Wellington
06-11-2003, 10:50 AM
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Wellington
I'm drawing a cad plans for this multi. I'm plan to put a pair of 0.061 or 0.074.
if any modeler want see my plan, this is in acad2000 format (to correct and put some ideas.
Now I'm looking for wing and tail incidence: how many?
Alessandro
if any modeler want see my plan, this is in acad2000 format (to correct and put some ideas.
Now I'm looking for wing and tail incidence: how many?
Alessandro
06-12-2003, 09:12 PM
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Wellington
One thing about the Wellington-it used both radial and inline engines (Merlins), and also it had geodesic construction and wings and fuse were fabric covered!! Only the Brits would do it! From everything I've heard about it, it was a tough old beast. There was a construction article in Model Aviation years ago, by a guy named Baker (I think). It seems to me that it was powered by two .09's. You might see if anyone has the article.
Sturmvogel
Sturmvogel
06-13-2003, 10:57 AM
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Wellington
I dont want reply geodethic structure: my plane may be similar like wellington: it dont want an exact reproduction.
How many wing span for 2 .061? is 1200 mm right?
Alessandro
How many wing span for 2 .061? is 1200 mm right?
Alessandro
06-13-2003, 11:25 AM
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Wellington
I think the side view you posted is of the full scale aircraft with it's proper wing and stab incidence....the drawing shows the wing incidence at the root but not the tip. I'm guessing the original aircraft had quite a bit of washout which would make the overall wing incidence less than shown.
Your model probably won't need as much incidence as the original, depending on the wing and stab airfoils, wing loading and speed. Just as a comparison, my "Twin Lizzie 2" with 2 .049's has 1.5 deg. in the wing, .5 in the stab and 2 deg. down in the engines. She flies great, with minimal attitude change, both high & low speed.
1200 mm (42.25 in.) is pretty small! I did a quick scan/vectorization/surface area calc. in TurboCAD and came up with a little less than 200 sq. in. for a scale wing at 42.25 in. span. (Sorry, I don't know what area measurement you Italian fellows use!)
That would be too small for .061's, in my opinion. 200 sq. in. would need to be LIGHTLY built with sticks & lightweight covering with 2 .020's maybe. I think 350 to 425 sq. in. for modern .061 power would be closer to what you need. The larger size would be IF you build light and could keep the weight down to 34 - 38 oz. Then you should be able to fly it "on the wing" at 1/2 power for scale-like flight.
Help me Bmatthews, where are you!
Your model probably won't need as much incidence as the original, depending on the wing and stab airfoils, wing loading and speed. Just as a comparison, my "Twin Lizzie 2" with 2 .049's has 1.5 deg. in the wing, .5 in the stab and 2 deg. down in the engines. She flies great, with minimal attitude change, both high & low speed.
1200 mm (42.25 in.) is pretty small! I did a quick scan/vectorization/surface area calc. in TurboCAD and came up with a little less than 200 sq. in. for a scale wing at 42.25 in. span. (Sorry, I don't know what area measurement you Italian fellows use!)
That would be too small for .061's, in my opinion. 200 sq. in. would need to be LIGHTLY built with sticks & lightweight covering with 2 .020's maybe. I think 350 to 425 sq. in. for modern .061 power would be closer to what you need. The larger size would be IF you build light and could keep the weight down to 34 - 38 oz. Then you should be able to fly it "on the wing" at 1/2 power for scale-like flight.
Help me Bmatthews, where are you!
06-15-2003, 05:31 PM
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Wellington
I'm BAAAAAaaaacck.... 
1200mm is WAY TOO SMALL....
Allessandro, you want to try to duplicate the original flying charactaristics which will be slow and statley with provisions for a "quick" but not fighter like high speed pass. At 1200 mm it would fly like an F15 ! ....
To my mind and background with sport and old timer models I'd say you want a model with at least 450 sq inches (2900 sq cm). 500 to 540 sq inches (3200 to 3400 sq cm) would be even better. This wing area will make for a bulky fuselage so construction would be best done using sticks and formers. No sheeting please. Using fully built up construction such as this will also help control the weight. I don't see why it can't be done to come in at around 2 to 2 1/2 lbs (1 to 1.2 Kg) with care and wood selection.
This would give a model that can fly at a scalish speed but will still use it's power to cut a nice pass. Loops and rolls will still be very useable given a slight dive to gather speed. All in all very scale like. Retract gear, if done light, is very much an option thanks to the wing being able to carry the weight. Bomb dropping out of the bays is a must, hope you have a 5 or 6 channel radio...
As for the geodetic construction I've got a possible shortcut for you. Build it up using formers and about 8 x 1/8 sq hard balsa stringers to set the basic fuselage shape. Then using strong button thread layed diagonally lay on the geodetic "webbing" over the whole fuselage. I doesn't need to be done to scale as that may form too tight a net effect but something close to that, like 1 cm spacing, would give the effect you're looking for. Cover with a light fabric or even tissue and dope. The geodesic netting will make the fuselage SUPER stiff in torsion so don't worry about the basic formers and stringers being floppy. This would almost ensure the weight stays under control in fine style. Of course the wings and tails would also be all built up using spars and ribs with no sheeting. The thread trick could also be used on those as well but just be very careful not to lock in any warps as the geodesic pattern would make them impossible to remove. If you keep all the threads loose at one end and tighten them in matched pairs with a tug through some holes in the wood to hold the tension you can do them all at once and then use the threads to hold in the alignment and then seal them with dabs of glue to lock it all down. Just be sure it's right the first time !!!!!
Decalage or incidence-
I'm going to go counter to Bipe Flyer and suggest that you want about +3 degrees in the wing and +1 or 0 in the stabilizer. This will produce a much more stable flight balance for this sort of "cruising" model. The side view you showed with what looks like the scale angles was meant for heavy load carrying. If you copied those angles in your model it would tend to fly around with the fuselage pointed down slightly in level flight. Kind of like a dog with it's nose to the ground.. With my angles the fuselage should be quite level in cruise and still a touch nose down in high speed passes for a more aggresive look.
For construction guides look over lots of free flight plans for methods relating to building strong structures that have lots of air between the parts.
Finally, (phew) I'd suggest that unless you want it to be totally scale that you increase the tip chord to reduce the chances of tip stalling. The tips should be about 60% of the root chord. With that size you'll still want about 2 degrees of washout. Either that or the tips should have a thin but more lifting airfoil that is washed out strongly. Going to a 10% Clark Y and -1 degrees incidence at the tips would be a good start. That would give you a 4 degree twist in the wing. But the lifting airfoil will help ensure reasonably even lift and greatly reduce the chance of tip stalling.
Be sure to use lots of differential throw in the airlerons as well. That will also help reduce the risk of adverse yaw and tip stalling at landing speeds.
An ambitious project but it sounds like great fun. Good luck and I hope all this typing helps out.
PS: After thinking about this I'd like to change the fuselage stringers to 1/8x1/4 hard balsa set on edge. 1/8 sq is much too free flight'ish. And the main 4 could should be 1/4 sq so you have something to use as a base for alignment and to provide a stronger point for the wing and other components to mount from. Guess I've been building too many rubber models the past few years.....
1200mm is WAY TOO SMALL....
Allessandro, you want to try to duplicate the original flying charactaristics which will be slow and statley with provisions for a "quick" but not fighter like high speed pass. At 1200 mm it would fly like an F15 ! ....
To my mind and background with sport and old timer models I'd say you want a model with at least 450 sq inches (2900 sq cm). 500 to 540 sq inches (3200 to 3400 sq cm) would be even better. This wing area will make for a bulky fuselage so construction would be best done using sticks and formers. No sheeting please. Using fully built up construction such as this will also help control the weight. I don't see why it can't be done to come in at around 2 to 2 1/2 lbs (1 to 1.2 Kg) with care and wood selection.
This would give a model that can fly at a scalish speed but will still use it's power to cut a nice pass. Loops and rolls will still be very useable given a slight dive to gather speed. All in all very scale like. Retract gear, if done light, is very much an option thanks to the wing being able to carry the weight. Bomb dropping out of the bays is a must, hope you have a 5 or 6 channel radio...
As for the geodetic construction I've got a possible shortcut for you. Build it up using formers and about 8 x 1/8 sq hard balsa stringers to set the basic fuselage shape. Then using strong button thread layed diagonally lay on the geodetic "webbing" over the whole fuselage. I doesn't need to be done to scale as that may form too tight a net effect but something close to that, like 1 cm spacing, would give the effect you're looking for. Cover with a light fabric or even tissue and dope. The geodesic netting will make the fuselage SUPER stiff in torsion so don't worry about the basic formers and stringers being floppy. This would almost ensure the weight stays under control in fine style. Of course the wings and tails would also be all built up using spars and ribs with no sheeting. The thread trick could also be used on those as well but just be very careful not to lock in any warps as the geodesic pattern would make them impossible to remove. If you keep all the threads loose at one end and tighten them in matched pairs with a tug through some holes in the wood to hold the tension you can do them all at once and then use the threads to hold in the alignment and then seal them with dabs of glue to lock it all down. Just be sure it's right the first time !!!!!
Decalage or incidence-
I'm going to go counter to Bipe Flyer and suggest that you want about +3 degrees in the wing and +1 or 0 in the stabilizer. This will produce a much more stable flight balance for this sort of "cruising" model. The side view you showed with what looks like the scale angles was meant for heavy load carrying. If you copied those angles in your model it would tend to fly around with the fuselage pointed down slightly in level flight. Kind of like a dog with it's nose to the ground..
With my angles the fuselage should be quite level in cruise and still a touch nose down in high speed passes for a more aggresive look.For construction guides look over lots of free flight plans for methods relating to building strong structures that have lots of air between the parts.
Finally, (phew) I'd suggest that unless you want it to be totally scale that you increase the tip chord to reduce the chances of tip stalling. The tips should be about 60% of the root chord. With that size you'll still want about 2 degrees of washout. Either that or the tips should have a thin but more lifting airfoil that is washed out strongly. Going to a 10% Clark Y and -1 degrees incidence at the tips would be a good start. That would give you a 4 degree twist in the wing. But the lifting airfoil will help ensure reasonably even lift and greatly reduce the chance of tip stalling.
Be sure to use lots of differential throw in the airlerons as well. That will also help reduce the risk of adverse yaw and tip stalling at landing speeds.
An ambitious project but it sounds like great fun. Good luck and I hope all this typing helps out.
PS: After thinking about this I'd like to change the fuselage stringers to 1/8x1/4 hard balsa set on edge. 1/8 sq is much too free flight'ish. And the main 4 could should be 1/4 sq so you have something to use as a base for alignment and to provide a stronger point for the wing and other components to mount from. Guess I've been building too many rubber models the past few years.....
