Scale Don Smith P-51 Mustang

[stangflyer]

That spinner is huge, when you see the spinner and the cowl the engine does not look that big.

Kind of crazy huh? Almost dwarfs the Kolm of death. I really like the back plate. It is very beafy. And very precision made.

 

[stangflyer]

I really don't know where we left off on the Behemoth Stang build. I guess I could look. But at present...I have the stab basically 75% complete. Top sheeting is done, all ribs are in place. All hinge point blocks are in place as is the control horn blocks. I bought some fiberglass control horns for the control surfaces. I plan to set the Mustang up similar as our 3d machines. If they can take the abuse, no reason this won't handle the stresses that big Kolm is going to put it through. About all that is left is to complete the servo bay door frame work. I could have done a number of different arrangements on installing the elevator servos. But my Hangar 9 Marie Stang does just great with the servos mounted to the doors, I am pretty certain the Don Smith will be too. I will just make sure those rails for the framework are deeply epoxied into the doubled stab ribs. Then plenty of attachment screws to hold them in place. I don't know of a cleaner design other than to try to make the elevators actuated with hidden control horns. I think that would be too difficult to do because of the size. Anyway, here is the progress on the stabs/elevators. I also have to add the stab tip extension blocks and the counter balance tabs and sheet the bottom of the stab. I really feel the stab will be ready to attach to the fuse by the weekend.



I spent most of the day Sunday looking at options for the outer wing panel tubes and sleeves for the main wing. I finally ordered two sets. I could not decide which one I wanted, so I bought both. I wanted cf but nothing in the appropriate size is available. So T6 6061 aluminum it will be. .049 thick walls. I think that will do it. The tubes should be here tomorrow or Friday. Then? Oh yes...that massive wing. Oh joy.

 

[Snoopy1]

Don’t forget the holes in the ribs to run the servo wires. You could have drilled them before assembly. And a tube for the servo wire.

 

[stangflyer]

Don’t forget the holes in the ribs to run the servo wires. You could have drilled them before assembly. And a tube for the servo wire.

Thanks for the heads up on that. But I already have that well under control. I really don't have to run the servo wires that far. They will actually come up through the top of the stab so as to connect with the extension harness that will run down the center of the fuselage through the servo lead tubes.

 

[stangflyer]

Actually, now that I remember there was a reason why I did not put Servo lead tubes in the stab. I had an old man moment for just a minute or two. LOL. You see the way that the stab will fit onto the fuselage, the servo leads for the elevator servos will actually drop out the bottom skin down into the center of the fuselage. Therefore I really didn't want to add any more weight to the tail than necessary and at the same time be able to make the easy connection. Once I get to that point, you will see what I'm talking about.

 

[stangflyer]

Decided to do some tinkering while laundry is going. I wanted to start planning the elevator servo installation. As planned, I will build a frame work spanning stab ribs 3 and 4. I will also cut lite ply servo bay doors that will attach to the frame work, they will have the servo mounting lugs attached to the inside of the door. This process should be fairly straight forward. With two exceptions. First, I owe Snoops an apology. I had planned a different servo lead route but have since realized it is not at all feasible. His observation of drilling the corresponding ribs to accept a servo lead tube, allowing easy installation of the servos was actually right on the money. Wish I had been thinking a little more in advance. In my defense I can only claim it was very late and my brain was broke. Lol. So I'll have to see what I can do to rectify my oversightedness. Second exception is I am really not 100% certain of which installation method would be the strongest configuration. They say that the shortest distance between two points is a straight line. While this is true, there can also be a mitigating factor of the distance of that straight line. I would appreciate you fellows thoughts and input on what you feel would be the best set up. Please note the photos that I have attached. It is my thought that the shorter turnbuckle would be the stronger of the two configurations. Also that the Servo arm output shaft closest to the hinge line would be the best way to go. Obviously I want to make the elevator connections has strong and absolutely flutter free as possible. There is no doubt in my mind that with the big 150cc up front pulling this plane through the air, there is going to be tremendous air pressure across those elevators. Any flutter at all could be seriously detrimental to the longevity of this massive Mustang. I am going to attempt using the 1" aluminum Hitec servo arms that are included with all Hitecs top line servos. If they are too short, I will go with the new 1.5" MPI arms I have been saving for this build.

What do you think fellas? I greatly appreciate all of your input and suggestions.

 

[WMcNabb]

Decided to do some tinkering while laundry is going. I wanted to start planning the elevator servo installation. As planned, I will build a frame work spanning stab ribs 3 and 4. I will also cut lite ply servo bay doors that will attach to the frame work, they will have the servo mounting lugs attached to the inside of the door. This process should be fairly straight forward. With two exceptions. First, I owe Snoops an apology. I had planned a different servo lead route but have since realized it is not at all feasible. His observation of drilling the corresponding ribs to accept a servo lead tube, allowing easy installation of the servos was actually right on the money. Wish I had been thinking a little more in advance. In my defense I can only claim it was very late and my brain was broke. Lol. So I'll have to see what I can do to rectify my oversightedness. Second exception is I am really not 100% certain of which installation method would be the strongest configuration. They say that the shortest distance between two points is a straight line. While this is true, there can also be a mitigating factor of the distance of that straight line. I would appreciate you fellows thoughts and input on what you feel would be the best set up. Please note the photos that I have attached. It is my thought that the shorter turnbuckle would be the stronger of the two configurations. Also that the Servo arm output shaft closest to the hinge line would be the best way to go. Obviously I want to make the elevator connections has strong and absolutely flutter free as possible. There is no doubt in my mind that with the big 150cc up front pulling this plane through the air, there is going to be tremendous air pressure across those elevators. Any flutter at all could be seriously detrimental to the longevity of this massive Mustang. I am going to attempt using the 1" aluminum Hitec servo arms that are included with all Hitecs top line servos. If they are too short, I will go with the new 1.5" MPI arms I have been saving for this build.

What do you think fellas? I greatly appreciate all of your input and suggestions.

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I would go with the shortest length of rod and the servo oriented with its output shaft closest to the control surface hinge line.
With the aircraft flying fast, large control surface movements are not required, so short arms and short linkages make the most sense.

 

[Snoopy1]

As I see it and please just trying to help.
1. The Fiberglas horn you are showing if you are only using one it is likely to fail or twist away in stead of moving the elevator you need to have to of them so that the arm cannot twist Fiberglas bord is strong in one direction but not in twist motion.
2. Rest looks good like it.
3. Last comment mounting a servo flat on its side into the stabilizer is difficult. When I have done it I have aluminum angle made a cut out on one leg and screwed the servo to the angle and screwed the angle to flat wood block glued to the sheeting and the ribs. I never been able to have little wood post stand up strong enough to hold the servo and glue down onto a flat piece of wood.
4. With the servo on its side you do not have contend with operating angels it is all in line so the shorter the better.

 

[BalsaDust]

I would also say go with the shortest method possible but in this case it does look like that big of a difference and would probably be fine either way.

 

[stangflyer]

I would go with the shortest length of rod and the servo oriented with its output shaft closest to the control surface hinge line.
With the aircraft flying fast, large control surface movements are not required, so short arms and short linkages make the most sense.

As I see it and please just trying to help.
1. The Fiberglas horn you are showing if you are only using one it is likely to fail or twist away in stead of moving the elevator you need to have to of them so that the arm cannot twist Fiberglas bord is strong in one direction but not in twist motion.
2. Rest looks good like it.
3. Last comment mounting a servo flat on its side into the stabilizer is difficult. When I have done it I have aluminum angle made a cut out on one leg and screwed the servo to the angle and screwed the angle to flat wood block glued to the sheeting and the ribs. I never been able to have little wood post stand up strong enough to hold the servo and glue down onto a flat piece of wood.
4. With the servo on its side you do not have contend with operating angels it is all in line so the shorter the better.

I would also say go with the shortest method possible but in this case it does look like that big of a difference and would probably be fine either way.

Thanks gents for chiming in. I am pretty sure that I am going to set it up with the shortest link possible. Also with the servo output shaft closest to the hinge line. This eliminates the biggest majority of any possible weak links. Of course a control system is only as good as the hardware being used, I think this should be a very robust system. I will in fact be using two control horns just like what we use on all of our aerobatic planes. I have seen them set up with just one and honestly it would worry me. I only used the one laying on its side as a reference of the general location in relation to the hinge line and the distance to the output shaft of the servo. I am still fairly certain that I will be using the same method to mount the servos on the servo doors like my other smaller Mustangs. I've also had aerobatic planes with the servos installed the same way. I haven't had any problems so I think that's the way I wish I could