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Old Mar 28, 2013, 03:18 AM
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I need your opinions guys, how much drag do you think 130mm tall tricycle LG will add to the plane? I am doing the maths right now for 17x12 E vs 16x12E and I have 17x12E edging out on cruise efficiency by a very (very!) slight margin, under the complete ass-pull assumption that the LG will add 10% drag.

What do you guys think? Is 10% too low? Too high? What should I set it to?
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Old Mar 28, 2013, 04:03 AM
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10% drag with fixed gear is fairly high - Looking at some examples of clean air frames, look at the Glasair FG vs RG.. Just 4 Mph difference with a cruise near 200 Mph. so this works out at just 2% drag. Look at the Cessna 210 vs 182 turbo.. same engine but there is 30 Mph different for a 170 Mph cruise. So around 10% but this is an OLD production aircraft and you should be aiming for 5%. You need to ask yourself, Why am I adding fixed gear ? I think you mentioned because you were intending to build a load carrying long endurance SH... But should you then not be looking at wheel pants.. gear fairings etc ? This will get you near your 5%
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Old Mar 28, 2013, 04:47 AM
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Quote:
Originally Posted by OzparkPilot View Post
10% drag with fixed gear is fairly high - Looking at some examples of clean air frames, look at the Glasair FG vs RG.. Just 4 Mph difference with a cruise near 200 Mph. so this works out at just 2% drag. Look at the Cessna 210 vs 182 turbo.. same engine but there is 30 Mph different for a 170 Mph cruise. So around 10% but this is an OLD production aircraft and you should be aiming for 5%. You need to ask yourself, Why am I adding fixed gear ? I think you mentioned because you were intending to build a load carrying long endurance SH... But should you then not be looking at wheel pants.. gear fairings etc ? This will get you near your 5%
I'm adding fixed gear because I find landing and takeoff rolls fun, and it's pretty chunky gear because I don't have much of a smooth surface by the way

4mph difference in speed at 200 works out to ~4% difference in drag by the way, since drag is by square of speed:

204^2*(drag)=200^2*(increaseindrag*drag)

sub the value of 1 into drag and you get increaseindrag=1.0404 i.e. 4.04% (obviously approximate due to other factors we haven't taken into account)

I think it's going to be interesting. What I'm getting here is just a few % increase in efficiency from 17x12 over 16x12, depending on what I am doing at the time (acceleration/cruise/climb). I wander if it will be measurable with the accuracy of my gear. Probably not, so after a few flights it might come down to whether the 17x12 looks dangerously close to booms/overheats the motor/sounds really awesome (which it might do). It has significantly more low speed thrust but I don't really care about that lol, 16x12 has more than enough.
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Last edited by Nereth; Mar 28, 2013 at 04:54 AM.
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Old Mar 28, 2013, 02:03 PM
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That eagle squawk at the end is epic.
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Old Mar 28, 2013, 08:04 PM
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Skyhunter Update on Build

Easy part is pretty much done. Fuselage together, Electronics tray sanded and it fits snug. Built the FPV shelf but Im not going to use the gimbal portion. Only installing pan and tilt for the Camera.

I did put additional carbon fiber bracing on the rear stabilizer elevator area along with the vertical fins. It just seemed to flimsy. Both wings done and booms measured and taped so they fit in the same way each time.

As you can see I used a little bit bigger servo than maybe is needed. Went with HS-85mg's all around. On the tail it sticks out just a little. No big deal in making the holes a bit bigger.

Now using only CA, seems to work much better than epoxy, and its easier. Just need to work fast with it.

I originally laid down Velcro on the bottom of the fuselage. Just took that out. Epoxy gave it up pretty easy. Who ever said the epoxy will crack was correct. Batteries were not sitting correctly. Will make a battery tray that sits on Velcro so I can slide the tray where it needs to be and the battery or batteries will remain secure in the tray. All kinds of room in this build so might as well take advantage of it.

Now its a waiting game. I have one item on backorder with readymaderc and its holding up everything.
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Old Mar 28, 2013, 09:38 PM
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For whatever it's worth, the way I stick velcro down to EPO is by putting
a thin layer of medium or thick CA on the foam (sanded to white foam for these dark
planes), then I spray a little kicker on the back of the velcro and then press it
into the CA. The accelerator makes it cure fast and hot, which activates the
glue on the Velcro backing and it all melts together with the CA and makes
a nice permanent bond. Will not peel off in extremely cold temps like straight
Velcro adhesive will.

ian
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Old Mar 28, 2013, 11:15 PM
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Thanks for the ca Velcro tip. Ill do that this weekend.
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Old Mar 29, 2013, 09:33 AM
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Quote:
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Thanks for the ca Velcro tip. Ill do that this weekend.
+1 ! The velcro in my SW kept peeling off after some use. I glued it with a bit of GG on the sides but after some use, want to come off again. Will try the CA.
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Old Mar 29, 2013, 10:22 AM
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for all you guys with your elevator and servo horns on the bottom of the elevator, try flipping the elevator horn to the top and cutting a slot for the servo horn so the linkage is now above the elevator. That way, you don't snag it on landing if you touch the tail, and it will prevent the servo from stripping the gears.
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Old Mar 29, 2013, 11:15 AM
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Quote:
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for all you guys with your elevator and servo horns on the bottom of the elevator, try flipping the elevator horn to the top and cutting a slot for the servo horn so the linkage is now above the elevator.
Hmm good point. I bent the excess control rod up toward the tail so it pushes whatever is coming at it down. I'm also using MG servos in my tail. I will admit that I picked up some tall grass on this past landing on the control horn. I'd flip my horn around but I decided to glue it. The screws weren't giving me the warm fuzzies.
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Old Mar 29, 2013, 11:26 AM
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Ya, this mod has been mentioned a few times before in this thread. I snapped a servo
arm off on a normal landing on a hard surface, because the tail group bumped the ground.
Moved the linkage to the top.
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Old Mar 29, 2013, 05:36 PM
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Got the Video link bugs worked out I think - Here is a video I did last night showing just how fast this SH is and its aerobatic capabilities aswell... No music yet

Skyhunter - FPV flight with aerobatics (12 min 23 sec)
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Old Mar 29, 2013, 08:05 PM
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tail skids

Quote:
Originally Posted by webdr View Post
for all you guys with your elevator and servo horns on the bottom of the elevator, try flipping the elevator horn to the top and cutting a slot for the servo horn so the linkage is now above the elevator. That way, you don't snag it on landing if you touch the tail, and it will prevent the servo from stripping the gears.
I glued tail skids on bottom of white plastic tube holder . Made from small dia. music wire solves problem of dragging tail . Works good Bob
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Old Mar 30, 2013, 12:12 AM
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Quote:
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I glued tail skids on bottom of white plastic tube holder . Made from small dia. music wire solves problem of dragging tail . Works good Bob
picture please!
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Old Mar 30, 2013, 02:21 PM
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tail skid

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picture please!
Sorry about pic quality not used to camera yet Bob
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