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Old Jun 23, 2012, 07:18 AM
Hey Guys, Watch This.......
mike2663's Avatar
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Great news thanks for the update.

Mike
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Old Jun 23, 2012, 08:24 PM
awrightbrother's Avatar
Florida
Joined Nov 2007
2,515 Posts
Well folks, I made more progress on the CAD design and have run into a problem.

The height of the rear fuselage is not high enough to accommodate a 90MM fan. Even going down on the foam wall thickness to 1/2" does not help.

The alternative is to use 70MM. One will not have enough thrust to fly this beast, two means more cost.

Your thoughts?
Fahim
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Old Jun 23, 2012, 08:31 PM
Capt. Z
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United States, NV, Las Vegas
Joined Dec 2004
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How close is it..would sizeing the kit up and inch or two make it fit.
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Old Jun 23, 2012, 08:55 PM
DELTAS RULE
corsair nut's Avatar
tehachapi, CA
Joined Jan 2006
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twin 70s wouldnt really vost more than a 90 and it would sound way cooler. a 90 fits in my 1/8 scale f5 but barely and itsmade from 6mm depron. either size up to 80" or go twin 70's....
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Old Jun 23, 2012, 09:12 PM
Hey Guys, Watch This.......
mike2663's Avatar
USA, TX, El Paso
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I'm still in on this. I trust corsair nut and falcon5, they both have a good working knowledge on what will work.

Mike
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Old Jun 23, 2012, 09:21 PM
Registered User
United States, TX, Grand Prairie
Joined Nov 2005
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You mentioned rear fuselage, most fans are slightly behind mid fuselage or 1/3rd from end of exhaust tube.

Twin 70s would take more power at 10lbs than a single 90, on the other hand twin 80mm eflights would take less power to be at 11lbs than a single 90...

Hmmm, come to think of it....

twin eflights at 5.5lbs thrust\55amps\6s x 2 sounds REALLY good...theoretically you can power 11lbs of thrust off a single 5000mah 6s..or bridge the escs and with two 3300mah 6s packs and fly "long time" if the AUW is round 12-13lbs...

There are some really nice ducting options for this aircraft at this size...

Are you CADing the ducts also?
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Old Jun 23, 2012, 10:25 PM
DELTAS RULE
corsair nut's Avatar
tehachapi, CA
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my 1/8 scale f5 from depron was 5.25 lbs and twin 70s...granted it only had a 4s 5000. i highly dought theres enough inlet for twin 80s
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Old Jun 23, 2012, 10:25 PM
awrightbrother's Avatar
Florida
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Falcon 5:
80.64" length is required for 90mm to fit.

CN & MIKE:
If we go to 81" do you think a single 90mm would be enough or do we have to go for twin 90mm? If so, then maybe the better choice would be to stay at 72" and use twin 70mm.

ERH7771:
The fans are located just aft of the wing TE.
As for weight, my swag is that it should come in around 10 to 12 lbs AUW.
Yes I can CAD the ducts, but will wait for us to decide the fan config first.

Fahim
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Old Jun 23, 2012, 10:43 PM
DELTAS RULE
corsair nut's Avatar
tehachapi, CA
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80" isnt that big for a f5. its long and skiny. a 90mm will fly it awesome. remember you can get up to 11-12 lbs of thrust grom a 90. go 81" and singlev90 amd dont look back
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Old Jun 23, 2012, 10:44 PM
awrightbrother's Avatar
Florida
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Quote:
Originally Posted by corsair nut View Post
my 1/8 scale f5 from depron was 5.25 lbs and twin 70s...granted it only had a 4s 5000. i highly dought theres enough inlet for twin 80s
Ah yes, I forgot about the inlets. Twin 90mm are out. I wonder if we have enough inlet for twin 70's. Let me check and get back.
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Old Jun 23, 2012, 10:48 PM
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United States, TX, Grand Prairie
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Quote:
Originally Posted by awrightbrother View Post
Ah yes, I forgot about the inlets. Twin 90mm are out. I wonder if we have enough inlet for twin 70's. Let me check and get back.
There are some REALLY REALLY neat things coming in 90s in the near future....I would do the 81, if you could do it for the price mentioned.

Fahim.....PM'd
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Old Jun 23, 2012, 11:17 PM
deltas are cool
AIR SALLY's Avatar
Tehachapi ,CA.
Joined Apr 2006
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81 and done .also due to where the c/G is on the 38 you might need to move the fan fwd some .due to fuse lift the c/g is way up front .if you had cad for ducts it would make makeing the plugs easier for me
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Old Jun 23, 2012, 11:23 PM
awrightbrother's Avatar
Florida
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At 72" fuse length, each inlet is 4.125 sq in. Total between the two is therefore 8.25 sq in. The FSA for a 70mm fan is 4.5 sq in. Since we need two, the min required inlet area is 9 sq in. Inlet is 92% of FSA.

At 81" fuse length, each inlet is 5.2 sq in. Total between the two is therefore 10.4 sq in. The FSA for a 90mm fan is 8.4 sq in. Since we need two, the min required inlet area is 16.8 sq in. Inlet is 62% of FSA.

The more I look at it, the T38 does not appear to be a good subject for scale modeling, unless it is really big.
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Old Jun 23, 2012, 11:29 PM
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eaticus's Avatar
Everett, WA
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Quote:
Originally Posted by awrightbrother View Post
At 81" fuse length, each inlet is 5.2 sq in. Total between the two is therefore 10.4 sq in. The FSA for a 90mm fan is 8.4 sq in. Since we need two, the min required inlet area is 16.8 sq in. Inlet is 62% of FSA.
I think CN/AS has hit the nail on the head!
CN's comment is the key:

Quote:
Originally Posted by corsair nut View Post
80" isnt that big for a f5. its long and skiny. a 90mm will fly it awesome. remember you can get up to 11-12 lbs of thrust from a 90.

go 81" and single 90 and dont look back
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Old Jun 23, 2012, 11:52 PM
DELTAS RULE
corsair nut's Avatar
tehachapi, CA
Joined Jan 2006
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single 90, you dont need two. trust me. why do you need two when you can get 10 lbs of thrust really easy, and 8 lbs of thrust super easy on a cheap 8s setup. the model isnt really going to weigh more than 9-10 lbs tops, and that would be with a 10s setup. you also need to look at keeping the power system fairly light.

go twin 70's or single 90. even at 80" i know it sounds huge, but its really not at all. not for a f-5/t-38. thats only a 44" wingspan. thats nothing.
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