rcdoug

My Feedback: (8)

Cody,

Try marking the top of the tanks and check with the plane upside down. Most of the mass is above the wing and it makes it unbalanced unless you are EXACTLY on the CG. What measurement are you using?

Doug

Grodus

Ok Doug, I will give that a shot. I was trying to start at the fwd range of 370mm from the rear of the tip tank.

Thanks,
Cody

KC36330

Cody,

you're UAT looks empty in the pic, it has to be full during the CGing..........BUT..........double check your measurements because it shouldn't take that much weight shifted forward to balance. I've got stock pipe and Titan SE in the tail, the only battery I've got in the nose is the ECU, RX batts are just above the nose retract and the UAT is attached to the intake ducting and i got a perfect balance.

Grodus

The UAT is actually full, and your results is why I question my cg measuring technique. I will measure the points again and try it upside down.

Thanks,
Cody

Rctofly

My Feedback: (18)

scoeroo

My Feedback: (9)

interesting -

Dave Wilshere

This is the Classic Flash thread, but Ultra Flash balance should be measured back from the wing joint front line, 230-232mm is about right for most pilots, but 225 Nose heavy and 240mm Tail heavy have been flown successfully.
Your KT 160 will have a high idle thrust figure compared to the turbines the UF was designed around, so you need 100mm flaps and possibly the crow at 6-8mm with at least 4.5mm down elevator

Rctofly

My Feedback: (18)

Auburn02

My Feedback: (1)

Warning, ancient thread bump!

Really I was just looking for various Classic Flash install pics and came across this reply by Grodus and figured worth bumping this since I have the same problem with an old Flash I’m resurrecting. With a K160G2 for power (because that’s what I had available), I’ve stuffed both 2100 LiFe rx batts and the 3800 LiFe ECU battery in the nose and it’s still tail heavy. Obviously I can add lead but I’m baffled how so many with similar weight engines managed to get away with putting the batteries in the side pockets.

This one does have the full bypass (minus bottom cover) so I thought of cutting that out as I think most of it is behind the CG, other than that I’m working to try shifting things forward. Would like to put the UAT behind the nose gear but my fuel lines interfere with the cockpit floor in that configuration.

I know this is one of the most popular jets that has stood the test of time, so what am I missing here?

Dave Wilshere

First thing is what balance are you trying to achieve? 365mm Forward of the tip tank back edge?
Cockpit with Pilot or no cockpit?

Dave

Auburn02

My Feedback: (1)

Correct, 365 forward of the back edge of the tip tanks is my target - cockpit is the original ABS floor/dash/seat (reinforced with a layer of 3/4oz glass) with a pilot bust similar to yours pictured.

txshan130

My Feedback: (114)

I believe I ran into the same problem as you when building my classic. I have a 120sx with full bypass which is quite heavy compared to today's turbines. To reduce weight in the back, I installed the new evo pipe which is about 4.5oz lighter. I have a full cockpit also. Running my cg between 365 and 370 with ecu batt in the side pocket and rx batts in the nose.

Auburn02

My Feedback: (1)

Nice clean install! I also like that you put the steering servo in front of that bulkhead, if I don't move the UAT there I might at least look at doing that.

I'd read of others installing other brand pipes, this original pipe really is the heaviest pipe I've ever seen in a model, didn't realize the EVO pipe was one such option as well. Good to know.

Any reason I shouldn't start with cutting out the rear inlet joiner? I know there are pros and cons of a full bypass, but since I'm already lacking the lower cover I wonder if I'm really even enjoying the advantages it could offer. Plus with one of those advantages being higher max speed, with a 160 I don't find myself very worried about eeking out a few more mph. This would also allow me to upgrade my fuel tank setup with an EVO tank down the line, which I would love. I do need to at least take a closer look to determine if removing that would actually help my CG, but I think most of that is behind the desired CG point.

Dave Wilshere

The wing acts as part of the duct it’s so close.
The original pipe is really heavy, but it will never fail!!!. My original model has a gas start P-120 full ducting, do you have fuel in the fuselage tank for the balance check? Removing the ducting is nothing much for helping the balance.
Either way, just add bigger batteries or lead. It copes just fine. If you want the wing tank for smoke you can cut everything out and use an Evo tank.

Auburn02

My Feedback: (1)

Thanks Dave. In full transparency, I’m not so much worried about all up weight, I just don’t want to have to deal with stuffing batteries into the nose and wedging them in with foam. Not really the best reason I know.

Dave Wilshere

Mine are in the pockets. There maybe lead in the nose, I’ve not looked in there since 2006!

jvaliensi

My Feedback: (1)

I have a spare light weight Grumania pipe that I bought but didn't use, if anyone wants to lighten their Flash.

Wayne22

My Feedback: (2)

I yanked out the old jetcat, and installed a lightweight xicoy x90 and well as tossed the pneumatic landing gear, with all the associated plumbing connectors and valves, and installed Electron retracts. This shaved 2lbs off the empty weight, but I still had to add a bit of nose weight. ( I can’t fit my big hands in the nose to install anything up there...)

scoeroo

My Feedback: (9)

Good move -
Electrons & turbine

Wayne22

My Feedback: (2)

thanks….I tend to drag my heels with new technology, but I'm not looking back after this move!

now I just have to figure out how to get more useable fuel out of that flat bottom tank!

jvaliensi

My Feedback: (1)

2l w/ an X90 will give you 5-min w/ reserve.
I have a X90 in my Rebel Hot w/ a 1.7l tank and land with 25-40% remaining after 5.5min flight. But you will need more power than I do.

Auburn02

My Feedback: (1)

I (re)maidened the Flash this past weekend, flew fantastic. No idea what the all up weight is but I'm looking forward to more stick time and may be bringing the CG back just a bit. All 3 batteries (2x 2500 6.6 LiFe and 1x 3800 9.9 LiFe) are in the nose, UAT is behind the nose wheel in front of the steering servo.

I was a little surprised at the lack of acceleration even with the K160 in the back. Obviously it has tons of power, but advancing from idle/low power to max takes a bit more to get moving than I expected. No clue if this could be attributed to the forward bypass/intake duct feeding that big engine or what. I'm not committed to cutting that out just yet, although if I had an EVO tank on hand and could get rid of the flat bottomed tank (and wing tank all together) I'd hack it out in a heartbeat. But I'm also flying at half power or less most of the flight, so even after 5-6 minute flights I still had half of the main tank left.

Set it up for landing with crow from the first landing, loved the nose up approach but with that hog of an engine I was idle from mid-base leg and still floating long. I think I have full flaps at 45mm (measured at fuse) and crow around 6mm (measured at tip), may try bumping both up a bit at a time.

No issues with the old pneumatic gear though.

Dave Wilshere

Did you balance at 365mm with some fuel in the fuselage tank? If so that is the sweet spot.
We have Classic Flashes with an Old P-80 and they come off a 360’ grass strip no drama. My one with the 18 year old P-120 gas start is off grass or tarmac in around 250’

The inlet does not reduce the performance on my P-160 Ultra Flash. I suggest you do nothing more than add 1/4 ply packers under the nose retract rails. I think yours is sitting slightly nose down.

Dave

Auburn02

My Feedback: (1)

Hi Dave, my balance of 365mm was achieved with a full UAT and nothing else other than whatever unusable fuel doesn't get picked up by the clunks. I could always add a bit of fuel to simulate the more likely landing load and recheck it at that point, may allow me to bring it back a little bit. Thanks.

Oh it has no problem getting airborne, I think my takeoff roll was probably in the 200-250' range. When I talked about the acceleration I meant in the air, I see now I didn't clarify that well. It may just be the nature of the plane but it just didn't accelerate like I would expect. Example, when shooting some practice approaches and punching the throttle to go around, it was sluggish to get up and going even after the engine had fully spooled up. But once I made the turn it was zorching. Nothing scary or unsafe, just a little odd. I'll get used to it.

Dave Wilshere

OK. My 365mm was with 3/4” fuse showing in the fuse tank standing on its wheels.

My JetCat 160 UF is called Saturn 5 by guys who watch it, I can come by walking pace, full flap, as I open the throttle stick I pull vertical and clean up the flaps together and you can watch its acceleration it just keeps on going. It is light at 10.8kg dry