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Scratch build Northop N9M - 8/15/2007 1:41:03 AM   
crashontakeoff



Posts: 76
Joined: 3/28/2006
From: Bayamon, AA, USA
Status: offline 		Building a Northrop N9M from Model Builder Plans. 80 inch wingspan. Going to try to post some pics.

crashontakeoff

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RE: Scratch build Northop N9M - 8/15/2007 10:54:33 PM   
speed lover


 

Posts: 130
Joined: 5/29/2006
From: , UNITED KINGDOM
Status: offline 		Just tagging along what kind of engine are you going to use also what sort of wing loading does a plane this size have

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       Post #: 2

RE: Scratch build Northop N9M - 8/15/2007 11:42:27 PM   
crashontakeoff



Posts: 76
Joined: 3/28/2006
From: Bayamon, AA, USA
Status: offline 		Have not decided what motor to use, the plans call for two astro 05's. I have lightend it quite a bit and my plan was to use two speed 400's or two GWS units with pusher props. As far as wing loading goes, the second sheet of the plans was not included, so my CG and wing loading is unknown. My plan and others agree is to make it nose heavy, and adjust the cg from there. The wing loadin is a concern to me, but I am using some foam in the center, and an aluminum wing spar through the whole wing. I am looking for a final weight of 32 oz without the batteries and radio. I am setting it up to be a glider as well so i can bolt on different power systems. i was thinking an engine pod facing forward with a 400 speed and folding prop. no matter what I plan on hand launching it. Thanks for the interest, I am going to do some more work today or tommorrow. It is a long process shaping the ribs with out templates.

Crash

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       Post #: 3

RE: Scratch build Northop N9M - 8/16/2007 12:27:38 AM   
BMatthews



Posts: 9011
Joined: 10/4/2002
From: Burnaby, BC, CANADA
Status: offline 		I'd run the wing planform through one of the online MAC calculators and set the CG at 18% of the resulting MAC length and position. That'll be a safe starting point. Plan on moving it back to around the 20 to 22% mark as part of the trimming and optimizing of the first series of flights and according to your comfort level.

How light do you figure you can make it? That's a lot of airplane for two Speed 400's to push around if you're looking for a bit of spirit in it.

The wing loading spec on the plans or article won't help you much since with all your mods to lighten things it'll have a much lighter loading than the original.

Frankly I'd shoot for a couple of 12 to 15 amp capable brushless motors that have a Kv of around 1300 to 1500 RPM/volt to provide a sporty performance. You likely won't need to run it much above 10 amps per motor but at least you'll have the option.

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RE: Scratch build Northop N9M - 8/16/2007 1:33:26 AM   
crashontakeoff



Posts: 76
Joined: 3/28/2006
From: Bayamon, AA, USA
Status: offline 		Thanks, I was wondering if someone knew what size brushless motors to use. My original estimate about wieght was probably way off by over 10 oz it will really be much lighter. I really think brushless is the way to go.

crash

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       Post #: 5

RE: Scratch build Northop N9M - 8/21/2007 12:24:19 AM   
crashontakeoff



Posts: 76
Joined: 3/28/2006
From: Bayamon, AA, USA
Status: offline 		A little more work. I was searching the AMA archives and found a build artical for a XB35, since the N9M is a third scale of the same plane I was thinking of chopping the canopy and putting 4 motors on the back.

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RE: Scratch build Northop N9M - 8/21/2007 12:50:28 AM   
BMatthews



Posts: 9011
Joined: 10/4/2002
From: Burnaby, BC, CANADA
Status: offline 		If you go full on scale with 4 motors on an 80 inch model and if you can keep the overall weight of under 60 oz then I'd say you'll get fairly spiritied but not fully aerobatic performance from a 4'some of any of these cheapie options.

Some options from RCU suppliers would be....
https://www.unitedhobbies.com/UNITEDHOBBIES/store/uh_viewItem.asp?idProduct=5112 This one is overkill but you don't need to prop them up to the full current. But the price is right.
https://www.unitedhobbies.com/UNITEDHOBBIES/store/uh_viewItem.asp?idProduct=5354 these are cheap and look like they would work nicely from the data.

Here's a motor and ESC combo for an inresistable price and the second (and presumably 3rd and 4th) combo is even cheaper...
http://www.graysonhobby.com/catalog/product_info.php?cPath=22&products_id=315

Another motor and ESC that doesn't have that open shell look to the motor...
http://www.graysonhobby.com/catalog/product_info.php?cPath=22&products_id=427

I've selected options here that all have lower Kv values so they can turn larger and more scale like props. The ultimate speed will suffer slightly as a result, as in it won't look like a racer doing high speed flybys, but the climb and medium speed regions will work out well.

For batteries you'll need to set up something that can handle the potentially 35 to 40 amp draw at full throttle. Keep that in mind. Either a honkin' big single pack or go for two smaller but still healthy packs that can run two motors each.

< Message edited by BMatthews -- 8/21/2007 12:52:37 AM >

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RE: Scratch build Northop N9M - 8/21/2007 12:13:46 PM   
crashontakeoff



Posts: 76
Joined: 3/28/2006
From: Bayamon, AA, USA
Status: offline 		Thanks for all of that info. It is almost the same price as the two brushless motors I was looking at in the LHS. I will definitly go with four motors and two batteries. How many ESC would I need, could I run two motors off of one ESC? I am a nitro guy other than two direct drive full fpeed 1/2a planes I have built, and flown sucsessfully only one was feasable, and that one was just a little too hot. I am looking for some thrust that can handle a semi decent breeze, but will fly low and slow. I appreciate the time you put into responding to my post.

crashontakeoff

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       Post #: 8

RE: Scratch build Northop N9M - 8/21/2007 10:57:51 PM   
BMatthews



Posts: 9011
Joined: 10/4/2002
From: Burnaby, BC, CANADA
Status: offline 		WHAT WAS I THINKING! ! ! ! For some reason I was thinking that this was the XB-36 with 4 engines. The N9M had two only. My bad.

If they were the old brushed motors then you can run more than one motor from a single controller. But with brushless the ESC reads the RPM from the motor via the current to voltage phasing and uses that to control when to switch each phase to the motor. So it's one ESC to one motor. No cheating here I'm afraid.

The catch now is that since I was basing this on using 4 motors you'll have to upscale a little since there will be only two. But no fear, both outfits have some nice 20 to 25 amp motor and controller options. Again though, go for the lower Kv values as those motors will turn larger props and for scale that's what you're after.

Here's a couple of options for running two motors...
http://www.graysonhobby.com/catalog/product_info.php?cPath=22&products_id=140

http://www.graysonhobby.com/catalog/product_info.php?cPath=22&products_id=337 This one MAY be a little down on power but with two of them I think it'll work fine. Especially if you can keep the weight to 60 oz or less. It may not have the jet like climb but two of these would fly it more like the original N9M.

http://www.graysonhobby.com/catalog/product_info.php?cPath=22&products_id=334 Two of these would DEFINETLY haul the freight! ! ! ! But the motor weight isn't too high.

< Message edited by BMatthews -- 8/21/2007 11:12:56 PM >

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RE: Scratch build Northop N9M - 8/21/2007 11:13:50 PM   
crashontakeoff



Posts: 76
Joined: 3/28/2006
From: Bayamon, AA, USA
Status: offline 		We will see what happens next payday, for right now I will continue to build. I only have a four channel radio for this project so no bomb drop or retracts I'm afraid. I really like the off set cockpit on the xb 35. I hope it does fly scale. I remember in the 50's war of the worlds, the yb 49 dropping the nuke, looked cool. Might be the weekend before I get to it again, work and all that. I don't want to try to finish in a hurry as it is coming very straight. Being up in the states while I am building is making it easier to get what I need to finish. I am thinking of picking up another kit while I am here. I was thinking something from balsa usa, always wanted to build a 1/4 scale ww1 plane and make it electric. There is a Taube on ebay right now i have my eye on. I will need to get rid of some planes soon, all I will have to do is start flying, gravity eventually will do the rest.

Just a thought, what about 4 gws units, would they work? I know brushless is the wave of the future, but it was designed and flys with two brushed motors. Also the B-35 in the 1996 AMA mag flew with four brushed motors. I just ask because they are available off the shelf at local Hobby Store. Also I have the charging gear to support the normal batteries, as if I go LiPo I will have to buy a charger too. Just thinking out loud.

Thanks for the reply,
crash

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RE: Scratch build Northop N9M - 8/22/2007 2:35:30 AM   
BMatthews



Posts: 9011
Joined: 10/4/2002
From: Burnaby, BC, CANADA
Status: offline 		Unless it's coming out VERY light then I doubt you'll get adequite performance out of two GWS brushed 350 or 400 motors... Well, two of the 400's MAY fly it if the weight can be kept under 50 oz. But given the pics and the fact that it was designed for two Astro 05's I'd say it's built a little too heavy for that. You basically need to see 20 amps at 7.2 volts going into this thing for scale sort of performace at least on takeoff. A little more would be a nice safety margin.

If you were doing an XB-35 then 4 GWS 350's would do the job easily assuming the same size and same 60'ish oz AUW.

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RE: Scratch build Northop N9M - 8/22/2007 12:30:48 PM   
crashontakeoff



Posts: 76
Joined: 3/28/2006
From: Bayamon, AA, USA
Status: offline 		Thanks,
I thought 4 GWS's might do it. Going to just build the plane for now, with the intention of four brushless motors. I will space out the purchase of the LiPo's, and Charger. The motors, and speed controlers will be purchased together when I get back to Puerto Rico, since I have to get them mail order anyhow. I planned on installing hatches for the wiring anyhow, and it will not be a problem to run the wires for everything even after it is covered. Not much going on after the 10 hour workday at the hotel so I should get a bunch done. Will post more pics soon, going to have bothe wings minuse control surfaces done by Sunday.

Crash

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       Post #: 12

RE: Scratch build Northop N9M - 8/26/2007 11:43:24 PM   
crashontakeoff



Posts: 76
Joined: 3/28/2006
From: Bayamon, AA, USA
Status: offline 		More work done this weekend. It is just under 14 oz so far, we will se what happens when I add gear, motors and especialy batteries. It is a little tail heavy still, I don't expect that to change until I put the gear in it. Pics not working, I really need to get a digital camera instead of using this phone. Motors should be here tommorow. I am going to get the Drag rudders started since they are the most complex part of the plane. I am a little worried about the "no horizontal surfaces". Has anyone flown this configuaration before? I have seen plenty on the ground, also the video of the N9M taxi test, but none in flight.

Crash

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       Post #: 13

RE: Scratch build Northop N9M - 8/29/2007 4:59:38 PM   
awood12345



Posts: 272
Joined: 11/23/2002
From: kent, UNITED KINGDOM
Status: offline 		I recently thought about scratch building a n9m. How accurate are these plans?

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