|
||
|
Quote:
By the time I started my first Starship this thread was already up to page 145. Thank you guys! I've had help from Australia, Canada, Turkey, the Pacific. all over Europe and the USA. With your help, optimism and a patient family, there's no end to the possibilities. Good fun and plenty more to come. I just wish some more people would have a go at the Rutan planes. This is the best thread! Nick |
|
|
||
|
|
|||
Thread OP
|
Nickchud
Quote:
Perdu Tony Quote:
Charles |
||
|
|||
|
|
Thread OP
|
Delta Duck Build
Both wings were aligned and mounted with dowels at leading edges and 10-24 nylon bolts at trailing edges. The motor mount and rear servo mounting plate was added.
Charles |
|
|
|
|
|
Carl, regarding your duck design. How much prop clearence from the water do you anticipate having? From the drawings it looks to me to be pretty marginal. Water being sucked into the props will ruin your day, and may prevent reaching flying speed.
|
|
|
|
|
|
Hi Joel, thanks for the question--it got me doing some maths.
Attached is a displacement of 214 cubic inches, or 7.72lbs. I'll have a crap if my bird ends up being that heavy, but it's good to account for dark matter when doing scratch builds in my experience. Given that number, you can see that a 9" prop will have a touch over 2.5" of clearance at rest, so big chop will probably stop the motors from fully spooling up. We'll have to see. You'll also note the location of the CG at 10% static margin, is a touch behind my concept sketch (under the spinners). This is in part a mistake, but I do not want to enlarge the canards anymore than I already have as balancing the model would then become really difficult. At a design-goal RTF weight of 4.5lbs I think she'll leap off of the water pretty quickly. I do love a long, steady plane for scale realism though, and I fear that my biggest enemy will be spray from the relatively plumb bow despite the spray rails that I've drawn in. It will be really overpowered though so I should be able to punch it onto a plane just like all the airboats that I used to make years back (they eventually started flying without wings LOL). Thanks for the constructive input! Helps keep me thinking. Carl Miller |
|
Last edited by Haole; Jul 23, 2010 at 12:33 PM.
Reason: editing
|
|
|
|
Hey guys,
Take a look and lend your opinions please. I'm leaning towards a single vertical fin even though it's a pretty big deviation from my concept sketch of yesteryear. I think it looks more classy and it has the same effective moment arm from the CG as the twin swept fins. Half the drag, same great yaw. Harrrr Carl |
|
|
|
|
|
If it has the same effective moment arm (which in your case looks pretty doggone short, which means your dynamic stability in yaw is probably going to be bloody awful), then your single fin needs to have the same total area as your twin fins.
With that long, high nose destabilizing the plane in yaw, the overall yaw stability looks to me like it's likely to be nearly neutral, not a good thing at all, especially for a flying boat. You might want to give it a pretty substantial water rudder to help offset the destabilizing effects of the forward part of the hull when on the water. On the plus side, fins sitting in the propwash will gain some rudder authority, which will definitely help in the case of an engine-out situation (and yes, that can happen with electrics too, been there, done that). On the negative side, fins sitting in the propwash will lose some of their stabilizing effect because of the straightening effect of the propwash. Winglets lifting inwards at the wingtips will help the spiral stability, for reasons we discussed here earlier, but will not have a rudder authority benefit from the propwash. It also looks like you need some more bouyancy at the wingtips. With little or nothing to keep the wingtips from digging into the water, plus the poor yaw stability, just a little crosswind gust on the water is likely to ruin your entire day. |
|
|
|
|
|
Gripen update
A bit of progress on the Gripen. Fan and thrust tube installed. Thrust tube tapered to 85% FSA. ESC hot glued into opening in inner wall of intake duct for plenty of cooling air. Canopy and hatch cover in spackle. Elevon servos installed. Ready to glue on fuselage top.
John |
|
|
|
|
|
Thanks for the reply. Meant to say same effective yaw moment (total). Yep, it's gonna get pontoons and a water rudder, all of which will help with yaw. It's already at 200+% lateral area behind the CG...
Carl Edit: Crap, my props didn't get here in time for some weekend bench testing. More Rhino for now I suppose... |
|
Last edited by Haole; Jul 23, 2010 at 08:17 PM.
|
|
|
|
Carl,
I really like the rudder up on the wing, I think it looks slicker or neater. I know nothing about design, I was going on looks only. Of course Don has the experience and engineering skills I don't have. Maybe some wingletts with the rudder on the second design. Who knows, guess you will have to test to see how it will work. Conehead Orrin Eldred |
|
|
|
|
|
Its a beautiful design, but I would consider leaving myself some option to raise the propeller clearance. 2 1/2 inches is far too little inmho. Props have a tendency to suck water into themselves when close to the water.How much up angle do you have on the step from the cg back?
|
|
Last edited by Joel K. Scholz; Jul 23, 2010 at 08:41 PM.
|
|
|
|
What about a V tail
|
|
|
|
|
|
I like the v tail. Carl I have not had a chance to go thru this entire thread so I don't know where you are in the build. I am looking at the angle on the step and as far as I can measure it appears to be about 4 degrees. I think your going to need around 7 degrees for the fuselage to be able to rotate sufficiently.
|
|
|
|
|
Thread OP
|
John, The Gripen is looking good. What will you do for yaw control?
Charles |
|
|
|
|
|
Carl, what is your boat going to be built of?
|
|
|