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        Boeing 727 airfoil/wing design question

#1 David A Ramsey May 26, 2003 02:05 PM

Boeing 727 airfoil/wing design question
 
Planning a 727 for EDF-50, or 75 Fans.

Observations in scale wing airfoil at root to around 35% outward, show a signifiantly higher camber on the lower half of the airfoil than at the top.

Would anyone know, or venture a guess as to why this is?

#2 cv990 May 29, 2003 04:59 AM

Lift creation requires airflow over the top of an airfoil to be accelerated more over the top surface than the bottom - hence more pressure drop on top and thus lift. Thus the airflow flowing over the top of an airfoil moves faster than the aircraft actually is - for example if you have a model flying at 40mph, then the local flow speed over the top wing surface may be (say) 45mph.

Now, airfraft that travel fairly close to the speed of sound (say > Mach 0.75) have a problem with traditional "curved top" airfoils as the airflow over the wing top may, over relatively curved sections, accelerate to near sonic speeds and form shockwaves which cause excessive drag and possible flow seperation (shock stall).

The "flat top" airfoil delays this effect by accelerating the air "more gradually" - and reducing/preventing shockwaves up to the designed maxium Mach No.

#3 David A Ramsey May 29, 2003 08:27 AM

TO cv990: Thank you for helpful reply.

As I understand the first paragraph of your response, that is what promted my question.

The remainder of your explination is what I was looking for to satisfy my curiosity. I think I can safely ignore this aspect of the scale airfoil for my model.

I wasn't sure this Forum would answer my question. What a pleasent surprise.

Thanks again.

#4 zbrubaker May 30, 2003 07:27 AM

Hi David...just my 2 cents here...I'm going down the same road as you in designing a 727 for the EDF50. I've spoken with quite a few people about airfoil selection for a park flyer like this. I wasn't convinced that an undercambered "flat plate" wing was the best choice. Because of the swept wing, I wanted something that would help to reduce stalling. What I eventually settled on was the GM15 airfoil...It's undercambered, but has a nice rounded leading edge. I'm also adding washout at the tips to help with tip-stalling.

Zeke

#5 David A Ramsey May 30, 2003 01:54 PM

Hey Zeke, As my Learjet flys so slow with a flat bottom airfoil with washout, I wanted the planned 727 to have a bit more speed. The airfoil for the Lear was a; That looks about right.
My question about the actual 727 airfoil arose from studying the 1/200 Hasegawa plastic model.
My 727/100 will have a span of 40", or so, with a semi symetrical root changing to a clark "Y" type at the tip with some washout. This will again be a; looks about right airfoil with "cracked rib" construction. Was thinking of 3, EDF-50s, but have settled on 2. With Kokam 2 cell, 1200mAh, hoping for a wing loading of around 7oz per sq. ft.
Won't start the 727 project till Lear article for Flying Models is finished.
Thanks for your 2 cents. Look forward to hearing more of your 727!

David

#6 zbrubaker May 31, 2003 09:16 AM

I agree with going with 2 EDF50's instead of 3...I was planing on 3 until I decided to run the numbers in Motocalc with 2. Motocalc predicted MUCH better results with 2....

#7 David A Ramsey May 31, 2003 12:28 PM

What put me off for the third fan was the thought of making the "S" duct and having that fan removable for service.
Motocalc sounds interesting, one day I'll have to check it out. In the mean time my wife says I have UMAX software for a scanner I've never used. See if I can get you pictures you asked for. I'm slow getting into the computer age. To me software is a piece of drawing paper.

#8 marvinf14 Dec 11, 2007 10:21 PM

Looking for plans for the Boeing 727 Airfoil,
 
Im building an B727-200 and i needhelp finding plans for the airfoil, if anyone has it and like to sell it to me please contact me or call me 305 300-1800, my name is Marvin, thanks.....

#9 Bill Covert Dec 11, 2007 11:42 PM

5 Attachment(s)
I'd have to go downstairs and weight this thing, but beyond that, I was surprised the 2 EDF50 fans with the older 4100kv bl Feigaos could ROG and fly this modified Cox airlifter quite well. The 5866 would simply be par for the course. The plane is around 40" span. Planes like Cox usually are nothing to write home about in terms of engineering, but I would actually reference this one. They were definitely onto something here, as the washout alone shows that they actually put effort into this design. In the case of this plane, a larger fan setup would have probably "ruined" the plane, as the weight gain from the much larger 20mm motors offsets so much of the performance gain. I'll have to dig up some relevant specs on the plane.

Specs are everything, as you know. My little brushed 12V EDF50 yellow DHL airliner was built to your wing loading spec David, and it worked beautifully. :D

I'm constantly more impressed with the little fans, as this 27" EDF40 ME262 was obviously not built to spec at 14.5oz AUW :eek: and still flew beautifully. You really need to try the 5866kv 12mm motors if you haven't, as this plane needed every bit of the performance at that weight, but it was there.

#10 David A Ramsey Dec 12, 2007 08:20 AM

Airfoil ...
 
1 Attachment(s)
Quote:

Originally Posted by marvinf14
Im building an B727-200 and i needhelp finding plans for the airfoil, if anyone has it and like to sell it to me please contact me or call me 305 300-1800, my name is Marvin, thanks.....

Here's a scan of the airfoil and templates I used for my 727. The cord length of rib No. 1 is 9 23/32". The templates are on a piece of 8 1/2" x 11" paper.

The front tapered spars are marked with an "X". The rear tapered spars are actually top and bottom and not in the "X" marked center space.

#11 David A Ramsey Dec 12, 2007 08:51 AM

Neat DHL!
 
1 Attachment(s)
Quote:

Originally Posted by Bill Covert
Specs are everything, as you know. My little brushed 12V EDF50 yellow DHL airliner was built to your wing loading spec David, and it worked beautifully. :D
I'm constantly more impressed with the little fans, as this 27" EDF40 ME262 was obviously not built to spec at 14.5oz AUW :eek: and still flew beautifully. You really need to try the 5866kv 12mm motors if you haven't, as this plane needed every bit of the performance at that weight, but it was there.

Very happy to hear your DHL flew well. And yes, I need to try the Feigaos'.
I have a pair of the first Feigao 6000kv mounted for use a Falcon 10 which I hope to start soon.
Can't believe I started my 727 almost 4 years ago as I finally just completed the plans and construction article for Model Aviation.

#12 Ed Waldrep Dec 12, 2007 01:03 PM

I wonder how much thrust the guys in the foamy edf forum are squeezing out of the EDF 40 and 30...might make for smaller nacelles.

Falcon 10 is a sweet looking bird!

#13 David A Ramsey Dec 12, 2007 03:34 PM

Quote:

Originally Posted by Ed Waldrep
I wonder how much thrust the guys in the foamy edf forum are squeezing out of the EDF 40 and 30...might make for smaller nacelles.

Falcon 10 is a sweet looking bird!

From what I've read for brushed motors the EDF 30 won't do it. The EDF 40 comes close at 7.4V, but at higher amps. An EDF 30 would have certainly made the nacelles look more scale. A brushless 30 might work, but then there's the added weight of the battery, extra ESC if needed and the added expense.

The Falcon 10 nacelles will scale pretty close with EDF-50s at roughly a 45" wing span.


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