Thursday, June 21, 2007

Heli comparison guide - Flight cost per min

There were a lot of new helis released over the past year or so. Especially so in the larger sized heli market segment , with lipos becoming more and more affordable, 30-50 size electric helis are making a storm. This has to be one of the best time to venture into larger helis.

Align first came out with the trex 600, Thunder tiger countered with the E550 and E620 series. Let's not forget the nitro helis although they have been around for quite awhile, they still have their plus points. Raptors having dominated the everyday flyer's market for so long are being given a run for their money by Align's Trex 600 Nitro.

With so many choices and factors to think about, we hobbyist have a hard time deciding which one to invest our hard earn money in.

I did some comparison between the more popular helis in the SG market today and this entry will examine the flight cost of the energy system which has to be one of the more important factors in making the decision as the cost for a year of flight can easily run up to a few hundreds of dollars and even more than the heli itself.

The following are compared : TT50 engine on CP 15% nitro, OS 50 hyper on CP20% , 15cells A123 , 6s 4900mah lipo , 10s 3700mah lipo, 90 size engine on CP30% and trex450SE motor on 3s 2170mah.

Some assumptions i made in the calculations. All prices in SG dollars. As i don't own or have owned all these power system before , some of these figures were estimated using details posted by users from various forums. I have gone through quite a number of threads and came up with the figure which i felt was a good estimate.

6 minutes of flight times for electrics is a rough estimate for mix sports/3D type of flying. Hard core 3D will see the flight time reduce and simple flying around will see longer flight time.

Lipos life time are estimated at 50 cycles per pack. Heli flying demands a lot more from the lipo packs, with amps draw hitting 20, 30C often, so 50 cycles are a good estimate. From past experiences if a pack can last 50 cycles is already considered very good. More often than not, they bloat or lose power/capacity before that.

A123 cells are spec at 1000 cycles . With our kind of use, 200 cycles are achievable as some users wrote in various forums. Some of them are running test right up to 1000 or more cycles and these cells have performed incredibly well. Only problems are getting them cheaply from ebay and the trouble of assembling the packs yourself.

For those using other power systems, the figures can be used to do a rough estimate. E.g. Ep8 or Hurrican 550 using 2packs of 3s packs in series just need to double the figure for that of trex 450 size.

The figures gave a rough estimate of the flight cost per minute of flying. Nitro helis are still fairly cheaper to fly. Coming in close are the A123 cells which combine many benefits of lipos at lower risks and costs. 10 cell dewalt packs are around USD100, add in shipping and other assembly costs, 15cells will cost around SGD300. There are now retailers selling them for USD17 per cell. If this figure was used, flight cost per min will come up to 0.35, still very comparable to nitro.

Using 10s lipos will costs almost 2 times that of 90 size engine on CP30%. It maybe to many people's surprise that cost of flying a electric 450 motor sized heli can be more than a 50 size nitro.

Well this is only one factor in comparing the helis, there are many others like power-to-weight ratio, flying constraints, cost and availability of spares, etc , etc , which i will try explore later on. Make your choices and go for it!

1 comment:

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