FUNJET ULTRA..

anything to do with foam or depron models
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retiredVTT
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FUNJET ULTRA..

Unread post by retiredVTT » Sun Jul 19, 2015 9:44 am

I have this Funjet Ultra that Chris handed me the other week and so far, between us, we have had four bad launches..!

So I'm searching RCG to have a look at other flyer's attempts to get this thing airborn.

Have a look...

https://www.youtube.com/watch?v=4DB4uUmP-L0

https://www.youtube.com/watch?v=2IkXuXpSj-w

https://www.youtube.com/watch?v=JXY0a5LAvEo

https://www.youtube.com/watch?v=8kgYlvgjGz0

https://www.youtube.com/watch?v=t2pNVBdUusU

https://www.youtube.com/watch?v=8zlWGqwtjlU#t=28

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Re: FUNJET ULTRA..

Unread post by retiredVTT » Tue Jul 21, 2015 10:54 pm

Launching a Funjet.....motor ON, and throw it high at a 30% angle,

https://www.youtube.com/watch?v=4xm9KSpb2ec#t=37


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Re: FUNJET ULTRA..

Unread post by astroflyer » Wed Jul 22, 2015 11:20 am

Two guys in our group been flying them for a couple of years bill. they just throw it with motor off and then fly away. I've never seen any nasty tendency with either of them.

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Re: FUNJET ULTRA..

Unread post by retiredVTT » Wed Jul 22, 2015 2:26 pm

I think I found the problem Al, ...the motor mount has a bottom screw that allows "thrust adjustment". On this one the screw was turned all the way in, so that the top of the prop was pointing toward the nose which was causing the nose to be pushed DOWN...upon launching. Several posts on the RCG thread insist that the thrust angle be "0" degrees with respect to the fuselage.

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Re: FUNJET ULTRA..

Unread post by JohnOSullivan » Wed Jul 22, 2015 6:20 pm

I have very little direct flying experience with pusher deltas (although I have had a few), but if the top of the prop is more forward of the bottom of the prop it is effectively producing UPTHRUST (See sketch). This is resulting in putting a stalled condition on the airplane (and consequent tip stall). A Zero - zero alignment with the wing would be more appropriate.
In my overall assessment of delta pushers in the club, I would suggest that the most realistic cause of problems with deltas is having the Centre of Gravity TOO far back.(what most people refer to as Tail Heavy).
Use a good MAC and CG % calculator and work out the correct CG position ( I find that many manufacturers don't have a clue as to where the CG should be) A good starting point for a delta is about 20% Mean Aerodynamic Chord.
This link should be a good start
http://fwcg.3dzone.dk/
Wings and deltas are a totally different beast from regular aircraft, when it comes to centre of gravity. To compare, I fly my sailplanes at 38 to 40 % Mean Aerodynamic Chord CG and my Free Flight duration models at 80-90% Mean Aerodynamic Chord GG (and in some cases 100% MAC CG). Wing and tailplane incidences are directly related to CG positions. The more forward the CG the more angular difference between wing and tail is required. This makes for a more stable but porposing trim.
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wing Thrust line.jpg
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Re: FUNJET ULTRA..

Unread post by saboo » Wed Jul 22, 2015 10:12 pm

I have a regular FunJet. Launching has been a stressful affair. If the CG is just a little too far back, and by little I mean 3 mm too far back, then you have a nasty beast on your hands.

There may be two small bumps on the bottom of the fuse /wing. The nose must be pointed slightly down when you balance the plane on these points. If in doubt, turn the plane over, and at the same point test the CG. If in doubt move the battery 5 mm forward of where you think it is balanced correctly.

The other thing to be aware of is that Mutiplex recommend that you use 1/3 to 1/2 throttle to launch. Full throttle will bite you.

Secure the battery so it does not shift on launch. Weigh the batteries being used, if you have more than one. Set the CG with the lightest battery and mark the point in the fuse where it goes. I got bitten by changing from a regular 3s2200 to a nanotech of the same 3s2200. The nanotech turned out to be 10g lighter.

Once in the air they are a blast to fly. Faster than a striker, lots of noise. Real pucker factor. Get the CG wrong and you may need even more pucker or a change of shorts.

Re the thrust angle; John O'S is correct. A pusher with the top of the prop leaning forward is up thurst.

Good luck.
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Re: FUNJET ULTRA..

Unread post by retiredVTT » Thu Jul 23, 2015 12:28 am

Here's a good picture of the adjustable motor mount. The bottom screw threads into the mount and butts up against a plastic stop inside so with the two side screws loosened you "jack" the mount by turning the bottom screw until the prop is in alignment with the fuselage, then you tighten the two side screws.

Last weekend the prop was NOT in alignment with the fuselage, because the bottom screw was turned all the way in. Three launches resulted in three trips into the dirt.
I was also having it launched by others with the motor OFF, which apparently did not help.

So this weekend we will try a different style of launch with some power on, and a zero degree alignment.

Bill
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Re: FUNJET ULTRA..

Unread post by saboo » Fri Jul 24, 2015 2:46 pm

Note on the bottom of the mount, there is a small pin and a set of lines on the molded plastic. As you adjust to find the sweet spot, you can keep track of which way the indicator pin has been moved. When you find the one that works for you, a small dry marker note on the fuse bottom makes a good reminder.

I was wrong in the launch throttle for the Ultra. From the manual

"The first flight ...
Do not attempt to hand-glide this model!
The FunJet is designed for hand-launching only - always launch
directly into wind.
If you are a beginner to model flying we strongly recommend
that you ask an experienced model pilot to help you for the
first few flights. The model should be launched at ½ to ¾-
throttle, with the wings level and the nose angled up at an
angle of 20 - 30°.
Don’t launch the model “downhill”, like a glider!"

And the adjustment of the firewall for thrust angle says this

"Fine-tuning
The FunJet ULTRA offers superb flying characteristics which
can be optimised by careful adjustment of the Centre of Gravity
(CG) and motor downthrust. The new design of motor mount
is very helpful here, as it enables you to adjust the downthrust
easily, and the set thrustline can simply be read off on a scale
(plastic bulkhead only).
Start by flying at full-throttle, and trim the model accurately, i.e.
straight and level “hands-off”. If you now switch the motor off,
the aeroplane should make a smooth transition to a steady
glide. If it climbs and slows down, the downthrust is too great
- reduce the downthrust angle. If the model goes into a dive,
the downthrust is insufficient - increase the downthrust slightly
and add a little up-trim before flying again. Repeat this
procedure until the model goes into a smooth descent when
you close the throttle, and responds to an open throttle by
spontaneously flying straight and level, with a slight tendency
to climb.
Fine-tuning the CG: fly straight and level at full-throttle, then
abruptly roll inverted. You will need to apply down-elevator to
maintain level flight, and this should be about 15 - 20% of full
travel. If you need less down-elevator to hold level inverted
flight, the CG is too far rearward; if you need more down-elevator,
it is too far forward. In almost all cases you will be able to
correct the CG by adjusting the position of the flight battery. If
not, add a little ballast to nose or tail as required. If you have to
alter the CG, you will need to re-check the downthrust setting."

So, in the German way of doing things, it is quite detailed. And not trivial.

Good Luck
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Re: FUNJET ULTRA..

Unread post by retiredVTT » Fri Jul 24, 2015 3:57 pm

Thanks Jim, good info considering I did not have the manual..! Guess I should have went for a download of it.

Should be a lot better now with all this new "knowledge"...!

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Re: FUNJET ULTRA..

Unread post by retiredVTT » Sun Jul 26, 2015 1:43 pm

Hurray...! Complete success..! Wow, she's fast with a five cell..!

With the 0 degree motor alignment, and launching with 1/2 throttle, she was a typical "homesick angel" ...away and westward bound; but hey, what a color,,,GREY, against a partly grey sky..!

The motor in it now is a Mega 22/20/2 with a KV around 2800 which back in the day was mostly used tied to a gearbox and spinning a 13 inch prop for thrust. The amp limit on it is an amazing 70 amps which means it just loafs along with a 45 amp draw on a 5 cell pack. The little pack was only an 1800mah 5S, so after three minutes I landed and had 31% left. After some trimming, I had two or three throttle blips just to see how quick it got from one end of the field to the other, and it did not disappoint.

Motor Specs: http://www.topmodelcz.cz/index.php?PHPS ... il&id=8178

Probably a 4S 2200mah would be a better pack, giving more actual flight time. So more experimenting will be done.

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