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Old Oct 22, 2006, 09:33 PM
Sam Talley
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Nashville, TN
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Dumas Cessna L-19 Bird Dog designed by P. Tritle / A Neophyte's Build

Here is my build of the Dumas Cessna L-19 Bird Dog, designed by P. Tritle. There is nothing special about the build, except for the power plant. I did have a little trouble with the instructions regarding the sanding jib for the tail section, but a PM to Mr. Tritle resulted in a quick response which provided the clarity I needed.

Specifically, the instructions refer to building a sanding jig, but the purpose of the jig was unclear to me. The jig is used to sand the balsa filler blocks that brace the vertical stabilizer and provide some contour from the end of the fuselage. The T1 parts rest on top of the fuselage where the horizontal stabilizer will sit. Here is a drawing with some additional labeling:
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Old Oct 22, 2006, 09:42 PM
Sam Talley
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Nashville, TN
Joined May 2003
299 Posts
Here are the specs:

IPS A Drive
3-Cell / 700 mAh Thunder Power Li-Po Battery
7X6 GWS Slowflyer Propellor (originally posted as 7X4)
HS-55 Servos (2)
Hitec 05S Receiver
AUW = 9 5/8 ounces

I chose to use of pushrod rather than pull-pull for the rudder. I also was not getting enough power from my original power setup, the GWS IPS A drive with a 2-cell / 450 mAh Li-Po battery and a 9X4.7 prop. I tried a couple of different props with no better results. I then tried the 7X6 (corrected) with the 3-cell Li-Po. I checked the amps with my Watt's Up meter and found the setup pulled 2.2 A at WOT. The Bird Dog will take off with authority at 2/3 throttle and cruises at less than 1/2 throttle, pulling right at 1.0 A. Hopefully, this will not burn up the drive.

Here are a shot of the interior:
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Last edited by Ranger13; Oct 22, 2006 at 11:19 PM.
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Old Oct 22, 2006, 09:46 PM
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Albuquerque NM
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Ranger, This is the first time I've seen a 7-4 prop recommended for the "A" Drive. I did all the test flying using a GWS 9-7 prop and a 2 cell 340 or 700 mah battery. 4.7 pitch won't be enough, and the 7-4 prop absolutley WON"T work -- on only two cells.

Sorry about the confusion, PAT
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Last edited by P. Tritle; Oct 22, 2006 at 10:39 PM.
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Old Oct 22, 2006, 10:02 PM
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United States, TX, Fort Worth
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That prop will work with the three cells he is talking about..
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Old Oct 22, 2006, 10:02 PM
Sam Talley
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Nashville, TN
Joined May 2003
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My error, it's a 7X6 prop. I'll change the second post. The L-19 climbs with authority, and cruises very nicely. It is no speed demon, but I don't believe it is designed for speed. Here are two shots of the finished model:
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Old Oct 22, 2006, 10:18 PM
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Economy, Pa.
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Your Bird Dog looks good Sam! Did you use the kit supplied tissue, or iron-on?
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Old Oct 22, 2006, 11:18 PM
Sam Talley
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Nashville, TN
Joined May 2003
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Thanks for your kind words. I used red and white Litespan from H-L, with Balsaloc as the adhesive.

http://www.hobby-lobby.com/litespan.htm

I've used this before and it works very well.
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Old Oct 22, 2006, 11:26 PM
Neophyte hacker
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Albuquerque, NM USA
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Nice job.

As long as you fly it more sedately the motor will last for a while. I'd keep one around as a backup though.

charlie
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Old Oct 22, 2006, 11:42 PM
Sam Talley
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Nashville, TN
Joined May 2003
299 Posts
I know that 2.0 A is death to a GWS IPS-A, so I plan to replace it with a Feigao 12x30mm brushless motor when the time comes. I may try a 9X7 prop again with a 2-cell Li-Po, but my build of this plane did come out quite a bit heavier than the prototype (8 oz ?? vs 9.63).

I'll try to post some video in the next day or so.
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Old Oct 23, 2006, 12:00 AM
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Quote:
Originally Posted by Thomas B
That prop will work with the three cells he is talking about..
Pretty well too. I'm setting one up right now. Underpropping to 7" for 3s with the A drive seems to work pretty well at acceptable current levels of 2A with a short 12mm Feigo. I need to measure thrust data, but I have no concers of it being underpowered, given reasonable wing loading. One of the reasons I'm using the setup is to avoid large, off-scale slowflyer props. Sacrificing a bit of efficiency is not a concern in this case.

Bill
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Old Oct 23, 2006, 09:32 AM
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Albuquerque, NM USA
Joined Sep 2003
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I flew IPS drives on 3s and kept current to about 1.8A. Did fairly well. I'd get about 50 half hour flights before the motor would give up.

With the availability of Feigao motors at lower prices and cheap ESC's they are really the way to go for IPS models. I use the Feigao's at 4A on 3s and they just humm away.

Sounds like your Bird Dog will fly OK, especially at your altitude. Up here it would probably be stressed a bit to climb.

charlie
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Old Nov 02, 2006, 08:03 AM
Sam Talley
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Nashville, TN
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Here is a link to some video:

http://www.rcgroups.com/forums/showt...62#post6322831
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Old Nov 02, 2006, 11:45 AM
Registered User
Lockport, Ill
Joined Aug 2003
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Hi Sam,
your Bird Dog looks vey nice. I'm debating weather to start the kit or Pat's 1#%^@*4tee. I found this motor and was planing on using it for either kit. Maybe you can give me your opion. http://www.xushobby.com/servlet/Detail?no=104
Rich
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Old Nov 02, 2006, 03:17 PM
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United States, CA, Garden Grove
Joined Oct 2000
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DXA Brushless

Looks like it may be a good setup. I ran a Faigao 12mm in DXA geardrive on 8x4 SF prop 3S 400mah lipo and it gave good power but ran hot and eventually died. Replaced it with a Medusa 12mm 4000 kv and it ran much cooler, still going strong. They are about $10 more than Faigao but lower internal resistance and better bearings ( I think). BTW I'm building the One-For-Tee, using Himax 1220-840 outrunner with shaft reversed and radial mount setup, 800mah 2 cell lipo, as recommended by Pat. I'm sure that the DXA/Medusa would power either model well too. I think that outrunners can have better longevity without gearbox.
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Last edited by E-Challenged; Nov 02, 2006 at 03:31 PM.
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Old Nov 02, 2006, 04:26 PM
Sam Talley
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Nashville, TN
Joined May 2003
299 Posts
Here is some data for a Feigao 1208436 12x30mm Brushless Motor in an IPS A 5.86:1 gearbox and an 8X6 propellor (sorry about the lack of spacing):

Volts Amps Thrust (oz) Thrust (grams) 340mAh 700mAh 1200mAh
7.4V 2.2A 5.40 oz 154.30 g 9 minutes 19 minutes 33 minutes
8.4V 2.5A 6.30 oz 180.00 g 8 minutes 17 minutes 29 minutes
9.6V 2.8A 7.90 oz 225.70 g 7 minutes 15 minutes 26 minutes
11.1V 3.5A 9.70 oz 277.10 g 6 minutes 12 minutes 21 minutes

The website you note shows the motor you selected providing up to 350 oz of thrust. As long as your ESC and battery can handle the amps, this is more than ample thrust for either the L-19 or the #&@@*$ One-For-Tea.

Let me hasten to add that I am no expert at motor selection, merely someone who embraces empericism, and faithfully uses a Watt's Up meter.
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