Brewster Buffalo?
Scale Foam Scratch Build: Inspired by David, For teaching everyone
- Thread starter willsonman
- Start date
Nope, Landing gear configuration is wrong. Fuse is too long in relation to tail surface area size... Keep guessing.
Argh! This is making me crazy! The lines and tail plane shapes scream Chance Vought. But, the gear pods are quite a hitch. Plus, the horz stab balance horn is angled and CVs are typically 90 degrees to the vertical.
Well, considering this is an airplane inspired by David's (Flight Test token Swede) heritage I think you are going too mainstream. 
Brewster Buccaneer?
Try again.
Ok, so I'm getting to the point where I am ready to start with the main wing and get into the flaps and figuring out where to position my main spar. The 3-view I am basing this plane off of has the ailerons drawn out but not the Flaps (top view only of wings with split flaps). So measuring on the plans I calculated the flaps to be roughly 1/3 of the wing chord. That does not seem right. I went and measured the ailerons to be 27% of the wing chord. Again... this is not scale. Since the views are from a 1/25 scale model I realized that the designer enlarged the control surface for better control. After digging for comparative scale 3-views and in-flight pictures I've come to a 24% chord length for the flaps. Much more consistent with full-size aircraft.
All I did was take a picture on the monitor and grabbed a ruler. Measure the chord of the wing and the depth of the flap. Divide the latter by the former *100 and you get your percentage. See the attached image for size/shape comparison. Its pretty evident that things are not drawn to scale.
Take away message here:
NEVER trust ANY 3-view. The majority of them have been drawn by artists, not engineers. Years ago I consulted Jerry Bates about a Curtis SB2C Helldiver (still on my work bench) and this was his finding when doing all of his plans. If you have access... get the real plans of the aircraft. If you do not have access then consult MULTIPLE 3-views and pictures. Remember, you are making flyable artwork. Do your homework and the art teacher will give you a good grade.
All I did was take a picture on the monitor and grabbed a ruler. Measure the chord of the wing and the depth of the flap. Divide the latter by the former *100 and you get your percentage. See the attached image for size/shape comparison. Its pretty evident that things are not drawn to scale.
Take away message here:
NEVER trust ANY 3-view. The majority of them have been drawn by artists, not engineers. Years ago I consulted Jerry Bates about a Curtis SB2C Helldiver (still on my work bench) and this was his finding when doing all of his plans. If you have access... get the real plans of the aircraft. If you do not have access then consult MULTIPLE 3-views and pictures. Remember, you are making flyable artwork. Do your homework and the art teacher will give you a good grade.
Attachments
Saab 17. BAM!
Nailed it! What finally made it click for you?
I suspected it was a Swedish plane, but when I was looking through aircraft of WWII, Sweden was sadly unrepresented on any list. Then, I read your latest about David's heritage. The only Swedish aircraft manufacturer I know of is Saab, so I just googled "Saab aircraft." It pretty much lept off the computer screen. Those landing gear pod are weird looking when down.
Those pods are actually one of the features that drew me to it. This was Sweden's FIRST all-in-country-built military aircraft. The engineers were all trained by US designers who all left with the onset of the war. One of the main problems of dive-bombers of the time is tail buffeting. This is when the speed of the aircraft creates a stream of turbulent air past the main wing and that air then shakes around the tail. Not good if you are trying to aim a bomb at a ground target. The primary thing to control is dive speed so that when you pull out the g-load will not rip the wings off. This is usually controlled by drag. Well, when adding drag you are also adding additional turbulent air.
US and Japanese designers both went in a direction of complicated flap configurations. Fowler flaps, split flaps, Upper and lower flaps, Perforated flaps. All of them added additional weight and complexity through hydraulic systems and strong materials to withstand the forces at high speeds. The Swedish solution was to simply use what systems would already be there. Hydraulic landing gear extends far down already. Simply adding the pods (I call them pontoons or nacelles) creates the drag naturally on the bottom pivoting the aircraft over and creating the drag to prevent overspeed. Saab used a split fowler flap to create an undercamber for lift AND drag to offset the pivoting motion. This would help keep the plane static in a dive. By creating the split flap the top of the wing remains fairly laminar and the pressure area created at the trailing edge of the wing keeps the turbulent air below the raised H-stab line of the tail... all thus preventing tail buffeting. Less complexity to solve a hard problem.
Another unique feature was that the wheels could be swapped out for skis or pontoons to fly off snow or water.
The overall look and layout of the aircraft is VERY similar to the Curtis SB2C Helldiver but development of the Saab B17 came first.
I have great respect and admiration for the folks who flew in dive bombers. This is one of my favorites.
US and Japanese designers both went in a direction of complicated flap configurations. Fowler flaps, split flaps, Upper and lower flaps, Perforated flaps. All of them added additional weight and complexity through hydraulic systems and strong materials to withstand the forces at high speeds. The Swedish solution was to simply use what systems would already be there. Hydraulic landing gear extends far down already. Simply adding the pods (I call them pontoons or nacelles) creates the drag naturally on the bottom pivoting the aircraft over and creating the drag to prevent overspeed. Saab used a split fowler flap to create an undercamber for lift AND drag to offset the pivoting motion. This would help keep the plane static in a dive. By creating the split flap the top of the wing remains fairly laminar and the pressure area created at the trailing edge of the wing keeps the turbulent air below the raised H-stab line of the tail... all thus preventing tail buffeting. Less complexity to solve a hard problem.
Another unique feature was that the wheels could be swapped out for skis or pontoons to fly off snow or water.
The overall look and layout of the aircraft is VERY similar to the Curtis SB2C Helldiver but development of the Saab B17 came first.
I have great respect and admiration for the folks who flew in dive bombers. This is one of my favorites.
Nice background on the plane. I have never heard of this plane, before. Thanks for the info!
I've got lots more. I really love the history about the aircraft I build. I'll share more as I build but I've included some photos for those that may feel a bit lazy to do a search.
My all-time favorite fighter is of Swedish decent. The FFVS J-22B. There used to be a site that posted results of CFD analysis of the airframe and it was rated as the best of the best... given its power. Had it had a larger powerplant it would have outperformed the Mustang and the like. Brilliant design and use of limited materials.
My all-time favorite fighter is of Swedish decent. The FFVS J-22B. There used to be a site that posted results of CFD analysis of the airframe and it was rated as the best of the best... given its power. Had it had a larger powerplant it would have outperformed the Mustang and the like. Brilliant design and use of limited materials.
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Ok, so my day off is here and I'm evaluating what to do next. I started off doing osme more sanding cleanup on the fuselage. Nothing major. I got the recesses for the inner flaps cut out. Simple dremel tool used to hog out foam. Smooth it out with sandpaper. Then to make the flaps its just balsa with an addition of balsa along the leading edge for a pivot point. Tail wheel was something easy to do that did not require a lot of thought. Block of wood for the post to go through and there is a control horn on the inside with a grub screw holding it vertically in place.
I placed an order for an ARF to do with my kids. It will take me on a side road from this project but I'll be in and out. Since I just blew a bunch of hobby money I'm looking at where to go next on this one. I wanted to get into the glass work but I need cloth and acetone. Outer wing panels are a no-go as I need more foam. Clean the shop? Really do not want to.
I placed an order for an ARF to do with my kids. It will take me on a side road from this project but I'll be in and out. Since I just blew a bunch of hobby money I'm looking at where to go next on this one. I wanted to get into the glass work but I need cloth and acetone. Outer wing panels are a no-go as I need more foam. Clean the shop? Really do not want to.
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Not much lately as I am anticipating the arrival of a new ARF. Had to strip another plane down. I'm building it with my kids so I got them a little excited today doing some prep work. I did manage to get the firewall cut out and the motor screwed on. I took a long hard look at the motor/battery/prop situation. Mostly an inventory of what I had. I ran things through a power calculator and decided to go with my old Eflite Power 15 950Kv. Its been in 4 planes and has never let me down but I really liked the prop situation better. I have a 1200Kv Turnigy SK3 motor that is just as reliable but I bent the motor shaft and would have to order a new one... from china. Its only a couple bucks but The prop.... I'd end up with a smaller prop that would not look as scale. A 9x6 prop would be perfect. My 10x5 would work but would push the batteries I have a bit on the amp draw. The 11x7.5 Master Airscrew prop looks quite the part and I have a back-up of the same size if I have a real problem. The 11x7.5 will give great efficiency on the Eflite motor and not tax the battery at all. The look is much better over the wood props I have. Awhile at a fly-in a fellow had a box of props he was selling $5 for as many as you could fit in your hand. I got 16. Yeah... I have big hands. No pictures as the firewall is just a round piece of wood. I'll show it later when I mount it to the front of the foam.
Ok, so I am done with my Summer project with my kids. and am getting back onto this one. So I am moving onto wing design and construction.
So for the spar I will be using a single piece of thin MDF. Its fairly light, very rigid, and nothing fancy... not to mention I've plenty on my garage. Looking at the views I am basing this off of I notice a couple things.
1: There is taper to the wing in the front-view. This can give me basically 3 angles for the dihedral. One for the bottom, middle, and top. Since I will be inserting the spar from the bottom I will use that angle. From there I can trim the top to suit the thickness of the wing.
2: I will more than likely be using an airfoil at the tip that will be thicker than scale. This really is not a problem per se, however if the angle of the dihedral at the top is not close the "look" will not be right and therein lies a sacrifice to be made. So, I need to plug in the numbers for the tip rib. If I go with the scale airfoil then I will more than likely need to cut the outer wing panels with some washout. Its not really more complicated that way but it will not look right from the side angle. This angle is not nearly as noticeable so I'm more inclined to do that. How much washout? To be determined. Depends on my wing loading. Heavier and I like more... lighter and I need less. The idea is to prevent tip stalling.
3: With the location of the servoless retracts I will have to locate the spar rather far aft of the calculated CG. This concerns me due to the fact that the CG tends to be toward the thicker part of the airfoil and is inherently stronger. Also, I'm placing more weight toward the rear. Never a good thing. I typically like to use Carbon fiber arrow shafts but working with angled shafts has not been a pleasant experience for me in the past. Not to mention... I'm out of them. I only buy them on sale in the fall when bow season is in. At $3 a shaft at Walmart... its hard to beat and yes I've looked.
4: learning from mistakes in the past I wanted to double-check my angles. I dug up my other view and got that angle. After that I googled images and found a decent front-view. Results were: 1st view was 7 degrees, 2nd view was 6 degrees, 3rd view (photo) was 6 degrees. NEVER TRUST YOUR 3-VIEW!!!! We are going with 6 degrees dihedral.
So for the spar I will be using a single piece of thin MDF. Its fairly light, very rigid, and nothing fancy... not to mention I've plenty on my garage. Looking at the views I am basing this off of I notice a couple things.
1: There is taper to the wing in the front-view. This can give me basically 3 angles for the dihedral. One for the bottom, middle, and top. Since I will be inserting the spar from the bottom I will use that angle. From there I can trim the top to suit the thickness of the wing.
2: I will more than likely be using an airfoil at the tip that will be thicker than scale. This really is not a problem per se, however if the angle of the dihedral at the top is not close the "look" will not be right and therein lies a sacrifice to be made. So, I need to plug in the numbers for the tip rib. If I go with the scale airfoil then I will more than likely need to cut the outer wing panels with some washout. Its not really more complicated that way but it will not look right from the side angle. This angle is not nearly as noticeable so I'm more inclined to do that. How much washout? To be determined. Depends on my wing loading. Heavier and I like more... lighter and I need less. The idea is to prevent tip stalling.
3: With the location of the servoless retracts I will have to locate the spar rather far aft of the calculated CG. This concerns me due to the fact that the CG tends to be toward the thicker part of the airfoil and is inherently stronger. Also, I'm placing more weight toward the rear. Never a good thing. I typically like to use Carbon fiber arrow shafts but working with angled shafts has not been a pleasant experience for me in the past. Not to mention... I'm out of them. I only buy them on sale in the fall when bow season is in. At $3 a shaft at Walmart... its hard to beat and yes I've looked.
4: learning from mistakes in the past I wanted to double-check my angles. I dug up my other view and got that angle. After that I googled images and found a decent front-view. Results were: 1st view was 7 degrees, 2nd view was 6 degrees, 3rd view (photo) was 6 degrees. NEVER TRUST YOUR 3-VIEW!!!! We are going with 6 degrees dihedral.
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Willsonman,
What adhesive did you use to laminate the foam? I'm going to be starting another project soon and I am going to use this technique.
Thanks!
What adhesive did you use to laminate the foam? I'm going to be starting another project soon and I am going to use this technique.
Thanks!
You mean the $tree board? I do two light sprays of Super 77 from 18" away on both sides. I hold the parts in front of my shop fan for 30 seconds or so to evaporate as much acetone as possible then squish together on a flat surface. Find something to keep even weight on it like a big book for another 5 minutes.
Edit: If you would like to go sparless on a part you can use white gorilla glue between the layers. It dries super stiff. The draw back is sanding. Dry gorilla glue will not sand. Just apply a thin layer of glue and press together. I suggest putting a fold of wax paper around it while a book sets on top. You need the pressure as the glue expands. The wax paper just makes easier cleanup. Oversize the foam and trim to shape after it dries so you are not left with glue oozing out and messing up the edge of the part.
Edit: If you would like to go sparless on a part you can use white gorilla glue between the layers. It dries super stiff. The draw back is sanding. Dry gorilla glue will not sand. Just apply a thin layer of glue and press together. I suggest putting a fold of wax paper around it while a book sets on top. You need the pressure as the glue expands. The wax paper just makes easier cleanup. Oversize the foam and trim to shape after it dries so you are not left with glue oozing out and messing up the edge of the part.
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I was referring to the foam board insulation you used for the fuselage.
Ahh. Same Super 77 method except for key strength positions. There I used the gorilla glue. I only applied it to the inside half of the surface very sparingly. Jab little holes for the glue to expand into and grip. You can use toothpicks to strengthen as well but more strength will come from the covering. Once covered any structural loads will be spread out over the area of the fuse. More or less just tack it together and the covering will help. Build it to fly... not to crash. Build lighter... flies better and makes it easier to land. Heavier makes it harder to fly and land.
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