vrijdag 29 juli 2011

Flight 4 Graupner Bellanca balsa decathlon

And yes I got it up without real damage for the 4th time in a row. This time I tackled to lack of power using a 3 cell 2200 mah lipo instead of the adviced 2 cell.

More than enough power this time. With the motor mentioned before it must be around 300 watts or just above with the 10x6 prop in place. Motor and lipo did get warm but still touchable. Prop needs replacement since you can see it bend as you throttle up.

takeoff was already much smoother. This time I was running it with larger foam wheels. Once up it needed again some trimming but once level it stayed level. I had one nasty wing drop but corrected it right away.

On this flight I also had the lost plane finder installed. It wasn't installed properly though. You need to initialise it properly. Power up tx, then rx, wait for beep, then give some stick input to the channel you have the beeper on. Then it will be initialised and only beep on signal loss. I've tested this behavior on the ground before and can confirm it works. If not initialised properly it beeps every 30 seconds or so.

Next challenge was to get it back to the ground. I lined it up and only throttled back on final approach (to avoid tip stalls). It glided in very smoothly. In the end I didn't have any power on it anymore. I missed my landing spot just by a few meters, landing in a field, still gently.

I had some battery time left so I got it up again, did some laps and tried to land it on the track this time. Again I got lost just above the track. This time I gave too much up elevator though causing a stall above the corn field. It dropped, luckily in the field so no real damage again.

Up to the next flights. Forgot to mention I did some aerobatics on the first flight this day. Loops and rolls very nice. Now practice those landings so I can end those aero flights gracefully.

donderdag 28 juli 2011

Graupner Bellanca super decathlon third flight

Well the weather has been very bad here lately. I found a spot when the rain was soft enough to get the plane through to test the updates I made to the Super Decathlon. Remember how the maiden and second flight wasn't that much of a success...

Okay this is what I modified to (hopefully) fix these issues:
  • trimmed the excess pushrod on the ailerons. Now they can move freely
  • fixed landing gear (it was getting loose, added some PU glue to secure the screws in the wood)
  • checked throws to limit to whats advised in the manual (expo still 50%, end points for tail were around 65%! ailerons now around 75%)
  • replaced the 40A esc with a 30A esc with proper BEC providing 3A (http://www.giantcod.co.uk/speed-controller-p-405437.html)
  • replaced the jittering servo
  • no more flaperons!
This time I took a picture. Remember to always make a picture before the maiden! I didn't. This is still no good picture, only smartphone style for now. I didn't apply any decals indeed. I don't think you can really spot the damaged wingtip on these pictures. It will be fixed some other time.

Again I struggled to keep it tracking straight on take off. And after 2 cut off landings dirt was all over the wheels making next attempts even worse. Without thinking I went full throttle and got up just in time. Except for my trouble on the road takeoff was nice and smooth. The struggle is much more caused by my replacement wheels and my skills than it has anything to do with this plane. The tailwheel is steerable.

I got it up very quickly thinking back of how I smashed that wingtip on a low altitude tip stall. Once up high I started testing the stall characteristics. Strange enough, when flying level, cutting off power it goes down very predictable and smooth. Must have been related to the throws that were too much also.

Trimmed the ailerons out. I had to adjust them quite a bit but that must be related to my tail section being not straight :s. Still need to redo that part of the build. Did some turns and noticed how the power was very scale like. I really needed more power, mostly for aerobatics (if I ever get to that) and especially to get or stay out of trouble.

Then landing. I was getting low, way to low and in the wrong direction. I tried to make a turn at low speed and low altitude to get it lined up... Don't do that, it will stall :). At least I knew this time why it stalled. Looked pretty similar to the previous stalls though.

For next flight I will replace the wheels with even larger ones and go from 2 to 3 cell lipo. The extra power is very welcome and I noticed the CG could be a bit more forward, that a heavier battery can do for me. 

woensdag 20 juli 2011

Arduino on Ubuntu bug with recently used files

Don't open a sketch in Arduino on Ubuntu using the Recently Used Files link. On my machine this blocks the Arduino IDE with a java error! Same sketch can be opened from the actual path without issues.

Libraries can be copied to /home/user/sketchbook/libraries. More info at http://arduino.cc/forum/index.php/topic,49082.0.html.

woensdag 13 juli 2011

Graupner Bellanca build log

Since this is an ARF I don't have that much information to share. Some tips or just how I did it:

Basically you need to glue the tail fins in and install the landing gear, controls and electronics. It took me 5 evenings (2-3 hours) but I bet a more experienced or concentrated builder (I have to do this late at night :s) would complete it much faster.

To glue in the tail pieces you need to clear the coating. As stated in the manual you could do it with a sharp knife, but to prevent weakening by cutting too deep they advice using a hot soldering iron. That's what I did and it leaves a clean cut. It's even closed thanks to the heat and you can use a ruler to keep it straight.

Then you'll also have to cut away the covering from the openings in the tail where these fins will be glued in. For that I used a sharp knife since the slots in the wood are already available. You can slice it in 2 and than hold some cardboard or other piece of scrap wood through the opening to cut it nice and straight as shown in these pictures.

Now it's ready for glue. Pre fit everything before you glue it in. I did but I didn't mount the wings so I never noticed the horizontal tail was in fact not in line with the main wing. Make sure to mount the wing in order to check so. You'll probably have to line it up. Something that is much easier if you didn't glue it in yet (like I did :s).

I used epoxy for this. On the next picture you can see how I used masking tape to have a clean glue joint.

Event the holes for the control horns are properly precut in the wood. You only need to open up the covering and glue it in. I used CA glue at first for this but one came loose on hitting my shoe on the runway (I know :)) so I replaced that one with epoxy already.

On the wings you need to put in the aileron servo's. The wings already have nice slots prepared for that. You take off some plate where the servo is mounted on (the HXT900 fits perfect) and then you mount that plate back on the wing.

The wires need extension (well in fact the HXT900 just fits but you still need extensions to get to your receiver) and to get these through the wing some white cord is already glued in while building. Just get it on both sides, attach the servo wire and pull it through. Here you can see my picking tool in action. That hole is where the wire comes out inside the fuselage.

Up to the installation of the servo's in the fuselage. There the HXT900 servo's almost fitted perfectly. The slots are like 1 mm too small. Enlarge and again a good fit.

For all servo mounting I used the screws that came with the servo's. Drilled a small hole in the wood to align them and then fixed the servo's in place.

The kit comes with some easy connectors that can be adjusted. As usual you need to drill out the servo arms quite a bit to get them in and spinning freely. Remember to secure the bolt using threadlock and make sure the connector itself still spins freely without too much slop.

That's about it. Like I mentioned before I never installed the wheel caps since I needed bigger wheels.

Graupner Bellanca second flight

This time I took the TowerPro 40A ESC that already proved itself to work on 2 cell lipo's (get it now since that price is increasing really fast now).

Since the maiden finished so quickly I was very eager to get it flying. I went to my flying spot and took off, again using flaps. Not at all much wind this time and strange enough it wouldn't get off before I ran out of runway... It took me some runs the realize that ESC was still on very soft throttle mode from use in helicopters. No time to fix that (since I don't know the beeps and didn't have a manual with me), just found myself a longer runway :).

Again very smooth handling in the air. I still used the advised 50% expo on all channels. For the ailerons I quickly wanted a bit more responsive controls so shut that off quickly. Like on the maiden I only noticed my flaps were still on once I started banking for the first turn. Neutralized flaps and really got it flying well this time.

I stayed up now. I just didn't want to loose it. Turned out to be the better choice. In mid flight one of the wings suddenly dropped out of the sky getting the plane in a very steep and dangerous spin. Got it out just in time.

On another turn it also slided and got close to a spin very soon. If you want to fly it properly you need to be smooth on the controls.

I was well after 4 minutes thinking what could have caused that dangerous wing drop! But I needed to come in for landing since I didn't properly test the motor consumption yet. I got to the pavement preparing to land, getting slower and slower... until just above the street that wing drop got me again. One wingtip smashed right into the street making it flip over... well I landed it.

Got to the crime scene fast to check damage. Again one of the nylon bolts broke and one of the struts of the wings was off. Only one wingtip had more damage this time. The one that hit the street first was smashed a bit. Still an easy fix though.

And now I need to find out what caused these nasty wing drops. Don't think it's just low speed and stalling because it looks way to aggressive to me and why the hell is it only a single wing while I'm flying straight!?

It might be the combination of a cheap ESC, providing only 1.5A through it's integrated BEC and the 4x HXT900 servo's. I recently discovered on rcgroups (search for it) that one of these servo's can draw just over 1A when under high load!

Another possible cause is the pushrods for the ailerons. If kept too long (you need to cut them once in place) they can hook up on the wing where the servo arm gets out.

Update: I'm going with this 30A ESC, it has a 3A built in BEC so that should do (and much easier on the connections, and much lighter as well): http://www.giantcod.co.uk/speed-controller-p-405437.html. Good flying weather today. Hope to get to some airtime! => check this blog post.

Graupner Bellanca maiden flight

Maiden resulted in a crash right away. No pilot error (unless you blame the pilot for not double checking all electronics) but a stupid ESC that clearly states on the package it supports 2 to 3 cell lipo's while in the real world in detected my 2 cell as a 3 cell and therefore cut out prematurely in the middle of my maiden flight. 

At least that is the theory. I used the ESC with a 3 cell many times before without any issues. But after this incident I tested the ESC with a 2 cell lipo loaded for storage. It does throttle up fine but cuts off shortly after. An ESC failure for sure.

Anyway I had a lot of wind that day so took off right into it and went off the ground almost immediately. I used the flaperon mix to lower both ailerons for even more lift. I had the wheel caps and small wheels already replaced by bigger wheels that suited my landing strip better.

It flew very well. I had just enough power for that wind, so flying into it the ground speed was very slow. Since all went well I did get closer to the ground to have a better view. And that is when the ESC failed on me! I was still into the wind so needed that power and way to low to recover. It dropped right out of the sky into a corn field. 

After a quick search, assisted by the servo noise (I really need to pick up some noisy airplane finder!) I found it upside down, not even completely touching the ground. Lucky me, the corn field took most of the impact.

The damage was minimal. One of landing gears was a bit looser than it should be, a nylon wing bolt snapped off (the black stock ones are very flexibel) and one wing lost the notch in front of the wings where they join the fuselage. All very easily fixed. So I did and replaced the ESC. Up to the next flight!

woensdag 6 juli 2011

Graupner Bellanca vs UltraFly Super Decathlon

I was looking for a balsa sport plane, capable of some basic aerobatics for some time now. Balsa planes get harder and harder to find in local hobby shops... and I didn't want to ship this large, damage sensitive planes. Some different sizes are available from hobbyking though (not to mention these are often out of stock):

Decathlon .25 EP/Glow 47.4inch Balsa/Ply Kit
Decathlon .46 EP/Glow 62.6inch Balsa/Ply Kit
Decathlon EP 48.9 inch ARF

And even a foam model that comes with electronics. This one has a review on rcgroups also btw. I don't like foam but if you do this might be a good choice: HobbyKing Decathlon Brushless Plug-n-Fly.

Another valid option for those who like foam is the parkzone super decathlon.

So far for the options I found online. Next is what I really considered buying.

At some point I thought I found a bargain from UltraFly, no electronics, full balsa and already sheeted. Just over 1000mm wingspan looks like a perfect match. Very cheap also but last one in stock. Until I got to the shop. Turned out the last one in stock was already gone. Too bad the website isn't up to date. This is a good review of the Ultrafly super decathlon.

Eventually I found the Graupner Bellanca, it was twice the price of the UltraFly model. This is a review of the graupner bellanca model, only in german. Couldn't find any other. Let me know if someone does.

There are some differences I can make up from the UltraFly reviews I read and the experience I have with the Graupner Bellanca. It's not finished yet, I'm still completing the build. Don't have much spare time so this will take some evenings.

These are the differences I discovered so far:

Utrafly has a one piece elevator. Therefore you need to cut through wood from the tail of the plane to get it installed. Also the connection could be a weak point.

The graupner version comes with 2 separate elevators that each are connected with their own control rod. These 2 rods then come together with some adjustable hardware towards a single pushrod for connection with the servo.

The ultrafly has a flat bottom airfoil like you can see on this picture from that review. The Graupner comes with a semi-symmetrical that should perform better upside down.

So far I prefer the Graupner version. Allthough it costs twice as much. If the ultrafly would have been available I would have bought that for sure. I like it's yellow and black colors better and the decals seem to be ironed on using different colors of cover. Much more durable than the blue (!?) sticker decals that come with the graupner kit.

According to this pic the blue seems to be authentic. Not sure if the ultrafly then has non scale windows, or is it the aft fuselage that looks different?

If you start building yours make sure to read the tips in this review about the seagull decathlon. It shows how to remove the sheeting, install the hinges and more.

According to specs from graupner website the recommended motor for this plane has the following specs:


Connecting plugG3,5
Operating voltage range7,4...11,1 V
Diameter35,5 mm
Recommended controller7185
Free shaft length17 mm
Case length34,5 mm
All-up weight, approx.105 g
No-load speed11100 U/min
LiPo battery, Order No.7638.2G3,5
Nominal voltage7,4 V
Thrust in N (1 N = 100 g)10
Max. charging rate27 A
Shaft diameter4 mm
Permissible motor directionR und L
Recommended propeller1341.25.15