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Old Jan 18, 2004, 07:21 PM
Registered User
Ravenna,Nbraska
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Center of Gravity for Delta wing ???

Could someone be kind enough to tell me how to calculate the CG of a Delta wing such as is used on the Convair F-102, F-106, and B-58 Hustler...This is a triangular wing that has a tip cord length of zero...

I have no problem calculating the CG on tapered wings, but I don't trust my findings on a Delta...Just doesn't look right...

Thank you for your time and consideration...

Jerry Hall
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Old Jan 18, 2004, 07:50 PM
Ascended Master
Sparky Paul's Avatar
Palmdale, CA
Joined Oct 2000
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For a 20 % c.g... it might look like this...Your chord and span will vary..
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Old Jan 18, 2004, 11:01 PM
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SparkyPaul...

Thanks for the input...I was puzzled at first that you quoted 20% MAC.. I have for years balanced models ( with constant cord and slightly tapered wing planforms) at 27-30 %... I had no idea that a delta would balance at 20 % MAC... Thats why my calculations weren't making sense as the CG I came up with fell aft of the scale position of the main landing gear...

I made a quickie glider out of fanfold foam and it glided quite well while balanced at the 20% MAC point....Ah, the things we learn while at play....

Thanks again for your help.....

Jerry Hall
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Old Jan 20, 2004, 11:25 PM
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DanSavage's Avatar
Trabuco Canyon, CA
Joined Nov 2000
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Quote:
Originally posted by JerryHall
SparkyPaul...

Thanks for the input...I was puzzled at first that you quoted 20% MAC.. I have for years balanced models ( with constant cord and slightly tapered wing planforms) at 27-30 %... I had no idea that a delta would balance at 20 % MAC... Thats why my calculations weren't making sense as the CG I came up with fell aft of the scale position of the main landing gear...
Hi Jerry,

I balanced my F-106 EDF at 23% MAC and it flew fine. In fact, I could've balanced it at 25% MAC and it would've flown even better. I wouldn't go any further aft than that, though.

Dan

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Old Jan 21, 2004, 01:40 AM
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Ravenna,Nbraska
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Dan...

Thanks for the reply, and especially the graphic...I started cutting foam for the F-102 today...
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Old Jan 21, 2004, 11:13 PM
Marion
USA, NC, Hillsborough
Joined Oct 2003
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All said and done, you will find that a delta wing should be balanced about 1/2 way between the wing apex and the trailing edge. That always turnes out to be near 25% of the MAC.

Have fun with the delta :-)
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Old Jan 22, 2004, 01:32 AM
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Ravenna,Nbraska
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The F-102 is going to have a 30 inch span..So to locate the MAC and compute the balance point I needed some room....The concrete floor was about the only place I could go since the workbenches were full...It worked well...Photos to follow:
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Old Jan 22, 2004, 01:36 AM
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Ravenna,Nbraska
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This photo shows tonites progress....I am going to start a thread in Scale on th F-102 build...I would be glad if youall would join in..
Thanks to everybody for your help in the technical area of finding the CG.... It really had me stumped, but now I see the light...
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Old Jan 22, 2004, 07:12 PM
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Trabuco Canyon, CA
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Quote:
Originally posted by JerryHall
The F-102 is going to have a 30 inch span..So to locate the MAC and compute the balance point I needed some room....The concrete floor was about the only place I could go since the workbenches were full...It worked well...Photos to follow:
FYI:

Looking at your drawing in the photo you posted, I can see that your CG calcs are incorrect. You neglected to include the portion of the wing inside the fuselage. As a result, your model will be tail heavy if balanced at the point shown in the photo you posted because the MAC is in the wrong location.

You must always carry the wing planform all the way to the centerline of the airplane in order to derive an accurate balance point.

Dan
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Old Jan 22, 2004, 07:33 PM
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Thanks Dan..

I almost shot myself in the foot before I got started...
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Old Jan 22, 2004, 10:15 PM
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Trabuco Canyon, CA
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Quote:
Originally posted by JerryHall
Thanks Dan..

I almost shot myself in the foot before I got started...
No problem, Jerry. I'd hate to see such a cool model lost for something like that.

As long as you're at it, you may as well put a vortex flap (conical camber) on the leading edge of the wing. It'll help keep the model from generating too much drag in the turns.

Here's a pic of the vortex flap on a real F-106.

The F-102's wing was exactly the same as was the B-58's.

If you go to my web site, you can see how I created a simplified vortex flap for my F-106.

http://members.cox.net/marsavage/Dart

You can find info on how I did mine by looking on the wing page.

Dan
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Old Jan 23, 2004, 12:35 AM
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Ravenna,Nbraska
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Hi Dan...

I got a chance to go over your web site...A lot of good information there... hat a really great looking model....
Thanks for the link...It always saddens me to hear of the demise of an aircraft such as the Six when it was used as a drone, but I guess they all have to come to an end one way or another...

I have a plan to make the vortice flap on mine...I have tho old Monogram 1/48 scale plastic kit for reference also..

I have a NIB fan and APL-29 motor designed for the Kyosho T-33... In your oinion, would the Kyo fan assembly put out more thrust than the GWS considering that I will throw awaay the stock motor and use a brushless motor in whichever fan I use......???
I will not use the stock GWS motor that comes with the fan ( GWS-64 ), I understsand that the APL-29 isn't all that great either...

There is so much to learn about Deltas, and EDFs, and I am beginning to wonder if I haven't gotten in over my head...

Thanks for the guidance...
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Old Jan 23, 2004, 06:19 PM
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Trabuco Canyon, CA
Joined Nov 2000
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Quote:
Originally posted by JerryHall
Hi Dan...

I got a chance to go over your web site...A lot of good information there... hat a really great looking model....
Thanks for the link...It always saddens me to hear of the demise of an aircraft such as the Six when it was used as a drone, but I guess they all have to come to an end one way or another...

I have a plan to make the vortice flap on mine...I have tho old Monogram 1/48 scale plastic kit for reference also..

I have a NIB fan and APL-29 motor designed for the Kyosho T-33... In your oinion, would the Kyo fan assembly put out more thrust than the GWS considering that I will throw awaay the stock motor and use a brushless motor in whichever fan I use......???
I will not use the stock GWS motor that comes with the fan ( GWS-64 ), I understsand that the APL-29 isn't all that great either...

There is so much to learn about Deltas, and EDFs, and I am beginning to wonder if I haven't gotten in over my head...

Thanks for the guidance...
Hiya Jerry,

Thanks for the kind words.

The KY/AP-29L is a good low-power combination that was especially designed for hand-launched jets and nicad battery packs of 7-8 cells. You have to be careful when you start increasing the power levels, though because if you spin them too fast, they'll start shedding blades.

I can't remember at what RPM this happens, though, so your best bet would be to do a search on the jet forum for this info as well as info about which is the best BL motor to use with the KY fan.

I have no experience with the GWS fan, so I couldn't comment on any comparisons to the KY fan.

I think you're doing a fine job. Keep up the good work. I'm looking forward to reading your flight reports.

Dan
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