scratch built F4 Phantom - RC Groups
Feb 19, 2002, 05:30 PM
Registered User

# scratch built F4 Phantom

My first E-project. I cut the fuse and wings from foam, and balsa sheeted the wings. It's powered by a speed 400. And, on the initial test flight, it fell nose first after about ten yards. A new nose and paint job later, and I fried the speed controller on the flight check. still waiting on the new one to come in.
I need to know how to calculate the wing loading, and determine the flying weight. otherwise, I may be cutting a new fuse. Any help would greatly be appreciated.
My camera is broken, so as soon as I can get pics I'll post em.
Thanks.
Feb 19, 2002, 07:19 PM
Registered User

# Re: scratch built F4 Phantom

Quote:
 Originally posted by OCTANE75 I need to know how to calculate the wing loading, and determine the flying weight. otherwise, I may be cutting a new fuse. Any help would greatly be appreciated.
I'm sorry to hear about your bad luck. In order to calculate the wing loading, you first need to know the weight. The easiest way to get this is obviously to place it on a scale. If you don't have one available, you can take it to the Post Office after hours (or during hours) and use their self-service scale. Plenty accurate for our purposes.

Secondly, you'll need to know the wing area (figure it to the centerline of the fuselage). Once you have these, the wing loading is easy to figure. It's the weight in ounces divided by the wing area in square feet, hence the oz./sq. ft.

It sounds like your F-4 is nose heavy. Unfortunately, there's too many variables involved to be able to diagnose the problem without more information, specifically:

- pusher or tractor?
- thrust line?
- wing planform
- wing incidence
- airfoil (flat bottom, etc.)
- tail plane incidence
- control surface throws

The simplest solution is the ol' trial and error. I would recommend making a scaled down "chuck-glider" using your planforms and incidences. Then take it out and give it a "chuck" and see what it does. Continue doing this, adding weight as needed until it has a normal glide. Then you can transfer this balance point to the powered model and it should be pretty close.

Please post photos when you can. I'd love to see your Phantom! I hope this helps.

Daren
 Feb 20, 2002, 01:59 PM Registered User The Motor is tractor, and I dont know the thrust line (or how to identify one). I took measurements off of an F4 model I have, and roughly doubled them. The airfoil is flat bottom, and I'm throwing at about +/- 1/4". The model glided pretty far (about 40') when I first built it. It had no radio equipment, battery, motor, etc... The tail touched down first when it landed. Maybe I should have taken CG then? Well, I'll post some pics this weekend. I'm getting my father-in-law's camera. Thanks Daren
 Feb 20, 2002, 02:20 PM Gravity sucks. You should ALWAYS use a fuse between the motor and the ESC also. 15cents could have saved \$\$.
Feb 20, 2002, 09:42 PM
Registered User
Quote:
 Originally posted by OCTANE75 Maybe I should have taken CG then?
Perhaps so if it seemed like it glided well. Here's a top view of the CG I used on my Phantom. This may or may not be useful to you as I used the scale wing planform. If your's is different, some adjustments might have to be made. Please post some pictures when you get them.

Good luck!
Daren

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 Feb 22, 2002, 04:26 PM Registered User Thatr looks about right where I centered the plane. My CG may be a lil further aft of your CG. I should get the pics tonight, and I'll post em tomorrow.
 Feb 22, 2002, 06:01 PM Registered User I have flown it with the CG about 3/8" forward of this point. It required a fair amount of uptrim in the elevator for level flight. I can't speak for further aft than this point (I'd be nervous to try!). If your's was aft of here, it may have been tail heavy and pitch unstable, in which case, the nose down was just the first direction it went rather than nose up. I will be doing my contest proof flight tomorrow with it balanced almost exacty on this CG mark. I'll keep an eye out for your pictures. Daren Last edited by Daren; Feb 22, 2002 at 06:04 PM.
 Mar 02, 2002, 06:07 PM Registered User Hey Darren, I didnt want you to think I gave up. I've been sick for the last week, and have had no time to tinker. My camera is still broken, my only alternative fkor digital pics is missing the software. I'll try to shoot some conventional pics and scan them. Should be soon.
 Mar 05, 2002, 10:16 AM Registered User Hey Darren, I forgot to ask you. How did your F4 fly? What motor/ battery combo did you use. Also, what ESC?
 Mar 05, 2002, 11:05 PM Registered User OCTANE75, Not a problem, I have the patience of a clam. My F-4 flies great! I'm very happy with it. The first flights were with the Ky fan, Hacker B40 11S, with a Jeti 40 3P using 10-CP1300s. Because this was built for the EDF contest, I've presently got the Ky fan/AP29L with a Astro 210 ESC and 8-CP1300s for the contest proof flights (hopefully this weekend if the wind and weather cooperates). Once this is successfully out of the way, I'll probably end up with a Wemotec HW-609 with either a rare earth motor or a BL set up to pick up the top speed a little bit over what the Ky fan can do. I'm leaning towards the BL. Daren Last edited by Daren; Mar 05, 2002 at 11:11 PM.
 Mar 07, 2002, 12:11 PM Registered User Thanks for the input Darren. My project is tractor, but I would like to build an edf version. I will have pics on it by tomorrow night.
Mar 10, 2002, 04:12 PM
Registered User
Here are the pics, Daren. Do you have any of your EDF version

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Mar 10, 2002, 04:13 PM
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Pic#2

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Mar 10, 2002, 04:13 PM
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Pic#3

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 Mar 10, 2002, 08:49 PM Schumacher USA FLAMES ROCK!