BMJR Profile Nobler

[GonzoBonzo]

  Anyone have any experience with this new kit from Brodaks?  I found a build thread on the net from someone in Singapore with pictures.  Looks interesting.  All laser cut.  8 pieces for one flap. Guess you're guaranteed a straight, and warp resisting piece.   Just wondering on the flight performance.

TIA

[bob whitney]

i built the first proto type  it flys good , it dose not need a lot of control movement ,if u use a 4 in bellcrank keep the pushrod close to the inside besure to keep it light in the back. ,the Kit nose is 1/2 in shorter than mine .  it will do the whole pattern with no trouble.

[Roger Vizioli]

I watched two of them fly yesterday. Bob's was one of them.
They look good!
Roger V.

[GonzoBonzo]

Thanks guys

[GonzoBonzo]

Question for you Bob,

  I received the kit.  The plans show the CG at 3.75".     Is this what you used?  Even at the center of the wing, it seems excessive.

Did you use a 4" crank?  I have one I can use.  And, when you refer to keeping the pushrod to the center, does that mean the inner hole, or the middle one?

 I do plan on taking out an inch, or so of the asymmetry of the wing too.

thanks,

[Leester]

Just wondering what hardware, instructions etc came with it. Can you show some pictures ??

[GonzoBonzo]

Hi Lester,

  The kit came with a Brodak 3" nylon bellcrank kit.  The wing looks like a standard 52' Nobler wing with an extra panel, or extra 2" on the inboard wing.  The bellcrank shown on the wing plan measures 2 7/8", and has no reference to the pushrod.  I'll have to draw new leadouts, and reposition the leadout tubes.  No problem.

The kit does come with instructions (your basic mount bellcrank with leadouts), and shows the 3" bellcrank with the pushrod in the farthest hole, or 15/16".  Being a profile, and the bellcrank nut right under the fuselage, I want to get the pushrod in the right hole to avoid major surgery.

My main concern is the CG.  3 3/4".  Measured at the fuselage.  Is this correct for a Nobler?  It shows it on the plans, and in the instructions.   Wing is 9 3/4" at centerline, flaps are 2 1/2" at the widest point.  Tail moment is 14 1/4".  

Thanks,

[Balsa Butcher]

Don't worry about the CG. Build the plane first. My guess is it should be further forward. Depending on what engine you are going to use, that should not be a problem. As far as the bellcrank goes, I put pushrods on 3" bellcranks in the holes closest to the pivot. It slows down the response which is a good thing.

[GonzoBonzo]

Thanks Butcher.

[bob whitney]

Gonzo , my C/G is a little further back than that and is a bit tail heavy so should be good .  3 in bellcrank is about right and i would use the inside hole and work with the flap and elavater holes   my 4 in bellcrank over powers the ship i have the pushrod too far out

[Andrew Borgogna]

The plane looks kind of cool.  It would be a natural for electric or IC.
Andy

[Ted Fancher]

Hi Lester,

  The kit came with a Brodak 3" nylon bellcrank kit.  The wing looks like a standard 52' Nobler wing with an extra panel, or extra 2" on the inboard wing.  The bellcrank shown on the wing plan measures 2 7/8", and has no reference to the pushrod.  I'll have to draw new leadouts, and reposition the leadout tubes.  No problem.

The kit does come with instructions (your basic mount bellcrank with leadouts), and shows the 3" bellcrank with the pushrod in the farthest hole, or 15/16".  Being a profile, and the bellcrank nut right under the fuselage, I want to get the pushrod in the right hole to avoid major surgery.

My main concern is the CG.  3 3/4".  Measured at the fuselage.  Is this correct for a Nobler?  It shows it on the plans, and in the instructions.   Wing is 9 3/4" at centerline, flaps are 2 1/2" at the widest point.  Tail moment is 14 1/4".  

Thanks,

Gonzo,

Here's a quick "formula" for getting the CG in a good spot to start.

Go halfway out either wing panel and measure the distance from the leading edge of the wing to the trailing edge of the flaps (seems I have to keep reminding people that flaps ARE part of the wing and should be included in any discussion of the same).  For simplicity let's say that distance is 10 inches.  With a vintage area design like the Nobler the area of the tail is going to be somewhere between 13 to 17 or 18 percent of the wing area; 15% is a good round number for an average of the era designs and is a safe bet for first flights of any such design.

Take that "average chord length measurement of 10" (in our example) and multiply it by that 15% average (10 X 0.15) and you get 1.5".  Adjust your CG so that, at the "halfspan" chord length you had determined) the CG is 1.5 inches aft of the leading edge.  Place the midpoint of the leadouts at the wingtip about an inch or a touch more behind the CG and go fly the airplane.  The CG and leadouts will be within fractions of an inch of the optimum position which you can determine through flight testing and "judicious" trimming...That means very small steps in any one direction from that point. 

This CG location is ahead of what is "optimum" for current era designs that utilize much larger % tails and can, therefore, support a more aft CG effectively.  A Nobler with a CG at the modern location of ~25% aft at the average chord is likely to be much to sensitive and will be difficult to both fly precisely and to land in a wind...tending to get light on the lines when coming into the winds.

Ted Fancher

[GonzoBonzo]

Thanks guys,  I was able to find a PDF plan of the Green Box online, and it shows the CG at 2.75", or right on the spar mid-span.   This is pretty close to what I came up with after using your formula Ted.  Didn't think about the stab playing a role in the CG, makes sense though.  Looks like I'll have to move the leadouts forward a bit too. 

[Dynamo]

  Anyone have any experience with this new kit from Brodaks?  I found a build thread on the net from someone in Singapore with pictures.  Looks interesting.  All laser cut.  8 pieces for one flap. Guess you're guaranteed a straight, and warp resisting piece.   Just wondering on the flight performance.

TIA

That would be a build thread I posted at our local (Singapore) control line forum. The link is here [url]http://s6.zetaboards.com/Just_Fly_It/topic/8823566/1//url]. I've only just completed the build - I got distracted halfway through - and the plane is now ready for her maiden which will be sometime next week. I hope that the photos and comments will be useful to potential builders. Cheers.

Tony

[Mike Lauerman]

Very clearly explained, Ted. Great thread here, thanks to all the contributors. Textbook stuff!

[Steve Helmick]

  Anyone have any experience with this new kit from Brodaks?  I found a build thread on the net from someone in Singapore with pictures.  Looks interesting.  All laser cut.  8 pieces for one flap. Guess you're guaranteed a straight, and warp resisting piece.   Just wondering on the flight performance.

TIA

Brodaks sells the BMJR "Profile Nobler" kit, but does not make the kit. BMJR is an independant kit maker, just to clear the water a bit. Steve