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About CTMI

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    Master Crew Member

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    Flying, sailing, iceboating
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  1. CTMI

    Which has more thrust?

    Ok here’s a brain bender. Engine 1: O-320 160hp and 311 ft/lbs of torque at the prop when: Engine RPM: 2700 Prop RPM: 2700 Engine 2: ROTAX 915 141 hp and 310.4 ft/lbs of torque at the prop when: Engine RPM: 5800 Prop RPM: 2386 Which will create more takeoff thrust assuming both have CS props with blades optimized for their rpm? this is really messing with my head, because engine 1 has more horsepower, they both have the same torque, and engine 2 has lower rpm which should be more efficient transfer of energy.... Thoughts? Which produces more thrust at takeoff? At cruise?
  2. CTMI

    Single lever control

    Roger have you heard anything about this system’s implementation in the field? Or anything on the 915 in general? This engine seems quite veiled in secrecy. Hard to get a handle on even basics like fuel burn etc. I called Michael stock in Germany to enquire about the sing lever control system; he said that the computer does 100s of checks a second and sets the prop based on all available data. He said that the “curve” which is essentially a complex quadratic equation/function of prop speed and throttle % can be changed/modified so as to be optimized for a given plane and mission. Unbelievable technology really.... A friend is considering putting two 915s on a Velocity V-twin. The numbers pencil out.
  3. CTMI

    Single lever control

    Not sure if everyone’s seen it, but Stock flight systems, who makes EMU systems for the 912is and now 915is teamed up with Rotax and M/T propeller to make a fully automatic CS prop. Basically the EMU uses the CANbus system to use readings from the engine to adjust the pitch of the blades according to pre made and modifiable “maps” On 912 the governing variable was MP but with the 915 its %throttle since it’s turboed. Long story short you just push the throttle forward and the system sets the pitch and everything else. Seems pretty neat but at the same time there’s a lot going on that you can’t control. Thoughts?
  4. CTMI

    Max rpm or?

    Ok so theoretically, though you wouldn’t do it, you can have WOT indefinitely as long as RPM is 5500 or less
  5. CTMI

    Max rpm or?

    Ever think about a simple thing so much you get your wires crossed? Ok 5800 is the max RPM that you can have for 5 minutes but if you keep your rpm at 5500 you could firewall the throttle indefinitely, right???? so FULL THROTTLE can be indefinite so long as RPM is equal to or less than 5500 right?
  6. CTMI

    Prop Issue -- Cosmetic or Serious?

    well, agree to disagree. I think our painted, carbon airplanes, if maintained, will outlast us all. cheers!
  7. CTMI

    Prop Issue -- Cosmetic or Serious?

    Runtoeat: That’s interesting! One of the biggest misunderstanding about carbon/Kevlar is the difference between strength and stiffness. Carbon is STRONG but it isn’t really stiff. Stiffness comes from the core. In fact if you do a flat layup of 4 layers of 12k 4x4, it will bend like a piece of paper. There’s YouTube videos that show it. now take that same layup but put 2 layers on either side of a 1/4” core and you can stand on it and it won’t bend. Such cool stuff.
  8. CTMI

    Prop Issue -- Cosmetic or Serious?

    Actually the big weakness of epoxy is not water it’s sun. Epoxy is not UV stable, which is why we need to take good care of our paint!
  9. CTMI

    Prop Issue -- Cosmetic or Serious?

    I raced a sailboat class called E-scows for over a decade. The boat is 30 feet long, 7 feet wide and only about 18 inches deep. (it even kind of looks like a wing) They made a batch of epoxy boats in the 90s instead of the standard vinylester/polyester used for the rest of the fleet. Those boats are still stiffer and lighter than the brand new ones being made. They are absolutely bulletproof. Epoxy does not have a weakness to water, and certainly and absolutely is not affected by moisture in the air. You’re thinking core materials. And even core materials are not all susceptible. Divynicell, keracell and similar products for instance, are a closed cell structure that is highly resistant to water. On the other hand, aviation cores like the rohacell used in our planes are much less resistant to water and chemicals. Water intrusion can happen with nomex Kevlar cores as well though it’s bonding that’s the major difficulty with honeycombs, which is why the bulk of those layups are prepreg bagged and autoclaved. There isn’t a different chemical property to aviation composite epoxy than is used in the marine industry, with the exception of high heat epoxy formulations used around jet engines.
  10. CTMI

    Prop Issue -- Cosmetic or Serious?

    someone said composite aircraft won’t age as well as aluminum. I think composite aircraft can last as long if not longer than aluminum provided the composite structure is properly designed, used, and maintained. I remember reading somewhere that aluminum weakens with enough routine loading for long enough, something about the flexure modulus or something of that nature. At the same time carbon and Kevlar can be loaded and unloaded within spec infinitely with no property changes. I have a friend who builds 50ft+ carbon racing yachts. He said carbon will last forever and ever if it’s maintained. The trade off is, if carbon is loaded beyond spec, it fails spectacularly. It basically explodes apart. Anywho, I think the issue is aluminum is more receptive to abuse, but if a composite aircraft isn’t abused and maintained it should last forever.
  11. CTMI

    Prop Issue -- Cosmetic or Serious?

    I have more experience with glass then carbon. That said, that looks like stress related cracks. Stacked hair cracks like these usually come from the layup flexing or “moving” in a way that’s incompatible with the paint system or gel coat above it. its hard to say if the flexure underneath which caused the hairline fractures was in or out of spec; it would depend on the paint system and underlying layup. It’s also interesting that the cracks are the entire length. Stress cracks have reasoning behind them; they follow load paths, or they propagate in areas where quality layup is difficult etc. On the other hand, “cosmetic only” is usually much more random. Now with all that blah blah said........if it were me I’d be ordering a new prop. Its pretty important to me that all pieces of my propulsion system are in unquestionably good order. It makes me nervous that it’s the whole blade length on all blades. Maybe not the answer you want but i won’t sugarcoat, -not with something this important! Ymmv
  12. Went all out for spring and tried a four step composiclean system. step 1. wipe down with wet rag, then wipe down with a wet rag with composiclean bucket wash in it, then wet rag, then dry step 2. Claybar using composiclean spray wax as clay lubricant. Straight alternating passes. This sucks out any impurities or dirt in the paint. You can “feel” it work. step 3. buff with random orbital buffer using composiclean Haze Glaze. This is a very fine polish and cleaner. step 4. composiclean spray wax. 2 rags. One to spread it, one to buff the haze off. It is a lot of work but it is absolutely 100% worth it. Every little imperfection I had Is gone, and despite it being a white epoxy based paint it has real depth to it. What’s more the paint has a *soft* feel to it. My plane was and is VERY well maintained so this was hardly a rehab project, but I can honestly say the plane looks brand new. I recommend this method. I’m expecting an extra five knots with the extra smooth surface ?
  13. CTMI

    What is that gunk in my carburetor bowl?

    in your earlier thread i asked when the last time your gaskets were swapped out. I asked because its very possible that was a little piece of gasket in there. thats what happened to me. it was tan too. granted, im no scientist but aluminum hyroxination occurring randomly in a carb bowl to the point of spawning some large piece of antimatter all while flying at X000 feet, which migrates finally to clog the jet.............. well. it just seems...... elaborate. sure it wasnt just a piece of gasket? the cork ones are tan........ if so, get the green ones. Please nobody imron their carbs.
  14. CTMI

    Amps going nuts

    This happened to me too. Cleaning fixed it. There’s nothing worse than a shoddy shunt.