PeterF's Chris Golds Northrop B2-A stealth bomber - Page 8 - RC Groups
 Jan 22, 2013, 07:01 AM Registered User Peter This is a very interesting project and you look to have done a great job. I have made many different flying wings. In my experience the best guide to the correct C of G position is what has worked on other models. I have small Chuck gliders for some of mine to check the position. C of G calculators with unusual models can give the wrong figure. Luckily you have Chris Golds C of G for this actual model. The flyable C of G will only be a narrow band. Don't be tempted to add extra nose weight to increase the 'safe amount' for the maiden. If this is your first flying wing you will be surprised and disappointed at the amount of lead you will need in the nose. On my Horten and Arado I had to have 1.5 Kg. You will only know the amount you need when it is fully painted and everything is finished. Most of the paint is aft of the C of G as are servos etc. I am very interested in the flying controls. They are very different to the Horten which flies quite well on pure elevons and does not need the drag rudders except in a crosswind. I have my drag rudders set up so they deploy one side only at a time. I guess that the Horten lift distribution is making the difference. I had thought about making a B2 so will follow your efforts with interest. John
Jan 22, 2013, 01:17 PM
Registered User
I used your B-2 image and did the calculations with the 3 panel method.
NP= (392 x 8)+(247.6 x 14.82)+(213 x 25.46)/ (392 + 247.6 + 25.46)=18.3"
25% MAC = ( 392 x 16.63)+( 247.6 x 10.15)+(213 x 5.33)/ ( 392 + 247.6 + 213)=14.39"
Np came out about where you calculated it to be. The 25% MAC is 3.7" (20%) from NP.
Your 25% MAC is at 1.66" (9%).
Will like to see what you came up with after rescaling.

### Images

 Jan 22, 2013, 02:37 PM Registered User John, thanks for the input, the empirical appraoch is the best in this case. The only thing I worry about is that I have changed the amount of material above the centreline in the body section of the plane compared to the prototype and plan. The prototype did not have any lead in it, but then it did have 24 sub-C NiCd cells and I have half as much weight in my LiPos so I may need some lead. p901P901 - I have run the measurements of my model through the VT analysis program and the MAC and location of this come out within 1 - 2mm of my hand calcs (1/16" error) so I am pretty happy with the calcs. However, I do not follow your numbers or where they are measured from or come from, as I said I am new to this level of detail. Where do the lengths for the NP come from (8", 14.82" & 25.46") and likewise those for the 25% MAC. There is an error in your first calc, you have divided by a mixture of area and length it should be (392 x 8)+(247.6 x 14.82)+(213 x 25.46)/(392 + 247.6 + 213) = 14.34"
 Jan 22, 2013, 05:51 PM Registered User Peter, Ivan Munignhauf said he had to have his rudders open 15 degrees for them to be effective. Very nice build and great info! Marty snell
 Jan 22, 2013, 06:21 PM Registered User Coming back to the CofG and MAC, I have gone through a couple of other calculators linked from RCG, another one dealing with mutliple wing panels and recommending a CofG at around 20% of MAC and they all come up with values for the MAC and the MAC position spanwise in line with the numbers I crunched and the Cof G at or very close to the position the plan gives for the CofG. All agree that the original prototype position at 30% of MAC was way to rearward and the 22% it ended up at is a good compromise. I am happy that I have done some math that confirms that the tested prototype had a CofG in the correct location based on therory and practise. Single panel CofG calc from user Z80 Mutli panel CofG calc from user SBruder
Jan 22, 2013, 08:45 PM
Registered User
Thanks for the corrections. Looks like you going in the right direction.
Just for general knowledge:
I overlayed your drawing over Compufoil's and 25% MAC came over your NP.
I also overlayed the B2 drawing over Compufoil's. Also the Mutli panel CofG calc from user SBruder over Compufoil's.
NP looks to be at 18" from the nose on the centerline. Author of calculator suggest 15% for new planes. Static margin at 25% MAC is 5%.

### Images

Last edited by p901P901; Jan 23, 2013 at 04:02 AM.
Jan 23, 2013, 06:00 PM
Registered User
Nose Gear Doors

Thanks everyone for the compliments, the useful information and taking the time to help me understand me some new stuff

Well the last few pages have been a new theory lesson for me and very interesting and it has explained why the prototype flew as reported by Chris Golds and how he arrived at the current CofG.

Now it is back to the practical side of things, I have decided to move onto the landing gear doors, I may as well complete the landing gear before I move on. I really am putting of fan installation as I am not yet sure what to do.

Anyway, I tackled the nose gear doors first, I had been thinking quite a lot about how to install the nose gear servos and kept playing around and could not come up with a solution, which was why I kept putting it off. Then after some thought I realised I could cut holes into the side walls at the bottom of the wheel well (top in photo with plane upside down) as there was only empty space behind the wheel wheels here, the battery packs are higher up so no clash. That has made things easy.

The doors were cut out earlier and hinging them was straightforward, Robart pin hinges for the front door and furry Mylar hinges for the main door. I have chamfered the hinge line on the main door as the plane has a slight curve and this allows opening without causing a clash.

Control rods have been bent from thin wire with an omega loop bent into it for ease of adjustment.

I have the proper sequencing of the main door as shown in the video below. I have two sequencers from SM Services here in the UK as the two doors operate differently; I still need to tweak the timing a bit. The servos are retract servos (LSX / Logic RC 260R) so they are relatively slow and do not slam open / closed. I do not want to leave the nose door open for long as it could act as a canard type rudder in front of the CofG causing some yaw instability. My current Tx programming opens the drag rudders further when the gear is down to get more yaw stability.

 RC B2 Stealth nosewheel retract and door test (0 min 21 sec)

### Images

 Jan 23, 2013, 06:26 PM Registered User Looking good
 Jan 23, 2013, 06:50 PM EDF Jet Jam 2017, June 15-18 Nice.
 Jan 23, 2013, 07:26 PM Registered User Looks awesome!
Jan 23, 2013, 09:05 PM
Registered User
Quote:
 Originally Posted by PeterF Complete upper fuselage framework The next stage was to cut out the shaped spar sections from the cardboard templates to go over the nacelles and cockpit. When I thought about the sections over the cockpit I realised that as these are very curved they would not transfer the flight loads from one side of the plane to the other very well. The original design has a large flat top over the whole of both nacelles and cockpit. Therefore, I let in a section of ¼” square hard balsa at the same level as the nacelles, passing through ribs B, A and B and being a straight piece will be OK for flight loads. The photos show how I have let in the straight section for the loads. As the section over the engines has to clear the fans when installed I had to make them ¼” square and profiled underneath, the picture will show what I mean. For these sections to be able to carry the flight loads successfully I cut them from ¼” birch ply. These are then epoxied onto the spars to give a good joint even if there are some small gaps. The shaped sections over the cockpit are then only required to support the sheeting over the cockpit and not provide strength, so these have been cut from ¼” light ply. I have made the shaped formers for the removable hatch at the front of the cockpit section to allow access to the batteries and these are put away until later. Having completed the shaped spars over the nacelles and cockpit the upper framework has been lifted from the board. This has allowed the upper and lower fuselage frames to be dry fitted to see how they marry up, and they go together well. There are a couple of small mismatches that will need to be sorted out but nothing troublesome. I have then shaped the Leading and trailing edges ready for sheeting. It is starting to look good and the difference from the original plan is starting to be visible. After making up the spar sections from ply and all the work on the ribs I was wondering if this should be in the scratch built section, it is sort of a hybrid.
Verry verry verry nice work, that a piece of art........Cheers
 Jan 23, 2013, 09:24 PM Registered User Nice job with the nose gear doors. That is just like the real jet. I am really impressed with your work!!
Jan 24, 2013, 12:12 PM
Registered User
Quote:
 Originally Posted by PeterF Nose Gear Doors Thanks everyone for the compliments, the useful information and taking the time to help me understand me some new stuff Well the last few pages have been a new theory lesson for me and very interesting and it has explained why the prototype flew as reported by Chris Golds and how he arrived at the current CofG. Now it is back to the practical side of things, I have decided to move onto the landing gear doors, I may as well complete the landing gear before I move on. I really am putting of fan installation as I am not yet sure what to do. Anyway, I tackled the nose gear doors first, I had been thinking quite a lot about how to install the nose gear servos and kept playing around and could not come up with a solution, which was why I kept putting it off. Then after some thought I realised I could cut holes into the side walls at the bottom of the wheel well (top in photo with plane upside down) as there was only empty space behind the wheel wheels here, the battery packs are higher up so no clash. That has made things easy. The doors were cut out earlier and hinging them was straightforward, Robart pin hinges for the front door and furry Mylar hinges for the main door. I have chamfered the hinge line on the main door as the plane has a slight curve and this allows opening without causing a clash. Control rods have been bent from thin wire with an omega loop bent into it for ease of adjustment. I have the proper sequencing of the main door as shown in the video below. I have two sequencers from SM Services here in the UK as the two doors operate differently; I still need to tweak the timing a bit. The servos are retract servos (LSX / Logic RC 260R) so they are relatively slow and do not slam open / closed. I do not want to leave the nose door open for long as it could act as a canard type rudder in front of the CofG causing some yaw instability. My current Tx programming opens the drag rudders further when the gear is down to get more yaw stability. http://youtu.be/KKkeRUYBL6c

Great work, what sequencer did you use for the doors?

Cheers
Jan 24, 2013, 02:16 PM
Registered User

# Build of an other B2

Hi guys and hi PeterF.
I have been missing from forum but i was reading and watching every steps that you've made here, you PeterF. Congrats for your job and i'm very glad to be tone of those who have inspired what you're doing today.
Right now my personal job on this B2 is stoped as i was unable to figure out the way to make the gears dors open and close as the act in the video you have made. Now that i see what you've done may be i will continue the work on my build. PeterFcan you tell us how you're panning to paint this baby. Will you use glass fiber before painting?