ST 19 & 23’s

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  • 08/17/2009 at 1:45 pm #41178
    Scott Lapraik
    Participant

    I am in the process of building a new A/B classic ship and I am planning on mounting either an ST 19 or 23 (G20). Wing area is 497 sq. in. My question is can you run these engines with out a venturi when using pressure and what nitro % would be reccomended and what prop size to start out with?

    Thanks, Scott



    08/17/2009 at 3:24 pm #47739
    DAN BERRY
    Participant

    No venturi insert and pressure will work. 35% pop and an 8×3 should get you started. There might be better choices, but that would work.
    What is the design?

    08/17/2009 at 3:33 pm #47740
    Scott Lapraik
    Participant

    Dan, it’s a 585 Geo. Galaxy with the length of wing reduced to a 57″ (497 sq. in.) wing. Stab Length reduced by 20%. Built on my own design fus. Wing aspect ratio reduced from 7.65 to 6.6.

    Scott

    08/17/2009 at 11:06 pm #47741
    DAN BERRY
    Participant

    That should work. Keep the wing stiff.

    08/19/2009 at 2:58 pm #47742
    Scott Lapraik
    Participant

    Dan, attached is a pic of the 497 Geo Galaxy. I am going to start out with the ST 19 with an 8×4 apc prop. With the Geodetic wing construction wing flutter will not be an issue.

    Scott



    08/19/2009 at 5:17 pm #47743
    DAN BERRY
    Participant

    @scottl0413 wrote:

    Dan, attached is a pic of the 497 Geo Galaxy. I am going to start out with the ST 19 with an 8×4 apc prop. With the Geodetic wing construction wing flutter will not be an issue.

    Scott

    Flutter could be an issue. More to the point, instead of flutter, just a washing-out syndrome.
    It looks good though.

    08/19/2009 at 5:35 pm #47744
    Scott Lapraik
    Participant

    Dan, I understand what your saying and with other style wing construction it may be a concern. Over the past 2 years I’ve built a no. of planes based on the Geodetic wing construction and have yet to experience any wing related issues. 😀 The only thing with geodetic wing construction you either build in your washin/out or you add shims after the fact, because once the wing is built with the geo. construction you’re not going to warp the wing to your liking!!! I am going to take your advice on the next wing build and construct the two center wing bays flat. I’ve already done this on a small electric (1/2A) and it appears to work great!
    🙂
    Scott

    08/19/2009 at 5:41 pm #47745
    DAN BERRY
    Participant

    I understand what you’re saying, Scott. I would suggest that you are about to start flying faster than you have been. That’s when rigid wings become a necessity.

    08/19/2009 at 5:51 pm #47746
    Scott Lapraik
    Participant

    Dan, I appreciate your comments and insights and that’s what I thought you where implying. I hope that this ship will be able to compete with you and the others. If the wings are not rigid enough I’ll cap the ribs with .003/.005 carbon strips! I am also going to cover the next wing with polyspan, should add structural strength also.

    Thanks again,

    Scott

    08/19/2009 at 6:14 pm #47747
    JIM MOSELEY
    Participant

    Your structure should be OK especially given a better covering than transparent plastic.

    For what little it’s worth .. waaaay back I flew a Midi-Pearl with a ST.23 and it was a real ‘moving machine’. I never experienced any wing problem even with straight ribs, tissue covered …. but finally after a bad launch the model zeroed out and the stabiliser exploded….. rapidly followed by comprehensive destruction.

    Later: corrected. MIDI- Pearl ….. not Mini-Pearl !!!

    08/19/2009 at 10:30 pm #47748
    DAN BERRY
    Participant

    Hey Jim, you used the magic word… tissue. Scott is looking at plastic wrap covering.
    Scott, that wing with polyspan wouldn’t be a problem. CF caps on the diagonals would likely be a good idea with iron-on stuff. CF caps wouldn’t add 4gms to it and it would be LOTS stiffer.

    08/20/2009 at 1:37 pm #47749
    Scott Lapraik
    Participant

    Dan, fired up the 19 last night on bladder pressure, w/out venturi on 35% pop, and 8 x 4 prop and it took a little coaxing to get it running since I have no idea when it was last run but after a no. of attempts it cleared it’s throat and pulled hard. Excited to get it to the field. It’l probably be a week or two before I can test fly it.

    Scott

    09/04/2009 at 1:52 am #47750
    Roger LaPrelle
    Participant

    What kind of CF strips would you use on the diagonals? Epoxy layups, raw tow, or what? I am getting ready to build a geodetic wing, and should probably use CF.

    Thanks,
    Cap’n Rog

    09/04/2009 at 2:05 am #47751
    DAN BERRY
    Participant

    I guess its an epoxy layup. Its unidirectional caron laminate. 003-005 thick. I just glue iy=t on with medium CyA and rub it down with visqueen over my thumb.

    09/04/2009 at 12:26 pm #47752
    Scott Lapraik
    Participant

    Well, got a chance last night to start trimming the 500″ Galaxy. First flight 3-4 second motor run, good right hand pwr. pattern very smooth transition, glide was very good 😀 😯 Second test flight same. 😯 Third test flight let it run for full 7 second engine time and same results 😀 😯 8) I think after these flights that the 19 ST is just a little light for this size plane. Went home last night and mounted the 23. Will see how it does next time out. I’m in the process of building a 585″ Galaxy fuselage right now and will mount an O.S. 25 FSR-S on it.

    Scott

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