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Measuring thrust angle?

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Tony Kenny15/09/2017 13:43:28
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282 forum posts
62 photos

My phoenix 2000 climbs nose up like a flippin rocket when I throttle up and a knowledgeable chap at the field suggested altering the thrust line down a bit. Easy enough. But, is there a way to actually measure the effect the adjustment has, without driving to the field and chucking the thing in the air?

I'm imagining some sort of frame where the model is suspended and then newton meters on the 4 axis. These, I imagine, would have to be positioned a close to the nose as is safe to do so near the prop so as to measure the actual forces.

Not being an engineer, actually I'm a software engineer, so I'm making this up as I go along, does it sound like it might work to at least put some numbers on the effect of the adjustments before trying them in the air?

What's the plural of axis? axes? or just axis?

john stones 115/09/2017 13:56:56
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10796 forum posts
1481 photos

It's supposed to climb under full throttle, gain height hunt thermals, use the height to do aeros, if you want to fly low n quick, feed down trim in or put a mix on, or hold down on stick. I changed the motor on mine, adjusting the thrust angle isn't easy it's a right faff. Plural of axis is "some axis or choppers"

Stuphedd15/09/2017 14:00:25
674 forum posts
353 photos

I measure my thrust angles with a very simple device ,

I use a spirit level bolted onto the engine instead of a prop , But to measure any angle you need a datum , ! Which in my case tends to be the wing incidence, measure this with and incidence meter , those i phone things have them on lots of free appsl Tilt the fuz till the bubble in the spirit level is centred and read the incidence level .then a bit ob subtraction will give you a figure ,

cheers

Tony Kenny15/09/2017 14:10:43
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282 forum posts
62 photos

Thanks guys,
John, that's makes things easier and it does make sense, I supposed low fast passes weren't on the designers mind which I sometimes do when using it more as a powered plane than a glider

Pete, thanks also, but I'm wondering about measure the 'effect' of the adjustments rather than the 'angle' itself.

Although I won't need it for this model, it will be useful on the old Mirage I'm renovating and about to fit the motor in this weekend without any data regarding the original IC set up it's going to be a case of trial and error (so i have a few spare props on hand!)

Andy4815/09/2017 14:36:47
1414 forum posts
5 photos
Posted by Tony Kenny on 15/09/2017 13:43:28:

What's the plural of axis? axes? or just axis?

 

axes

pronounced axease

Edited By Andy48 on 15/09/2017 14:37:23

KiwiKid15/09/2017 15:16:15
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484 forum posts
474 photos

You might be overthinking this Tony - just whack in a couple of washers and go flying. laugh

One trick you can pull if you have a model that climbs significantly under power is to turn the climb into a spiral which has the effect of reducing the lift created by the wings and will avoid any stall while keeping the model in close proximity.

eflightray15/09/2017 15:22:00
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595 forum posts
128 photos

Generally if a model wants to climb steeply with full throttle, it could be a combination of incidence angle, CG position, or just being flown too fast for the original design, (the faster it goes the greater the lift generated).

Moving the CG back, a bit at a time and test again, can help reduce the 'zoom'. Most models have fixed incidence angle so down thrust is often used as a 'cure-all'.

Good aerobatic models don't deviate too much, (if at all), with throttle, because they are designed not to.

Low or zero incidence, symmetrical wing section, CG fairly well back so that no elevator 'up trim' is required, (up trim is just increasing the incidence angle), and often little in the way of down thrust required.

Everything else is a bit of a compromise.

Broken Prop15/09/2017 15:35:01
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612 forum posts
1 photos

Most motorised gliders climb like a scalded cat under power. This is because the model is set up for gliding with a rearward CG and trims to suit. Thus, opening the throttle does what the throttle is supposed to do: make the model climb, but to an extreme. Either feed in some down elevator to compensate or if you have a tranny with mixers it may have 'throttle/elevator compensation' that you can select on a switch to ease pilot load.

Following on from what KK has said, if the glider climbs quickly under power, it will often stall if the throttle is closed quickly, thus losing 15m or so of hard earned height. A lot of glider guiders have the 'throttle' on a switch and so the power is either on or off, leading to the above problem.

One way to avoid it is to bank the model as the power comes off. The turn bleeds speed off without loss of height and you will find that it settles down into glide mode much more quickly this way.

Pete

Edited By Broken Prop on 15/09/2017 15:44:52

SIMON CRAGG15/09/2017 19:41:06
509 forum posts
15 photos

I run a "One Design" comp for this model in our club. Fifteen models purchased, average turnout about seven. Best bet is to either carry out lots of practice launches and hold in some down, or mix in a bit of down elevator / throttle. All our models are identical, which has led to some fantastic competition!.

ron evans15/09/2017 21:25:45
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401 forum posts
22 photos

I'm with eflightray on this one,

My P2K has the lipo under the wing and bringing the CG back tames the climb under power a lot.

In a dive test the model still pulls out positively, so there is some scope for it to come back a little more.

Ron

G194015/09/2017 21:38:43
3523 forum posts
1 photos

I've had to put weight under the tail plane to get the CoG somewhere near on mine. I have had to replace the motor because the original packed up but the CoG wasn't affected. I used a Turnigy Gliderdrive motor which fits well and has the motor connections on the back which neatly gets round the problem of potential motor suicide when the spinning outer frays the wires.

I use an incidence meter (Robart IIRC) to measure down thrust (or right thrust for that matter). I set the model up with the tail plane level and bolt the meter in place of the prop. To measure side thrust just lay the fuselage on its side and set the fin level. The meter is designed to be used like that. No mods were needed.

Geoff

Stevo16/09/2017 12:47:37
2699 forum posts
419 photos

Careful here.. It looks like thrust angles.

I had an AcroWot foamie, everytime I opened the throttle it went into a violent steep climb. Eventally sussed that the tailplane was 4.5 degrees (yep 4.5) incidence to the wing. After an hour and a scalpel, I got this to 0.5 degree.

Never had the problem again.

Tony Kenny16/09/2017 13:18:51
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282 forum posts
62 photos

Thanks you all, some great replies.

It sounds like the glider is performing as per design and I just need to stop thinking of it as a "powered" model and follow some of this advice. The C of G is spot on, I found out by mistake when I put the battery in half an inch too far back on one flight and it was a handful to keep straight and level. Putting it back where it was and it was stable as ever.

I won't make any changes just yet, first I'll try out some of the suggestions for what to do when I throttle down.

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