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Old Jun 12, 2014, 11:39 AM
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Build Log
2x 64mm Avro Arrow

Hi guys,

Very soon I will be beginning a build on a foami Avro Arrow powered by 2 Hobby King 64mm EDF units on a single 2200mAh 3s. I'm not aiming for flight time, just for this thing bring able to fly

As of now, I haven't chosen the dimensions, but they will revolve around the EDFs.
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Old Jun 12, 2014, 12:39 PM
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Do it Right, the first time!
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I'm sure you have all these measurements::
General characteristics

Crew: 2
Length: 77 ft 9 in (23.71 m)
Wingspan: 50 ft 0 in (15.24 m)
Height: 21 ft 2 in (6.25 m)
Wing area: 1,225 ft (113.8 m)
Airfoil: NACA 0003.5 mod root, NACA 0003.8 tip
Empty weight: 49,040 lb (22,245 kg)
Loaded weight: 56,920 lb (25,820 kg)
Max. takeoff weight: 68,605 lb (31,120 kg)
Powerplant: 2 Pratt & Whitney J75-P-3 turbojets
Dry thrust: 12,500 lbf (55.6 kN) each
Thrust with afterburner: 23,500 lbf (104.53 kN) each

Now the trick is to find good 3-views. You go on the say:
Quote:
As of now, I haven't chosen the dimensions, but they will revolve around the EDFs.
Find the FSA of the fans, and see how large the intakes and exhaust need to be, so you can base the scale size you need.. This is where the 3-views really need to be accurate.

Keep us informed.
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Old Jun 12, 2014, 04:48 PM
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Hi,

Very good choice! but 2200mAh for 2 x 64mm seems little light regarding amps.
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Old Jun 13, 2014, 08:48 PM
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Quote:
Find the FSA of the fans, and see how large the intakes and exhaust need to be, so you can base the scale size you need
And...the fans dictate what these area's need to be. With the large number of high count blade fans available, if these fans are used, the exhaust and intakes need to be 100% for these fans. 85% for low count blade fans.

And stef is correct. A 3s system is going to be a high amp system to gain the needed watts. You may need to go with a higher cell count pack and reduce the motors Kv to get the same needed watts. This will lower the total amp load considerably. Two 3s 40c Zippy packs (in series) are 6 oz. Kv's are dependent on type of fan. But a goal of 20A per fan will allow the 2000-2200 size 6s packs @ 40A total..

Most ESC's allow 6s use, and cheap. Two 30A ESC's would save weight.

Fuzz
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Old Jun 14, 2014, 01:37 PM
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Okay so I'll address the twin fan on one 3s first.

First of all, I need to correct a mistake. The title should say 50mm not 64mm.
The fans being used are:
http://www.hobbyking.com/hobbyking/s..._version_.html

They're rated at 19A max so I don't think its going to be much of a problem.

I don't even trust the thrust data hence the reason why I'm using 2 fans on only a single battery. I'm aiming for a really light setup.

Next:

These are the measurements I've come up with so far.
Length: 115.8cm
Wingspan: 78.6cm
Intake opening: 4050mm^2 per duct

I've started drawing the templates and cutting them out. I'm using Elmer's board for the body and wings and pink insulation foam for the nose and exhaust sections.

Thanks for the tip guys and pictures are coming soon

BTW this is my first scratchbuild so forgive me if i seem ignorant at times
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Last edited by acebonse; Jun 15, 2014 at 11:34 AM.
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Old Jun 14, 2014, 01:51 PM
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Quote:
Originally Posted by CoolerByTheLake View Post
Find the FSA of the fans, and see how large the intakes and exhaust need to be, so you can base the scale size you need.. This is where the 3-views really need to be accurate.

Keep us informed.
Please just link to my blog post in the future when passing out my FSA calculator

http://www.rcgroups.com/forums/showthread.php?t=1160865
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Old Jun 14, 2014, 03:50 PM
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Progress on the fuselage. I'm not gonna add air ducts
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Old Jun 14, 2014, 09:17 PM
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Okay so Ive finished the wings with some help. Turned out really nice
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Old Jun 15, 2014, 12:13 PM
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Quote:
Originally Posted by SteveC68 View Post
Please just link to my blog post in the future when passing out my FSA calculator

http://www.rcgroups.com/forums/showthread.php?t=1160865
My appologies, I shall. I had downloanded the aap, but did not have the link saved.
Cooler
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Old Jun 15, 2014, 12:51 PM
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Quote:
Originally Posted by CoolerByTheLake View Post

Find the FSA of the fans, and see how large the intakes and exhaust need to be, so you can base the scale size you need.. This is where the 3-views really need to be accurate.
Okay so my intakes have come out to more than 100%. Is that okay?

I know that I have to make the exhaust tubes around 85-90%
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Old Jun 15, 2014, 02:34 PM
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Quote:
The intake came out to be 245% :O
http://www.rcgroups.com/forums/showp...9&postcount=26


Doesn't seem you folllowed your plan-
Quote:
As of now, I haven't chosen the dimensions, but they will revolve around the EDFs.
Quote:
These are the measurements I've come up with so far.
Length: 115.8cm = 45.59"
Wingspan: 78.6cm = 30.9449"
intake opening: 4050mm^2 per duct = 6.277 sq/in
Those sizes intakes will create tremendous drag, and the fans won't preform well.
Correct intake FSA and exhaust dia, are not set in stone, different fans require different parameters. On all my scratch builds, I use the JF 90, intake and exhaust FSA for it should be approx 100% for both for max thrust.

Corsair Nut uses a number of JF's, and his are different (smaller) than what I might use -- he likes SPEED!

Alot needs to be taken into consideration when planning a scratch build.

AUW, wing loading, actual power you'll get from your fan/'s-- etc etc--

I have looked up the Avro Arrow, and they do have large/huge intakes for a 50mm fan-- there is the problem, trying to do a model to scale -
From my point of view, those intake are just too BIG. Bigger fans migh help if they will fit in the same size fuse.. look at using a single 70/80mm,

Perhaps others will chime in with some better advice.
Good luck

Ace, you said you ended with 245% FSA-- = intake opening: 4050mm^2 per duct = 6.277 sq/in

100% would be 1653mm^2 = 2.56 sqin per duct.
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Last edited by CoolerByTheLake; Jun 15, 2014 at 04:43 PM. Reason: corrected dimensions
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Old Apr 05, 2015, 11:09 PM
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I did in fact finish the airframe, but I just never got around to uploading the pics.
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Old Apr 05, 2015, 11:11 PM
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Here it is all painted!
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Old Apr 06, 2015, 05:56 AM
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Oh no, not again!
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Nice paint job and great looking model. What are you using for cog?

Cooler, please excuse my ignorance, but why would oversize inlet ducts cause huge drag? Wouldn't a restrictor at the inlet itself create just as much drag hanging out in the airflow, or have I missed something?

I ask b/c a depron CF 105 is on my bucket list. The original design was criticized for the long inlet ducts b/c they took up so much fuselage volume.

Still a striking airplane though, isn't it. I hate Diefenbaker.

Regards,
Jeff
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Old Apr 06, 2015, 06:12 AM
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nice job
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