ultra flash cg
 

Where is a good starting point? My manual shows cg for classic. I assume they're close but gives measurement from tip tanks, which, well you know...
tia

If I remember correctly mine is at 225mm from leading edge of the wing where it joins the fuselage at the center. 220mm would be a safe start but double check on the following thread. You can also ask your question there.

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

Its also here, on the second page "Balance point, gear up 220-225mm back from the wing/fuselage joint."

http://carf-models.com/files/product...tionmanual.pdf

That is the safe point I gave, but I would start at 230mm back from the wing/fuse join line.
The UF copes with a big range, we have flown it between 220 and 240mm (3/4" range) and it has control power and balance to cope with both extremes. A lot of guys end up 230-235mm gear down and a little fuel in fuse tank....but always with balance its down to what you feel comfortable with.

Dw

Perfect. Thank you

Hey Randy,

When and where are you going to do the maiden flight?

I'm building one myself so I've been reading threads. Have copied useful information to a folder in notes and just cut and pasted here. I think some of this is from Dave W but generally find it useful set up information:

Ultra Flash Settings

As the UF is such a popular model this topic on flap settings/crow etc is going to go on and on.

I have found the UF the most pleasant of my jets to land so far.I have posted my settings on this thread before but here they are again and in my opinion are just perfect.

All measurements at tip.

Take off Flap 27mm ( - 1mm down elevator mix)
Landing Flap 75mm ( -5mm down elevator mix)
Crow on full FLap + 6mm
+ 1mm up trim on elevator for normal flight.
CG 232mm from LE cut line (tanks empty,ATU full,wheels down)

I found operating manual travel settings for aileron too powerfull so reduced to;

Ailerons +9mm/-10mm (up/down) 40% expo.

Rudder 45mm each way (40% expo)

Elevator +10mm/-11mm (40% expo)

If you go with these setting you cant go wrong and will have a very pleasant and easy model to fly.

Phil.


FLAPS: Take off 25-28mm. Landing 95-100mm both figures measured at the root, trailing edge of each flap. The Ultra Flash requires down elevator with flap. Take off 0.8mm and Landing 4mm measured at the elevator trailing edge tip. Exact figures will be affected by balance position.
CG: Gear up 220-225mm back from the wing/fuselage joint.

They are on the update sheet!
My figures are :
The flap settings for the Ultra Flash. Take off 25-28mm (1-1 1/8”). Landing 95-100mm (3 ¾” to 4”) both figures measured at the root, trailing edge of each flap. The Ultra Flash requires down elevator with flap. Take off 1mm and Landing 4mm measured at the elevator trailing edge tip. Exact figures will be affected by balance position.

My model checked on Sunday was 232mm full of fuel.

I'm probably update the manual and say for people to start with a little less flap and increase to personal taste. Many people flying UF models will be experienced in deciding their set up, when I test flew my UF October 2010 I had practically no data but went with my preference of a tonne of flap and I have not changed the setting from that day. When I test flew my Classic Flash in 2006 I had a tonne of Flap and hated the elevator feel, so reduced it and cam off the power even earlier. Then Little Stevie said we should try CROW and it was a revelation on the CF, my model still flying with it now. I didn't add CROW to the UF when I built it because of the bigger flaps and different wing, I've never felt it needed it. The second or third UF I test flew was set up by an ex CF owner who used the same basic program and he left the CROW in and I didn't like the way it landed. In the end we reduced the CROW down to 5mm raised ailerons and 80mm flap and he liked that.

If you want High Alpha approach go for (on landing setting) 60-65mm flap and 8-10mm raised ailerons, but you will need more down elevator and I have no data as I still prefer my set-up.

Hopefully Sunday in BG

Randy,

Thanks for the info, I might come up to get the maiden done on my Rebel Pro. Just need to get the CG done and double check a few things.

You will love the rebel pro.

What size battery packs and how far forward are they to obtain correct CG ?

Using the electronic cg machine, we got the cg dialed in at 225. I have the saddle tanks, no wing tank for now. Two 2500mah a123''s and one 3800mah li-fe in the slots beside the nose gear. The 2 2500 are slide to the rear of the slot, the 3800 is about in the middle. Gear down and uat full. Maiden as soon as the weather permits

Randy

How much weight was indicated on the nose wheel scale -

I don't recall, but it wasn't much.