Ultra Lightning CG Settings
 

I'm about to maiden my Ultra Lightning. I've set up my CoG based on some of the older threads I've seen here, and cross checked that against what is in the manual for what I assume is wings on (it doesnt actually say that), ie. 15mm back from leading edge of inner gear door line.

Can anyone give me a tested CoG position with wings on and gear down? I'm using one of the Xicoy CoG meters, so if anyone has CoG setting for that it would be much appreciated!

Geoff White from the UK did a really good set up thread for the UL that I used to set up mine. Worked perfect the first time. I tried to search for it but can't find it. Maybe PM him.

PaulD

The ones I test flew were set at 15mm behind the door lip, but I think you can go further back-20mm. Wings off, its just behind the centre of the wing tube.
I'm sure Geoff will chip in if he sees this, he's flat out working before going to a meet in France tomorrow. He was flying his Saturday at a show here in England.

Dw

http://www.rcuniverse.com/forum/atta...mentid=2100220

Agree - for first few flights start with cg 15mm aft of leading edge of gear door lip - this is with wings off and nose gear down. Just set the fuselage on the wing tube at the balance point. You can shift the cg farther aft depending on your flying style.

http://www.rcuniverse.com/forum/atta...mentid=2100286http://www.rcuniverse.com/forum/atta...mentid=2100287http://www.rcuniverse.com/forum/atta...mentid=2100288http://www.rcuniverse.com/forum/atta...mentid=2100289

Guys,

Thanks, but we would realy like to know what all the before mentioned wings-off/on measurements are equavilent to when the UL is sitting on it's wheels on top of a Xicoy cg balancer.

Cheers,

Jan

This is the original thread that has my setup included in it.

http://www.rcuniverse.com/forum/rc-j...lightning.html

Best of luck with the maiden.

With this balancer you need to stand it on its wheels to get the axle position, seen pictures of models upside down measuring distances, this does not allow for wheel movement. Also the UL axle moves back a good distance with weight on it.

Thanks guys, but my understanding (or reading of the unclear manual) is that the 15mm aft of the leading edge of the gear door is with wings on, gear down. Can someone confirm this? If not what is the CoG position with wings on and gear down. As Jan said above, I want to put this on a Xicoy CoG meter, which you need the wings on for. I'm totally fine with how to use the Xicoy unit, just need to confirm the correct CoG position.

Thanks!

The instruction manual is confusing about the 15mm distance but it is clear that you can balance it at 45-50mm with the wings off using the wing tube which is how I balanced my Ultra Lightning.If you want to use the Xicoy balancer maybe you could just use this method to get the proper C.G. and then install the wings and see where the balance point is with the wings installed. Then you would know for sure where the cg location is with the wings on and could use the your Xicoy balancer going forward. You may want want to make some changes after you fly the plane and then you could easily use the Xicoy balancer.

[QUOTE=sc0tt;12049179]Agree - for first few flights start with cg 15mm aft of leading edge of gear door lip - this is with wings off and nose gear down. Just set the fuselage on the wing tube at the balance point. You can shift the cg farther aft depending on your flying style.

In the manual it doesn't say to put the nose gear down when balancing. I don't remember if I did it this way or not but is there a reason for doing it this way? My assumption is because this will be landing configuration and with the gear down it will make the plane more nose heavy. Is this correct?

I only ask because I am having a hard time getting mine to slow down on landing and I balanced it with the nose gear in the up position..

A very good point as this slow down problem has been mentioned a few times before. Again, if anyone (including Geoff) could dial in here (even better if they can give us the Xicoy result). I have noticed there are guys using crow - did this help the slowing down, if so, how much and what is the rest of the setup?

Thanks for the input.

Jan

Nothing to do with the balance! The UL (UF too) has huge elevator power, so you always have enough to flare. Then its 1/Weight, some people add a tonne of unnecessary weight. 2/ Trimming, nose heavy or not you can trim it to not drop its nose and pick up energy.

Most people would balance gear down, some fuel in the main tanks...cause you will likely always land with some fuel!!

Balance is subjective, Anyone who has flown one of Stefan Volker's designs will know for most its nose heavy. The Boss of CARF is the opposite, he likes neutral, more tail heavy. These balance positions get you flying safely, then adjust to suit your thumb-brain requirements.

It was 3-4 years ago, so I can't be absolutely sure, but I think mine was balanced gear down.

Regarding slowing down, I can honestly say I have never had a problem with this aspect and that is without any crow. Yes, it is more 'floaty' and slippery than other models in my fleet(F104, hunter, carf Viperjet) but nothing that is going to cause a problem, just make sure the circuit speed isn't to high. Also make sure you are running plenty of flap.

Geoff.

Another friend of mine at our club with a UL said he balanced it on the wing tube, nose gear down, wings off. I appreciate the inputs guys, but it looks like nobody has an answer to the original question, so I'll balance it wings off, nose gear down, on the wing tube, and then use the Xicoy to determine where that is with wings on, gear down.

I'll post it here for the information of others.

Re the other discussion, same friend above converted his Classic Lightning to an Ultra. His flight report said it was noticeably more slippery, takes off easier, but needs more time to slow down. That's pretty much what I'd expect. I've flown an Ultra Flash for years, so in that respect pretty similar.

Maiden is tomorrow... :-)

Thanks Geoff, your response appreciated as always (but I cannot say the same to some other soap boxers).

Cheers,

Jan

We have moved our CG quite a bit back over time with no problems I'm guessing behind the wing tube (I have the ultra lightning) we will check it once our new balancer shows up also.

I have reduced the flap 15-20% and added as much crow as travel will allow (around 1inch up) which helps the plane settle constantly thru ground effect. It very deceiving as it will fly much slower than most are willing to fly it! and has a lighter wing loading than the ultra flash and carries energy due to weight much better than the flash which makes it appear harder to slow down. Just takes good energy management and practice, its a great flying plane.

http://www.rcuniverse.com/forum/atta...mentid=2100666

....like your collection in that photo Don.....LOL

CARF finally got back to me and confirmed the 15mm back from inner gear door leading edge lip is with wings on and gear down. I did the COG the standard way first with wings off, nose gear down, on the wing tube. This equates to a wings on point probably 5-10mm forward of the 15mm reference point (as you can see from the Xicoy screen shot below). Given most seem to move it a little back from that point after flying, this seems right. For those that want to use the Xicoy unit for CoG the attached photos will give you the settings. I did the maiden flight today with it as shown below, and it flew beautifully. That said, I will move it back a bit from here.

http://www.rcuniverse.com/forum/atta...mentid=2100736http://www.rcuniverse.com/forum/atta...mentid=2100737

A few photos from my maiden flight today. The UL flys beautifully. I'll do a few tweaks for the next flight (more flap, more elevator compensation, and maybe more crow), but even as it was today it is an awesome plane to fly.

http://www.rcuniverse.com/forum/atta...mentid=2100738http://www.rcuniverse.com/forum/atta...mentid=2100739http://www.rcuniverse.com/forum/atta...mentid=2100740http://www.rcuniverse.com/forum/atta...mentid=2100741

Congrats Colin.

Was out flying mine again today and its a great model.

Thanks Geoff... appreciated your list of settings on the other thread too. You are spot on with the neutral point on the elevators. I set it up that way and needed zero trim adjustment in flight.

....

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Hi Craig... thanks mate. I'm running a Jets Munt 200XBL (thought I'd try one of these rather than my usual Jetcat), Jeti RX gear (I've gone across to a Jeti DS-16 Tx from my Futaba 18MZ, still have the Futaba, but really love the Jeti system). Battery, Airspeed and ECU telemetry. Electron retracts, servo operated gear doors, Powerbox smoke pump, Intairco air trap (I'm using the standard CARF air trap as an air trap for the smoke).

Good point on the Festo fitting, well spotted. There is a bit of sideways on it (better photo below), but a solid fit and it doesn't feel like the connection is under any significant side load. No leaks at all on the maiden, but I'll take a closer look at it and make sure it comes straight out - maybe put an elbow on it.

Cheers,
Colin
http://www.rcuniverse.com/forum/atta...mentid=2100875