CG question for a tapered delta (Harpoon from Jepe)  
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All Forums >> RC Airplanes >> Aerodynamics >> CG question for a tapered delta (Harpoon from Jepe)
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CG question for a tapered delta (Harpoon from Jepe) - 3/17/2008 10:05:48 PM   
Cliffhanger


 

Posts: 13
Joined: 10/14/2005
From: Leiden, NETHERLANDS
Status: offline 		Hello fellow RC friends,
I am currently rebuilding an old Delta from jepe models called the Harpoon.

ATM I am struggling with the CG of this plane.
I have asked the manufacturer but because I am planning to mount a pulsejet on this former EDF, the manufacturer does not want to help me out.

can someone please help me find the CG of this plane.

any help is much appreciated...



< Message edited by Cliffhanger -- 3/17/2008 10:08:18 PM >
       Post #: 1

RE: CG question for a tapered delta (Harpoon from Jepe) - 3/18/2008 12:18:10 AM   
crasherboy


 

Posts: 112
Joined: 10/21/2006
From: Bryant Pond, ME, USA
Status: offline 		Question; what does the company care what you are putting on it for power? As to balance ,if it were me I would start at about the front of the finns,you can test glide it to see how that would work out.

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Do unto others as you would be done unto,well most of the time anyway!

(in reply to Cliffhanger)
       Post #: 2

RE: CG question for a tapered delta (Harpoon from Jepe) - 3/18/2008 3:42:00 AM   
Mike Connor



Posts: 1384
Joined: 1/10/2002
From: Tulsa, OK, USA
Status: offline 		Delta's typically balance 15%-18% MAC.

_____________________________

Mike
http://www.mikesrc.us/

(in reply to crasherboy)
       Post #: 3

RE: CG question for a tapered delta (Harpoon from Jepe) - 3/18/2008 7:24:32 AM   
Cliffhanger


 

Posts: 13
Joined: 10/14/2005
From: Leiden, NETHERLANDS
Status: offline 		And that is exactly the problem..

I have the foggiest clue on how to calculate MAC and or an X percentage of it.
After examining some XLS calulation sheets and trying to understand the principles of MAC, i decided to give RCU a shot.
I'm stuck..

The picture of the plane is taken right from above.
Is there someone who can photoshop the CG on top of that?

Thanks

(in reply to Mike Connor)
       Post #: 4

RE: CG question for a tapered delta (Harpoon from Jepe) - 3/18/2008 11:28:23 AM   
da Rock



Posts: 6705
Joined: 10/11/2005
From: western, NC, USA
Status: offline 		Well, it is quite a bit of drawing and such. Since it's a two-taper planform, it would have been about three times as much as shown. Since I knew the area I chose to work was going to be 90% of the working area, I only did that area.

See the yellow line. That's the MAC of the primary area of the wing.

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< Message edited by da Rock -- 3/18/2008 12:01:39 PM >

(in reply to Cliffhanger)
       Post #: 5

RE: CG question for a tapered delta (Harpoon from Jepe) - 3/18/2008 11:37:20 AM   
da Rock



Posts: 6705
Joined: 10/11/2005
From: western, NC, USA
Status: offline 		The star is about .18C of the MAC of the primary area.

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(in reply to da Rock)
       Post #: 6

RE: CG question for a tapered delta (Harpoon from Jepe) - 3/19/2008 10:53:28 AM   
Cliffhanger


 

Posts: 13
Joined: 10/14/2005
From: Leiden, NETHERLANDS
Status: offline 		YOU ROCK DA ROCK !!!!

Thanks for the effort in calculating the CG.
One last thing though, my gut says the CG looks a bit too much to the aft..

What's wrong with my gut?!

(in reply to da Rock)
       Post #: 7

RE: CG question for a tapered delta (Harpoon from Jepe) - 3/19/2008 2:53:46 PM   
da Rock



Posts: 6705
Joined: 10/11/2005
From: western, NC, USA
Status: offline
quote:

ORIGINAL: Cliffhanger

YOU ROCK DA ROCK !!!!

Thanks for the effort in calculating the CG.
One last thing though, my gut says the CG looks a bit too much to the aft..

What's wrong with my gut?!



Well, as I mentioned in post #5 above, I didn't calculate the CG for you. I only did about 1/4 the work that'd be required for that double-taper wing. And then just estimated the 18% location.
Because the area I did not consider was only around 14-15% the total wing area and is where it isn't very effective as a wing. And I figured most who looked at the lines would see what I was leaving out.

I was really hoping someone with a lot more time would benefit from the work I did positioning the picture and doing a bit of the drawing, and would pick up from there.

You might try this application:
http://pagesperso-orange.fr/scherrer/matthieu/english/mce.html

It should work for a wing with double taper planform.


(in reply to Cliffhanger)
       Post #: 8

RE: CG question for a tapered delta (Harpoon from Jepe) - 3/20/2008 7:22:44 AM   
DanSavage



Posts: 577
Joined: 4/17/2002
From: Trabuco Canyon, CA, USA
Status: offline
quote:

ORIGINAL: Cliffhanger
can someone please help me find the CG of this plane.

any help is much appreciated...


Here's what I got. The front line represents 20% MAC and the rear line is 25% MAC. Anywhere in between should work.

Dan

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(in reply to Cliffhanger)
       Post #: 9

RE: CG question for a tapered delta (Harpoon from Jepe) - 3/20/2008 10:37:26 AM   
Cliffhanger


 

Posts: 13
Joined: 10/14/2005
From: Leiden, NETHERLANDS
Status: offline 		Hello Dan,
that looks like the hotspot to me.

I will start at the front line and work my way back if needed.

Thanks for all the help guys and kudos to this forum!

Cliff

(in reply to DanSavage)
       Post #: 10

RE: CG question for a tapered delta (Harpoon from Jepe) - 3/21/2008 11:12:13 PM   
Flypaper 2



Posts: 4308
Joined: 3/29/2002
From: Kingston, ON, CANADA
Status: online 		Easiest, cheatin way is to build a balsa or depron glider with the same planform, bout 1 ft wingspan. Put a little up elevon, or reflex if you will, Put weight on the front to get a fast flat glide and you'll be very close. % wise it will be in the same place.

< Message edited by Flypaper 2 -- 3/21/2008 11:13:32 PM >

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Dreamed I was a muffler. Woke up exhausted.

(in reply to Cliffhanger)
       Post #: 11

RE: CG question for a tapered delta (Harpoon from Jepe) - 3/23/2008 5:37:06 PM   
DanSavage



Posts: 577
Joined: 4/17/2002
From: Trabuco Canyon, CA, USA
Status: offline 		I don't think building a glider is the easiest way. It took me less than 5 minutes to do the calculation in CAD. I've done many models this way and the the CG is usually right on the money. If you don't have access to CAD, then the glider method is a good substitute.

< Message edited by DanSavage -- 3/23/2008 5:38:35 PM >

(in reply to Flypaper 2)
       Post #: 12

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