Recent content by Marc Zeitlin

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  1. Marc Zeitlin

    Raptor Composite Aircraft

    If you assign material properties to each part, then yes - it can give you a weight roll-up for parts, sub-assemblies and overall assemblies. With composites, it's harder to be accurate, as wet layups can vary substantially in thickness and resin content, and even with prepregs, it's harder than...
  2. Marc Zeitlin

    Raptor Composite Aircraft

    Yeah, Aircraft Single Engine Land / Glider / Instrument / Commercial. Can't speak for anyone else. Too bad this wasn't a bet - I've got a couple, from MIT, which along with $5 gets me a cup of coffee at Starbucks. I know of a number of other folks on here who also have degrees in AE or ME. Aside...
  3. Marc Zeitlin

    Continental and leaning.

    I'm no engine expert, but it sounds to me as though your carburetor is jetted way too rich.
  4. Marc Zeitlin

    Raptor Composite Aircraft

    In what way? And I was a project manager for a large program in a small aerospace company. We had 33 engineers when I got there, and ~133 engineers when I left. There might have been a few who were overly optimistic about their own capabilities, but for the most part, everyone was competent...
  5. Marc Zeitlin

    Raptor Composite Aircraft

    Not everything that Peter does is wrong - blind squirrel, etc., and there's more than enough to beat him up about without doing so regarding things he gets right. In this case, he switched from a shear nut to a tension nut. That's perfectly acceptable. He also put standard washers, rather than...
  6. Marc Zeitlin

    Spar cap material

    I'm not dismissing the IDEA of prestressing, but it has to be used in appropriate situations. Concrete is really good in compression and very crappy in tension. Hence the desire to compress the crap out of it when it's going to be in bending and will have part of it in tension (bridge beams...
  7. Marc Zeitlin

    Raptor Composite Aircraft

    This is true. Ran into this a LOT with the SS2/RM2 project - every rocket motor consultant had their own view of how the universe worked and what we should do. As with Jews (the Jew says), get 5 rocket experts in a room and you'll get 17 opinions. Made for interesting meetings. And here lies the...
  8. Marc Zeitlin

    Spar cap material

    You may be right, but the first question to ask is why anyone thinks that there needs to be pre-tension on the fibers. Any pre-tensioning (strain) will only decrease the total amount of tension (strain) that the fibers could accept in use. The only reason I can see to put any tension on the...
  9. Marc Zeitlin

    Raptor Composite Aircraft

    Not if you understand who knows their butt from a hot rock and to whom you should listen. Then it's very simple to get accurate information. No one is inventing cold fusion here - the answers are well understood by many.
  10. Marc Zeitlin

    Spar cap material

    Nope. E-glass on the VE, LE, COZY, E-Racer, etc. See: https://www.aircraftspruce.com/catalog/cmpages/unitape_01-01651.php
  11. Marc Zeitlin

    Control via Hydraulics

    Nothing wrong with electric actuators - I've got them all over my plane for pitch and roll trim, A/P servos, etc. But none of those things are the primary flight control actuators, so none need to be redundant, and all of them can either be turned off or are overridable by the pilot's arm, if...
  12. Marc Zeitlin

    Control via Hydraulics

    Can't guarantee it, but depending upon the diameter of your prop bolts and the diameter of your crush plate, the answer is generally yes.
  13. Marc Zeitlin

    Control via Hydraulics

    Sometimes yes, sometimes no. Generally, failure rates don't include age, but the handbook I referred to does have some curves of failure rates of components as a function of age. You should read Mike Busch on the theory of TBO and how it's really not a good measure of maintenance needs. So the...
  14. Marc Zeitlin

    Control via Hydraulics

    It was an example to show the process. Obviously, hydraulic systems don't fail that often. So if you believe that there's any single moving device with fluid in it that will last 10e6 hours (114 years) without failing, you've never actually dealt with device failure rates. But let's postulate...
  15. Marc Zeitlin

    Control via Hydraulics

    Not that I believe that anyone should believe anything that someone says merely because they have some "qualifications", but I'll talk about hydraulic and electric actuator System Safety Analysis (SSA) a bit because I did the SSA/Fault Trees for the systems on the SS2/WK2/RM2 aircraft/rocket for...
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