jeteffx

My Feedback: (2)

Just wondering if I could get any info on the Kangaroo c.g.......this plane I have has many many flights on it, but we Dave Hudson and myself just can't seem to get this plane down on a short runway without the sucker doing the dreaded hop................I'm not exactly sure where the c.g is, suspect that it is nose heavy, but flies great......just don't install missle rails on the tips, really jacks with the roll rate......so if anyone can please give me the correct c.g. so I can limit the hopping I will owe you a beverage of your favorite choice.....thanks.....Perry and David

AMTdude

When it has no fuel in it, if you lean the plane back, it should sit on the fins in a wheelie and stay there. Sounds like you might need to add an air-brake on final once you clear the thresh-hold of the runway. You must have it pretty close, because if the plane is too nose heavy it won't want to rotate on take-off, the main gear will lift off before the nose gear and it would spin out. (Ben-Dare-Dun-Dat) If you don't have an airbrake use a longer approach...but not TOO long. :-)

erbroens

From the manual...
The center of gravity of the model should be located about 95-100mm forward of the front leading edge of the wing tube joiner

And be ready to hold a lot of up elevator right after takeoff or while flying at less than full speed while the turbine is at 100% thrust . this of course is caused by the high
trust line.

Regards, Enrique

Thud_Driver

My Feedback: (1)

Enrique has it correct. That works out to around 1/2" or less in front of the main struts or, in other words, right on the forward bolts of the main retact units. Mine only needs a lot of back stick when taking off with full smoke tanks. Even so, and even with the speedbrake out, if you're the least bit fast and you twitch the elevator, it will likely lift off again. As a last resort, you might also try less stiff springs in the stuts to reduce the bounce action.

erbroens

Yes, I hold too a lot of up elevator on the take off run, mostly because I want to make the take off as short as possible to minimize the wear out of the landing gear... (more than once I saw a tire
running down the entire strip just at the takeoff, nor to mention the landing, haha) a nice feature
of the high trust line of the roo is that you simply can't overotate it, so you only need to hold up
full elevator and see the beast take off... easy as that.

hornet driver

My Feedback: (7)

btw

roo hops happen from still being above flying speed.... the roo glides as well as any bird there is ( which isnt good ) and makes approaches tuff where as you have to guess where to cut your throatle " way out there "...as she comes in ....usually to fast...you say oh shi$ and slam her down too quickly in which she just pops right back where she was ( aka kangaroo hop )...as she is not done flying yet..the best thing on a roo is a BIG speed brake that is 90 degrees ...this will help her slow down....and even allow you to add a little to hold her up ...try it....get her in the pattern..cut your throatle out there at 25 feet high...when she finally starts to sink add touch of throatle until you know you will hit the 2 wire ....and get off it ( still not over the runway as if your over the runway your too late as she is too fast )

always put your brakes on your snap button....the slider will make you fumble to much

NEVER EVER PUT YOUR BRAKES ON THE DOWN ELEVATOR...she will wheel barrow ( as any delta wing plane ) and any cross wind will lift the windward wheel and you will be heading off the runway in a second or two...it took 56 eventful landings to figure that out!!!

hornetdriver

erbroens

Well, I only use the wheel brakes on down elevator, and never had a problem... the only thing that
I avoid is to use the brakes when the nose wheel is still above ground. But if you put the
brake in a slider or a switch it will work fine too.

Anyway, in a good roo landing the airspeed is so low that you will not need to use the brakes at all...

Thud_Driver

My Feedback: (1)

Duh, 300 flights on the Roo with down elevator brakes and I have yet to see the mains lift, nor on any of the other 1200 turbine flights with my other airplanes. And I do fly in heavy winds in the desert. Land on speed.

hornet driver

My Feedback: (7)

Well, I only use the wheel brakes on down elevator, and never had a problem... the only thing that
I avoid is to use the brakes when the nose wheel is still above ground. But if you put the
brake in a slider or a switch it will work fine too.

Anyway, in a good roo landing the airspeed is so low that you will not need to use the brakes at all...

******************

grass is easy



300 flights on the Roo with down elevator brakes and I have yet to see the mains lift, nor on any of the other 1200 turbine flights with my other airplanes. And I do fly in heavy winds in the desert. Land on speed

****************

oh they are lifting.....

and your 1200 turbine flights with other planes is mute....as i assume they were not all delta..duh...airframes do wear out if you can keep them up for 400 flights

and heavy winds...well no shi$....nothing like a 17 mph head wind to slow you down


you guys are cracking me up

hornetdriver

you guys are crackin me up

piethein

Any idea to avoid ROO twitching in the TO run?

My roo is really critical to steering/rudder. If the speed is too low, rudder is not effective enough and she might just turn about 60deg and head out of runway.

OK. This is with springair wires, so putting stiffer legs might help, but I have read, that even with those it might do that. This is in pavement, not on grass.

I think, that I have the same situation as AMTdude mentioned. Well I have a AMT Mercury in it...

BR,
Jussi

erbroens

nope, this is the club I fly... and a short landing is a must here, because there is no scape areas at
the end of the runways. (the club is in the top of a hill) .

erbroens

do you have a pic of the nose strut/servo setup and of the plane too?

piethein

No pics now. I can take few later.

Generally the setup is the following:
- To aid TO and keep TO run short, the nose is set a bit high.
- 4mm wire legs in mains, without spring loops
- 4mm wire leg in nose with 3loop spring
- The nose wheel geometry is set to be without trailing and nose steering axle points a few degrees forward
- The nose retract is modified to retract forward instead the original backwards (The first Roo in Finland landed more without the nosegear fully locked than normally).
- CG as mentioned in instructions
- Robart wheels in mains (soft), Kavan wheel in nose (hard/slippery). Tried also soft tire in front, but is even worse.
- Some toein set to mains, but no effect.
- No gyro.
- Turbine thrustline lifted up from the back to compensate the high thrustline in flight.

Just wondering, if anyone else has had problems in TO run.
The landings are OK with the airbrake opened to full.

BR,

Jussi

erbroens

Piethein, i didn´t understood very well about the nose strut, so i did a quick draw of it... if you are
using the first example, you could have trouble in the TO run. I use the second example, and in
my opinion , as the distance "d" goes greater, then more stable the TO run. (no need to install a gyro) Another point is that I didn´t use a totally rigid steering setup. I left a about 5 degrees each side of steering slop. This setup works very well to me, making takeoffs uneventful, even in crosswinds.

I´ll post later a pic of my 5+ years old homemade strut.

All the other items listed seemed fine, specially the turbine angle.

Thud_Driver

My Feedback: (1)

Well, here's how mine sits. Mostly level and maybe slightly nose low, probably level with the wings on. Notice the trailing arm nose gear unit. Steers perfect, no taxi, takeoff or landing issues. Less than half stick to rotate without smoke, something over half with smoke tanks full.

No, the mains don't lift with braking cause they're too busy kicking up a large dust cloud from the lakebed when I use the brakes. A 17 mile headwind is not a heavy wind and we do get tons of gusts and crosswinds. Besides, the wing doesn't know the wind is blowing. You still have to make good on the correct landing speed at touch down. And well, the TopCat is sort of a delta with with a stab and accounts for 850 of those other landings.

BTW, every Roo I've seen with a straight strut for the nose gear has trouble with steering.

erbroens

Same thing here, and not only with roo´s!

Enrique

grbaker

My Feedback: (29)

Jussi

I suspect that your steering problem has more to do with how much your nose wheel turns than with the geometry. You need/want very little movement in your steering on takeoff. I used low rate on my take off and high rate for taxiing.

Also if you have steering cables, you want to make sure that there is not too much slack in them.

I had my nose strut angled forward and had no issues with the steeing until my cables got slack. I had rubber bands going from the middle of each cable to the each side of the fuse. One of the rubber bands was broken. You can also use the zip tie method as described by Todd here: http://www.rcuniverse.com/forum/m_27...tm.htm#2747929

BTW 200 MPH motorcycles have the front strut angled forward.

Here's a pic of my old ROO.

Good luck

grbaker

My Feedback: (29)

Jussi

I just reread your post and realized you are using 4mm wire struts (equivalent to 5/32" ) That may be part of the problem. You need to drill out your yokes and install a stiffer wire. 3/16" (4.76MM) is the minimum that I would use. The retracts you are using are for about a 10 - 12 pound plane. I'm sure yours is a little heavier than that.

erbroens

that´s why people fall so often from those things!

Enrique

erbroens

Ok. here it is the homemade strut, works very well althought it is somewhat ugly.. spent 15$ on it
and it never breaked...wheels and wire rear struts by bvm... a little more expensive, but they work quite well too.

Enrique

piethein

Thanks all,

My nosegear setup is just as Enriques first drawing. I will bend it back some and test it again. Also I am waiting for new strut from Eurokit any moment.
The basic idea was to get the bicycle type self tracking setup as in RCJI article some time ago. Maybe it needs more d.

The 4mm wires from mains will change to steel struts. One is allready changed.

I will report once tested.

BR,
Jussi

piethein

Hello All,

Attached is the photo of my gear setup.

Today I have recieved the Eurokit parcel, so I will install a new trailing nosegear and hopefully it helps.


BR,
Jussi

jonkoppisch

My Feedback: (162)

It looks like your nosegear is bent forward. That along with a semi flexible strut will make it very sensitive. The strut should be straight in line with the strut mount. I also have dual rates set for steering/rudders. I use minimal throw for takeoffs and landings. I have the spring airs in my kangaroo and don't have any problem with takeoffs and my brakes are on my down elevator and they work fine.

piethein

OK.
Finally my Roo track straight now. For the time being anyhow.

I changed the mains wire from 4mm to 5mm with struts and robart tires to eurokit ones. I also filled the eurokit tires inside cavity with foam to make them sturdier in compression, as we saw marks in the sides of the robarts, that flex sideways a lot more.

I also changed the 4mm wire nose to eurokit nose strut.

On the first flight it tracked OK in the start, but I managed to land 1m wide of our tarmac, to guite heavy gravel (first jet flight of the season...). The nose strut lower part broke as this was cast aluminium and about 7mm in dia. At this state I still has the 4mm wires and struts in the mains. The mains also bent back heavily.

Then I made a new lower part to the nose from my earlier Yellow A-4 main strut and changed from 4mm to 5mm wire for mains crank/strut fix. After this the plane has been trouble free in 4 flights with 90 deg sidewind.

But... My friend has quite a similar setup and he still has problems with tracking. He has even sturdier mains now, but with robart tires and had problems with tracking. His nose setup also has a bit less lag. So I will advice him to make two changes, that should help.

- More lag to the nose steering. With lag I mean the distance between the steering rotation axis to wheel rotation axis.
- Stiffer, low profile tires to the main, so that the rubber will not flex under the weight.

We also use harder tire in the nose and softer pair in the mains to prevent oversteering. (Note! Hitech Formula one tire selection here!!)

BR,
Jussi

erbroens

Good to hear that your Roo is fixed.. about the tires softness I mostly use bvm wheels, and sometimes the softer eurokit tires... I didn't found a difference at all in handling between them, but seems that the bvm can handle more abuse. that's why I prefer them.

p.s. I bet that the people at your club started saying that you finally learned to take off a plane!

BR, Enrique