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Not sure what folks are getting for cruise speed at 3-5k msl but I can only do about 100mph in my Onex.

I have a tri-gear and typically I'm have a forward CG and I'm thinking that if I can move the CG back, then I should get a bit more speed.

Currently I have a lead acid battery mounted in the cockpit floor about where the panel is.

I was thinking of replacing the battery with an EarthX or similar and moving it to the baggage compartment.

I'll have to calculate what that will do to the CG to see if I can get it less nose heavy.

What do you guys think?

Greg

Sounds like a plan.

Be sure to get some good advice on the right electrical cable, to suit the distance between battery & starter motor.

I'd start with simply replacing the lead battery with the X-brand. By the time you get a 5lb battery back far enough to do any good, you'll have added enough weight/complexity to have a net 0 effect on the weight side of the equation. .

There are a lot of other things to check before you go moving the CG. First share your W&B so we can see how much forward it is. Side story: I bought mine as a project. The original builder had installed the Nikasil cylinders. I asked Sonex about them before I first ran it. I forget who I talked to but they recommended I put the steel ones back on. Somewhere in the conversation they also mentioned the Onex could use the nose weight. I put new steel cylinders on it before it ever ran. The battery is on the engine side firewall. I'm 150 and with a full tank CG is at 25%. It flies great there and no issues with elevator authority on landing. It cruises at 140 indicated at 3150.

Are you sure your indicated speed is correct? How are you sure? What compression ratio did you build to? What RPM are you seeing at cruise? Have you checked that against an optical tach on the ground? How are the wheel pants? Some mis-rigging there could be a speed killer.

Greg,
Our Waiex is pretty aft CG and we cruise about 100 kts behind the AeroVee. But we often see more like 90 if we are really heavy, and it's not hard to do 110 solo. So I think weight is a bigger factor. I'm with Area 51 - weight is the enemy. EarthX is awesome.

During phase 1 I ballasted to get to my aft CG. I did not notice any big speed change. I cannot get to my forward limit.

Edit: we also put the hollow spinner on last year. Good for another couple of pounds. Moves CG aft a little bit.

Scott,

Empty weight is 649#

With a 195lb pilot (I'm working on it) and full fuel that puts the arm at 62.43 and moment at 58317.5
With fuel at 12lbs and 20lbs baggage that puts the arm at 66.76 and moment at 56734.4

I purchased my OneX complete but it hadn't had phase 1 completed. I've done the EAA flight test and with GPS I believe the airspeed is correct.
Compression ration is 7.0:1
I typically cruise at 3150 rpm too. I haven't put a tach on it to confirm.
Wheel pants are good.
I do get a right bank tendency and have been adjusting to correct that.

Originally this was build with conventional gear and was updated to try-gear before I owned it. I have considered converting it back to conventional to save the weight of the front strut, wheel, etc

See attached pic of the existing location of the battery. Moving it to the luggage compartment would add about 4' of copper.



Greg

Empty weight and arm would make it easier to check all the math. It appears slightly wonky. Your moment of 56734.4 over an arm of 66.76 makes the weight 850. However your weights add up to 876. Looking at the book numbers for mine, 66.76 puts you behind the aft limit, assuming you used the Sonex datums. I don't have the POH in front of me to look it up but I'm pretty sure I followed their example. I plugged your weight, fuel, and moment into my spreadsheet and got an arm of 62.44 so that checks out. Changing your fuel and adding baggage puts it at 66.57, which is still behind the aft limit. You should double check all that before you consider moving the battery aft. If you remember next time you fly it, put your smart phone on the fuse side and note the angle you are cruising at. I have heard good things about the Prince prop but it could be the wrong one. The only other obvious thing that would affect your speed that much is aileron or flap droop.

Scroll on the photo for more info.

Hi Scott, have you put a smart level/phone on the side of your fuselage while in cruise? I’m thinking of doing that.
If you have, what did you find your angle to be?

Randy

Sorry Randy but I have not. I was never trouble shooting any issues that required it. I was always thrilled I was getting the performance stated by Sonex. I will the next time I fly it.