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Fresh breeze Sportix VS. Kobra Rocco super


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Gary, a brand new completely non-porous dry wing can be stalled by a very moderately powered motor if the power is mishandled (unsynchronised pitch and power handling). A powerful machine will do it without mishandling.

As Pete and co say above it is all about not unloading the wing. My clip in weight is typically 100kg in my usual set up. Lets say this 110kg thrust machine weighed 5kg more so my clip in is now 105kg. Assuming a modest 5:1 L/D and a 5kg wing weight I need 22kg of thrust for level flight. Double that figure to 50ish kg (like most standard paramotors currently sold) and I climb very well thank you. The important point is that there is a very safe balance of climb rate/ angle of attack/ loading of the wing. Double that figure again to full throttle and my thrust to weight ratio has gone above 1 and as Colin says in theory you wouldn't need the wing any more. Problem is that before you get to that steady state (it wouldn't actually be steady because of torque, etc) you would have pushed yourself a monumental distance forward of the wing and rotated the whole unit backwards. Angle of attack will increase, drag would initially reduce before then increasing rapidly (back side of the drag curve) and wing loading would reduce as more pilot weight becomes supported by engine thrust vertical component rather than being borne by the wing.

If the power is applied gradually then gyroscopic precession is not going to be a big issue however flying at such high angles of attack would give huge levels of asymetric blade thrust, possibly enough to induce riser twist without even looking at the effect of engine torque.

Please, please don't try it.

Forgetting the engine/prop extra issues there will come a point where the wing will lose loading, pressure and upper surface airflow and will stop working.

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OK OK I wont try it......I will try it on a radio control model .......I understand your explanation of what in theory should happen but I am still of the opinion it will just drag/fly along behind you in a mushed state ......untill I see a video or pictures to the contrary ......my opinion remains unchanged.....

(What is needed is some Russian input) as I am sure they have already tried it :lol:

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hmmmm difference of opinion here/there.......can you stall a paraglider wing i( none porus ) ie in good condition with engine power alone.......I dont think ! you can

it will just settle in a climb come pull not a very efficient way to fly I know but if you dont touch the brakes or use momentum from a previous manover it wont stall.......this is what I was told by

Noel humphreys ex Paramotor instructor & freeflight instructor and ex UK paramotor Team member....... and the First Uk Pap dealer (now thats some CV ) of course if you use a high hang point you might get riser twist......or get a very bad torque reaction

(high and low hang points )

Hi Gary.

I can see what you are saying is correct ie loads of power will always provide airspeed over the wing despite increased angle of attack (AOA) however this may or may not be the same for our floppy aerofoil. For example you can see a large passanger airliner (jumbo jet) climb out at incredible high angle without stalling as long as the power from the engines exceed all the other forces trying to slow the aircraft down pushing the aircraft along providing sufficient airspeed over the aerofoil (wing) regardless of AOA.

With our less efficient flying machines with high profile and enduced drag coupled with narrow speed range this theory may or may not work. The speed range of a paramotor wing from stall to best climb to max speed is very narrow compared to a solid aerofoil. When the paramotor wing reaches its max airspeed and power / thrust continues to increase the wing will be unable to keep up with the power unit creating increased AOA. But imagine if this was to continue and the power was sufficient (weesplat on everest machine) the wing may continue flying but maybe in a loop the loop fashion. :acro:

Or could it climb vertically? Could it be possible to maintain a verticle climb, if flying fast enough to maintain enough airspeed over the wing why not?

Actually I think Gary might be right, however massive thrust would be required.

We need input from our Guru Norman.

Food for thought.

Whitters.

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Just adding a little more Simon:

Cavitation on the upper surface = stall = loss of internal pressure = collapse = not good.

Alan

But cavitation etc on the upper surface would only occur if the airspeed / pressure over the upper surface was reduced to the point where the wing would stall.

What I believe Gary is saying is if the thrust were sufficient to push the wing through the air fast enough to maintaing enough airspeed / pressure over the wing regardless of AOA the wing wouldn't stall. Think big, more than 110kg thrust.

:acro:

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You can tell we're all snowed in ! LOL I'm sure it is possible to stall a wing with masses of power. You might get riser twists first or torque steered into an upward spiral.

One of the things that gives it away is the power landing. You apply a little brake and then some power to increase the AOA thereby increasing the brake authority because it's nearer to the stall point.

I guess a light chap on a big wing with lots of power will stall first. Fat one on a smaller wing with lots of power looks like this. The full power climb starts at 1-30 and ends at 2-20.

[youtubevideo]

[/youtubevideo]

That was nil wind...nil thermal. Level flight would've took me across 2 fields in that time. 50 secs only took me across one field there. The rest was up 400 ft +. It feels steep. I wouldn't lean right back. Will try to get some footage of the angle of the risers next time.

Is there a formula for working out what max thrust a pilot could cope with before the risk of a power stall ? I'd quite like to know how close I'm getting :roll:

Dave

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..... if the thrust were sufficient to push the wing through the air fast enough to maintaing enough airspeed / pressure over the wing regardless of AOA the wing wouldn't stall. Think big, more than 110kg thrust.

Fine if the thrust is in line with the wing, but it's not.

The thrust is at the bottom of a large pivotal 'assembly' and as the angle increases the vector of thrust acting on the wing reduces.

Cheers,

Alan

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We have 2 methods for pitch control on our machines. Fine control is achieved through symetrical brake application/removal while crude control is achieved by addition/reduction in thrust due to the massive lever arm this possesses to a degree that is not seen in any other form of aviation. Massive levels of dynamic thrust allow our already crude power controlled pitch authority to become dangerously so if mishandled (without even considering the other issues). Airfoils stall at a defined angle of attack. The speed that this stalling angle is achieved at is variable based on load factor at that time.

edit - just seen Pete's reply. hadn't seen those pages but they look like a great place to start.

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But cavitation etc on the upper surface would only occur if the airspeed / pressure over the upper surface was reduced to the point where the wing would stall...

Whitters, are you sure you're happy with this line of thinking?

Lateral thinking fanman.

You are missing the point. I am not talking about what generates lift (Bernoulli effect). Can you seperate the Bernoulli effect Vs what keeps a wing from stalling. Are these one and the same?

Different type of aerofoils have different limitations and have changed over the years. What is the limitation of a soft wing like ours?

Aerofoil_types.gif.04ef19e17546d7751790b

Aerofoil_types.gif.c97e46f9b2b54862a41b4

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OMG... some of the page 2 comments show some scary lack of understanding of what keeps us up. :shock:

Fan man I totally agree with you I think a few on here need to brush up on how a wing creates lift

pmcflight.php

Pete: Trying to think beyond basic principles of flight. :wink:

Creating discusion and debate is healthy.

Insulting others knowledge because they are introducing other ideas / thoughts is not :roll:

:?:

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OMG... some of the page 2 comments show some scary lack of understanding of what keeps us up. :shock:

Fan man I totally agree with you I think a few on here need to brush up on how a wing creates lift

pmcflight.php

Pete: Describe why a paramotor type wing can not climb vertically.

Think still air, unlimited power (exceeds all forces, drag gravity etc) and an aerofoil that generates enough lift to maintain enough loading between pilot and wing regardless of atitude (angle relative to gravity). And consider that because of the Bernoulli effect verticle climb would mean the pilot is not in a horizontal position relative to the wing.

Then with this setup, imagine increasing the power beyond the verticle climb, remember the Bernoulli effect keeps the wing loaded between pilot and wing and the power available exceeds all forces including gravity.

The angle between thrust line and the wings flight direction would have to be maintained / controlled to keep the wing loaded which is probably where this theory fails. Pete Searle (Lemmings fame) experimented with a small wing under the seat that when pitch was altered the loading on the wing changed. Perhaps introducing more control surface gadgets like this could make a fully aerobatic paramotor possible.

Remember ladies, only food for thought. :D

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Can anyone post up a video of a power stall? I've watch loads but not seen one yet. I'll put the nearest one up if I can find it

D

Not sure if you are just asking this to get me to post a Dell S clip again :lol:

This clip includes a whole series of forced stalls, but what I think you were after is at ~30sec

[youtubevideo]

[/youtubevideo]

Cheers,

Andy

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OMG... some of the page 2 comments show some scary lack of understanding of what keeps us up. :shock:

Fan man I totally agree with you I think a few on here need to brush up on how a wing creates lift

pmcflight.php

Pete: Describe why a paramotor type wing can not climb vertically.

Think still air, unlimited power (exceeds all forces, drag gravity etc) and an aerofoil that generates enough lift to maintain enough loading between pilot and wing regardless of atitude (angle relative to gravity). And consider that because of the Bernoulli effect verticle climb would mean the pilot is not in a horizontal position relative to the wing.

Then with this setup, imagine increasing the power beyond the verticle climb, remember the Bernoulli effect keeps the wing loaded between pilot and wing and the power available exceeds all forces including gravity.

The angle between thrust line and the wings flight direction would have to be maintained / controlled to keep the wing loaded which is probably where this theory fails. Pete Searle (Lemmings fame) experimented with a small wing under the seat that when pitch was altered the loading on the wing changed. Perhaps introducing more control surface gadgets like this could make a fully aerobatic paramotor possible.

Remember ladies, only food for thought. :D

In theory it should work in practise it would not.

To keep the wing flying you need to keep it loaded the only way you would do this (other than with gravity ) would be to have the wing lets on your motor so as they would cause the the motor to be forced away from the wing causing the wing to be loaded, if you can understand the way I explained it

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Like I said before we need some Russian input on this one.......

how about this one then,,,,, if I fly my microlight at full power and push the wing forward (not a whip stall ) ie I carry no momentum from a previous dive /ect

the wing continues to fly in a mushed state ie it is spilling air ......the steering is no good and I have to balance it against the power as it is reluctant to stay in this mode of flight ....but it will continue to fly in effect I am dragging the wing......

.I know this happens because I do it....... :shock:

I am sure the paraglider will go into a kind of deep stall and you will just drag it thought the air

where is a Russian when you need one :lol:

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Thanks Andy, but we are discussing power induced stalls, not deliberate stalling induced by the brakes. I found this one which is the left side stalling. He might have had some left brake applied to climb straight though.

[youtubevideo]

[/youtubevideo]

D

Its a strange one that. Shame you can't see more of the wing.

The motor torque / presession http://en.wikipedia.org/wiki/Precession

is turning the motor to the right and as the left wing stops flying you can see the trailing edge come into view which appears not to have any brake input but more a e reflex shape. I think he had a knot in one of his D risers deforming his wing and desturbing the airflow creating a stall.

This very same thing took me out of the sky in 2006. Unfortunately not until I had gained 800ft AGL. :shock:

Any more theorys?

Whitters.

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Like I said before we need some Russian input on this one.......

how about this one then,,,,, if I fly my microlight at full power and push the wing forward (not a whip stall ) ie I carry no momentum from a previous dive /ect

the wing continues to fly in a mushed state ie it is spilling air ......the steering is no good and I have to balance it against the power as it is reluctant to stay in this mode of flight ....but it will continue to fly in effect I am dragging the wing......

.I know this happens because I do it....... :shock:

I am sure the paraglider will go into a kind of deep stall and you will just drag it thought the air

where is a Russian when you need one :lol:

I think this happens to your microlite Gary due to what the hangliding people call washout (I think its called that). Its where the wing tips (on a delta wing) rotate as the angle of attack (AOA) increases. (Not to be confused with washout / turbulance created off the wing tips by the difference in speed of air either side of the aerofoil). In your description Gary I think the root cord section of the delta wing (nose to trailing edge and a few feet either side) have stalled however both wing tips have rotated decreasing the AOA at both wing tips and are still flying. Due to dihedral shape / effect the wing and the washout it remains level. Higher performing delta wings are less forgiving.

I have a solar wings typhoon hanglider that has lots of washout and dihedral allowing you to push the bar out to the stall, the glider goes heavy and mushy, sink rate increases but due to the washout at the wing tips it still flys. However push too fat and it will stall however the speedbar (controll bar) is very heavy trying to force itself back to get the airspeed up again. Its a very stable glider and the worse thing you can do to it is clip a pilot into it because it flys better on its own or with a sack of potatoes strapped in.

When I fell out of the sky as mentioned above I sent the wing to the loft for inspection. Before I found out the cause (knotted shortened D lines) poor pre flight and post take off checks. I asked Mike and Pascal C J's ref possible causes. Pascal described that it is possible to launch a paramotor wing in a semi stalled state where it is hanging behind and can remain like this until pilot input ie pull on the A risers to get the wing flying or try and turn which would probably create a stall similar to the clip above.

All interesting stuff eh.

Whitters.

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