PDA

View Full Version : Junkers JU-52


Geoff_Gino
10-04-2006, 09:47 AM
Hi All

Well my Graupner kit arrived today and it is all excitement at the moment.

This is my first kit I'll be building and I will be in and out of this forum all the time.

Specs:

Wingspan: 1500mm
Length: 1000mm
Wing area: 26 sq dm
Tail area: 5 sq dm
Total area: 31 sq dm
AUW: 1600 grams (Before motor & electrics)
Area loading: 52 g/sq dm

First question: It is a Tri motor plane, but I would like to power the plane with a single motor and have dummy props rotating on the wings.
Will this work if I have the appropriate size motor and prop in the centre and what will I have to look out for?

vampire67
10-30-2006, 12:14 PM
First question: It is a Tri motor plane, but I would like to power the plane with a single motor and have dummy props rotating on the wings.
Will this work if I have the appropriate size motor and prop in the centre and what will I have to look out for?
Just go for nonbrushless with three cheap 400er ferrit motors.
I personally fly with 8x1700AUP NIMh cells and 3x Muliplex Permax400.
Performance is scale like and a non-issue.
Use the cheap Guenter rubber probs.
http://www.mfv-biebertal.de/index.php?show=./php/galerie_show.php&pic=697

Using a 3cell LiPo of 2000..3000mAh will also work well.
The plane is already lightweigt enougth.

Using a single motor may also cause problems with ground clearance.
You would need more power and a larger prop which may be a problem.

No need to change a running system.

kind regards Peter

Geoff_Gino
10-30-2006, 12:36 PM
Hi Peter

Just as I was giving up of ever getting a response, there you are. Thanks for the reply.

Must admit though I have decided to go with the Graupner speed 400's - as you point out, clearance will probaly be a problem.

Please let me know what current your 3 are drawing. I have not yet decided on battery and would like to go with a 2S1P, seeing as the motors are 7,2 volt. I do have a 40 amp ESC and will be running all 3 off that.

Had an idea for the 'corrugated' skin - please give me your opinion of the idea.

Geoff_Gino
10-30-2006, 12:39 PM
Hi Peter

Here's the colour scheme I'm trying to replicate.

Sky Sharkster
10-30-2006, 12:41 PM
Hello Geoff, I wouldn't suggest using "dummy" engines with free-wheeling props, these will create so much drag I doubt if it will even fly. The powered motor can't create enough thrust to propel two discs of the same size, into the air. A free-wheeling prop not only presents a (prop-diameter-sized) huge "wall" to the airflow but spins at an uncontrollable rate, causing unequal drag. If you only use one motor, you'd be better of either leaving the other props off or fixing them in place.
Peters' suggestion of using 3 brushed motors sounds like the best overall solution. Fairly inexpensive, too.
If you would like to see an example of the drag created by a free-wheeling prop, try this; Take a small Free Flight model with a free-wheeler prop, run with the model until the prop is spinning, and launch it. It will fall out of the sky like a rock! First the prop will pull it forward, the prop slows down, bad stall, thunk! Even with another motor pulling it forward, the unpowered prop blades can't spin as fast as the powered one.
JMO
Ron

Geoff_Gino
10-30-2006, 12:43 PM
Thanks Ron

From the above you'll see that I have gone for 3.

Sky Sharkster
10-30-2006, 12:46 PM
Hello Geoff, Yes, I was typing my answer and heard "You've Got Mail". Should have checked it, but Nooooo! Had to finish my reply!
Glad to hear you're going with 3 motors, I believe you'll have better luck.
Ron

vampire67
10-31-2006, 08:14 AM
Hi Peter
Please let me know what current your 3 are drawing. I have not yet decided on battery and would like to go with a 2S1P, seeing as the motors are 7,2 volt. I do have a 40 amp ESC and will be running all 3 off that.

2s seems to be to low as it would account for 6 Nixx cells only.
At least you would need 6V motors.
I've been using 8x1700AUP which has rather good voltage level.
I definitely recommend 3s.
I have to measure current, but WOT with 1700mAh is about 6..7min which equivalents average current to ~20A.


Had an idea for the 'corrugated' skin - please give me your opinion of the idea.

Idea is good, but the fuse top was almost straight as can be seen here: https://www.lufthansa-ju52.de/fotos/diaflug/017.jpg

https://www.lufthansa-ju52.de/fotos/diaflug.htm is a good source of fotos.

regards Peter

Geoff_Gino
10-31-2006, 08:33 AM
Peter

Thanks for the battery info. Was just a little dubious about the 3S as the motors are definitely marked 7.2 volt.

As for the fuse top - that angle was to save weight by using less material, doesn't look too bad I guess :-)

Walt Thyng
10-31-2006, 02:17 PM
Geoff:
I'd didn't know the Graupner kit was still available. I had one several years ago and flew it with three speed 400 motors and the Graupner scale (6/4?) props. It was a great flyer until a "friend" snuck up behind me and yelled "Boo" on a windly take-off.

for my money this is a difficult kit to build. Lots of balsa crushing and poor fitting parts, but it's really worth the effort the first time you hear those three motors wind up or make a low pass.
Walt
PS don't use Lustre-cote on the plastic or the canopy. makes for a curly mess. I know from personal experience.

Geoff_Gino
10-31-2006, 02:42 PM
Hi Walt

Thanks for that tip. I have as you can see added 'corrugation' and will be painting the fuse with acrylic paint after the sanding sealer coat.

Do you by any chance remember what your current draw was.

Walt Thyng
11-01-2006, 11:32 PM
Sorry, but there's been about 20 airplanes in between and I lost my log book when I moved.
Walt

Geoff_Gino
11-03-2006, 12:06 PM
Well here she is - nearly ready for the maiden.

vampire67
11-09-2006, 07:43 AM
Well here she is - nearly ready for the maiden.
For maiden chose a runway with extreme short grass.
I can only fly it after the greenkeeper has just finished :rolleyes:.
Otherwise the props will do the job and the plane has difficulty getting speed.

Also be carefull with the nose down attitude on the ground. Have bend the gears about 1cm to the front to get a little less problems.
Still critical on grass.

Also a good advice to not use the rubber prop adapter of the guenter props. Had a chrash as one came loose just on take off by the right wing getting airborne earlier than the left. Left prop got cought in the grass and teared off.
Result was a vertikal wheely, fortunely just broken off nose and disassembled tail stab.

regards Peter

Geoff_Gino
11-09-2006, 08:37 AM
Hi Peter

Fortunately we have a blacktop runway and I don't forsee a problem there.

Could please let me know how your CG worked out. I have mine at the 75mm suggested and there seems to be no problem with the nose over.

The plane is well balanced at 75mm but I am just a little scared about it being tail heavy.

Thanks

vampire67
11-09-2006, 08:26 PM
I'm using the 75mm CG according instructions to and also have no problems flying.
However on grass I get a heavy nose over attitude.
I need ~15mm elevator throw to keep her in the ground.
Moreover I need to push the plane with my feet the first few inches to overcome the initial resistance of the grass.
I need to keep the elevator active during acceleration.
Once she just get airborn she almost jumps to the sky and I need to release the elevator rather quickly.

kind regards Peter

up_ya_go
11-09-2006, 10:21 PM
Good luck Geoff ... the weekend is getting nearer !!! Hope the WX is good for the maiden . If she goes as well as she looks in the photos ... will be great!
Cheers Ray
________________
OK here we go

Geoff_Gino
11-10-2006, 05:31 AM
Thanks Peter. Sounds much like my Moth which I am handling with no problems. Glad to hear that the plane seems to be nose heavy at 75mm.

Ray, thanks for those kind words.

vampire67
11-10-2006, 09:03 AM
Glad to hear that the plane seems to be nose heavy at 75mm.
It's actually not nose heavy in flight.
It's just the grass resistance and position of the engines causing a nose over momentum at the ground.
The low wing position may attribute to the poor effect of the aileron on the ground, so I need to keep the aileron fully pulled during takeoff.
It's drastically changing once airborne.

Peter

Geoff_Gino
11-10-2006, 10:12 AM
Peter

Thanks once again. A nose heavy airplane I can handle, but tail heavy is totally different.

Let you know on Monday how it went.

Geoff_Gino
11-13-2006, 05:54 AM
Hi Peter

Well – that was the single most disappointing moment in my life.

Taxied up and down the runway twice and got the feel of the rudder and had her tracking nice and straight and ready for take-off.

Ran nicely down the runway, rear wheel lifted nicely and started to rise off by herself. By this time was approaching the end of the runway and the moment I touched the elevator it all turned to 'crap'.

Tail heavy like you won’t believe with the usual stall and consequent crunch into the ground.

Going to be rethinking my understanding of CG as given by model makers. Have yet to find a single one that has the CG where recommended.

Ah well back to the drawing board. L

vampire67
11-13-2006, 09:26 PM
Hi Geoff,

Sorry to hear this, but the plane here just flies with the CoG according plan.
So you may have to search for the reason of the different behaviour.
Possibly the wing or stab angle of attack got wrong. This is an ancient wood kit and requires carefull check of the geometry.
Last but not least there are the landig flap adjustments (middle section).
The split flaps have very strong effect. They have to be precisely parallel to the wing lower surface.

kid regards Peter

Geoff_Gino
11-14-2006, 05:39 AM
Peter

You may be right, but from the way it rose off there was no sign of anything that was not straight. The rear of the plane came up nicely, was positive on the rudder and the wing was completely level. During the build I had the measurements to within a mm of what the plans said and spent 3 nights on the CG using rubber tipped pencils. It was exactly at 75mm.

The moment I touched the elevator it started to crash. The tail went straight down and with not enough power would not get to flying speed due to the high angle of attack.

Flaps and ailerons were also exact, made sure of that with a template I made up.

Anyway as I said back to drawing board and perhaps I'll have the CG right next time.

Thanks for your input.

vampire67
11-14-2006, 08:50 AM
Peter
The moment I touched the elevator it started to crash. The tail went straight down and with not enough power would not get to flying speed due to the high angle of attack.

Doesn't sound like CoG but aileron throw.
I will measure mine and give some detailes later ...

Peter

Geoff_Gino
11-14-2006, 02:08 PM
Peter

All my planes are set up with 60% exponential and my max elevator throw is set to 10 mm and low to 6mm.
Needless to say I was still on low rates.

What I did NOT do was to check the CG with the plane inverted.

up_ya_go
11-14-2006, 10:30 PM
......."By this time was approaching the end of the runway and the moment I touched the elevator it all turned to 'crap'."......

What a bugger Geoff.... :( .... really disappointed for you that happened . Gee ... as you went to so much care with that C of G makes one wonder just what eh? ( hardware / servo / etc ???? ) Anyway mate ... sure it will be better with the next one.
Cheers Ray
______________________
OK here we go

vampire67
11-15-2006, 07:55 AM
All my planes are set up with 60% exponential and my max elevator throw is set to 10 mm and low to 6mm.
Needless to say I was still on low rates.

What I did NOT do was to check the CG with the plane inverted.
I checked my throws: +/-10mm/40%expo on low, 15mm/60%expo on high rate. So pretty much the same as you had.
Start is usually on high rate.

My CoG is also not checked inverted.
It's at 75mm as precise as it's possibel to check.
If you check CoG inverted it will be less sensitive. You can move the CoG by a few mm fore and aft without realy seeing it.
The problem of this low wing crafts is that the battery and CoG is rather high and the plane develops a momentum depending wether nose is up or down.

However CoG would not being the sole cause and you may have to do a little more investigation on the cause.
As reported my has an odd behaviour on take off too. I need all aileron throw during roll and once it's aiborne I need to neutralise the aileron rather quickly. Else I expect also to get trouble as the power is not very high and high AoA are impossible.
It currently has around 20 flights on the counter.

I know how it sucks to ditch a plane. My Ju52 also chrashed on one take off due to one prop being teared off. Luckily turned out repairable.
Does yours seem repairable or is everthing turned to splinters ?

kind regards Peter

Geoff_Gino
11-15-2006, 08:45 AM
Pretty much splinters Peter. Thing is I am so disgusted that I've lost interest at the moment. All the plastic bits are damaged and the cockpit is pretty much destroyed.

I know for a fact that I did not differ in my take off in any way and I am used to just giving a little elevator and then releasing immediately. Also I did not have the nose over problem you seem to have with yours.

With the centre prop in a vertical position and touching the floor the plane would immediately come back down onto it's tail wheel when released.

I am convinced that tail heavy is what my problem was. I say that because of the sudden way the tail went down and stayed down, even after I had released the elevator.