Ballast weight and location

Discussion in 'Starduster' started by mreinh3233, Mar 3, 2018.

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  1. Mar 3, 2018 #1

    mreinh3233

    mreinh3233

    mreinh3233

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    OK, so I’m thinking of adding ballast weight to my engine mount. What would be the maximum that I could safely go. Or where and how much in another location as a better alternative. Just kind of thinking out loud here.
     
  2. Mar 3, 2018 #2

    EAABipe40FF

    EAABipe40FF

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    When I discovered my mount was 4" too short because of my brain fart I considered several things. Prop extension, heavy starter(if you have a lite one)?

    Nothing reasonable did enough so I made a 4" longer mount which was still slightly short.
    My final W&B suggested I'd bust the aft limit with less than 7 gal of gas. Then I bolted 13# to the gen. pad on the engine. (nice 4 bolt pad on the IO320B1A)

    PS. I figured everything as a single place. When I converted to 2 place it was bad news again. I need at least a 2 " longer mount. Oh well, I also need a new engine. Maybe I can get it right?

    I HATE ballast. I suggest a correct length mount.

    Jack
     
  3. Mar 3, 2018 #3

    DanSalcedo

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    I saw one on a Alternator mount pad, but you need to have the B&C alternator on the vacuum pump drive. It was about 4x6x2 lead, don't remember the weight.
     
  4. Mar 3, 2018 #4

    DennisV

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    At about .41 lbs/cu-in for about 48 cu-in, that should be about 20 lbs., if my arithmetic serves me.
     
  5. Mar 3, 2018 #5

    mreinh3233

    mreinh3233

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    I agree the longer engine mount is the way to go, but also the most expensive and time consuming. Adding ballast (Which I hate to do) is (I think) the quickest and easiest way to get back in the air.
     
  6. Mar 4, 2018 #6

    EAABipe40FF

    EAABipe40FF

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    Yea, my 13# was steel at what, .30#/ cu-in. Lead would be better.
     
  7. Mar 4, 2018 #7

    TFF1

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    How much weight are you needing? I would calculate that number at the aft and front of engine stations. I did see a Starduster Two that had a weighted flywheel maybe from a Piper? He was not doing crazy stuff with it so he was not worried as if you did tumbles. Heavier tube engine mount? At least you can do the math to see how deep you have to jump.
     
  8. Mar 4, 2018 #8

    DennisV

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    Even better if you can get some Osmium: .81 lbs/cu-in. And you can pick it up for a mere $1479 an ounce! :D
     
  9. Mar 4, 2018 #9

    garyg

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    Use tungsten. A little expensive but nowhere near the price of Osmium. It is 1.7 times heavier than lead. I used tungsten to balance my ailerons but that was only about 2-3 lbs.
     
  10. Mar 4, 2018 #10

    EAABipe40FF

    EAABipe40FF

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    I use to have access to depleted uranium by the ton.......but I didn't bring any home.

    I recall early on the argument for DU vs. tungsten for tank ammo. They were about equal in penetration. Of coarse DU is also pyrophoric which is useful(understatement)

    The main advantage of DU is that it was cheap(relative) and we had an almost unlimited supply......

    Jack :rolleyes:
     
  11. Mar 7, 2018 #11

    walkon3083

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    Several years ago when I had a tail heavy Starduster ll a fellow poster gave me a pair of 40 lb lead weights that bolt onto the engine mount. I never used them and you are welcome to them for the cost of shipping.
     
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  12. Mar 8, 2018 #12

    mreinh3233

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    PM sent
     
  13. Mar 11, 2018 #13

    Dana

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    The main disadvantage is that it's really really toxic. Of course for tank ammo you don't really care...
     
  14. Mar 12, 2018 #14

    DennisV

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    Yeah, if you're sitting in a tank being shot at with the stuff, your immediate concern is kinetic energy, not radiation. :eek:
     
  15. Mar 12, 2018 #15

    EAABipe40FF

    EAABipe40FF

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    Radiation isn't that bad. The granite walls in the main BRL building were worse. DU isn't toxic and can be handled safely, it's the oxides made when it goes thru steel @ 6000 ft/sec that will hurt you. But indeed it is the chemical hazard more than radiation that's a concern.

    We shot DU on an outdoor range at first. We were told there were two primary oxides of U. When it burned the initial one was really nasty but it quickly turned into a "calmer" oxide in a couple minutes. You could see it after the shot, a yellow/greenish cloud that quickly turned to grey. For safety sake we waited 10 min. Then cotton coveralls, booties, face mask, etc and normal cleanup. And the range was set up so the firing position was up wind.

    The formed/machined metal itself is not much worse than lead......
    So we were told:rolleyes:

    OTOH I might worry if buying any surplus shot-up T-72 tanks:)

    Jack
     
  16. Mar 13, 2018 #16

    mreinh3233

    mreinh3233

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    OK all you aeronautical engineers out there. What is the formula for estimating how much ballast I need to get my big butt in the aircraft and still be in CG with zero fuel. I tried a basic WT and balance (WT X arm problem) but than I realized my empty wt and balance would change and I couldn’t figure out what formula to use to calculate that. See what I’m saying. If you add 20LBS to the nose it changes the weight on the main and tail wheels but by how much? Is there a formula you can use or do you have to put the old boy on scales and play ”let’s see how much this weight will change it” with different weights until you get it where it needs to be. I would like to be somewhere in the ball park before I get my mechanic involved just to save me time and money.
     
  17. Mar 13, 2018 #17

    IanJ

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    If you do basic weight and balance calculations, it should be straightforward. Measure the arm from the datum, plug in the weight you want to put there, see new CG. Your pilot/pax weight, fuel weight, etc. all stay the same, so if you know you're busting aft CG by 2", calculate adding weight at your -20 inch (or whatever measurement) "back of engine case" arm location until you see the basic empty CG move forward by 2".

    For example, on my Champ, my empty weight is 996 lbs at 16.16", which is too far aft for my comfort. My basic CG envelope is 10.2 - 19.2 inches aft of datum. If I add a 20 lb weight at -25" (kinda maybe the arm of the back of the engine case), I subtract 500 lb-in of moment from the base moment of 16095.36 lb-in to get 15595.36 lb-in and a new total weight of 1016 lbs. 15595.36 divided by 1016 is 15.34", which is my new empty CG. So, I gain less than an inch of CG at the cost of 20 lbs less payload. I'd need to add even more weight to move that 2" I really want. Just keep changing that weight number at your desired arm until you get the result you want.

    I think you're on the right track. Don't make the math more complicated than it needs to be.

    Screenshot_2018-03-13_13-50-24.png
     
    Last edited: Mar 13, 2018
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  18. Mar 13, 2018 #18

    IanJ

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    I only wish I knew what made the Champ so tail-heavy.
     
  19. Mar 13, 2018 #19

    Beej

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    Your belly?:D
     
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  20. Mar 13, 2018 #20

    Dave Baxter

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    Mike I am not an aeronautical engineer, but basically to move the C.G. forward one inch you have to move the engine forward four inches, ad a metal hartzell C/S prop out on the nose, over a F/P metal prop and you add approximately 40 # more out where you need it. Add a 540 and you have another 100# on the nose, which usually solves the C.G. problem. I have an A&P/IA friend that added about 5 steel bars under the starter on a similar O-320 short engine mount Starduster that solved the W&B problem on that airplane, and I am trying to find out just how many bars length width weight, and how they were mounted, if I get the details will post them. Dave
     
    Last edited: Mar 13, 2018
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