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Thread: Carbon Cub EX-3 Turboprop?

  1. #41

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    Cool pictures! Where did you find them? Do you know what turboprop they used?

  2. #42
    Steve Pierce's Avatar
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    Do a serch here. Was disscussed here at length back when it was making the rounds.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

  3. #43

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    Quote Originally Posted by Steve Pierce View Post
    Do a serch here. Was disscussed here at length back when it was making the rounds.
    Sweet, thanks! Here’s an idea of what it could look like.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  4. #44
    CamTom12's Avatar
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    Quote Originally Posted by Rob View Post
    It's not suprising we are looking at some of this stuff from opposite sides given your RR/Allison experience, and the differing airframes. My minimal exposure
    to that engines sister in the Bell airframes tell me they are a hot start looking for a day to happen.
    Rob, I’ve got some pretty good experience in helicopters with various examples of the M250. This is a pretty good way to describe the early models.

    Later models with a FADEC (my experience is with the C30/R) make starts a non event (so long as you have a strong battery and don’t drop below the 10.8 or whatever voltage is required to keep the ECU alive), but the community had a memory and they were still hawk-eyed.

  5. #45
    Rob's Avatar
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    That picture reveals one of the reasons the concept doesn't work well for me. It's pretty common to see T-Prop conversions shift to multi bladed smaller discs for props.Works pretty good when the airframe is a go fast model just looking for a boost in thrust.

    In fact the Thrush I am currently flying is an overweight example with a PT6-34 in a 500 gallon airframe. This size of airframe has never been the best bed for a -34 IMHO (750 hp), and too small for the -60/5/7's (1050-1300hp). It was a perfect mate to the (obsolete) -45 (1100 hp). Then came along an STC to go from the standard 3 blade Hartnell to a 4 blade. What a difference! It's not the same as having a -45, but it is a good mate to the airframe now.... Proof that I'm not alone in this thinking is the current trend to re-engine this size ship to -42/2's (900 hp). But I digress ...

    Back to the picture... I am of the opinion that raw thrust alone is not what makes the magic in the lighter cubs. I believe if you took Frank Knap's Lil Cub, removed the Lyc up front and mounted a turbo fan of equal power above the cabin, it would get off the ground in considerably longer distances. In fact, I believe it would take a good amount more thrust to catch up to the recip.

    My theory is that super long prop Frank is turning is getting a bigger portion of the wing up to flying speed long before the cub even starts to roll. I've been watching the pireps on Greg's exp Maule, and was intrigued that he went with the compact Hartnell, and now see he's going to try (or maybe already has) the longer fixed pitch he used to run. That's a bit heavier platform (not a bunch) so it will be interesting to see what happens.

    How much more thrust do you need to get a shorter span up to flying speed to match up to the bigger disc is beyond my level of education, but I am certain one of the engineer types here could tell you lickity-spilt.

    FWIW, I am not an engineer, not even very well educated, but I have spent a whole bunch of time watching and playing. I know we can build a cub that will leave the ground from a dead stop, even with a recip. And that is why as cool as a T-prop sounds to me, it doesn't work for me. I hope to see you work it through. I really like the idea.

    Take care, Rob

  6. #46

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    Rob,
    You are partly right about the thrust, but to me it is a big factor on initial performance on takeoff. Look at the geared engines on a Helio Courier, swings a 96" prop and yanks the Helio's right out of the gate, slower turning big prop has the thrust unequaled by smaller high speed ones. Fly a straight drive 0540 Helio with smaller blades and simply does not have the initial thrust and performance. The prop blast on a Helio blows the slats in on one side from the thrust of the prop initially. Widgeons with the geared engines and longer blades have the thrust unequalled by straight drive engines too. Once up flying the thrust is equal, but not on takeoff. Even cycling the prop in a Helio sets one back in the seat on floats.
    John

  7. #47

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    I guess your only option for additional fuel would be a belly pod, and have Frank Farr hold a bladder in his lap...

  8. #48

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    For more fuel, since the tanks require larger outlets to handle the turbines higher fuel flow, add more fuel in the wing as well.

  9. #49

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    Sourdough,Good one on Frankie boy! Check out the Husky A-1 project build on nearby thread on this site, has belly pod for Frankie boy in that one.
    John
    Last edited by john schwamm; 03-25-2019 at 06:59 PM.

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