A scale Mustang on a budget
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RE: A scale Mustang on a budget
Brown came this morning with the Mustang laser parts. I just had to snap fit the parts together to see how they fit. The tabs needed a light trim with a small square file to remove the kerf taper. Other than that, everything fits together very snugly. A bit of adjustment around the edges of the front and rear bulkheads will be needed – just light sanding. (I always worry that I've forgotten a laser kerf adjustment on apart or made some other mistake in setting up my laser cut files.)
BTW the tabs help straighten any warps in the plywood. They also make it easier to glue the parts together.
The motorbox parts are cut from 1/8" Baltic Birch which has three equal thickness plies. So the pieces were arranged on the cutting sheet to take advantage of the major grain. As I mentioned I'm working hard to keep the weight down and so was concerned about the weight of the motor box. The cut parts came to 5.3 ozs. That's without the firewall and triangular corner reinforcements, so I think the assembly installed will be about 8-9 oz total. Subtracting the firewall that was cut out (3 oz) and a motor mount that would normally be used (say 2.5 oz), the weight gain looks moderate at this point.
(In the pictures the square hole in the rear bulkhead over the top of the motor box and the two holes in the front and rear bulkheads under the motor box are for incoming and exhaust cooling air. The top of the motor box will have lightweight flanges added that will seat against the removable cowl and force the incoming air to flow to the front of the engine.)
Finally the lightening holes in the motorbox will be covered on the inside with 1/64" plywood.
BTW the tabs help straighten any warps in the plywood. They also make it easier to glue the parts together.
The motorbox parts are cut from 1/8" Baltic Birch which has three equal thickness plies. So the pieces were arranged on the cutting sheet to take advantage of the major grain. As I mentioned I'm working hard to keep the weight down and so was concerned about the weight of the motor box. The cut parts came to 5.3 ozs. That's without the firewall and triangular corner reinforcements, so I think the assembly installed will be about 8-9 oz total. Subtracting the firewall that was cut out (3 oz) and a motor mount that would normally be used (say 2.5 oz), the weight gain looks moderate at this point.
(In the pictures the square hole in the rear bulkhead over the top of the motor box and the two holes in the front and rear bulkheads under the motor box are for incoming and exhaust cooling air. The top of the motor box will have lightweight flanges added that will seat against the removable cowl and force the incoming air to flow to the front of the engine.)
Finally the lightening holes in the motorbox will be covered on the inside with 1/64" plywood.
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RE: A scale Mustang on a budget
Yes, it sure does. And having the parts in your hand is much more satisfying than looking at them on paper or on the computer screen.
As you know I've been using CAD and laser cutting for some time now. And it doesn't always work out that way! It's a real PITA to get the parts back and find you made a mistake. I think I've made evey mistake there is to make. It's embarassing and it delays the project. So now I always do a match check by moving each part over the part it fits into or that is next to it to make sure everything lines up. This works well to check for errors even though my CAD software is 2D.
(My favorite mistake by the way is to put the kerf adjustment on the wrong side of the edge line. You'd think I'd learn.)
Some have said that having parts laser cut is not really true modeling. Personally I'm comfortable exhanging the time drawing the parts so I can have them laser cut rather than cutting them by hand. To each his own I guess. One thing doing it this way does is give me a parts detail if I ever need replacement parts or want to do another.
Tony
As you know I've been using CAD and laser cutting for some time now. And it doesn't always work out that way! It's a real PITA to get the parts back and find you made a mistake. I think I've made evey mistake there is to make. It's embarassing and it delays the project. So now I always do a match check by moving each part over the part it fits into or that is next to it to make sure everything lines up. This works well to check for errors even though my CAD software is 2D.
(My favorite mistake by the way is to put the kerf adjustment on the wrong side of the edge line. You'd think I'd learn.)
Some have said that having parts laser cut is not really true modeling. Personally I'm comfortable exhanging the time drawing the parts so I can have them laser cut rather than cutting them by hand. To each his own I guess. One thing doing it this way does is give me a parts detail if I ever need replacement parts or want to do another.
Tony
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RE: A scale Mustang on a budget
Thanks Mike, I appreciate the heads up.
I've been watching his listing but with two identical kits already I'm reluctant. FWIW I paid less than he's currently asking for both my kits. Still it's a reasonable price for what is a fairly light fuselage. The main problem is the Bridi undersized spinner.
I'd still like to find one of these same kits for the B/C models.
Not too long ago I came across an RCM review of the Bridi kit but I've either lost or misplaced it. Wish I could find it. As I recall they seemed to think it flew well but their's (which had some sort of early retracts) was not a floater. That's not surprising considering the wing and tail construction which was typical of the period - heavy. Maybe it will be possible to save few ounces in those areas.
Tony
I've been watching his listing but with two identical kits already I'm reluctant. FWIW I paid less than he's currently asking for both my kits. Still it's a reasonable price for what is a fairly light fuselage. The main problem is the Bridi undersized spinner.
I'd still like to find one of these same kits for the B/C models.
Not too long ago I came across an RCM review of the Bridi kit but I've either lost or misplaced it. Wish I could find it. As I recall they seemed to think it flew well but their's (which had some sort of early retracts) was not a floater. That's not surprising considering the wing and tail construction which was typical of the period - heavy. Maybe it will be possible to save few ounces in those areas.
Tony
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RE: A scale Mustang on a budget
Tony,
Could you please run through again/or explain how you set the 'Pitch' or 'Thrust' line of your fuselage in the jig?
Yoy said you made sure the cowl/ spinner face was vertical/parallel to the front of the jig. Is this assuming there is no down thrust built into the front of the cowl?
If my kit has down thrust built in, how then is the best way to measure and level the fuselage in the jig to set incidence of wing and horizontal stab?
Oh yeah,,,, any more updates to your build would be appreciated too.
Regards
Brad
Could you please run through again/or explain how you set the 'Pitch' or 'Thrust' line of your fuselage in the jig?
Yoy said you made sure the cowl/ spinner face was vertical/parallel to the front of the jig. Is this assuming there is no down thrust built into the front of the cowl?
If my kit has down thrust built in, how then is the best way to measure and level the fuselage in the jig to set incidence of wing and horizontal stab?
Oh yeah,,,, any more updates to your build would be appreciated too.
Regards
Brad
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RE: A scale Mustang on a budget
Brad, I'm sorry I didn't explain better what I was doing.
By using the cowl face to square the fuselage in the jig vertically, I was actually aligning the thrust line – not the fuselage reference line - to the base of the jig.
Once the fuselage was square in the jig, I established the wing and stab center lines by measuring the distance of the leading and trailing edge of each surface's centerline from the base of the jig. By subtracting those dimensions from each other and using each surface's chord length in a trig function, the angle of each could be calculated. The resultant angle is with reference to the thrust line / jig base. The difference between those two surface's angles is the angle of incidence. (I confess that rather than using trig to compute the angles, I draw measured dimensions as a diagram in my CAD software and let it calculate the incidences for me.)
The fuselage center line is an arbitrary line and really has nothing to do with the aerodynamics of the airplane. So I didn't feel I needed to establish it with my glass fuselages. What I did want to check was the incidence between the wing and stab. However with the computed angles I could have remounted the fuselage in the jig to bring the wing incidence to zero for example.
Finally I should mention that all the horizontal cowl lines on the Mustang are parallel to the engine thrust line. That meant I could leave the fuselages in the original jig position with the thrust line parallel to the jig base for marking the horizontal cowl cut lines. That was handy!
I find it hard to describe this, so if I haven't done an adequate job, let me know and I'll try again.
More in the morning on project progress - there's not too much to report.
Tony
By using the cowl face to square the fuselage in the jig vertically, I was actually aligning the thrust line – not the fuselage reference line - to the base of the jig.
Once the fuselage was square in the jig, I established the wing and stab center lines by measuring the distance of the leading and trailing edge of each surface's centerline from the base of the jig. By subtracting those dimensions from each other and using each surface's chord length in a trig function, the angle of each could be calculated. The resultant angle is with reference to the thrust line / jig base. The difference between those two surface's angles is the angle of incidence. (I confess that rather than using trig to compute the angles, I draw measured dimensions as a diagram in my CAD software and let it calculate the incidences for me.)
The fuselage center line is an arbitrary line and really has nothing to do with the aerodynamics of the airplane. So I didn't feel I needed to establish it with my glass fuselages. What I did want to check was the incidence between the wing and stab. However with the computed angles I could have remounted the fuselage in the jig to bring the wing incidence to zero for example.
Finally I should mention that all the horizontal cowl lines on the Mustang are parallel to the engine thrust line. That meant I could leave the fuselages in the original jig position with the thrust line parallel to the jig base for marking the horizontal cowl cut lines. That was handy!
I find it hard to describe this, so if I haven't done an adequate job, let me know and I'll try again.
More in the morning on project progress - there's not too much to report.
Tony
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RE: A scale Mustang on a budget
Tony, thank you for clearing that up for me.
Now I do understand most of what you have told me but it seems way too deep for me. I am after a real simple way to start setting things up and checking wing incidence when i get that far so how does this sound?
Ive heard that Mustangs have about 1 degree 45' (45 minutes) down thrust, so i will set the front part of the jig to that. The mould does have it built it.
Hopefully this will set the fuselage reference line in the horizontal. (that would be the aircrafts flying attitude right Tony?)
Then if I set the wing and horizontal stab at +1 it should be about right,,,, right??? Wing is semi symetrical.
I understand that you set yours up the way you did now because of the work you have to carry out on the new cowl.
I wish to join the fuselage just behind the cockpit section so actually have to get the flying surface mountings in relation to each other.
PLease if you have any different ideas or can see something glaringly wrong with what im guessing then please let me know.
I also appreciate that you have much to do and dont and I dont want to hijack your thread. I shall start my own when I get going.
Just so you know, my kit is quite old and i dont have any angles or incidences etc to work with so I am relying on the generousity of RCU members for any onfo I can gather.
Regards
Brad
Now I do understand most of what you have told me but it seems way too deep for me. I am after a real simple way to start setting things up and checking wing incidence when i get that far so how does this sound?
Ive heard that Mustangs have about 1 degree 45' (45 minutes) down thrust, so i will set the front part of the jig to that. The mould does have it built it.
Hopefully this will set the fuselage reference line in the horizontal. (that would be the aircrafts flying attitude right Tony?)
Then if I set the wing and horizontal stab at +1 it should be about right,,,, right??? Wing is semi symetrical.
I understand that you set yours up the way you did now because of the work you have to carry out on the new cowl.
I wish to join the fuselage just behind the cockpit section so actually have to get the flying surface mountings in relation to each other.
PLease if you have any different ideas or can see something glaringly wrong with what im guessing then please let me know.
I also appreciate that you have much to do and dont and I dont want to hijack your thread. I shall start my own when I get going.
Just so you know, my kit is quite old and i dont have any angles or incidences etc to work with so I am relying on the generousity of RCU members for any onfo I can gather.
Regards
Brad
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RE: A scale Mustang on a budget
I think I see what you want to do. My approach would be to:
1. Build the jig base with the end plates that support the nose and tail left unfinished and extra long. Draw a centerline on the end plates as well as the base.
2. Build the center support first and level the fuselage from side to side (the "roll" axis) – that's the center support on my jig that is under the wing saddle.
3. Block the fuselage fore and aft until the dimensions of leading and trailing edge of the wing are the same distance from the base of the jig and thus level with it. (If I wanted a slight positive incidence in the wing – like a 1/16" – I'd make the leading edge dimension 1/16" higher than the trailing edge.)
4. Finalize the supports for the fuselage at the front and rear plates, keeping the fuselage centered on the lines and leveled as in step 3.
With the fuselage aligned in the jig this way the stab can then be set parallel to the jig base by making its leading and trailing edge dimensions equal and so that its center line will be in line with the wing.
BTW if I thought I might want have the thrust line parallel to the jig base later – possibly for working on the firewall for example - I'd make two sets of front and rear support plates and bolt them on like I did with the front plate on my existing jig so I could switch back and forth.
The problem with assuming your kit has exactly 1.75° downthrust is the designer may or may not have been able to get it exact. The important alignment is the wing to stab incidence settings. Downthrust has less impact on flying characteristics by comparison. So focusing on the surface incidences as you are is the critical setting.
Hope this helps. And don't worry about hijacking the thread – it was a good question.
1. Build the jig base with the end plates that support the nose and tail left unfinished and extra long. Draw a centerline on the end plates as well as the base.
2. Build the center support first and level the fuselage from side to side (the "roll" axis) – that's the center support on my jig that is under the wing saddle.
3. Block the fuselage fore and aft until the dimensions of leading and trailing edge of the wing are the same distance from the base of the jig and thus level with it. (If I wanted a slight positive incidence in the wing – like a 1/16" – I'd make the leading edge dimension 1/16" higher than the trailing edge.)
4. Finalize the supports for the fuselage at the front and rear plates, keeping the fuselage centered on the lines and leveled as in step 3.
With the fuselage aligned in the jig this way the stab can then be set parallel to the jig base by making its leading and trailing edge dimensions equal and so that its center line will be in line with the wing.
BTW if I thought I might want have the thrust line parallel to the jig base later – possibly for working on the firewall for example - I'd make two sets of front and rear support plates and bolt them on like I did with the front plate on my existing jig so I could switch back and forth.
The problem with assuming your kit has exactly 1.75° downthrust is the designer may or may not have been able to get it exact. The important alignment is the wing to stab incidence settings. Downthrust has less impact on flying characteristics by comparison. So focusing on the surface incidences as you are is the critical setting.
Hope this helps. And don't worry about hijacking the thread – it was a good question.
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RE: A scale Mustang on a budget
I've been working on other projects the last few days and haven't done much on the Mustang as a result. I did take a few minutes to fabricate a cover for the fuel tank lines where they exit on the top of the motor box. I want them to be sealed to prevent any engine fuel residue from getting into the tank cavity and I needed to be able to get to the front of the 16oz slant tank to get at the fuel lines after the tank was installed from inside the fuselage.
The cover is a piece of 0.030" epoxy board. Underneath it is a 1" hole that I can reach thru with a hemostat to grab the stub fuel lines and attach them to the bottom of the two color coded Foremost bulk head fittings. The cover is attached to the top of the motor box with a couple of 4-40 machine screws and 'T' nuts. I'll use a gasket or liquid gasket material to seal the cover to the box.
The cover is a piece of 0.030" epoxy board. Underneath it is a 1" hole that I can reach thru with a hemostat to grab the stub fuel lines and attach them to the bottom of the two color coded Foremost bulk head fittings. The cover is attached to the top of the motor box with a couple of 4-40 machine screws and 'T' nuts. I'll use a gasket or liquid gasket material to seal the cover to the box.
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RE: A scale Mustang on a budget
I've been asked off-line about possible alternatives to using wire or tubing wrapped around the outside of a fiberglass fuselage to 'trace' the shape of internal attachments. One shortcoming of the wire method is that it's progressively harder to get a smooth outline the closer to a full perimeter that is being copied. In those cases here's what I've used for a number of years that is pretty accurate.
The process is to layup a thin fiberglass band over the outside of the line you want to capture. It requires very little work and not all that much time.
Here's how it's done…
I start by using a thin-line pen to mark the location of the line - or area - that I want to copy on the fuselage or part. In many cases this line can be hand sketched so long as it is in the right location and is reasonably close to being a flat slice of the fuselage.
Next run a line of masking tape all along one side of the marked line. I normally use 1/4" wide tape. Away from the line a second tape line is put down short distance away. The exact distance is not critical and will vary with the size of the body being measured. For a fuselage like the Mustang a band width of 2-3" would be adequate. A smaller part would not need as wide a band. Then I wax the area between the tape lines with 2-3 coats of a mold release wax or a wax with lots of carnauba in it.
This next step is important as far as I'm concerned. I spray on a sealing coat of Poly Vinyl Alcohol (PVA) over the area. THE PVA can also be wiped on. It's not necessary to worry about overspray – PVA is water soluble and rinses off easily. (Some may say the PVA isn't needed and that's true. However I've been working with fiberglass for 50+ years – laminating, repairing and modifying – and I still use it to make sure things come apart easily. And I've never had the laminate stick using it.)
Now I cut strips of cloth an inch or two wider than the taped band. They just need to be wide enough to easily cover the area between the tape lines. Short strips are easier to get to conform to highly tapered areas of the fuselage. The thickness of the layup isn't critical – for example to go around the largest part of the Mustang fuselage I'd use a total layup of 12 oz of cloth in whatever combination of layers would make that total.
You can use laminating polyester or epoxy resin – either one. I like to use polyester because of the shorter cure time. As I saturate the cloth I impregnate the cloth up to and slightly over both tape lines.
When the new laminate band is fully cured, I use a Moto Tool with a cut-off wheel to carefully slit it apart. The trick is to cut thru the new laminate without getting into the fuselage itself if possible. Depending on the shape being copied, sometimes a single cut will allow the part to come off by carefully bending the halves apart. Other times the band has to be cut into halves. I like to make the cut(s) along the fuselage seam if that's a true centerline.
I next wash off the PVA and trim the band back to the inner edge of the tape reference line. After the slits are taped back together I can lay the band down on a piece of paper – or plywood – and trace around the inside of the band. And mark a centerline if I split the band into two halves along the fuselage center line. The only thing left to do is offset to the inside of the traced line to adjust for the thickness of the fuselage. Now I have part outline that requires very little final adjustment.
Try it – you'll like it!
The process is to layup a thin fiberglass band over the outside of the line you want to capture. It requires very little work and not all that much time.
Here's how it's done…
I start by using a thin-line pen to mark the location of the line - or area - that I want to copy on the fuselage or part. In many cases this line can be hand sketched so long as it is in the right location and is reasonably close to being a flat slice of the fuselage.
Next run a line of masking tape all along one side of the marked line. I normally use 1/4" wide tape. Away from the line a second tape line is put down short distance away. The exact distance is not critical and will vary with the size of the body being measured. For a fuselage like the Mustang a band width of 2-3" would be adequate. A smaller part would not need as wide a band. Then I wax the area between the tape lines with 2-3 coats of a mold release wax or a wax with lots of carnauba in it.
This next step is important as far as I'm concerned. I spray on a sealing coat of Poly Vinyl Alcohol (PVA) over the area. THE PVA can also be wiped on. It's not necessary to worry about overspray – PVA is water soluble and rinses off easily. (Some may say the PVA isn't needed and that's true. However I've been working with fiberglass for 50+ years – laminating, repairing and modifying – and I still use it to make sure things come apart easily. And I've never had the laminate stick using it.)
Now I cut strips of cloth an inch or two wider than the taped band. They just need to be wide enough to easily cover the area between the tape lines. Short strips are easier to get to conform to highly tapered areas of the fuselage. The thickness of the layup isn't critical – for example to go around the largest part of the Mustang fuselage I'd use a total layup of 12 oz of cloth in whatever combination of layers would make that total.
You can use laminating polyester or epoxy resin – either one. I like to use polyester because of the shorter cure time. As I saturate the cloth I impregnate the cloth up to and slightly over both tape lines.
When the new laminate band is fully cured, I use a Moto Tool with a cut-off wheel to carefully slit it apart. The trick is to cut thru the new laminate without getting into the fuselage itself if possible. Depending on the shape being copied, sometimes a single cut will allow the part to come off by carefully bending the halves apart. Other times the band has to be cut into halves. I like to make the cut(s) along the fuselage seam if that's a true centerline.
I next wash off the PVA and trim the band back to the inner edge of the tape reference line. After the slits are taped back together I can lay the band down on a piece of paper – or plywood – and trace around the inside of the band. And mark a centerline if I split the band into two halves along the fuselage center line. The only thing left to do is offset to the inside of the traced line to adjust for the thickness of the fuselage. Now I have part outline that requires very little final adjustment.
Try it – you'll like it!
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RE: A scale Mustang on a budget
I haven't been unable to do work much on the Mustang for a few days. When I have had a few minutes I've worked on the engine box and finally it's almost finished and fuel proofed. I'm pleased with how rigid it is. Conveniently the complete assembly slips into the fuselage opening with everything attached. I had some reservations about that, thinking that the ears on the rear bulkhead that fit into the wing fillets might not let it drop into place. That will make it easier to glass into the fuselage.
I couldn't help myself and mounted the RCV 91SP on the box.
About all that remains is to add a couple of triangular birch strips under the horizontal flange. These will provide more contact area with the fuselage and will make it easier to cover the joint on the underside with strips of glass cloth. This motor box is one component I want to have the strongest possible joints.
The total weight of the 'box is now 7.8 oz including the engine mounting screws / Tee nuts and the fuel cover. Considering I've removed and eliminated roughly 5.5 oz's with this setup, so I'm happy about that.
I couldn't help myself and mounted the RCV 91SP on the box.
About all that remains is to add a couple of triangular birch strips under the horizontal flange. These will provide more contact area with the fuselage and will make it easier to cover the joint on the underside with strips of glass cloth. This motor box is one component I want to have the strongest possible joints.
The total weight of the 'box is now 7.8 oz including the engine mounting screws / Tee nuts and the fuel cover. Considering I've removed and eliminated roughly 5.5 oz's with this setup, so I'm happy about that.
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RE: A scale Mustang on a budget
No, unfortunately not much.
The scale manifolds I made up for my kit developed into a business making scale exhaust manifold kits for the various sizes of Mustang kits and that's been taking most of my time up until now. ([link=http://www.rcuniverse.com/market/item.cfm?itemId=229149]RCU Market[/link])
I keep hoping to get back on the project soon. It's not dead, that's for sure.
I appreciate knowing someone was looking at the thread!
Tony
The scale manifolds I made up for my kit developed into a business making scale exhaust manifold kits for the various sizes of Mustang kits and that's been taking most of my time up until now. ([link=http://www.rcuniverse.com/market/item.cfm?itemId=229149]RCU Market[/link])
I keep hoping to get back on the project soon. It's not dead, that's for sure.
I appreciate knowing someone was looking at the thread!
Tony
#67
RE: A scale Mustang on a budget
Oh we are watching alright
Mustang crazies can smell a thread like this in the pile...
Great and inspiring work Tony... keep it going...
G
Mustang crazies can smell a thread like this in the pile...
Great and inspiring work Tony... keep it going...
G
#68
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RE: A scale Mustang on a budget
I'd second that Tony, please continue when you can...... oh by the way, your scale exhausts are sensational and well worth the money.
Cheers
Falcon
Cheers
Falcon
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RE: A scale Mustang on a budget
Hmmm ... what am I going to do with 3 of the darned things when I'm not getting anything done on one?
Actually it hasn't been delivered yet. But I expect it to arrive on my doorstep any day now.
Tony
Actually it hasn't been delivered yet. But I expect it to arrive on my doorstep any day now.
Tony