Vertical CG

[Sean McEntee]

      In addition to bigger, heavier wheels and longer landing gear, is there any other way to bring the verticle CG down?

      I lengthened the landing gear on the Texan by an inch and put 3 inch rubber tires on it.  It's looking pretty silly right now and STILL isnt hanging completely vertical but I'll give it a try tomorrow morning and see if it works.  If not, are there any other options?

[Tim Wescott]

I think you're building it for slime, so moving the battery down is out of the question.

Do you have it finished yet?  You may be able to sneak in a half inch or so of goodness by moving the leadout guide up in the wing.

It needs more dihedral, but that's not something that you can just crank in easily!

[Sean McEntee]

I think you're building it for slime, so moving the battery down is out of the question.

Do you have it finished yet?  You may be able to sneak in a half inch or so of goodness by moving the leadout guide up in the wing.

It needs more dihedral, but that's not something that you can just crank in easily!

Hey Tim,

        Yeah its a finished product....

[Randy Cuberly]

You might try wrapping solid solder around the landing gear and then disguising it as gear door covers.  a little work but you wouldn't have to actually change anything that is already built!
A drop tank under the fuselage would also be a way to disguise it but I doubt that they were used on the full scale airplane...not sure though maybe a little investigation is in order.

Randy Cuberly

[Sean McEntee]

You might try wrapping solid solder around the landing gear and then disguising it as gear door covers.  a little work but you wouldn't have to actually change anything that is already built!
A drop tank under the fuselage would also be a way to disguise it but I doubt that they were used on the full scale airplane...not sure though maybe a little investigation is in order.

Randy Cuberly

Hey Randy,

       Well the bad news is those big, stupid-looking wheels and long, equally stupid-looking landing gear helped:  Square maneuvers are now possible. 

Going to switch back to the shorter gear and try to cut out the faux-spokes in the wheel hubs and fill them with lead, and maybe hang some weight from the wheel doors and landing gear. 

I couldnt find anything on Texans carrying external fuel tanks, though I'm not opposed to doing it in order to get this thing flying right

[Dan McEntee]

   Hey Bud;
    Leave the long landing gear on for now, put the right size heavy wheel on it, and wrap the gear wire with solder like it was suggested. If you get it hanging right static, then flies right, then you figure out how to come up with that kind of weight in a better looking package. Have you had to add nose weight? If so, you may want to replace the tung muffler you have on it with a bigger muffler. It's weight will be below the center line. Remember the ST.51 I showed you that I mounted an OS .35/.40 muffler on? That is what I'm thinking about. Weight below the center line and ahead of the balance point. if you need a muffler, I can send you the one I fixed up, or make up another one. If you have one, you just cut a slot towards center where the bolt holes are until it matched up with et Tigre exhaust, then JB-Weld some blind nuts in place for 4-40 screws. Once it's all cured, you can grind and file it to make it look better.
  Type at you later,
   Dad

[Tim Wescott]

I couldnt find anything on Texans carrying external fuel tanks, though I'm not opposed to doing it in order to get this thing flying right

Texans, like most serious military trainers, have been used as COIN aircraft in various banana republics.  If not drop tanks, then I'd expect bombs or rockets or something else that goes "bang" should be found dangling down from those wings.  They'd probably make an excellent cheapo early-warning bird, too, so you may find something with a radome -- it'll look like it needs surgery followed by chemo, but it'll move the CG downward.

[Sean McEntee]

Hey Dad,

       Another problem with the long landing gear is physics.  The outboard didnt survive the landing and ripped the alluminum tube support in the wing off, so I need to fix that.  The gear is 3/32 music wire (per the plans) and theyre way too flimsy for that length.  

        The muffler I got on it is above the chord line.  The OS muffler youre talking about is a bit longer, but isnt heavy enough to make much of a difference being that close to the center line.

       I hung the model and set one of those Heavy Hub spinners on the wheel and it balances out.  I dont have enough places to hang 2 1/2 ounces of lead anywhere, so now the drop tank idea that Randy pitched is looking like an option.  Remember Leo Loudenslager's ferry tank that he made out of some bomb shells?  Thats kind of what i'm thinking.  Using the brass hub and some balsa block and crafting a drop tank.  

      No more low-wing airpanes after this  

      Randy: Good thinking, though this is a non-mil color scheme

[Tim Wescott]

Wickerpudlia shows a drop tank on a Texan used for forward air control in Korea: https://en.wikipedia.org/wiki/North_American_T-6_Texan.



Edit: I see no reason why that tank on your yaller airplane wouldn't look plenty authentic enough.  I think that if it were me I'd go ahead and put it on a pylon instead of on a web of struts, out of sheer laziness.

More edit: Actually, I'd go totally non-authentic and hang a FLIR Star SAFIRE II off of it, because that was the last product that I worked for at FLIR systems; I was in charge of motion stabilization for it, being 100% in charge of the algorithms and being given considerable influence over the electronics and mechanical details.  The success is definitely the team's, but the lion's share of any potential failures would have been mine alone.

[Randy Cuberly]

Hey Sean,

That drop tank Tim came up with in that photo is the ticket.  I thought I had seen one of those things with a drop tank in the distant past but wasn't sure.

Make the thing hollow and you can add lead shot as required to get the vertical CG exactly where you want it, and keep the scale look at the same time!

Perfect solution!

Happy flying!

Randy Cuberly

[Jim Kraft]

Find a pair of Kraft Hayes wheels. Those babys weigh a ton.

[Joe Gilbert]

Put the right gear and light wheels on and cut wing open move lead outs where they should be. You do not to be caring all the weight around. It is only balsa fix it. You will be way better off.
 

[Tim Wescott]

Put the right gear and light wheels on and cut wing open move lead outs where they should be. You do not to be caring all the weight around. It is only balsa fix it. You will be way better off. 

And put on the drop tank, but leave it empty!  Because -- cool looks.

[Avaiojet]

Find a pair of Kraft Hayes wheels. Those babys weigh a ton.

I think I might have a set.

[Steve Helmick]

So, the VCG is off because of the heavy engine? The G.51 is about 10.5, and the .40FP/.46LA the AT-6 was designed for is a bit over 9. I'm thinking that the problem is because you don't have that 5 oz (?) of nose weight, which was probably mounted low in the nose on the prototype? I'd get some heavier wheels, myself, perhaps make my own hubs or something. Some old Veco spoked wheels, maybe?

While the belly tank is kinda cool, the chances of it coming off in flight and losing an official would be a chance I wouldn't take. If you go that route, make it "bomb proof"!  Steve

[Sean McEntee]

So, the VCG is off because of the heavy engine? The G.51 is about 10.5, and the .40FP/.46LA the AT-6 was designed for is a bit over 9. I'm thinking that the problem is because you don't have that 5 oz (?) of nose weight, which was probably mounted low in the nose on the prototype? I'd get some heavier wheels, myself, perhaps make my own hubs or something. Some old Veco spoked wheels, maybe?

While the belly tank is kinda cool, the chances of it coming off in flight and losing an official would be a chance I wouldn't take. If you go that route, make it "bomb proof"!  Steve

    Hey Steve,

       That is exactly what I think is happening. 

        Been playing with weight opions some more.  I can tape 3 oz to the bottom of the wing and get it to balance.  Think Ill secure it better and give it a try.  While 3 ounces sounds like a lot, it will still leave the model at 49 oz.  Prototype is 48.

[Don Hutchinson AMA5402]

Sean-
Don't understand why you have the vert. CG so far off. Did you put 1and 1/2 inches dihedral in each wing per the drawing? Here is a shot of the original airplane and looks pretty level to me.

[john e. holliday]

Sean, going back and looking at the pics I think you forgot the dihedral.   Is that so?

[Sean McEntee]

Doc and Don,

     Nope it's all there--all 1 1/2 inches. Even made some jigs for when i mated all the wing panels together. Could be a bunch of things causing it: the decals, the extra clear.  Not a lot of weight alone but collectively and that far from the wing they could be a factor.

Who knows, just trying to fix it.

[Chris McMillin]

I have some Kraft wheels, Sean. What size do you desire?
Chris...

[Don Hutchinson AMA5402]

Upon checking the plans, I find the center line of the wing at the fuselage is 2.25" below the C/L of the engine and the leadouts at the tip are .75" below the engine C/L. I would guess the all up finished wing with L/G, bellcrank, pushrods etc. would weigh about 15 ounces with most of it down around the center of the wing. Guessing about 10 ounces that would put the vertical CG real close to the spot the leadouts come out of the wing. How for off is it? I would almost expect it to be below the leadout exit point. Does the model fly with one wing high? Is the pitch trim (CG) adjusted to where you get good corners? Do you have more elevator than flap per the plans? Hate to see you having problems with the T-6 after Joe's worked so well!

[Sean McEntee]

Upon checking the plans, I find the center line of the wing at the fuselage is 2.25" below the C/L of the engine and the leadouts at the tip are .75" below the engine C/L. I would guess the all up finished wing with L/G, bellcrank, pushrods etc. would weigh about 15 ounces with most of it down around the center of the wing. Guessing about 10 ounces that would put the vertical CG real close to the spot the leadouts come out of the wing. How for off is it? I would almost expect it to be below the leadout exit point. Does the model fly with one wing high? Is the pitch trim (CG) adjusted to where you get good corners? Do you have more elevator than flap per the plans? Hate to see you having problems with the T-6 after Joe's worked so well!

As Sparky is so fond of saying, " no two airplanes fly alike". Mine has those decals and quite a lot more clear than Joes. That could be a potential cause.  It's just time to fix it. I taped 2 1/2 of lead to the bottom and it helped quite a bit.  Not a permanant fix, just trying to get it flying right in the short term.   I like Joes idea of moving the leadouts but I'm going to wait on that till winter.

Now I'm down to INBOARD tip weight/ flap tweaking to finish leveling it out. After that it will be time to fine tune. Model turns well in spite of its sickness.

This is also only the 5th stunter I've ever built and is a much more complex build than anything i've attempted...im sure that has a bit to do with it as well

[Sean McEntee]

I have some Kraft wheels, Sean. What size do you desire?
Chris...

Talk to Dad a couple nights ago.  He has some in stock.  Will take a look at them.

[Tim Wescott]

Now I'm down to INBOARD tip weight/ flap tweaking to finish leveling it out. After that it will be time to fine tune. Model turns well in spite of its sickness.

Don't fix upright flight and screw up inverted with your inboard tip weight.

And keep in mind that your flap tweaking will only exactly cancel a vertical CG problem at exactly one speed.

Jus' more stuff to make you worry....

[Dan McEntee]

   To update this story, Sean stopped here at home on his way to Oshkosh so I could check out the airplane and he could help me test fly Dusty. Dusty has some dihedral in it also, and other than on a Yates Dragon I had never had to deal with the issue.
   I sighted the wing like I had always learned to do looking from the trailing edge forward and he has a slight, gradual twist in the wing starting at the inboard tip and going out to the out board tip, inboard down and out board up. That is what is causing his outboard wing down issue I believe. We had a heat gun and twisting session in the garage last night before turning in, and may have corrected the issue. He left early this morning for Oshkosh and we'll test fly it again there, and I just packed the iron and heat gun for more wing abuse if needed. The model looks nice, first time I got to see it in person. He'll have some other wrinkles to get out, but I think we have found the actual cause of the problem. All the weight in the world taped to the belly of the airplane wouldn't over come the way the wing was twisted, gradual but long. Too much aerodynamic force to over come.
    I want to take this opportunity to thank ALL of you guys out there that have been so supportive of Sean and his military career, and for all the help you have given him on the flying field. Through our modeling efforts, we have a network of good, fast friends he can count on if he needs them just about every where he has been or is likely to go. My wife and I greatly appreciate it!!!
    Best Regards,
   Dan McEntee