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Jun 05, 2021, 01:13 PM
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vonBird's Avatar
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My experiment


I'm finally getting around to building this.....Now I'm checking component location to make sure it'll all fit my CG calculations. Looks like it will. I'm expecting about 20-22oz per sq.ft.

....just an experiment to see if I can more closely control the wing votex.
Last edited by vonBird; Jun 06, 2021 at 09:33 PM.
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Jun 06, 2021, 09:30 PM
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So far so good. It's all coming out as designed. Everything is going to fit fine, tho the cg is a bit forward of where the battery is in the photo, enough room for 2 servos behind the bat, and two servos in front. The ESCs sideways on each side. The fuselage will be 4.5" in diameter....the span is 33", EDF nose cone to nose cone, so in total 58" of wing after the fuselage is built. It's very strong.

Last edited by vonBird; Jun 06, 2021 at 09:37 PM.
Jun 07, 2021, 01:27 AM
jofro
Rather interesting looking flying craft, tho, no idea what it will look like when fully complete?
With such a light wing loading you won't have any problem power-wise but an assimetrical power thrust might create bit of a handful.
Jun 07, 2021, 01:56 AM
If it flies, I can crash it.
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With the motors out at the "wingtips" ("wingloops"?), you're going to be fighting yaw from uneven thrust unless you match the motors very closely. The most obvious risk is probably the lowest, but if you lose a motor in flight, the plane will be corkscrewing in to the ground before you have a chance to react and dead-stick it in. But you may have trouble getting it to track straight across the full throttle range, since unless the KVs are identical (which isn't always the case in spite of what the motor's label says), the motors will run at different speeds and make different thrust at different throttle settings. And the motors probably wouldn't speed up and slow down at the same rate, so you may experience squirrely yaw changes as you change throttle even if it's tracking straight before you change the throttle... And with the mass out at the ends of the wings, you're also adding a lot of inertia that may make it slow to respond in roll (and you probably have to add some weight for strength that you could reduce if the motors were more centrally located).

However, assuming you'll use differential thrust for yaw, a gyro would take care of most of the issues I'm listing, above.

Looks cool, for sure. But there aren't a lot of aircraft with engines on the wingtips for a reason... though that being said, I've done the "I wonder if I can make this fly?" thing a few times myself, so I appreciate your lofty objective. It's probably going to be a challenging one to hit.

I look forward to your future updates.
Jun 07, 2021, 04:42 AM
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JP Hobby builds and sells them specifically as a counter-rotating matched set. I'll find out, I guess.

I 'spose I could check their numbers with the little watt meter I bought. I tested them when they arrived, but just to make sure they worked.

...tho a gyro might be the right idea, but I'll see that in initial testing before any flights.
Last edited by vonBird; Jun 07, 2021 at 08:31 PM.
Jun 08, 2021, 03:33 PM
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I've been thinking about the landing gear for some time...search thru parts, wheels. I'm not putting retracts on this model and I've got a real rc runway 30 miles away, a really nice one. I didn't want giant wheels...drag and weight, so I got 33mm rubber wheels. I don't remember what size whole is in them, but smaller than the 5/32 wire found on many steering kits, etc. I knew the 3/32 wire I've been using for pushrod would go in, however a bit loosely.

Just for the heck of it, I tried the 5-40 (not 4-40) threaded rod I have....fits perfectly.

So I ordered 1/8 x 1/2" T6061 bar to bend into a U-shape for the main gear. Now I have to, 'cause I can't put any component mouting board in till the main gear strut underneath is installed. No problem. There's other stuff to do....maybe even a couple of the chores I've been neglecting.
Jun 08, 2021, 09:48 PM
jofro
[QUOTE=vonBird;47264353]JP Hobby builds and sells them specifically as a counter-rotating matched set.

I run few counter rotating multi powered EDFs, to minimize the torque roll effect, one recently (Tri-jet) gave me a trouble, the clock-wise rotating 50mm unit impeller nut, un-wined itself, disintegrating, resulting also with the braking off both side booster 30mm EDF rotors.
The ideal set up would be left hand thread to secure the rotor.
For a piece of mind I re-tightened both rev. rotation units on my "quad" powered EDF.
Jun 08, 2021, 11:03 PM
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How old, or how many hours? Any guess? What make EDF?

Yeah, I just found out JP Hobby voids their warranty if you don't use their ESCs. I got Talon90s.
Jun 09, 2021, 04:29 PM
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This, the back end fuselage rib is ridiculous. I don't know about anybody else, but cutting something this small is hard for me. Of course that's why I wish I'd bought the JP Hobby 105mm EDFs. They were just over my budget and would've really crowded my work space.

I drew two fuselage ribs today and only cut out one. This one being on the very back end, on the main backbone. I'll go from this one to a perfect 4.5" circle in 10.75". I've had to cut a couple smaller pieces...can't think off hand what they were. There will be a couple more small ribs at the front, before the balsa block nose cone. Carved balsa block at the back too. If I was using anything smaller than 3/32 plywood, I'd broken it several times.


Jun 10, 2021, 04:26 AM
jofro
Quote:
Originally Posted by vonBird
How old, or how many hours? Any guess? What make EDF?

Yeah, I just found out JP Hobby voids their warranty if you don't use their ESCs. I got Talon90s.
It un-wined itself on first flight, catapult launch! No prob during number of static test runs prior. It's irrelevant what brand of ESC one uses, the problem is the right hand thread to secure the rotor! Reversed fan should have left hand thread on the shaft to secure it!
Jun 10, 2021, 03:45 PM
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Originally Posted by jofro
....It's irrelevant what brand of ESC one uses....
Actually I threw in a separate issue, as I just found out about the EDFs warranty being void by using any other brand ESC other than JP Hobby, so I'm trying to figure out if I made a mistake purchasing the Talon 90s .


...........
Sometimes a little force IS required. I couldn't find landing struts that were sized for my model, mostly because everything is either huge or made for giant wheels, or pathetically flimsy. My little model is still going to weigh probably 6 Lbs. My wheels are 33mm because there's a really good runway about 30 miles from my house......so I ordered some T6061 and bent my own for the main landing gear.

7" wide and 3" high with 33 degree angles on the struts. The T6061 bar is .5" x .125". I've used T6 extensively for many projects. It's maybe, my favorite material. Even this small size bar requires a sledge to bend.

Jun 10, 2021, 08:31 PM
jofro
Mate, "the warranty being void" is just another salesman's trick, and an excuse just in case, LOL.
It never does any harm to upgrade ESCs.
Jun 10, 2021, 10:35 PM
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Originally Posted by jofro
Mate, "the warranty being void" is just another salesman's trick, and an excuse just in case, LOL.
It never does any harm to upgrade ESCs.

I knew that was most likely the case, but the two settings JP says are critical are 2250kv and 15 degrees timing. Castle Creations wasn't much help on the phone...it appears the timing can be set, but not the 2250kv. There is no documentation on their programming software, but they say it's self explanatory. I like to know what I'm getting into before I do it...I read just fine.


I also asked....their software "phones home". It connects to their server. So I have to install it on an os partition I don'tuuse much. At least my computers are already set up for that. I can format a partition and reinstall an os image in 15 minutes. Still, why do they have to do that?

I know some ESCs can be adjusted thru the transmitter.
Jun 14, 2021, 03:13 PM
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Quote:
Originally Posted by jofro
Rather interesting looking flying craft, tho, no idea what it will look like when fully complete?
Maybe this'll give you a little idea. I got tired of doing wood work and I needed to know if instead of ribs on the front and back, I might be able to use XPS Foam. I'd used the xps blue foam for the fuselages during my free-flight building, but never had any idea if you could SPRAY Paint it. The 5x12" piece in the middle is my test piece. With a few tricks it can be well painted with rustoleum 2x.

I'll cut about half off the nose peice. I left that length on the back end for holding it during sanding. It will also be carved out underneath for the nose landing gear and some of the front wing. So the nose will stick out a bit less than half way to where it is now. I still have a good bit of sanding left.

Last edited by vonBird; Jun 14, 2021 at 03:43 PM.
Jun 18, 2021, 11:59 AM
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Hello vonBird,
once I built a slope soarer in this configuration.
It flew very well untill the antenna of the receiver (a long wire in the times of 27 MHz) slung around my finger during launch. The result was an unrepairable crash.
Decades later I built such a thing again driven by a ducted fan. But something I missed and the model didn't really fly to my satifaction.
Later I read an essay about this sort of tandem aircraft and learned that the upper wing should be in front and the lower one in the rear.
So I know from experience that it can be a very fine model but as well that it isn't easy to hit the spot.
Good luck for Your experiment.


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