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Old Dec 08, 2012, 12:31 PM
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FlyBoy20's Avatar
United Kingdom, Wales, Swansea
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Noob maidens a RadJet

Despite dire noob warnings, I thought as I'd had it couple of months, I'd give the Radjet a whirl on the beach (no trees!). Dead calm day for it, and set the expo really low - so no excuses if I crashed.

I was expecting a strong torque effect on launch, which didn't happen. But what I didn't expect was a belly-flop! Using the out-of-the-box stock set-up and prop (5x3?), it bench tested @ 150 watts, so I thought there'd be plenty of oomph, but with my videoman giving it a decent upward chuck on full throttle - it just sank to the sand after about 30 feet. I guess I should have given it a modicum of up-elevator too?

Worse thing was, even though I'd cut the throttle, I still bent the motor shaft. Also I got sand in the motor - so I had to come home to clean it out and straighten the shaft.

Disappointing, but at least it flew level...I'll try again tomorrow over the park - despite the tree danger!
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Old Dec 08, 2012, 03:57 PM
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I assume this is a rear prop pusher type plane? If it is, try launching it at no more than half throttle and maybe just a tad less. Pusher prop planes tend to dive when at full throttle. That isn't a problem up high, but it makes them hard to hand launch without diving into the ground.
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Old Dec 08, 2012, 04:11 PM
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Were you using the stock power system and prop from the PNF or ARF version? What were the rest of the wattmeter numbers (current and voltage)? It sounds like you need more prop. If you were using the stock prop, stock motor, and recommended gear, then don't prop up. The prop is almost definitely on backwards. Just flip it and try again- things should improve substantially.

Leave the elevons neutral until the plane is on-step and flying. That's another common mistake, trying to use up-elevon on takeoff to somehow make the plane rise. All you'll do is make the situation worse unless the plane has the thrust and speed it needs to fly, and in this case it certainly doesn't.

Quote:
I assume this is a rear prop pusher type plane? If it is, try launching it at no more than half throttle and maybe just a tad less. Pusher prop planes tend to dive when at full throttle. That isn't a problem up high, but it makes them hard to hand launch without diving into the ground.
Launch at full throttle. With planes like the Hawk Sky/EasyStar or others that have the motor mounted high above the model's centerline, this takeoff dive can be a problem. With the RadJet's centerline-mounted motor, though, a diving condition on takeoff is just an indicator that something is wrong somewhere else. I've flown lots and lots of pusher planes of all different types; I can tell you that a centerline-mounted motor will take off and climb out just as straight as you please.

It sounds more like the model just sort of glided out and settled down rather than dove for the ground, which definitely indicates a lack of kick from the prop. I'd say this sounds like a class-A case of a backwards propeller.
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Old Dec 08, 2012, 04:49 PM
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Originally Posted by C₄H₁₀ View Post
Were you using the stock power system and prop from the PNF or ARF version? What were the rest of the wattmeter numbers (current and voltage)? It sounds like you need more prop. If you were using the stock prop, stock motor, and recommended gear, then don't prop up. The prop is almost definitely on backwards. Just flip it and try again- things should improve substantially.

Launch at full throttle. .. I can tell you that a centerline-mounted motor will take off and climb out just as straight as you please.

It sounds more like the model just sort of glided out and settled down rather than dove for the ground, which definitely indicates a lack of kick from the prop. I'd say this sounds like a class-A case of a backwards propeller.
It was the PNF version, and the other numbers were Vp 11.75, Ap 12.69. The launchman indicated a definite pull before he launched, so the prop was not on backwards. It didn't dive for the ground, just sort of glided.

I just fitted a regular APC-copy 6x5 prop (on backwards) and it seems to give more thrust - enough to really rustle the blinds from 10 feet away.

Reading the columns, opinions seem divided about half-throttle launches. I did try at first and it bit the dirt. It was definitely better the 2nd time at full throttle (but maybe there was sand in it by then?). The videos I've seen do suggest trouble-free take-offs at full throttle.

I think I'll give it a go with the bigger prop, though not tomorrow - it'll be raining, I'll have go over the tree-laden park, not the beach next time out. Tuesday looks promising.

BTW should I order some proper pusher props from APC?
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Old Dec 08, 2012, 05:03 PM
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The launchman indicated a definite pull before he launched, so the prop was not on backwards. It didn't dive for the ground, just sort of glided.
A backwards prop will still produce some noticeable thrust, but not nearly as much as it will in the correct orientation. The thrust will still be going the same way, too; reversing the prop does not reverse the direction of the push (another common point of confusion).

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I just fitted a regular APC-copy 6x5 prop (on backwards) and it seems to give more thrust - enough to really rustle the blinds from 10 feet away.
That's propwash, not thrust. They're not even slightly related Before you try with the bigger prop, make sure that the motor's not drawing too much current with it. Stepping from a 5x3 to a 6x5 is a more significant jump than it sounds like. ALSO be absolutely sure that the prop isn't on backwards in the first place- I hate to sound like a broken record, or sound like you don't know what you're doing, but I cannot begin to tell you how many new guys have sat there and said "Yes, yes, yes, the prop's on right"... and it's on wrong.

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BTW should I order some proper pusher props from APC?
Ugh. No... "Pusher" props are the same exact things as "tractor" props. They're just made to spin the opposite direction. In brushless-powered applications, there's literally no difference in performance. Life would be so much simpler if everyone just called them "clockwise" and "counterclockwise" props, but no, instead we use this mindlessly stupid pusher/tractor holdover from the slimers.
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Old Dec 08, 2012, 06:08 PM
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Originally Posted by C₄H₁₀ View Post
A backwards prop will still produce some noticeable thrust, but not nearly as much as it will in the correct orientation. The thrust will still be going the same way, too; reversing the prop does not reverse the direction of the push (another common point of confusion)...That's propwash, not thrust...
Ok, now I'm really confused! First I don't know what sort of prop the plane came with - there are no markings on it. It's 5" long, but whether pusher or tractor, who knows...

The motor is wired to run 'clockwise' (as viewed from the rear of the plane). The prop is on 'backwards', but only as far as the motor is concerned. If viewed from the front it runs CCW - the right direction of rotation for a normal prop? It's just the motor that's pointing backwards, and so two of the wires are swapped to change direction of rotation...I think that's it!

Anyway, as far as I can tell, this replacement TGS 6x5 prop is running in the direction it's supposed to, so when I'm holding the fuse towards me and the blinds in front are rustling like crazy, this propwash/ thrust is trying to strongly drive the nose straight through my abdomen.

The only problem I can see is - since I don't want to break props - the prop saver I bought specially won't work with this orientation because the rear prop's opening is now facing 'forward' so that the inserts just drop out.

Or is SuperGlue the remedy?
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Old Dec 08, 2012, 06:29 PM
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Ok, now I'm really confused! First I don't know what sort of prop the plane came with - there are no markings on it. It's 5" long, but whether pusher or tractor, who knows...
Again, it doesn't matter whether it's a "pusher" or "tractor" prop. The stock prop, if we must do this, would be considered a "tractor" prop with this terminology because it produces thrust in the forward direction when rotating CW as seen from the back of the plane. The fact that the motor is mounted on the plane's back and "pushes" makes no difference. There's no point in worrying about ANY of this, though, because it simply doesn't matter. It all has zero bearing on the plane's performance.

What matters is whether the prop is physically mounted facing the right way. The fact that the plane just glided out and settled to the ground is a dead giveaway that the prop was on backwards. There should be plenty of power with that setup if the prop is mounted correctly.

Quote:
The only problem I can see is - since I don't want to break props - the prop saver I bought specially won't work with this orientation because the rear prop's opening is now facing 'forward' so that the inserts just drop out.

Or is SuperGlue the remedy?
Don't use a prop saver on this plane. Pusher designs generally just don't break props... at all. I've had a few props that have outlasted whole airframes on pusher jets and flying wings. Unless you're planning to land on concrete, gravel, or dried bones, you'll be fine with a solid mount.
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Old Dec 08, 2012, 07:29 PM
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Originally Posted by C₄H₁₀ View Post
..Don't use a prop saver on this plane. Pusher designs generally just don't break props at all...you'll be fine with a solid mount.
Nevertheless, I ended up with a bent motor shaft!
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Old Dec 08, 2012, 07:55 PM
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Originally Posted by C₄H₁₀ View Post
I'd say this sounds like a class-A case of a backwards propeller.
Thats exactly what I thought. To the letter! lol

Also, there should be a "rougher" sound to a reverse mounted prop.

and +1 on the solid props for pushers. As long as you cut the throttle a lil before landing, the prop will settle in the space with least resistance which is horizontal to the ground due to the airframe, parallel to the wings like 99.999998% of the time. At least thats what i have come to understand.
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Old Dec 09, 2012, 01:35 AM
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her is a nice way to know if prop is right
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Old Dec 09, 2012, 01:45 AM
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Maybe it was a poor hand launch?There has been a bit of discussion on launching:http://www.rcgroups.com/forums/showthread.php?t=1738809
"a decent upward chuck " may not be the best technique.Some people never learn how to launch, I have seen people think they need to run several paces, and then launch, of course all they are doing is making themselves look foolish, as the momentum for the launch just comes from their arms, which they could better do standing still.Others just throw the plane upwards, in the belief that the quicker it gets into the sky the better.It is the model that needs the airspeed, not the launcher or even his arms, so a horizontal or even slightly downwards launch at less than full throttle should get a plane away.It may be different with edfs, I don't have any experience with them.
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Old Dec 09, 2012, 02:33 AM
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Originally Posted by FlyBoy20 View Post
Nevertheless, I ended up with a bent motor shaft!
Just for future reference, if you cut the throttle before it lands you will most likely not do any damage, the prop will just flick to one side.

But as stock setup, it should fly just fine, if you dont have the power to hold a level flight it could be like said above prop on backwards or even your battery drops voltage too quick, OR you could just try again, it might have just been something you did.
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Old Dec 09, 2012, 06:20 AM
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Joined Aug 2009
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Fly... Check your lipo is charged, when installed, check CG is close to manufacturers recommended. Check the prop is on correctly and tight, generally the prop ID faces front of plane. Launching, don't try to gain height too quickly, you need some airspeed before you try to climb, so a slightly above level throw from your wing-man should do the trick. It could even be too much expo dialled in, try about 50% and see if your elevon's pick it up a bit more. Anything outside of stock... make sure you are not stressing any of the electrics if you 'prop-up' as you could end up with a short final flight for this model.
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Old Dec 09, 2012, 07:03 AM
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I'd say this sounds like a class-A case of a backwards propeller

I agree 100 %.
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Old Dec 09, 2012, 09:43 AM
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Thanks for all the advice guys. I'm now convinced it was a reverse-prop error - so easy to do with an unmarked stock prop if you're a noob.

Just one thing regarding broken props/bent shafts. Should I set the brake-on or off on the ESC? I did shut down the throttle when I could see it was sinking, but what if the prop was still spinning, and suppose it was to come to a dead stop in the 6 o' clock position?
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