Thread: Build Log Hobby Lobby Grob G103C
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Old Nov 30, 2011, 09:58 AM
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Hi Kholder116,

I really like the physical set up of the xpower unit. However, I do think it's right on the line of what I think of as a power source for the Grob. But I'm not a glider guy.

I'm use to having lots of headroom in my set ups and typically use a ESC that will handle at least 25% more amp draw then my motor will pull. I also tend to over spec my motors so that I am only running them at about 80% of their rated power when I'm at full throttle. For example; Let's say I have a 10lb warbird and want 1,200watts of draw form the motor/prop set up. Then I get a motor rated for 1,400watts or more. But I choose the prop that will make it run pulling 1,200watts. I make sure I am well within the amp spec for that motor and not stressing my batteries. In this example I might see 50amps maximum at full throttle. So I get a 75amp or higher ESC.

Buy doing all of the above I always have a system that is never stressed and runs cool. I only have to worry about flight times due to normal battery drain when flying. Heat and over stressing my motor are not a concern....

Back to the Grob. In my way of thinking this power system is just enough. But as I said I'm not a glider guy and know just enough about flying them to be dangerous. If you fly the Grob like you would a standard sport plane or warbird then the stock system is lacking.

However, I am learning to realign my thinking when flying gliders.... They are, well........ Gliders !!!! The xpower system on the smaller prop mentioned earlier is plenty of power to climb to altitude. If you watch my video you can see how it pulled away nicely from George's hand when hand launched. The second flight was the same and George mention how he knew it would fly well as it was pulling hard at launch.

I got sick and the weather is now cold and messy here so I haven't flown it again. But from the flights on the day I maidened it, my plan is to do 4 pulls to attitude and hunt for thermals on the way down. If I need to add a little power once or twice for a very short burst to keep me in position so that I can approach our field from the correct direction I will have battery to do that with no trouble.

I'm running a BEC for the RX so no matter what I do I will have battery to fly with no worries about RX brown outs.

I felt my motor when I got down an it was just hot.... Not overly ouch kinda hot, but hotter than warm..... I also have a VQ KA-7 with a Super Tiger .15 electric motor. I thought that was too wimpy a set up and was getting short flights.

Thin I figured out that the KA-7 is a glider Climb to altitude(4 pulls), shut the motor off, thermal hunt, and land. The motor is perfect for that.

Sorry for the long post, but I'm finding I have to adjust how I think of power systems. I'm use to flying around with the spinney thing on the front making me go

If you want to fly like a sport plane (spinney thing working all the time) then this xpower is not what you want. But if you want to climb to altitude and hunt thermals then its good. My one caveat is we have a 400ft altitude limit at our field and I was only doing the maiden and some shake down flying. When I go to a field where that is not an issue I my only get two pulls to a higher altitude.

I'm using 2 3s 2100 Hyperion packs wired so that I have a 3s 4200 battery set up. This battery set up falls dead center in the space available for batteries when you CG the Grob at the 61mm mark.

I'm finding I don't need as much power as I think I do with gliders. If you like to climb like a hotliner, get a few more pulls to altitude, or fly like a sport plane hooning around all over then the xpower falls short.

One last thought. Remember you don't have down or right thrust so when you power up the Grob (and my KA-7) goes nose high and climbs on it own. You have to control the assent with down elevator. You can mix that in with your throttle which I've tired on my KA-7. I prefer doing it manually with no mix.... Anyway, if you are going to trim the Grob to fly straight an level at say 1/2 throttle or above like you would a sport plane then it's going to be much different when you shut the motor off.... I prefer it to fly good with the power off and trim for that. On the spoilers I set them up to a three position switch. 0 - fully retracted, 1 - Deployed about 1/3'd of their travel, 3 - Deployed fully. The landing you saw on my video was with the 1/3 deployment. Full deployment and the Grob descends really well. I like the 1/3'd for a nice feel till I need more.

Did I mention.... It's glider? Trim it to fly good with the power off and start from there.

If you fly like a glider and actually glide to let it stay cool, don't over use the battery available then it's great. Perfect no... but certainly good enough for a glider noob like me.

Hope this helps. I'm learning what works for me when coming from the world of normal powered sport flying. It took me realignment of my approach to things but I'm really enjoying it. So much so I now have a 3.4m Minimoa and a 2.6m ASK-21 that will be built next spring to join my little fleet of scalies. I have to spec the motor bit for those myself and I'm sure I will have more headroom in my set ups. But I need to get some advice from others here about how much power I actually need. The Mini just needs to get to altitude and the ASK will be closer to a sport plane but not need power for a full powered flight. I think....

I'll post a thread on those next spring when I get to them.

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