Aerodynamics Discuss the physics of flight revolving around the aerodynamics and design of aircraft.

Center of gravity for delta wing...

Reply
Old 06-02-2008, 04:04 PM
  #1
neuroza
Thread Starter
 
Join Date: Nov 2007
Location: Porec, CROATIA (HRVATSKA)
Posts: 128
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default Center of gravity for delta wing...

Hi!
Now I'm building my first delta wing, so please, how to find where must be the center of gravity???
Any help is welcome!
Thanks!
neuroza is offline  
Reply With Quote
Old 06-02-2008, 10:55 PM
  #2
mjfrederick
 
Join Date: Aug 2006
Location: Denham Springs, LA
Posts: 1,175
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Center of gravity for delta wing...

This might help : [link=http://www.nasascale.org/howtos/cg-calculator.htm]CG Calculator[/link]
mjfrederick is offline  
Reply With Quote
Old 06-03-2008, 06:41 AM
  #3
neuroza
Thread Starter
 
Join Date: Nov 2007
Location: Porec, CROATIA (HRVATSKA)
Posts: 128
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Center of gravity for delta wing...

Thanks!
But there ask me to enter the CG, I just don't know how to use it...

Can anybody help, this is my measurement:

Root Chord (A): 350
Tip Chord (B): 241
Sweep Distance (S): 150
Half Span (Y): 500
%MAC Balance Point: ???

neuroza is offline  
Reply With Quote
Old 06-03-2008, 09:48 AM
  #4
mjfrederick
 
Join Date: Aug 2006
Location: Denham Springs, LA
Posts: 1,175
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Center of gravity for delta wing...

I'm not positive on delta wings, but most aircraft use 25-33% MAC for the CG. Try using these and it may give you a decent range as to where the CG should end up.
mjfrederick is offline  
Reply With Quote
Old 06-03-2008, 10:20 AM
  #5
neuroza
Thread Starter
 
Join Date: Nov 2007
Location: Porec, CROATIA (HRVATSKA)
Posts: 128
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Center of gravity for delta wing...

OK, thanks, I will try with 30% and that we will see...

Thanks!
neuroza is offline  
Reply With Quote
Old 06-03-2008, 07:44 PM
  #6
Ron S
 
Ron S's Avatar
 
Join Date: Dec 2001
Location: Fort Worth, TX
Posts: 1,838
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Center of gravity for delta wing...

Here's an extra data point for you. I've flown an F-106 Delta Dart model for several years now, and the CG is at approx 22% of the Mean Aerodynamic Chord. The planform of the model is not a pure delta shape, though, because of the (small) contribution of the fuselage.

It is packed pretty tight, so it isn't really easy for me to test fly with different CG positions (without adding dead weight...) If I could, I'd like to go aft a bit more. Also, there might be some minor contribution in CG shift due to the fuselage, but I've never checked to see if it would drive the Aerodynamic Center fwd or aft - I'd assume fwd...
Ron S is offline  
Reply With Quote
Old 06-03-2008, 11:48 PM
  #7
pimmnz
 
Join Date: Nov 2005
Location: Auckland, NEW ZEALAND
Posts: 1,958
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Center of gravity for delta wing...

For any 'usual' delta of around 60 degrees L/E sweep you will find that the balance will be at about 50% of the centre chord.
Evan, WB#12.
pimmnz is offline  
Reply With Quote
Old 06-05-2008, 12:17 PM
  #8
Ron S
 
Ron S's Avatar
 
Join Date: Dec 2001
Location: Fort Worth, TX
Posts: 1,838
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Center of gravity for delta wing...

Ah, I've never heard that before! Lets see. For a simple delta wing (tip chord = or approx zero), mac length will be 2/3 the length of the root chord. 75% of the mac (measured from TE) is normally a reasonable spot for aero center, and correspondingly, 75% X 2/3 X Root Chord = 50% Root Chord! [8D]

So 50% Root Chord (measured at centerline of model) corresponds to a 25% mac or aero center.
Ron S is offline  
Reply With Quote
Old 06-06-2008, 12:40 AM
  #9
pimmnz
 
Join Date: Nov 2005
Location: Auckland, NEW ZEALAND
Posts: 1,958
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Center of gravity for delta wing...

Yes, a good safe place to start, adjust to taste as usual. It's all really simple, you see.
Evan, WB#12.
pimmnz is offline  
Reply With Quote
Old 06-13-2008, 08:37 PM
  #10
Mustang Fever
 
Mustang Fever's Avatar
 
Join Date: Nov 2003
Location: Cadillac, MI
Posts: 3,225
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Center of gravity for delta wing...

Tail less deltas should balance at 20-25% of mean aerodynamic chord (dry, with a tank forward of the CG), as long as the nose isn't way out there in front affecting the center of pressure. Ron S' F-106 is a perfect example. Right in the middle at 22%. It has a very skinny nose, even tho it's way out there, that doesn't affect the CP much. Some deltas, like Laddie M's Arrow, have a monster nose (5" wide) with a curved upper surface that generates lift. That puppy won't fly at 20-25%. It needs to be at about 15 or even a bit less.

The hard part is finding the Mean Aerodynamic Chord. You either have to draw out one wing panel and fuse, full size, on a big piece of paper, or lay measuring sticks on the floor parallel to one wing panel.

1. Find the root chord (RC) on the CENTERLINE OF THE FUSE (C/L)(or wing). Extend the LE to the centerline to do this. Measure along the Centerline (C/L) to obtain RC.
2. Measure the tip chord. (TC)
3. Draw a line (or place a stick) extending forward along the centerline (C/L) from the LE for the distance of the tip chord (TC), and aft along the centerline from the TE.
4. Draw a line (or place a stick) extending forward, parallel to the tip, from the LE for the distance of the root chord (RC), and aft from the TE.
5. Connect the four corners obtained diagonally as shown. The two lines will cross somewhere near the center of the wing. The location of the MAC is where they cross. Measure from the LE to the TE at that point, and you'll have the dimension of the MAC. Multiply by 0.80, and that is the CG location as measured from the TE, which is usually much easier than measuring from the LE. That should be good for a first flight. Have PLENTY of elevon up travel, and use lots of expo so they won't be too sensitive, and you'll have no trouble flaring the beast even if it is a bit nose heavy. You can always creep the CG aft as you gain experience.

It's a huge pain in the ***, but it works. My drawing isn't so good, but it works, too.
Attached Thumbnails
Click image for larger version

Name:	Vt57861.jpg
Views:	806
Size:	50.8 KB
ID:	970051  
Mustang Fever is offline  
Reply With Quote
Old 06-15-2008, 09:32 PM
  #11
Mike Connor
 
Mike Connor's Avatar
 
Join Date: Jan 2002
Location: Tulsa, OK
Posts: 2,025
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Center of gravity for delta wing...

Quote:
Can anybody help, this is my measurement:

Root Chord (A): 350
Tip Chord (B): 241
Sweep Distance (S): 150
Half Span (Y): 500
%MAC Balance Point: ???
%MAC Balance Point: 18
Balance Point @ Root Chord (CG) =124.18

Your measurments are as much a flying wing as a delta.
15%-20% MAC is a good place to start.
Delta's fly by their own set of rules.


Mike Connor is offline  
Reply With Quote
Old 06-28-2008, 07:09 AM
  #12
neuroza
Thread Starter
 
Join Date: Nov 2007
Location: Porec, CROATIA (HRVATSKA)
Posts: 128
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Center of gravity for delta wing...

How can I know the best "%MAC Balance Point"???
Is it ok to start with 15 - 20 %

Thanks!
neuroza is offline  
Reply With Quote
Old 06-28-2008, 09:45 AM
  #13
Mike Connor
 
Mike Connor's Avatar
 
Join Date: Jan 2002
Location: Tulsa, OK
Posts: 2,025
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Center of gravity for delta wing...


Quote:
ORIGINAL: neuroza

How can I know the best "%MAC Balance Point"???
Is it ok to start with 15 - 20 %

Thanks!
I designed a delta using proven concepts from other delta designs and it flies excellent. Mine flies best balanced at 18% MAC. Most delta's I researched like the Diamond Dust, SlipStream and others balanced between 15%-20% MAC.
Mike Connor is offline  
Reply With Quote
Old 06-29-2008, 07:27 AM
  #14
neuroza
Thread Starter
 
Join Date: Nov 2007
Location: Porec, CROATIA (HRVATSKA)
Posts: 128
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Center of gravity for delta wing...

Thanks!
I'll try with 18%...
neuroza is offline  
Reply With Quote
Old 02-15-2009, 12:23 PM
  #15
longtalltexankwg
 
Join Date: Feb 2009
Location: crystal lake , IL
Posts: 1
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Center of gravity for delta wing...

I am building a profile r/c electric convair pogo vtol with a length of 20 inches and a 24 inch wing span.I am starting with a small one to save on cash. When I can get the small one to work then I will make a bigger and full fuselage version.I already have a counter rotating prop design that I have been messing around with to make it work for a bigger version. Thanks for your time, Kerry
longtalltexankwg is offline  
Reply With Quote
Old 04-05-2009, 07:21 PM
  #16
donnyman
 
donnyman's Avatar
 
Join Date: Jul 2008
Location: Manor, TX
Posts: 1,239
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Center of gravity for delta wing...

Neuroza

I sent you a pm I trust you received it.

the information you seek is a subject often answered in our magazines. and example.
Attached Thumbnails
Click image for larger version

Name:	Jh14536.jpg
Views:	594
Size:	70.5 KB
ID:	1173436  
donnyman is offline  
Reply With Quote
Old 04-12-2009, 11:20 AM
  #17
Flypaper 2
 
Join Date: Mar 2002
Location: Kingston, ON, CANADA
Posts: 4,922
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Center of gravity for delta wing...

This old Pogo is at the 50% root chord mark.
Attached Thumbnails
Click image for larger version

Name:	Vt56743.jpg
Views:	249
Size:	57.5 KB
ID:	1178595  
Flypaper 2 is offline  
Reply With Quote
Old 12-14-2009, 10:35 PM
  #18
beyeriii
 
beyeriii's Avatar
 
Join Date: Dec 2009
Location: Boca Raton, FL
Posts: 3
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Center of gravity for delta wing...


Quote:
ORIGINAL: donnyman

Neuroza

I sent you a pm I trust you received it.

the information you seek is a subject often answered in our magazines. and example.
Hi DonnyMan,

Please post the name of the magazine and issue (April 2009) that has this diagram. I want to order a back copy to read the entire article.

Thanks,
Keller
beyeriii is offline  
Reply With Quote
Old 12-16-2009, 04:02 PM
  #19
donnyman
 
donnyman's Avatar
 
Join Date: Jul 2008
Location: Manor, TX
Posts: 1,239
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Center of gravity for delta wing...

THE MAGAZINE ARTICLE IS MODEL AVIATION THE A.M.A. MAGAZINE. APRIL 2009 ISSUE. AS I SAID IN A EARLIER POST, A HOST OF INFORMATION IS AVAILABLE, I THINK I HAVE SEVERAL ARTICLES ON THE SUBJECT. JUST HAVE TO FIND THEM.
donnyman is offline  
Reply With Quote
Old 12-16-2009, 04:31 PM
  #20
Mustang Fever
 
Mustang Fever's Avatar
 
Join Date: Nov 2003
Location: Cadillac, MI
Posts: 3,225
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Center of gravity for delta wing...

I wouldn't put too much faith in that "25%" figure in the article. That may work for almost all conventional wing and tail section designs, but it won't work for any delta that I know of. Maybe the F-106 wing plan, because it has so much of the wing area aft, rather than forward. (After all, it's the wing area aft of the CG that's stabilizing the delta in pitch. Any kind of long or large projection in front of the wing makes that job harder, and requires a more conservative CG to compensate.)

I've built several of the Laddie Mikulasko "Arrows", which is a pure delta design, and the CG that gets you a controllable and stable airplane is between 0 and 5% of MAC. It does not have a severe sweep to the leading edge, and so has much of the wing area located forward, plus it has a rather long and wide nose with a square cross section, as it's a flying boat. It also has an aft mounted tank, which makes things even goofier.

The Lanier Shrike is a "sorta" delta with a short tail section tacked on just aft of the wing, and the factory CG works out at a little over 16% of MAC.

The CG tape is on both the pictured birds, so you can get an idea.

I wish there was a formula or a rule of thumb that used wing area opposite each 10% section of the root chord, plus a fiddle factor for the effects of the nose, but there's not. When you start getting into "tailed" deltas like the F-4 Phantom II or the Mig 21, then everything seems to go out the window.

The Pogo looks like it has a lot of wing aft. I'd start with 10-15% and go from there.
Attached Thumbnails
Click image for larger version

Name:	Pn36834.jpg
Views:	162
Size:	125.5 KB
ID:	1335767   Click image for larger version

Name:	Rm38927.jpg
Views:	173
Size:	106.0 KB
ID:	1335768  
Mustang Fever is offline  
Reply With Quote
Old 12-17-2009, 12:19 AM
  #21
beyeriii
 
beyeriii's Avatar
 
Join Date: Dec 2009
Location: Boca Raton, FL
Posts: 3
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Center of gravity for delta wing...

Hi Donny,

Thanks for posting the magazine name and issue, I hope I can someday return the favor

I have sent Academy of Model Aeronautics a $7 check for an April 2009 back issue.

Keller
beyeriii is offline  
Reply With Quote
Old 12-17-2009, 12:38 AM
  #22
beyeriii
 
beyeriii's Avatar
 
Join Date: Dec 2009
Location: Boca Raton, FL
Posts: 3
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Center of gravity for delta wing...

Hi Bob (Mustang Fever),

Thanks foryourearlier (6/14/2008) explaination and drawing,it is very similar to the MODEL AVIATION April 2009 article.
Thanks also for the new posting with advise regarding thevarianciesof delta wings.
I am very new to RC Planes but have some expierence with electric cars.
I will be rereading your explainations as well as theModel Aviationarticle until I get a firm grasp on these topics.

Thanks again for your helpfulness
Keller
beyeriii is offline  
Reply With Quote
Old 12-26-2009, 01:17 PM
  #23
CloudyIFR
 
CloudyIFR's Avatar
 
Join Date: May 2006
Location: Helena, MT
Posts: 86
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Center of gravity for delta wing...

Go to www.TailwindGliders.com and download "Flying Wing Calc". There is a tutorial on how to use on the "Article/Files" page of the website. The article is for "Sailplane Calc" but it'll work for you. Deltas are a little different than most but they are very similar to flying wings except for the very low aspect ratios.

Just a little background:
All airfoils have a pitching moment around the 23-25% of the Mean Aerodynamic Chord (MAC). This means if you balanced your model here it would be neutrally stable, if balance further aft it would become unstable and if balanced forward it would be stable, i.e. it would try to self correct any wind shear changes, pitch changes etc....
The distance of the MAC from the neutral point (NP) is called the static margin (SM). The SM I recommend for first flights would be about 8% forward of the NP.
Wings are funny and you'll notice that you may be able to really backup the balance point with a small SM but and it'll fly fine but then be very squirrelly on landing. This is caused by the higher AoA on landingand movement of the pressure points. Thus wings normally fly with a little higher SM than conventional planes.

Curtis
CloudyIFR is offline  
Reply With Quote
Reply


Thread Tools
Search this Thread
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -8. The time now is 12:11 AM.