turboparker's blog archive for December, 2010 - RC Groups
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Archive for December, 2010
Posted by turboparker | Dec 29, 2010 @ 01:27 PM | 9,971 Views
The question of which LiPo cell is the best for the UM planes & helis comes up often in the ultra-micro forums. Many of us have found that Hyperion cells outperform most of the competition, and that Thunder Power & Intellect UM cells perform as well as, or very close to the Hyperions. Objective tests back up our experiences.

Remember - loaded voltage is what determines the performance of a battery - not usable capacity. Loaded voltage is a function of the cell's internal resistance (Rint). The lower the Rint, the less power will be dissipated within the cell as heat, and the lower the voltage-drop will be under a given load. The cells with the highest voltage under load will provide the most thrust & speed in a given application. Also of importance is the voltage slope over time. The shallower the slope, the more power the cell will deliver over the course of the flight. Also, a shallow slope means that more power will be available toward the end of the flight.

It has been proven many times that Hyperion cells maintain voltage under load better than nearly all of the currently-available LiPo cells. The notable exceptions are the Thunder Power 160 & Intellect 130/160 UM cells - which perform similarly to their Hyperion counterparts. The Hyperions can be charged @ 5c for hundreds of cycles with no reduction in performance or longevity. 300+ 5c charge cycles with no reduction in performance is common. Of course, this assumes than the cells have been properly...Continue Reading
Posted by turboparker | Dec 28, 2010 @ 12:01 PM | 13,999 Views
For those who are seeking more thrust and speed from UM planes that use the 8.5mm motor/gearbox with the 1.5mm propshaft (such as the PZ Sukhoi 26m, XP, P-51, 4-Site, T-28, HobbyZone Champ, and HobbyZone's latest addition - the excellent Sport Cub S 4-channel primary trainer), the GWS 5043 prop is a great choice. Along with the prop, an adapter is required to fit the 4mm hole in the prop to the 1.5mm propshaft. Of course, you want an adapter that spins true; but the weight of the adapter is also something to consider. If the plane is already on the nose-heavy side (which is the case for the Sukhoi 26m), or is is borderline (as is the case with the XP), the last thing you need is extra nose-weight at the far end of the fulcrum, as this can make it difficult or impossible to set the CG properly. If the plane has a wide CG adjustment range, adapter weight may be of minor concern. If the plane is already on the tail-heavy side (as is the case with the HZ Champ), a heavier adapter may be just what you need.

Here are a few choices. Other vendors may also carry the items below. I suggest that you shop around.

I'm using the spinner below on the Champ. It's heavier than some of the others, but my Champ was a tad tail-heavy anyway. You get two of each: 1.5, 2 & 2.3mm:


Some people like these wooden inserts. They're very light - well under 0.1g. They may need to be glued into the prop hub:

http://www.radicalrc.com/...Continue Reading
Posted by turboparker | Dec 27, 2010 @ 03:48 PM | 20,606 Views
For those who are new to the world of purpose-built aerobatic planes, I decided to post the following information on flight-trimming:

Aside from creating an unflyable condition, CG settings are largely a matter of preference. However, many pilots find that with purpose-built aerobatic ships, adjusting the CG for neutral or near-neutral handling usually works best for all-around aerobatics & precision flight, while a slightly aft CG usually works better for 3D, and a slightly forward CG typically improves stability & tracking - which may be desirable when flying in turbulent air. Understanding the effects of flight-trimming & CG placement, plus experimenting to find the settings that work best for a given airframe and flight condition, will allow the pilot to optimize most any airframe to suit one's purpose and flying style.

The neutral handling point, or CG 'sweet spot' as it is called by some, is the balance point which provides neutral pitch stability. No pitch-change with changes in throttle or airspeed. No pitch change when rolled to knife-edge or when rolled inverted. When balanced at this point, an aerobatic plane simply goes where it's pointed until commanded to do something else. Pattern planes are usually balanced at or slightly forward of the sweet spot. 3D planes are usually balanced at or slightly aft of the sweet spot. The manufacturer's recommended CG range for most trainers & sport planes is typically well-forward of the sweet spot....Continue Reading
Posted by turboparker | Dec 26, 2010 @ 05:14 PM | 16,032 Views
Just finished making my lightweight Hyperion packs. I used two bare Hyp 180 cells, double-sided tape from a 3M window film kit to hold the cells together, the available pigtail w/stock JST 'PH' connector, a couple dabs of hot-glue between the tabs to provide some strain-relief and prevent shorting, a couple dabs of liquid electrical tape on the connections, a short strip of plastic for a tab, and a Velcro dot. I also built a 240 mAh Hyperion pack.

Weight & static RPM comparisons (RPM measured with a calibrated optical tach under natural light @ 30 sec into the run on a freshly-charged pack):

UMX Beast
Stock prop
70 F
910' AMSL

Eflite 2s 120 ----------------------------------------------- 9.45g; Static RPM: 10200
Eflite 2s 180 ---------------------------------------------- 12.92g; Static RPM: 10500
Hyp 2s 180 ----------------------------------------------- 11.84g; Static RPM: 11100
Hyp 180 'UM' cells x2 + RC-Connectors series harness -- 12.34g; Static RPM: 11000
Hyp 180 'UM' cells x2 + Eflite series harness ---------------- 13.01g; Static RPM: 10700
Hyp 2s 240 ----------------------------------------------- 14.51g; Static RPM: 11100

RPM data suggests that the stock 120 is a bit overtaxed in this application. Note the significant RPM increase with the Hyperion 180 pack. Also note the significant reduction in performance when using the Hyp 180 'UM' cells & the factory series harness - 400 RPM in this case. Interesting that there was no increase in static RPM...Continue Reading
Posted by turboparker | Dec 22, 2010 @ 10:29 PM | 8,711 Views
The P-51 motor I put in the Champ started to die at the indoor-fly last night. Not even an hour of time on the thing, and I even broke it in easy on the 5030. So.....I just swapped it for the SP motor I got from RC. After a couple of flights, brought it back inside to check the RPM @ room temp. As usual, a freshly-charged Hyp 180 cell was used for the test, and natural light was used to prevent erroneous tach readings.

HZ Champ:

SP motor/GWS 5043/Hyp 180
AUW: 47.15g

Static RPM:

30 sec: 6700 RPM
60 sec: 6480 RPM

Flight conditions:

Alt: 910' AMSL
Temp: +16 F
Wind: 0-2 MPH

The flight below used 90 mAh, or 50% of the charge.

Performance demo: HobbyZone Champ w/SP motor/GWS 5043/Hyp 180 - vertical, aerobatics, outside loop! (6 min 50 sec)

EDIT: 5/24/2011:

Here's my first attempt at shooting video of my own plane. I'm flying the Champ low & slow around my side yard & backyard. No HD - just my #3 keychain cam attached to my hat.

Hatcam - flying the UM Champ low & slow in my yard (5 min 52 sec)
...Continue Reading
Posted by turboparker | Dec 22, 2010 @ 10:25 PM | 8,564 Views
Here's my second video of the UMX Beast. Temp was +16 F, and there was no wind. The Beast is stock, except for the Hyperion 180 mAh cells. I haven't built my new Hyperion 180 & 240 packs using bare cells and the factory JST 'PH' connector, so I'm just using the shrink-wrapped Hyp 180 'UM' cells and Eflite's series harness. The Hyp cells + harness only weigh 0.13g more than the Eflite 180 pack, so I'm sure my homebrew bare-cell packs w/stock connector will be considerably lighter than the Elfite 180.

I'm flying from the road next to my north yard. I managed to hit a power-line about 2:24 into the clip. Knocked one of the wheel spats off, but that was all. The power-line was the same one that ate two of my Sukhoi XPs.

As you can see, vertical is essentially unlimited - even 3-4 minutes into the flight. After 5+ minutes of aggressive flying in cold wx, there was still enough power for extended verticals. The flight used 90 mAh, or 50% of the charge.

UMX BEAST in the snow: vertical performance, powerline hit, aerobatics, takeoffs & landings (5 min 49 sec)

Posted by turboparker | Dec 05, 2010 @ 02:40 PM | 8,229 Views
Hello again...

Looking at the 2+ feet of snow in my backyard got me thinking about flying UM planes off skis in my backyard. With its generous payload capacity and ample power, the Champ seemed to be the best candidate in my UM hangar.

After fixing some pre-shucked corn-on-the-cob, I found myself eying the packaging. Looked to be pretty strong, and the ends already had a nice radius that looked to be about right for the upward curve at the front of the skis. My first set ended up a bit heavier than I had planned. Although my gut told me that rear bungees would likely be required, I decided to try them with front bungees only.

Tried them out this morning (12/05/10). Temp was +10 F with a 2-5 MPH breeze. They worked pretty well - especially on hardpack or crusty snow. ROS takeoffs looked cool. When landing in deep fluff, she tended to nose-over on landing - unless I executed a power-on, full-stall 3-pointer. So, I rigged up some rear bungees. Heading out for a test-flight right now...

I'm also making a lighter set that uses foam for the uprights. This time, the rubber-band bungees will be incorporated into the ski design. Should weigh considerably less than my first set, and the install should be a bit cleaner.