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Old Sep 14, 2008, 09:16 AM
Gentle 'Bella'
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Ryan -

Airplane in the video in post# 7 is of the Martin A-30 Baltimore, not a Maryland. What a surprise to see this footage, in color yet, of a plane that is mostly 'extinct'.

Watching your thread with interest. I completed a Baltimore model a few years ago but as yet haven't flown it - 48" span, geared sp.400s.
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Old Sep 14, 2008, 09:55 AM
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I noticed when watching the video there are a few things different from the drawings and photos of other Maryland's I've collected. The most noticable is that the engine nacelles extend past the trailing edge of the wing in the video but don't in any of the drawings. There are very few pictures or anything of the full scale aircraft around at all that I've been able to find.
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Old Sep 14, 2008, 11:47 AM
Gentle 'Bella'
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Ryan - Yeah, the Baltimore (model 187) was basically an improved Maryland with larger engines and a deeper fuselage for additional payload. Decent drawings of these early attack bombers are not easy to find though there is some interesting history with both types as they were primarily built for foreign coutries.

I'm confident that these will be fine flying planes as models. Wing Manufacturing had some short kits and plans for the Baltimore until recent years. I haven't ventured to fly mine yet due to my somewhat 'erratic' flying skills. Soon as I get some practice on speedy type warbirds I'll probably tackle it.
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Old Sep 16, 2008, 09:36 PM
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Tonight I got the tail feather ribs drawn and done. I cooked up the wing panel on profili and was getting ready to export it out only to discover that the registered version no-longer supports printing or DXF export so I need to get the Pro-version or find another program for plotting wing ribs to continue on this.
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Old Sep 18, 2008, 12:41 PM
...design-build-fly-publish...
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The comments about differences between the Maryland and Baltimore had me reaching for my reference books and I note from Owen Thetfords 'Aircraft of the RAF since 1918' that the rearward extended nacelles of the Baltimore were one of the differences between the two, the Maryland having nacelles finishing on the same line as the wing trailing edge. This feature had been found to be aerodynamically inefficient - probably due to interference between vertical and horizontal surfaces producing turbulence and drag - which was perhaps one reason that DeHavilland extended their nacelles for Mosquito, Hornet etc., which went significantly faster.

The book tells me that the Maryland's maximum speed was only 18 mph faster than the Blenheim that got seriously mauled in Europe - hence its use in the African campaign. Which leads me to a slight concern occasioned by gnat's talking about getting practice on 'speedy warbird types'... If the model Maryland is going to be speedy, does this mean it's on the heavily-built side? In which case, with that short nose and cowlings, where will the balance point be? Do you know yet?

One of the problems I have found with the new generation electric power is that it weighs so little compared with the power it chucks out that it is normally essential to get the batteries as far forward as possible. So rather than get the batteries in the way of the props....
Or perhaps you are going to resort to that materiel they use for church roofs... but one dare not say the four-letter word 'l***' for fear of the moderator!
I have always passed over the Maryland for this reason. It seems it would need a particularly light build at the tail end. So I'd love to hear how you sort it... I might be worrying un-neccessarily!
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Old Sep 18, 2008, 02:28 PM
Gentle 'Bella'
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Augusta, KS USA
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eye4 - I was mindful of the battery placement on my Baltimore build and it ended up being just ahead of the bomb bay under the cockpit.

I built the wings as separate R and L, mounting to a stub spar that locks in as a carry-through structure in the fuselage due to the mid-wing location.

It is a very 'slippery' design and I expect it to be fast - it is a belly lander and though it's not too heavy (38 ozs. auw), I did want it to withstand the rigors of that so I elected to build from hot-wired blue foam with epoxy and fibreglas skin.

My flying skills were fairly well honed when I flew glow planes but after a 15 year lay off and returning to fly the much smaller electrics, I find myself struggling with habitual expectations and the electrics do get ahead of me from time to time. I do think the Maryland and Baltimore will be fine flyers but the models will be speedy.
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Old Sep 18, 2008, 04:25 PM
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I think the nose is not too short. From the 3-views it doesn't look any worse then my B24 was and that balanced alright and I did just about everything possible to make the tail of that plane overly heavy.

This plane is going to be light. Stick construction of the fuselage and minimal sheeting. Only stringers on the fuselage except for a little sheeting around the cockpit and gun turret area. The wing is only getting sheeting on the top leading edge and bottom at the nacelle. I'm aiming for a maybe 6lb max flight weight. It may very well have 2 speed 600's hanging off it rather then anything more exotic. I'm using the same battery as my B24 which could potentially give up to 800 watts. Unless the props somehow take a magic flight off the motors and threw the fuselage sides and then manage to go through the SPT tubes I don't really see much threat to the batteries from the props.

I won my struggle with Profili last night and got my wing ribs plotted out and imported into TurboCad. I went with a 15% ClarkY at the root tapering to a 11% ClarkY at the tip. I just need to check now to make sure my retract position isn't going to send the wheel or the landing gear leg through the wing spar where I located it.
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Old Sep 19, 2008, 03:21 AM
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Thanks guys - I fell into the trap of assuming that everyone was going the same way I am!
Because I happen to have given up on can motors as being inefficient I assumed that you would also be using outrunners, which for a twin pretty much dictates that the battery packs are stored not in the fuselage but in the nacelles with the motors and speed controllers. Even the short nose of the Maryland has enough length to use Nicads or Nimhs for balance.
That's the only disadvantage of going outrunner and LiPo!

I'm impressed by guys like Ryan who can use the computer to do wing ribs and so on. I learded draughtsmanship on a parallel-motion drawing board and could never get it out of my system. To learn CAD looked as if it would take a month full time so, since I could have two sets of drawings done in that time, I fought shy of the time investment.
I did a couple of B-24s too Ryan, one at 60" and the next 100". I enjoyed both, sold on the first and crashed the second, since when I kept on toying with doing yet another - perhaps about 130" (or as big as I can get in my little van). Both models used nicads and can motors, the first 400s and the second geared 540s and as you say, no problems with balance.
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Old Sep 19, 2008, 05:30 AM
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There is nothing special about brushless that makes you put batteries in the nacelle instead of in the fuselage. My B24 has 4 brushless motors all running off 1 battery pack in the fuselage. For this if I do it brushless I'll put both ESC's in the wing center section instead of putting the ESC at the nacelles. There really is nothing keeping you from putting the battery in the fuse. It's either a 4S A123 at each nacelle or a 4S2P in the middle.

I took several years of drafting in highschool that was mainly using paper and pencil though we did some autocad also. Then in college for a co-op I worked on the call center for IDEAS 3D modelling software for 2 semesters. I can actually do 3D modelling pretty well but don't have access to software that I can do the design with. It's either my $12 copy of TurboCAD off Ebay or a $600 copy of Rhino or something more expensive. My occasional design work doesn't justify more then $12 for my CAD software.

You can use www.profili2.com to do all the wing ribs with blended airfoils and chord shapes your heart desires in very little time. That part is the easy part.
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Old Sep 19, 2008, 12:35 PM
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Ryan, I guess you're a bit younger than me (a bit??) CAD wasn't around when I was at college! Sometimes it feels like the Ark had only just gone aground!

I had a lot of problems with my DC3 trying to run only two ESCs and motors off one pack in the nose. I was getting spurious pulses generated in the ESCs so that strange things happened like when increasing the throttle both motors would accellerate up to a third power then suddenly one would cut out. Maybe they were not the best ESCs in the world, but I only cured that by separating the power supplies into two packs. It seemed to be the length of the wiring between battery and ESC that was too long.

As a result I have since kept the wiring as short as possible and, since I am tending to build ever larger, that means the LiPos joining the rest of the power train in the nacelles. Only the ESCs three-core leads go down the wing into the fuselage to plug into the receiver. Following on from that if/when I get round to my next B-24 both this arrangement and my desire for more impressive size will dictate the way I design it.

Presumably your B-24 ESCs were in the nacelles? or in the wing? Still quite a way to the batteries... can't have been the ESCs I used - but then you wouldn't have needed 40A handling capacity. Interesting!
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Old Sep 19, 2008, 01:02 PM
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As far as wire length goes. The length between ESC and battery needs to be kept short. The length between ESC and motor can be relatively long without causing problems. The impedence of the motor wirings are high so no spikes will occurr due to the on-off switching. The impedence between ESC and battery are low so large voltage spikes can happen due to the on-off voltage cycle from the ESC operation. That is the reason for the large capacitors near the battery inputs on the ESC's to damp this. There are several good threads on this in the power systems section and also Astroflight has a really good article also.

My B24 has esc's at the nacelles but current was relatively low. If I was doing that again I'd put the esc's at the center of the wing which I will do for this if I do go brushless.
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Old Sep 20, 2008, 01:59 PM
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I am looking at the landing gear position in the wing this morning with the ribs lined up over the nacelle. Where I put the wing spars in the pretty normal position, the tire will be going right through the main spar. Scale wheel size is 4.25 inch, which will be really good for ground handling but not so good for ability to fit the wheel up into the nacelle and wing when retracted.
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Old Sep 20, 2008, 02:54 PM
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All the ribs are replotted again after a few tries with spars now that fit around where the retracted wheel will be. In the process I made both spars the same size and will build with shear webs on both sets.
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Old Sep 21, 2008, 06:08 PM
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I got the wing design pretty well done today. Just some detail work left to clean up here and there and it will be ready to print and start cutting parts. I'm hoping to start cutting parts around Nov 1st to have it kitted out by the Dec1st building start date.
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Old Sep 27, 2008, 09:26 PM
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Tonight I think I have the drawings done enough to be able to build from. I have all the cross sections filled out enough to work with and enough of the nacelles drawn to work with.

On another note. I got my October Model Avaition today. The main topic of the Control Scale section is a scratch built Martin167. It has some good notes on the full scale and 1 image of the control line models construction which looks quite a bit more simplified then even I am doing here.
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