Fairings, more

[1avidflyer 1983]

Hi Paul,  I did see Mikes video about the CF fuselage cover.  He sure can get things done.  Course somewhat unlimited funds have to make a bit of a difference.  JImChuk

[akflyer 1427]

Hey, go for it! Makes little difference to me since I didn't get mine for speed anyway. 60-65 is just fine for me since most anywhere I go is an hour or less. I live in the mountains so going to the mountains is walking out the backdoor, or flying a pattern around the strip.

Something to think about, especially in the mountains.  If there are things we can do to clean these birds up that translates into less power needed to keep them in the air.  This also is a direct benefit to having more that required power available when you get caught in that downdraft etc to help you power out of it and perhaps keep you from becoming a statistic.  When I was putting some fairings on mine, I was not really impressed on the speed increases I got.  I was very impressed with the increase in rate of climb.  As one who plays in the mountains, this should be of utmost importance to you.  As we all know, when you are dicking around and change one thing, it probably has some unintended or unforeseen consequences, and as such, can also have unforeseen or unintended benefits!

 

[Allen Sutphin 705]

You being In the real mountains know there are some places that you stay out of and places to avoid. Yes, everything you said is correct but any plane has its limits. If a hundred foot better climb rate is the difference between dragging the trees or clearing them, then the problem started long before take-off.  After 40 years of flopping around in these mountains, I have my own rules for mountain flying. And they are unbreakable!

!. Be able to fly a target airspeed within 1-2 mph.

2. Be able to hit your spot within 10' every time.

3.Know your wind at all times.

4. Know your location at all times.

5.Know your weather.

6.Know your aircraft and what it can and can't do. (mandatory)

There are a few more but unless one can do these, they need to stay out of the mountains.  And your mountains are even less forgiving of mistakes. And you know about always having an out. No explaining needed. Not meaning you, but if one is going to play off road, they need their head in the game.  Yeah! I am a hard a%$.

[TJay 1041]

That is incredible  I have been thinking about streamlining my Ca-bane Just didn't think it would make much difference but now you got me rethinking.

Edited 8 Dec 2019 by TJay

[109jb 181]

I am really skeptical about putting a few fairings on an Avid and getting 10 or 15 mph more cruise out of it. Physics argues otherwise.

Drag goes up by the square of speed, so if you want the same power to get you from 90 mph to 100 mph (let alone the 120 mph someone posted here!), you have to cut the drag by 20%. How many gas caps does it take to equal the drag of that big wing? Or the fuselage cross section? Or those long double struts?

To get to 120 mph, you have to drop the drag by almost 80%. 

This is wrong. Total drag is not proportional to V^2.  The portion of drag proportional to V^2 is the parasite drag. Induced drag is inversely proportional to V^2. So at lower speeds induced drag dominates and at higher speeds parasite drag dominates. Think of it this way, reducing parasite drag gets a bump in speed, and the bump in speed gets a reduction in induced drag. So, when you reduce parasite drag you also get an induced drag reduction as a bonus. If you are in a region where induced drag is dominant then the induced drag reduction could be very large for a modest parasite drag reduction.

[nlappos 413]

Oh for Pete's sake, save us the internet version of anti-vaccination, ok, 109jb. Or else write NASA and tell them your crackpot theory. Until then, drag goes up by V squared, and in fact power required goes up by V cubed. 

https://www.grc.nasa.gov/WWW/K-12/airplane/drageq.html

 

 

Edited 8 Dec 2019 by nlappos

[akflyer 1427]

    I'm just here for the show.  keep it clean, no holding, no hitting below the belt.  Gents, lets see a good clean fight.  Ding!

 

[109jb 181]

Oh for Pete's sake, save us the internet version of anti-vaccination, ok, 109jb. Or else write NASA and tell them your crackpot theory. Until then, drag goes up by V squared, and in fact power required goes up by V cubed. 

Hurl all of the insults you want. Call me a crackpot or whatever makes you feel good about yourself. 

I will say it again, Total drag is not directly proportional to V². No ifs ands or butts.

It is true that Drag = 0.5*rho*V²*S*C_D, but that ain't the end of the story.

C_D = C_Dparasite + C_Dinduced.  The C_Dinduced term has a C_L in it. Namely, C_Dinduced = C_L²/(pi*AR*e). So substituting C_L = 2*L/(rho*V²*S) into the drag equation creates 2 terms 

Drag = 0.5*rho*V²*C_Dparasite + 0.5*rho*V²*S*(4*L²)/((pi*AR*e)*(rho*V²*S)²)

reducing, Drag = 0.5*rho*V²*C_Dparasite + 4*L² /((pi*AR*e)*(rho*V²*S))

which give a parasite drag term that is proportional to V², and an induced drag term that is inversely proportional to V²

From the equation above, if lift remains constant, which it has to for level flight, then an increase in V results in a decrease in the induced drag term.

Logically, a reduction in parasite drag would result in an increase in speed. If nothing is done the airplane would climb since L=0.5*rho*V²*S*C_L and V has increased. So in order not to climb, a reduction in AOA with a corresponding change in C_L happens. Reducing C_L reduces C_Dinduced which is the same as reducing the induced drag.

Graphically, This reduction in parasite drag looks like the attached graph and a parasite drag reduction WILL result in a decrease in induced drag. 

 

 

[109jb 181]

If you start out closer to the "bucket" of the total drag curve the resultant Induced drag decrease can be larger because the induced drag has a stronger presence the farther left you go.  

The Minimum total drag at the bottom of the "bucket" is the point of best efficiency and longest range, but is a little problematic because if you slow from here, drag increases and you slow more and more, so most airplanes use a speed slightly right of this point for the best efficiency cruise because it is stable. If you slow, the drag decreases and you sped up, likewise if you speed up drag increases and it slows. This yields a stable equilibrium.  So if we start just right of the minimum, we see that a reduction in parasite drag can result in a larger decrease in induced drag.

[TJay 1041]

109JB I would say you won. Very nice detailed information.  And you didn't even need to do the 5 year old name calling BS.

Edited 9 Dec 2019 by TJay

[nlappos 413]

109jb,

Your discussion is helpful, your math, not so much.

Total drag = Parasite + Induced drag. That means the Vsquared Parasite drag is ADDED to the Incuded drag to make total drag, so Total drag goes up by MORE that Vsquared. Somehow you think Induced drag is subtracted from parasite drag in the process, where this came from, I don't know. The fact that Total Drag line on the plots you provide is ABOVE Parasite drag is lost you you, but it shows that total drag is more than parasite, so it goes up to a higher value than parasite drag. Total drag rises faster than Vsquared, my friend.

Here is nice discussion:

http://www.pilotfriend.com/training/flight_training/aero/drag.htm

[109jb 181]

Your discussion is helpful, your math, not so much.

Huh?  Bold statement for not showing one bit of evidence that my math is wrong, which it is not. 

Total drag = Parasite + Induced drag. That means the Vsquared Parasite drag is ADDED to the Incuded drag to make total drag, so Total drag goes up by MORE that Vsquared.

Yeah.  Show me where anything I said is contrary to Total drag = parasite + induced. 

Also, let me correct your statement as it is slightly incorrect. here is what it should say 

Total drag = Parasite + Induced drag. That means the Vsquared Parasite drag is ADDED to the (1/Vsquared) Incuded drag to make total drag which makes TOTAL DRAG NOT PROPORTIONAL TO V²  

Somehow you think Induced drag is subtracted from parasite drag in the process, where this came from, I don't know. The fact that Total Drag line on the plots you provide is ABOVE Parasite drag is lost you you

So show me where I said that induced drag is subtracted from parasite drag.  I'll give you a little hint....I didn't and claiming that I did is just poppycock.

You are flatly wrong in your understanding and clearly don't understand that once you perform a drag cleanup on an airplane you aren't just moving up the original drag curve.  You have created a whole new drag curve and have to  first move to that new drag curve to find the new equilibrium where Thrust=drag.  At the new equilibrium the drag makeup is such that the induced drag is lower than before. The parasitic drag coefficient is also lower which is why the parasitic drag curve, and consequently the total drag curve have shifted downward, but the total parasitic drag at the new equilibrium is higher because the airplane is operating at a higher velocity.

 

[nlappos 413]

Simply said, you said that Drag is not proportional to Vsquared, and implied that it is not that big. It is, in fact it is bigger than Vsquared. Can you at least admit that?

[109jb 181]

Simply said, you said that Drag is not proportional to Vsquared

And that is a true statement, total drag is not proportional to V². One more time. Parasite drag, which is only a portion of the total drag is proportional to V². Induced drag is proportional to 1/V². The sum IS NOT PROPORTIONAL TO V²

  and implied that it is not that big.

And where did I imply this?   I said "So at lower speeds induced drag dominates and at higher speeds parasite drag dominates.", which is an absolutely true statement. If you chose to interpret this otherwise then it isn't a matter of me implying it, it is a matter of you assuming it..

It is, in fact it is bigger than Vsquared. Can you at least admit that? Like thi 

Oh for Pete's sake!!!!  I NEVER SAID THAT TOTAL DRAG WASN'T LARGER THAN PARASITIC.

Fine, I will go ahead and state what is blatantly clear in all of my posts, graphs, and equations but for some reason you chose to totally ignore.

Total drag is greater than parasitic drag alone.

Now will you either provide a quote where I said otherwise, or admit that I never said that?

 

[akflyer 1427]

I got the popcorn but they don't let us have beer here at work.  Kind of pisses me off that I can't have both for the next week or so.  Pretty sure the point has been made pretty clear.  Shake your dicks boys this pissing contest is over.. don't go chasing waterfalls.  <bonus points to whoever can tell me where I got that from   hint, cmon captn you gotta know your making references to the songs...

 

[109jb 181]

Thought the OP might like to read an old Sport Aviation article about Jim Younkin's Piper Pacer. He took a 160 hp Pacer, which from Piper is about a 130 mph airplane and with aerodynamic cleanup got 155 mph out of it using the same engine.  The stock pacer was probably cleaner than the average Kitfox in terms of what could be improved since it would have already had some fairings on things that aren't normally faired on Kitfoxes. I'm hoping the article might give some ideas. I have always admired this airplane and saw it a few times at Airventure. Anyway, here is the article.

 

 

1989_03_02.pdf

[akflyer 1427]

I think the 63 pitch prop has more to do with the speed than anything else.  Piper was really stretching it calling at 130mph plane.  well. maybe is you have 500 tires on it and high pitch prop, but then its just a pavement pounder and you need lots of runway to get her in the air.  A pacer, configured for off airport use is a 100 MPH plane at best.  Most of my cruise is in the high 80s on the GPS unless I have a tail wind.

However, it is cool to see what can be done with fairings and cleaning a plane up!  The RupRacer (experimental pacer built by a local guru) was about as clean as one can make it.. and I don't think he hit the speeds that Jims is reported to have hit. 

 

[Fly-n-Low 181]

I got the popcorn but they don't let us have beer here at work.  Kind of pisses me off that I can't have both for the next week or so.  Pretty sure the point has been made pretty clear.  Shake your dicks boys this pissing contest is over.. don't go chasing waterfalls.  <bonus points to whoever can tell me where I got that from   hint, cmon captn you gotta know your making references to the songs...

 

A pop hit song from the 90s? Seems like it was three black girls? What do I win?

[109jb 181]

I think he meant used in a movie. I remeber it but can't think of the name.  Comedy cop movie with Will Farrell and Mark Wahlberg I think. Lots of good one-liners in that movie. If only I could remember the name.

[akflyer 1427]

I got the popcorn but they don't let us have beer here at work.  Kind of pisses me off that I can't have both for the next week or so.  Pretty sure the point has been made pretty clear.  Shake your dicks boys this pissing contest is over.. don't go chasing waterfalls.  <bonus points to whoever can tell me where I got that from   hint, cmon captn you gotta know your making references to the songs...

 

A pop hit song from the 90s? Seems like it was three black girls? What do I win?

that quote was from a movie.. that's what gets ya the good guy bonus award... 

 

[Fly-n-Low 181]

Well...

 

Edited 12 Dec 2019 by Fly-n-Low

[Dusty 126]

Thought the OP might like to read an old Sport Aviation article about Jim Younkin's Piper Pacer. He took a 160 hp Pacer, which from Piper is about a 130 mph airplane and with aerodynamic cleanup got 155 mph out of it using the same engine.  The stock pacer was probably cleaner than the average Kitfox in terms of what could be improved since it would have already had some fairings on things that aren't normally faired on Kitfoxes. I'm hoping the article might give some ideas. I have always admired this airplane and saw it a few times at Airventure. Anyway, here is the article.

 

 

1989_03_02.pdf

great article but I don't get the mystery ship logo thing? I can't find anything on the interweb either. Am I missing something?

[109jb 181]

The logo when pointing upward has the letters TRAVEL AIR in it.  The wheel pant is the AIR.

[wypaul 448]

Here you go.

 

Edited 14 Dec 2019 by wypaul

[TJay 1041]

Thats awesome. How do the avid flaperons do at those speeds?