|May 02, 2014, 10:56 PM|
MacroSpot Power Test
Ok... got my first power test and near-finished weight & CG test.
First... before I share the numbers...
I've been wrestling for the past several days regarding the landing gear. What I currently have installed is a micro servo with a nose wheel directly mounted on the servo arm for steering. Before you respond... I don't think I'm going to keep it. It theoretically might work and hold up for a few flights, but I just don't think its going to be strong enough to last.
I tried several idea for a steerable nose wheel, and this was probably my 2nd best idea... but rather than trying another approach which will add more weight, I think I am going back to a gear-less design.
Since my primary concern is stability at launch, after talking with a local flyer last week, I think I'm going to go for a gyro-stabilizer. I've ordered an Eagle Tree Guardian 2D/3D unit that should be here mid next week. The idea is to use the stabilizer to get you airborne safely from the hand launch. With a high-speed plane, I may want to quickly turn it off once it gets going, or at least make sure I've got the gains turned way down.
Anyway... back to my power vs weight findings. Right now, totally loaded with a 2350 mah 4S battery I'm weighing in ~ 730 grams. Using my 4S battery NOT at peak charge (only on a storage charge) I measured 850 grams initial thrust. This was also without a nacelle/thrust tube, as that isn't finished yet. So by the time I put a fully charged battery in it and add a thrust tube, we should be topping 900 grams or more.
Thrust was measured simply by placing a kitchen electronic scale on its side, taring it in that position, rolling the nose of the plane up to it, and powering up!
So, I may not break any speed records, but I think I'm going to get pretty good performance out of this setup.
Still not sure what I'm going to do with the hatch/canopy "lines". I cut a couple different bubble/teardrop shaped addons, but didn't like them at all. I may just end up going with the flat top for now. I could easily make a new top for it later. Guess artistic design isn't my strong suite!
I have reinforced top & bottom of wing panel seams with fiberglass & WBPU (Water Based Polyurethane). Also reinforced the inside of the fuselage with that while I was at it.
Servos have been installed and push-rods cut. They just weren't installed for this test & pictures.
I'm trying to decide whether to go with traditional hinges or just tape. Leaning towards tape, but for now the one side is just on with monokote...
So, hopefully the next time I post pictures it won't still be naked!
Guess that's about it for now...
Thanks for watching!
|May 12, 2014, 02:29 PM|
You might want to check this one out...
He's reporting close to 200 MPH... I'm thinking of your larger build where you were struggling for a power setup...
|May 14, 2014, 03:34 PM|
After losing my carefully drafted notes due to being an idiot (closing page before saving)... here are some photos of current status.
I'll have to add some commentary later, as I'm currently "out of time"....
|May 16, 2014, 10:28 AM|
Ok.. .so here are the details that I previously forgot to save....
1) I have tested the Eagle Tree Guardian stabilizer in another plane. I'm convinced the unit will be a great add to this plane, especially for "managing" potential hand launches, ground take-offs, and even landings. More about that below...
2) I have elected to install a functional rudder. This was done by slitting off part of the existing stabilizer, gluing face plates on both parts of the slit, sanding, and installing hinges. The servo mount was a bit of a challenge, but I positioned it just underneath the tail end of the foam hatch. Laying on its side, the servo arm will exit the fuselage side and point "up".
3) Like the aileron servos, the rudder servo position is a compromise and is not very well aligned with the hinge angle. So again a micro ball joint will be used. Although not shown in the photos above, the linkage has been tested and should work fine (using the ball joint). The ball joints I'm using are all spare parts from steerable retracts (where I didn't need the steering parts) but similar parts could probably be sourced a number of other ways, including heli spare parts or other ball joint parts for airplanes.
4) One of the reasons I put in the rudder was to take more advantage of the Guardian stabilizer. Another is that scrapping the steerable nose gear means going back to non-steerable tricycle gear. Based on learnings from my previous eFlite F-16, I am intentionally going to set the gear so that there is an upward pitch in the wing, when setting on the gear. This will lift the nose (or at least reduce the weight on front wheel) as soon as it gets moving. With the functional rudder (which the F16 did NOT have) I should be able to make reasonable tracking adjustments during a hard surface take-off (or just the the Guardian stabilizer take care of that).
5) After looking at lot of colors & schemes, I've selected to stick with Lee's original Yellow/Black color selection. I plan to implement a final scheme pretty close to Lee's, but it probably won't be identical.
6) Foam Hatch: I've sanded this to a rounded top and contoured it into the nose and tail portions of the fuselage. I've painted it with black acrylic paint, coated it with WBPU, sanded that, touched up the paint, and applied a second coat of WBPU. My touch-up painting is just a little visible up close, so I'm not sure if I'll do another layer of paint & WBPU or not.
7) Canopy: I have cut and painted (silver) a small "bubble canopy" but I'm still not sure if I'm going to use it. Clearly my hatch/canopy lines are not as well contoured as Lee's design, but they are very aerodynamically clean. I'm probably going to try painting on a silver canopy directly in front of the black hatch. If that looks good enough, I'll probably go with that just for aerodynamic reasons. If I'm still unhappy, I'll revisit mounting the bubble.
Final comments on color.... I ended up selection a "Pearl Yellow" Ultrakote covering. This has a lot of sparklies in it, and I think its going to absolutely glisten in the sun. That doesn't show up real well in the photos, but I'm really happy with this color selection. Top & rudder will will probably be accented in black similar to Lee's scheme. For contrast, I will probably just put a couple black stripes on the bottom of the wing. Nacelle/EDF will be black too.
I'll try to update a current photo in a moment, but you'll have to excuse the messy workshop desk...
Although its getting close, given graduation season arriving it will probably be at least next week sometime before I can get a maiden flight in.
Thanks for watching,
|May 20, 2014, 09:09 PM|
Ok... [nearly] final pics for the covering job attached.
Work left to do before maiden:
1) re-install fixed tricycle gear
2) install Guardian stabilizer & route servo wires
3) Install battery straps
4) Final push-rod installations
There are few more minor things... but with the holiday weekend coming up... maybe I can get a maiden in. I won't be finishing the nacelle till later, but it should have more than enough power for initial flights without the nacelle.
|May 26, 2014, 09:37 PM|
Failure to Launch
Well.. to cut straight to the point, the first flight attempt of the MacroSpot never got off the ground.
The tail section (including the EDF) unit broke off, when the plane ran off the runway at high speed, and planted itself into the soft ground.
Surprisingly the nose was undamaged, but with inertia from a good rolling speed the abrupt stop broke the EDF unit loose, taking the rudder and back end of the fuselage with it.
Its far from a total loss, though I'm going to have to replace the fan unit and replace the motor shaft.
As with most failures, I think there were several contributing factors.
1) The plane didn't want to lift, even after obtaining a pretty good speed.
2) The leading edge of the delta wing, which was exposed under the nose of the fuselage as a air inlet is primarily what "stuck" in the soft ground (not the nose).
If it hadn't been for #2 above, there probably wouldn't have been any damage.
As to the reasons the plane wouldn't lift off, my theories include all the following factors:
1) the rear wheels of the tricycle gear were probably too far behind the CG for a normal "rotation".
2) There probably wasn't enough positive angle of attack in the neutral stance of the airplane. I expected it to just lift off the ground. But it would apparently have taken a lot more speed than anticipated.
3) There was about 3 degrees of "upward" thrust angle in the EDF. This was just a wild guess at how much might be needed to counteract the EDF being above the wing. But whatever was there certainly didn't help me in regards to getting the nose up.
I'm far from giving up on this design. But the incident did break the fan unit and bend the shaft. So by the time I get the motor repaired, a new fan installed/balanced, and the rear of the fuselage redesigned and built, its likely going to be at least 2-3 weeks.
In hind sight, I probably should have stuck with a hand launch, with reliance on the Guardian stabilizer to get me aloft. Since I don't think I'll be going back to steerable nose gear, I'll probably go for hand launch next time, with the Guardian in 3D mode for a high alpha launch. But in all honestly, had I gotten airborne today, with the way that delta tip dug into the dirt, I'd probably have had the same damage on a grass landing (which was the plan).
I'll be back in touch in the coming days....
|May 27, 2014, 06:07 PM|
Ok... here are some pics and further info.
One thing I couldn't quite put my finger on was... why I went from straight down the runway at a high speed one moment to... in the grass off the runway the next moment.
I think I found the answer... and it wasn't a slip of my fingers or a crosswind. Upon a closer inspection I found that the front wheel was locked up. You can see in the one picture below that the wheel was a bit ground off/flattened on one spot. So I'm pretty sure this is what caused the plane to go off course, and then jam into the dirt on the edge of the runway.
Talked to Don's RC already and he's going to be able to easily repair the outrunner with a new shaft and put in a new fan (with balancing). So that will go into the mail tomorrow.
As far as the fuselage repair goes... I'm trying to decide my approach. As the breaks were all pretty clean, I could just re-glue and reinforce it. I had originally planned for two horizontal fins, similar to Lee's original Nanospot design. Had I done that, this likely would not have broken loose... but who knows.
Bottom line If I do that now after a simple repair job, it will probably work. But there's one other issue I didn't mention yesterday....
Even after all my monitoring during the various stages of the build, I still ended up being about 1 inch "tail heavy". So I ended up putting almost 2oz in the nose yesterday to get into the middle point of the calculated CG range. I'd really like to drop that weight.
So to do that I'll need to move the EDF even further forward on the wing. If I'm going to do that, now's the time. Its probably going to be my approach, along with a stronger overall mounting process.
For now, here's some free entertainment with the aftermath. You can also see how the front tip of the delta wing provided a nice sticking point. That will have to get fixed for sure too.
When I look at the angle of attack on the wing when sitting on the gear, I'm still surprised that the plane didn't lift. Perhaps if the wheel hadn't locked up it just might have.... no way to tell for sure.
By for now....
|Jun 07, 2014, 09:32 AM|
Glider CG Test
Well, the repaired EDF from DonsRC came back yesterday and I've decided to rebuild the tail of the fuselage, and reposition the EDF further forward to eliminate the nose weight.
This spawned some good discussions about where the CG really should be, and the best guidance I found was to build a foam glider where I could easily test it. So the video linked below (in YouTube) is that glider.
Its wing is a foam wing formed with spray foam pressed and set inside the actual clam shells left over from cutting my wing cores. So although I didn't bother sheeting the wing like the real one, this is a very close replica of my actual MacroSpot wing.
I then added a profile foam fuselage and vertical stab very close to my original.
After a few attempts I settled on the CG point about 10 1/2 inches back from the front of the delta tip, which according to the online calculator mentioned above is just slightly more than 25% of MAC.
There had been some good articles forwarded to me that indicated delta wings usually needed a CG much farther forward, as far as 7 to 10%. It was that big difference that caused me to want to do this test before I continued my repairs & next test flight.
I'm no aeronautical engineer, but this wing appears to be performing much more like normal wing, rather than a delta. Perhaps it is because of the wing tips & sweep. Either way this CG point is the furthest one back that gives me some rather consistent hand tosses without going into the nose up "bobbing" pattern.
After viewing the brief video, if you have any other thoughts, happy to hear them!
|Jun 07, 2014, 03:31 PM|
Joined Dec 2005
Its hard to do glide tests. Since you are adjusting the cg to the models trim state, at a slow flight speed. Its more about checking to see if the cg is even reasonable. My jets usually fly best with the cg slightly forward of where a simple glide test would indicate. Since it needs a little more stability at higher speed. Many delta's, and wings are flown with a little up elevator trim. So if you add up elevator the cg may appear to need to be moved. Can get you all confused. Was it the cg, or the aerodynamic forces that need adjustment.
Since your tests indicated a good glide at 25%, I would start a little bit forward of the 25%, and adjust from there.
|Jun 07, 2014, 04:31 PM|
I agree that glide tests aren`t exact, but the will give you a max rear point. Actual cg will be forward of the glide cg like RR said. I`d start at 15% and go back from there.
|Jul 07, 2014, 07:02 PM|
Okay it has been quite a while since I gave you an update. It is been a busy summer with graduations and family health issues. But I have been making some progress.
I have decided to rebuild a new structure for holding the EDF unit.
I've also added side horizontal supports and a way to secure those to the EDF unit. After the CG study with the foam glider, I've decided to move the entire EDF unit approximately 3 inches forward on the wing in order to avoid the need for about 2 ounces of nose weight.
The final unit is not yet assembled and the skin and canopy aren't reworked yet, but you can see the progress pictures here and the approximate position where I soon hope to mount the final unit.
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