numbers (in "input" and "direct calculation"), or fill in the air density and prop efficiency and take a look at the data for a reasonable estimate.

Let me know what you think, input is more than welcome.

Edit 13/8/13, updated version with polar-converter and another half a dozen types added.View attachment Flat_Plate_equivalent_V9.xls

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#### Norman

##### Well-Known Member
HBA Supporter
Re: Aircraft efficiency, a tool and list of Equivalent Flat Plate Areas of various pl

Ooo that could be handy

#### jumpinjan

##### Well-Known Member
Re: Aircraft efficiency, a tool and list of Equivalent Flat Plate Areas of various pl

Okay, so you are calculating the apparent thrust, which will equal the total drag. Could you show the equation that you used? It might be good to list the equation in plain text in the spreadsheet.
So, to know the HP, I would need to dynamometer the engine and read out the rpm in the air.
Jan

##### Well-Known Member
Re: Aircraft efficiency, a tool and list of Equivalent Flat Plate Areas of various pl

Okay, so you are calculating the apparent thrust, which will equal the total drag. Could you show the equation that you used? It might be good to list the equation in plain text in the spreadsheet.
I didn't do it because if people don't have a full knowledge of the topic it might provoke more doubts as clarify things. Simple = better as to speak.

But it's plain old Bernouilli. Calculate the drag, multiply it by speed and you have power required. Take the prop efficiency into account and by using the knowns you have a drag coefficient and an area that are mutually dependent. The product of those two is the equivalent flat plate area, in square feet in this spreadsheat.
So, to know the HP, I would need to dynamometer the engine and read out the rpm in the air.
No. Just use the max rated RPM. Most aircraft that are interesting have a constant speed prop anyway and those who don't, well, they are so large that I don't bother at all.

On these kind of topics there's always endless discussions about prop efficiency, RPM range, minimal atmospheric differences and such. When you realize that a typical speedometer has an accuracy of 3% or worse and even calibration instruments seldom are over 1% accurate, you won't even be able to measure the difference between a 80% and 90% efficient prop, or the difference between 160 and 180 HP.
Just a sidenote, even the differences between two aircraft from the exact same model might be a couple percent.

Flat Plate Equivalent is ideal to compare (very) different aircraft. For detailed analysis, we need to go to a big windtunnel, pay a couple grands and fly in the tunnel.

I like the idea that you can compare a P51 to the AR5 and say something useful about their total drag, idem for the glider and (for example) the Nemesis.

#### jumpinjan

##### Well-Known Member
Re: Aircraft efficiency, a tool and list of Equivalent Flat Plate Areas of various pl

Seb,
Thank you for posting naca reports. I didn't know it existed.....Thanks
Jan

#### Jan Carlsson

##### Well-Known Member
Re: Aircraft efficiency, a tool and list of Equivalent Flat Plate Areas of various pl

Good work Jarno,

Maybe use altitude and temp to calc the density. easier for most.

Jan

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#### craig saxon

##### Well-Known Member
Re: Aircraft efficiency, a tool and list of Equivalent Flat Plate Areas of various pl

Thanks Jarno, another great tool.
Seb, I second Jan, I haven't seen these NACA reports before either. I just went to the index of what you posted, there is so much info here.
Thanks the US government. Whilst historically i can't approve of all the actions of any government , the free availability of all the NACA and NASA reports has probably done more for the advance of aviation than any other action.
Craig

#### Kristoffon

##### Well-Known Member
Re: Aircraft efficiency, a tool and list of Equivalent Flat Plate Areas of various pl

This is very interesting.

Regarding the White Lighthing it has incredible performance (cruise speed given power and weight) so IMHO if its quoted performance is actually true then the flat plate must be really low as given in your spreadsheet.

#### Voyeurger

##### Well-Known Member
Re: Aircraft efficiency, a tool and list of Equivalent Flat Plate Areas of various pl

Thanks Auto,
Now I have something to practice my math with.

##### Well-Known Member
Re: Aircraft efficiency, a tool and list of Equivalent Flat Plate Areas of various pl

Good work Jarno,
You're welcome, as are the others
Maybe use altitude and temp to calc the density. easier for most.
Well, problem is that ISA (international Standard atm) isn't exactly easy to define and I wouldn't get into the more advanced math. For the US guys; 1.25 kg/m3 is the sea-level density, since the model is metric.
This is very interesting.

Regarding the White Lighthing it has incredible performance (cruise speed given power and weight) so IMHO if its quoted performance is actually true then the flat plate must be really low as given in your spreadsheet.
To be honest, I doubt those kind of optimistic numbers. Many manufactures claim unrealistic numbers (the French Eclipse for example claimed 225 kts on 100 HP, for a two-seater in their initial ads). I actually made this list as my BS-check, to have quick look whether claimed numbers are realistic. To be honest; I don't think those (of the White Lightning) are.

##### Well-Known Member
Re: Aircraft efficiency, a tool and list of Equivalent Flat Plate Areas of various pl

Jan Carlsson took the effort to put in a altitude converter, thnx for that!

I've also added some other aircraft. Please take note that you can only input one altitude at a time (either metric or feet).

See first post for version 2 of this spreadsheet.

#### topspeed100

##### Banned
Re: Aircraft efficiency, a tool and list of Equivalent Flat Plate Areas of various pl

This is very interesting.

Regarding the White Lighthing it has incredible performance (cruise speed given power and weight) so IMHO if its quoted performance is actually true then the flat plate must be really low as given in your spreadsheet.
Flat Plate Area was heavily discussed when Tsunami racer was introduced ( 70% of Mustang FPA ) and it never clocked faster than a Dago Red even with a bigger engine.

So flat plate area is not everything.

OTOH White Lightning actually still is the fastest ever built 4 seater in its weight gategory. It has an other remarkable virtue besides FPEA..it is the low drag coefficient and wetted area.

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##### Well-Known Member
Re: Aircraft efficiency, a tool and list of Equivalent Flat Plate Areas of various pl

Flat Plate Area was heavily discussed when Tsunami racer was introduced ( 70% of Mustang FPEA ) and it never clocked faster than a Dago Red even with a bigger engine.

So flat plate area is not everything.
Well, except for the limitations (it's only applicable in the speed range the aircraft can reach) and realizing the induced drag is ignored (which is simply proportional to the aspect ratio) it actually is everything. Even cooling drag or transonic drag are in it. It's simply a matter of total aircraft efficiency, expressed in drag area.
OTOH White Lightning actually still is the fastest ever built 4 seater in its weight gategory. It has an other remarkable virtue besides FPEA..it is the low drag coefficient and wetted area.
Those two are the FPEA...

I'm unaware of any speed measurements, other than claims. Compared to well designed other aircraft, I think it's unlikely to achieve such low drag. It has similar dimensions as a Legacy or Glasair III and I would expect it's FPEA to be at least 50% higher.
As always, marketing or some tiny iffy details (turbocharger for example) make it a lot harder to get reliable data...

#### Mac790

##### Well-Known Member
Re: Aircraft efficiency, a tool and list of Equivalent Flat Plate Areas of various pl

Theoretically it might be possible to confirm or deny some of those White Lighting specifications, I've read that he was starting in Reno races in 90's. I did small research and I found one result for Mike Jones in the year 2000, he achieved 259mph, in Sport Class, but the question are, was it that Mike Jones, was he flying White Lighting, did he make some changes to the engine, etc. Without answering those question it's hard to say anything, I was looking also at official Reno web page, but I couldn't get access to results from 90 in Sport Class Reno Air Racing Association - search the race results database

Seb

#### topspeed100

##### Banned
Re: Aircraft efficiency, a tool and list of Equivalent Flat Plate Areas of various pl

Well, except for the limitations (it's only applicable in the speed range the aircraft can reach) and realizing the induced drag is ignored (which is simply proportional to the aspect ratio) it actually is everything. Even cooling drag or transonic drag are in it. It's simply a matter of total aircraft efficiency, expressed in drag area.
Those two are the FPEA...

I'm unaware of any speed measurements, other than claims. Compared to well designed other aircraft, I think it's unlikely to achieve such low drag. It has similar dimensions as a Legacy or Glasair III and I would expect it's FPEA to be at least 50% higher.
As always, marketing or some tiny iffy details (turbocharger for example) make it a lot harder to get reliable data...
Right...I am sorry..I got FPA and FPEA totally mixed...sorry I have to concentrate more.

So minor flat plate area ( i think I mean frontal area ) in Lightning has also other virtues like low drag coefficient and wetted area...and interference drag. Is this now plausible ?

Ok ok...now I am confusing even more...the frontal area of Tsunami was 70% of the Mustangs.

And all in all...i have to convert my opinion once and for all...YES the flat plate area of W.Lightning has to be quite small indeed.

http://www.studiomoonart.com/whitelightning.htm

Insert; We are very confident that we will meet our performance projections. It seems to be running right along the low drag curve that Len Niemi came up with.

It has been long out of the market AFAIK. Len Niemi was designer of the SISU glider.

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#### topspeed100

##### Banned
Re: Aircraft efficiency, a tool and list of Equivalent Flat Plate Areas of various pl

This chart could be handy too.

There are many know ac:s and their wing loading has been under scrutiny.

White Lightning would be right where the G of the Glasair III would be...on its top part !

Dotted line that goes to Pond Racer has been drawn via 1/3 sized Pond Racer model ( thus the curve ).

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#### PeterJC

##### Well-Known Member
Re: Aircraft efficiency, a tool and list of Equivalent Flat Plate Areas of various pl

It's better to repost this here - for obvious reasons... :}
[Was: https://www.homebuiltairplanes.com/forums/aircraft-design-aerodynamics-new-technology/9161-triple-tandem-wings-future-2.html#post88745 ]
###
That rings the bell... yes, Raymer, Aircraft Design, page 24: (see attachment. 1 page is fair use, np

"Aspect ratio could be used to estimate subsonic L/D, but for one major problem. The parasitic drag is not a function of just the wing area, as expressed by aspect ratio, but also of the aircraft's total wetted area."

It could be interesting to compare b^2/Swet ratios of high-performance GA designs to modern sailplanes, like LS-7. Just that wetted areas are not readily googl'available.

Some EFPa and Swet values I have come across found here in efpa_swet2.xls file, gathered from various sources. If you have something, please do contribute here. These figures are hard to find, and essential to even napkin-level design comparison. Cheers.

####

As for "wetted area divided by EFPA"... I think it is not entirely useless figure.
Just like EFPA is an outcome of design choices, so is the economy of internal volume - namely, how much of it, and how well they got the air flowing around it...

EFPA in itself doesn't serve as a direct "efficiency number", since it is naturally bigger for bigger planes - even if they are hugely efficient compared to their size.
Eg. C182 has virtually the same EFPA as Avanti...

Code:
Model          EFPA ft2   Swet ft2   Swet/EFPA
Avanti P180    5,55       1273       229
Cessna 182     5,27       690        131
Swet/EFPA is something that could lead a bit closer to usable "aerodynamic efficiency factor" than many other approaches. The only thing is... as you implied, this doesn't correlate for design choices like Sref/Swet, L/D, wing loading etc. That's something for us to think about

Perhaps we need another Sref for cabin size, something like Sint. That would compensate the diff between BD-5/Eclipse -type tandem sleds and proper side-by-side GA cockpits

Regarding the hard data about wetted areas... this page is from Bruce Carmichael's "Personal aircraft drag reduction". Set is made by Dave Lednicer, by using his VSAERO package... so at least these numbers should be quite accurate.

What's odd in spreadsheet numbers, is that warbirds have ratios of nearly 300, but very sleek GA planes like Glasair III and Avanti get 200-230 figures... Cabin cross-section and reynolds effect?
Btw: regarding the dataset: AR-5's Swet is 236 ft2. That's now corrected.

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##### Well-Known Member
Re: Aircraft efficiency, a tool and list of Equivalent Flat Plate Areas of various pl

Updated the file. It now includes a way to directly calculate the EFPA from a given glide ratio (L/D). Take note that the best L/D occurs when half the drag is induced drag. If the frontal drag is constant with varying lift coefficient, you can use the double L/D to calculate the EFPA, based on only the frontal drag (for high speeds).

If you have a polar; use the highest plotted speed at the lowest plotted weight. This gives you the closest result if you want to exclude induced drag.

#### brehmel62

##### Well-Known Member
Re: Aircraft efficiency, a tool and list of Equivalent Flat Plate Areas of various pl

*The White Lightning has an extremely low quoted number. To me that looks like pure marketing, the lowest-drag 4-ship has twice the (claimed) drag of the lightning.
*The rather low drag of the Mooney 201
Aren't you comparing apples and oranges? These two are simply not the same.

Mooney 201
Last aerodynamic cleanup was 1977 with the M20J model.
Has riveted aluminum skin on wings and fuselage.
Has standard sloped windscreen.
Has gear retracted into wings.
Has 50% more weight than WL.
Has double the wing area of WL.
Has about 1/3rd more wing span than WL.
The engine cowling only slopes on bottom from the spinner; the top is nearly flat.
The fuselage/wing junction has both aerodynamic fillets and structural root thickening.

White Lightening
Had aerodynamic help from both Ed Swearington's SX300 and A.J. Smith's AJ-2 racer.
Has smooth fiberglass skin on wings and fuselage.