|Feb 20, 2013, 10:53 PM|
Nice! What a joy to see your creation take flight. Looks like you have a nice combat plane there. I bet it will be a real rocket with a 450 or 480 size motor!
As to the horizontal and vertical stabilisers: Why not make them 3/16" Balsa, and omit the Carbon?
|Feb 21, 2013, 09:53 PM|
I think I am going to alter the design a bit to lengthen the nose and shorten the tail slightly. I've been toying with a few different self jigging wing designs. I should have something drawn up tomorrow morning.
I think I will swap out that 400 for a 450 and see how the plane balances with that. It's one of the 450's from Value Hobby. Has been a good little motor with a 9x7.5e or a 10x7. I'll have to order another 25-30amp ESC though. I prefer an ESC with switch mode type BEC.
|Feb 26, 2013, 04:35 PM|
I took a bit of a break to "distance" myself from the project a bit. Needed to get a different perspective on the dry balance and the wing leading edge issues. I think I've got a solution for the balance that I like.
Dry, the prototype balances a bit over an inch and a half too far aft. Without a battery, I want the plane to balance at the wing tips (slightly behind the spar) with a 400 sized outrunner, slightly nose down with a 450 outrunner, and slightly nose up with a 370 outrunner. The idea is to be able to balance the plane with the battery centered in the battery tray with a 400, battery aft in the tray with a 450, and battery forward with the 370 sized outrunner. I need to shift the dry balance point forward an inch-and-a-half to two inches, without adding extra ballast weight.
The tailfeathers are a bit oversized in proportion to the wing area. If I remember right, the horizontal is about 28% and the vertical is about 23%. I think I can get away with shortening the tail by a couple inches without losing stability. If I reduce the tail moment too much I risk corkscrewing out of ultra tight loops and/or adverse yaw in the yank and bank type turns.
As it is now, the prototype performs almost identical to the RealFlight model. Neither has performance issues with the tail dropping in turns nor twisting out of loops. With the tail shortened by 2.5" on the RealFlight model it just starts to exhibit a bit of the corkscrewing out very tight loops but still no adverse yaw in aileron/elevator only turns. With the tail shortened only 2" I don't see either issue in RealFlight. It seems that 2" is the magic number in the sim model.
Now the question remains, "how does the plane look with the tail shortened by two inches?"
I took a couple photos of the prototype and did some photoshop work to compare the differences. Remember I am shooting for a precise aerobatic design intended for streamer combat type flying. I personally like the look of the plane shortened. What do you think of the looks with the shortened tail?
|Feb 26, 2013, 07:27 PM|
Now if I made separate wing kits, I could design other optional wing kits to fit this fuselage like a 2 meter glider wing or a trainer wing with dihedral and a longer span. In either case the longer tail moment would be desirable, but the dry CoG issue still remains. Balance without the battery pack still needs to be shifted forward a couple inches. Nose would have to be lengthened significantly more than the tail would have to be shortened.
Maybe do both? Extend the nose 1/2" (or more) and shorten the tail moment by an inch (or less)?
|Feb 26, 2013, 09:11 PM|
Maybe do both? Extend the nose 1/2" (or more) and shorten the tail moment by an inch (or less)?[/QUOTE]
Now you're talking!
|Feb 28, 2013, 06:35 PM|
Flight Testing Results
I did some more flight testing yesterday between rain squalls. The prototype is getting heavier from the coating of mud that's accumulating on its undersides. Tested that OrangeRX brand 3 axis flight stabilizer and a few different motor/esc/battery combos. Let me post some of the results here:
Orange RX brand 3 axis stabilizer:
My opinion about the ORX3 gyro thing is, well... it's not for this plane. It took a considerable amount of time, and 3 batteries, to get the gain dialed in on all three axis'. Got it adjusted so that each axis just starts to gyrate at full speed and backed off slightly so there is no "porpoising." The unit works well enough for compensating for wind. It does make this plane feel a lot "bigger, " however, it also reduces a lot of the control authority. It just doesn't feel right. This plane becomes too stable with the unit. It's neat, but first chance I get it will swapped out of this plane and into a more appropriate plane. A slower more docile plane would be a better fit for the ORX 3 axis gyro thing.
370 Class Motors (2826):
I tested two 370 motors, a 1350KV 140watt with an APC 8x4e, and a 1000KV 130watt with an APC 9x3.8SF.
I had a hard time getting the prototype Snickersnee to balance with the 1.5 ounce motors. I had to use the shorter 1300mah battery packs all the way forward AND add half and ounce of ballast to the the nose to get the plane to just balance at the aft end of the CoG range. Oddly enough I had to add a full ounce to the nose to use the longer 2200+mah packs.
The 1350kv motor struggled to get the plane into the air, but once airborne it was surprisingly quick. Had speed, but lacked pulling power. Best I could maintain a climb was about at 20-25 degrees. I was just barely able to lift off from grass with the 1000kv 370 motor. Speed was considerably less, but the thrust was better with the larger prop. Climb out was around 35-40 degrees, but seemed like the plane was always right at the edge of a stall.
400 Class Motor (2830):
I used an APC 9x6e prop with this 1150kv motor. This is the setup I used for the initial maiden flights. The setup that I used with that last video.
Was able to balance the plane without added weight with either 1300 or 2200 mah packs all the way forward and no extra nose weight. There was enough thrust to pull out of a hover, but not quite enough to accelerate vertically. Plenty of thrust for a grass field take off. Was able to just manage a 6 minute full throttle flight with the 1300 mah pack, but the battery and 20amp ESC came down hot. Not quite melting hot, but uncomfortable to the touch. I didn't bring a 9x4 or 9x5 prop to test. I assume they would have been a better fit.
450 Class Motor (2836):
I used an 1100KV with an APC 9x6e prop and a 30amp ESC for these tests. The plane seemed to leap from the grass! Definitely able to accelerate vertically out of a hover. Speed seemed about the same as the 400 tests, but the ESC and battery came down MUCH cooler and the thrust was a marked improvement. Balance was a bit easier to achieve with this motor and was able to actually get it to sit slightly nose down while hanging from its wingtips.
On this original prototype design I specced for 370, 400, or 450 class motors. The reason I was leaning toward this range was because they all share the same X type motor mount. One motor mount makes it easy to accommodate all three motor sizes. Downside is, as designed, the airframe is tail-heavy and underpowered with the 370 and just barely balances with the 400. The 450 seems the most appropriate motor to use with this airframe as designed and will be the motor that remains on this plane after testing. Maybe I will design a scaled down version for the 370 motors later.
I also found a few weak points in the design. My tendency was to reach for the nose of the plane (just ahead of the wing) for carrying. I heard and felt a bit of a crunch under my thumb at the field. Nose needs a bit more reinforcement under the top and bottom nose sheeting. No big deal there.
I know Maxxnut was wondering about the "motor box" too. My reasoning there was simply to keep the motor shaft from puncturing the battery in the event of a nose in crash. Now, what if I gave that motor box design more of a reason. If I set up the motor box assembly to fit the 28mm X mount for the 400 and 450 motors, but as an option have the basic (no motor box) firewall fitted for the 35mm X mount then I could support the heavier 480, power 10, and power 15 sized outrunners. I would, of course, have to strengthen the tailfeathers. Probably use 3/16" instead of 1/8" there.
I was talking about shortening the tail moment and lengthening the nose, but I don't think that's needed. At about 35degrees elevator deflection I was able to get the prototype to start to corkscrew out of tight (15') loops. From a flight performance point of view, I think the tail moment is just about right as it is now, especially with the heavier 35mm motors. If anything maybe stretch the nose a half-an-inch or so.
TLDR (too long didn't read):
Only a few design changes are needed.
|Feb 28, 2013, 09:31 PM|
I'd like to congratulate you on the splendid effort you put into designing the model, making the plans, prototyping and testing. Great job!
I also agree with the motor mounting options- having as much versatility as possible is a good, especially if you're planning on kitting it.
|Mar 02, 2013, 04:28 AM|
If I don't mess with the aft of the fuselage I wont have to do all the projecting of the angled parts again. If I exclude the 370 sized motors (too weak for this airframe anyway) and go with the larger of the 28mm motors and perhaps the smaller of the 35mm motors I don't think balance will be an issue.
400 class, 1.9 ounces - 30mm long (from firewall to prop arc)
450 class, 2.6 ounces - 36mm long
480 class, 2.6 ounces - 30mm long
P10 class, 3.7 ounces - 36mm long
All four motors are either 30 or 36 mm long. That's about a quarter inch of difference. What I'm thinking is I can simply provide a set of three or four 1/8" motor mount spacers and include two separate firewalls with the kit. One with a hole spacing for the 28mm X mount and one with hole spacing for the 35mm X mount. No real need for the "motor box" at all. The spacers might help the builder with getting a proper final balance.
Also, I did more physics testing with the RealFlight model. I zeroed out the wing incidence and the down thrust angle. Most of the "balooning" went away in the sim. I'm going to zero out these angles for the next prototype as well. I do notice a bit of ballooning with the first prototype. If RealFlight is as accurate here as it has been for me in the past, zeroing out the angles should make for a better flying final result. Will see.
|Mar 14, 2013, 09:59 PM|
Well guys, I've been busy working on redrawing most of the parts for the second prototype. One small change to one part tends to have a cascading effect on other parts. The wing design is essentially the same as before but now has a keyed strip along the leading edge. That should help square the ribs up prior to leading edge sheeting.
I decided to keep the control surfaces at 1/8" thick, but I made a few design changes. Basically I widened a few parts to make the whole assembly a bit more rugged. In effort to reduce tail weight, I removed the pre-cuts for the rudder attached tail wheel. That can be added later by the builder if they want a steerable tail wheel. A simple looped skid should work better for holding a streamer anyway. The rudder on this aircraft has a ton of authority.
Will be including three firewall types with future kits. One fits 2800 series X mount type motors (400 & 450 class), another fits 3500 series X mount type motors (480, Power 10, & Power 15), and basic firewall that can be customized by the builder for other motors. To help the builder balance their model, I decided to include an optional set of spacers to offset the motor forward. The shorter and lighter motors can be moved forward easily with the spacers. As an option to offset the weight of the heavier Power 10 and Power 15 sized motors, I added a few extra optional parts to install the tail feather servos in the aft part of the fuselage. This also allows the battery pack to sit further back in the battery tray. I also increased the length of the nose by about half-an-inch.
Lastly, I modified the landing gear structure area to to use 1/8" music wire instead of 3/32". I also changed the way the crutch structure goes together. Should be a much simpler build now.
I should have some 3D samples in a few days. I'm doing my best to get a beta kit ready for Fred to build. My deadline is first of April. If I can stay healthy 'till then I don't think I will have a problem getting one ready for him on time.