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By Thumper
#1546554
Have been reading some interesting stuff about them and how they work. I also read they can increase the permissible MAUW of an aircraft. Ha anyone experience of this happening?

Ty
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By Flyin'Dutch'
FLYER Club Member  FLYER Club Member
#1546611
Whether the MAUW is increased once the VGs are installed depends on whether the VG manufacturer has convinced the regulator that this is indeed safe.

MAUW is determined by aeroplane performance and controllability.

Sticking on VGs does change the performance and controllability of an aeroplane, in my experience, positively.

I have operated a Maule with and without VGs and the difference in controllability was remarkable. Roll control was very much better at the approach speeds, and the added elevator gap seal kit made pitch control at idle engine speeds very much better.

The stall speed is supposedly reduced on the Maule by 3-4 mph but that is such a small reduction that I did not particularly notice that (those who have flown with me know that my skills are not such that such speed variations are well within my normal speed variations!)

Every type is different but in my experience they I found them to be very good and do as advertised on the tin - and not just snake oil.
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By Thumper
#1546620
Excellent real life observations there on an aeroplane already known for its STOL.

I wish i could study in depth what determines the MAUW of an aeroplane but did read VG's increased it for twins in America. I'm concluding its one of those things you would conclude why not add them??

Elevator gap sealing is also interesting and wonder why more aircraft don't have this too.
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By Flyin'Dutch'
FLYER Club Member  FLYER Club Member
#1546630
Thumper wrote:I wish i could study in depth what determines the MAUW of an aeroplane but did read VG's increased it for twins in America. I'm concluding its one of those things you would conclude why not add them??


1. They cost some money
2. There is some paperwork hassle involved
3. They are said to reduce speed a bit at the high end
4. Not everyone thinks they work

The increase in MAUW in twins is related to the reduction in minimum speed required to maintain directional control when flying one engine out.
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By Morten
FLYER Club Member  FLYER Club Member
#1546636
Things are never black and white... Even with the extreme conservatism of the aviation industry, if a feature only has positive effects, it would normally be there.

Some thoughts on VGs:
Their primary function is to 're-energise the boundary layer' and an therefore delay flow separation. This should e.g. delay the onset of stall on a wing at high AoA and/or increase effectiveness of control surfaces downstream of the VGs.
However, side effects include that the centre of pressure, especially at high AoA, will move compared to the design range. It can therefore have an impact on the allowable CG range. Another side effect can be that when the VG equipped wing does stall, it does so with different characteristics than without VGs, potentially with less warning and more violence. Another side effect is that, in cruise, the VGs add (potentially significantly) to the friction drag, thereby impacting cruise speed, consumption, range... The forces on the skin where the VGs are attached are small but also possibly not (in magnitude and direction) what the skin was designed to withstand.

On aileron gap filling, if you are concerned about low speed characteristics, then the gaps actually help to keep the airflow attached for longer (by allowing air to bleed from the high pressure area to the low pressure area) and should help the controls stay effective for longer.
Gliders are big on gap fillers, though, but not for low speed handling reasons. Gliders also religiously wash the dead bugs off their sleek laminar aerofoils... something power pilots tend to do less often. Some gliders also have 'negative flaps' for high speed cruise - again something which power pilots might be able to adopt but don't tend to...

Anyway, there's room for both/either/neither. The original aircraft was designed with a set of compromises to cater for a broad spectrum of users - you may well tweak it to your specific use - but most adjustments with a positive effect in one area will have a negative effect in another one.
But do keep in mind that if there is no 'approved' mod and you choose to experiment yourself, you have just become a test pilot ;)

Morten
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By Thumper
#1546642
LAA have a pretty decent form to fill out if you add these to your aeroplane. I am sure it would cost a bit to approve the mod so seems prudent sharing the cost amongst several owners.

I do feel they look a great addition to those two critical areas of flying - slow flying and taking off. Losing a few knots in straight and level would be acceptable for me.
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By MichaelP
FLYER Club Member  FLYER Club Member
#1565796
Vortex generators when they work they can make a bad - potentially unsafe design into a safe one.

The Fantasy Air Allegro had a bad wing drop at the stall... VGs fixed it, and the aeroplane now stalls off the clock and straight ahead.

The Ekolot JG05 is simply dangerous.
I was warned to expect to lose 2,200 feet in a full flap stall... I didn't but the stall was nasty, and one had already spun in in the local area.
VGs solved the problem, like the Allegro the Ekolot stalls benignly when fitted with VGs.
Another Ekolot was not fitted with VGs even though the one I flew proved the safety improvement. The non VG Ekolot spun in... It was replaced with a new one, and VGs were fitted immediately.
Yet another Ekolot was bought by a friend in Canada. The previous owner would not show the purchaser a stall, far too scary.
On my advice VGs were fitted, and the new owner did stall testing and was very happy.

Some LSA designs are sold without proper testing.

The Ekolot gained a reputation for losing its wings... This shortens one's ownership pleasure.
The factory test pilot went up to find out what was happening, and the wings came off for him too, RIP.
Ekolots now have better balanced flaperons.

We tried VGs on a Mustang II, on this aeroplane they did not work, so we took them off.

In my opinion aircraft built as 'Light Sport', Microlight, Ultralight, and VLA, should be docile around the stall, and forgiving. Many are not.
Some are built with retractable undercarriages, variable pitch propellers, and have performance characteristics that really require a lot more training than even a PPL has.
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By Genghis the Engineer
FLYER Club Member  FLYER Club Member
#1565863
VGs will only really increase MTOW insofar as some aeroplanes may have a stall speed limitation but excess strength. So, VGs will allow you to bring the stall speed down, and eat into the structural MTOW a bit. The maths behind that is definitely a task to be undertaken by aeronautical engineering grown-ups.

MichaelP wrote:Vortex generators when they work they can make a bad - potentially unsafe design into a safe one.

Maybe...

The Fantasy Air Allegro had a bad wing drop at the stall... VGs fixed it, and the aeroplane now stalls off the clock and straight ahead.

Probably dropped the stall speed and moved the stall origin much closer to the root.


The Ekolot JG05 is simply dangerous.
I was warned to expect to lose 2,200 feet in a full flap stall... I didn't but the stall was nasty, and one had already spun in in the local area.
VGs solved the problem, like the Allegro the Ekolot stalls benignly when fitted with VGs.
Another Ekolot was not fitted with VGs even though the one I flew proved the safety improvement. The non VG Ekolot spun in... It was replaced with a new one, and VGs were fitted immediately.

I don't know the type, but have flown a Slovak aircraft with similar characteristics - we resolved it with toblerone strips on the inboard leading edge.


Yet another Ekolot was bought by a friend in Canada. The previous owner would not show the purchaser a stall, far too scary.
On my advice VGs were fitted, and the new owner did stall testing and was very happy.

Nobody but a fool, an aeronautical engineer, or a test pilot buys an aeroplane under those conditions. Hopefully from what you say he was the latter.


Some LSA designs are sold without proper testing.

Yes - hence that the UK, Germany and a few other countries insist on proper evaluation of aircraft from overseas. This inevitably leads to bleats from people who don't understand the issues about the air in these foreign countries obviously being different to here.

The Ekolot gained a reputation for losing its wings... This shortens one's ownership pleasure.
The factory test pilot went up to find out what was happening, and the wings came off for him too, RIP.
Ekolots now have better balanced flaperons.

Sounds possibly like somebody who wasn't paying attention to all the safe progression and risk assessment stuff in test pilot school, or wasn't a properly trained test pilot at all.

We tried VGs on a Mustang II, on this aeroplane they did not work, so we took them off.

Define "work" ?

In my opinion aircraft built as 'Light Sport', Microlight, Ultralight, and VLA, should be docile around the stall, and forgiving. Many are not.

Depends upon the role of the aircraft. Nothing wrong with a training aeroplane that bits *a bit* about the stall, or say a racing aeroplane only fit to be flown by a highly experienced pilot. But, everything has its place - something for a recreational PPL yes, it should be pretty docile.


Some are built with retractable undercarriages, variable pitch propellers, and have performance characteristics that really require a lot more training than even a PPL has.

Agreed.

G
By Lefty
FLYER Club Member  FLYER Club Member
#1569498
A friend recently bought a Saratoga that had Vortex Generators fitted by a previous owner.

By direct comparison with another identical (but non VG equipped) Saratoga, my impression is that there is no advantage whatsoever.

I would have expected the VG’s to reduce the speed at which the a/c rotates and consequently reduce the ground roll. But if anything, it seems to need more speed, and a longer ground roll.

I’m told that the a/c docs contain a whole stack of correspondence indicating that (a) independent flight tests proved that the advertised benefits were not being obtained and (b) that the (then) owner tried unsuccessfully to take legal action against both the kit manufacturer and the installer.

My overall conclusion is that they can, sometimes, deliver a benefit, but I would be extremely suspicious of any claims contained in advertising. Before I parted with any money, I would want to witness a flight test on an identical a/c (to mine).
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By MichaelP
FLYER Club Member  FLYER Club Member
#1569950
The Saratoga has a laminar flow wing I believe, as does the Mustang II, perhaps VG's are not effective on this wing section.