STO, and fast cruise

[bones]

Ok i was thinking about the fact that you seem to need to pick a short take off, or a fast cruise speed, so it got me thinking.

 

Now for a STO you need a big cambered wing with a fair amount of pitch, a fast cruise you need a low cambered wing with low pitch.

 

So why cant you have a low cambered wing, but here is the real question, why not have the whole wing assembly to be pitch adjustable, so with the low cambered wing, with heaps of pitch to get off quick then slowly remove the pitch of the whole wing assembly, to get your fast cruise.

 

So obviously i have not yet researched the legalities of this, as they very may well be a ruling that the pitch must not be adjustable or such.

 

But if not is there any reason why this would not work, it just seems too easy, so if it was this wasy i would thing one of the manufactorers would have already done it??

 

 

[Guest GraemeM]

Or you could go the swing wing way, seems to have been working ok for a wile now.

[facthunter]

If you are talking rigger's angle of incidence ( which I assume you are) changing it will mainly affect the fuselage attitude in flight. The wing works the same.

 

For a wing to lift at low speed , it needs lift devices like slats/slots for the Leading edge and efective trailing edge flaps,( slotted or fowler) or have "blown" wings. Other wise it will have a lot of area and a thick wing section, all of which mitigate against fast cuising. Nev

 

 

[rgmwa]

Modern airliner wings would be the way to go.

 

 

[facthunter]

The type of aircraft that we are able to operate, being light, simple, and price sensitive, don't really lend themselves to having a high speed range of flight.

 

The earlier draggy ones climb descend and cruise at almost the same speed (55 knots). Nev

 

 

[bones]

If you are talking rigger's angle of incidence ( which I assume you are) changing it will mainly affect the fuselage attitude in flight. The wing works the same.Nev

Ok so there is something i had not thought of, and didnt realise.

 

Just to clear what i was talking about in very loose terms, would be like a helicopter blade, the ability to change the pitch of the wing, heap of pitch for T/O, using the hp for climb, then after reduce pitch(climb ability) and turn the hp into forward speed.

 

Is this possible.

 

i have a vage idea of how to do it simply, the biggest unknown is would it work, in theory it should(well in my head anyway )

 

For a wing to lift at low speed , it needs lift devices like slats/slots for the Leading edge and efective trailing edge flaps,( slotted or fowler) or have "blown" wings. Other wise it will have a lot of area and a thick wing section, all of which mitigate against fast cuising

But is this only the case because the wing is fixed in position?

If the pitch of the wing was increased by say(ball park figure here) 10* it would lift earlier? would it or not? or would it just stall the whole wing out?

 

Increasing the pitch on the wing to me would be similar to the modern Air Liner wing, as this is what it looks like it does, i sat beside one the other day hense my asking this question.

 

 

[bones]

The type of aircraft that we are able to operate, being light, simple, and price sensitive, don't really lend themselves to having a high speed range of flight.The earlier draggy ones climb descend and cruise at almost the same speed (55 knots). Nev

If this would work the difference in weight,price, and complexity would be minute, if this would work, just that it has been many years since i have had my head in FW world, and i dont have any actual experience with what i am talking(asking) about.

I am thinknig it wouldnt work other wise the manufactorers would have been all over it by now, as my idea of how to do it is so simple its rediculis.

 

Need to thinking about stuff while im flying i think

 

 

[David Isaac]

Changing the wing profile in flight would definitely change the lift, drag and speed characteristics even without altering the angle of attack. It could no doubt be done with clever engineering, but I would suggest the complexity of the mechanisms and the increased weight from the mechanisms and the increased weight required to strengthen the wing so it could have a profile adjustment would negate the benefit.

 

I doubt you could do it with the current RAA weight limitations. I doubt it is economical otherwise it would have done.

 

They have done all sorts of other things like slots, slats, inverted flap systems (Maule), and even blown' the wings as Nev mentioned. Even leading edge slats add weight and if they are automatic (Rallye) they add more weight.

 

 

[Old Koreelah]

Your musings are interesting, Bones. Plenty of designers have pondered the same issues. Many aircraft have an adjustable tailplane (as well as a movable elevator) to allow what you are talking about. Lowering the angle of incidence of the tailplane a few degrees allows the wing AoAttack to increase a few degrees. But. The mechanism required has to be dead reliable, it adds weight (not a big issue with heavy transports, where economies of scale apply) and also increases the workload on the pilot. I once forgot to retract my air brake when I had to do a go-around, and couldn't understand why she was climbing so slowly. Add turbulance, a heavy load or engine issues and you could be in a pickle.

 

Some small planes, such as most of the Jodels, have an all-flying tailplane which seems to allow a much bigger range of wing AoA.

 

 

[facthunter]

You achieve the same thing by pulling the stick back and reefing it off at just above the stall speed. This is not recommended as there is too much drag and not much margin above stall for manoeuvering and gusts etc. If STOL performance could be had that easily everyone would do it that way. You get what you pay for. A fast plane is a dog to get in the air. Example GBee racer and similar. Schneider Cup seaplanes. etc.

 

Quick off the ground, Personalised Cub with big motor and flaps. Fiesler Storch, Westland Wyvern etc, but slow cruise. Nev

 

 

[bones]

Thanks all, as i thought way too easy to be true, ohhh well on to my next brain storm then

 

Seriously though thanks to all who replied.

 

 

[facthunter]

Don't lose your enthusiasm . It's precious.

 

Actually I am going to say something here. I believe an engine driving a centrifugal compressor and feeding slightly compressed air into a plenum and exitting it at controlled ports can provide thrust and boundary layer control as well . There would be no propeller to walk into and the engine could be near the centre of gravity giving good vision and manoeuverability. (and it wouldn't cost much either).. Similar things have been done...Nev

 

 

[Guest Crezzi]

Changing the wing profile in flight would definitely change the lift, drag and speed characteristics even without altering the angle of attack. It could no doubt be done with clever engineering, but I would suggest the complexity of the mechanisms and the increased weight from the mechanisms and the increased weight required to strengthen the wing so it could have a profile adjustment would negate the benefit.I doubt you could do it with the current RAA weight limitations. I doubt it is economical otherwise it would have done.

This is actually how the trim system operates on a great many weightshift trikes

 

I'm sure your observations are quite correct for fixed wing aircraft though!

 

Cheers

 

John

 

 

[Guernsey]

Don't have any of those problems with my 'Flying Cow'.

 

Short take off is achieved by increasing the wing flapping speed. slow approaches achieved with high angle of wing incidence and more flapping giving a stall of only 5 knots.

 

High speed cruising achieved with ears folded back, all four undercarriage legs sloped backwards, tail kept out straight and mouth open to act as ram-jet with high propulsion methane after burners.

 

Maximum cruise not specified as I wish to keep it as RaaUs registered, however it really Mooooooooves.

 

Alan.

 

 

[drifter45]

Steve Wittman solved the problem in 1938 and Boeing etc are using it now.

 

http://www.luceair.com/

 

This critter has a MTOW of 1320lbs (600kg) as well.

 

cheers John

 

 

[David Isaac]

Steve Wittman solved the problem in 1938 and Boeing etc are using it now.http://www.luceair.com/

This critter has a MTOW of 1320lbs (600kg) as well.

 

cheers John

Looks very interesting John,

I reckon just looking at the plans would be enlightening in itself, I would love to see how those wing mechanisms work and all below 600Kg. 30 to 150 MPH is a hell of a speed envelope.

 

 

[drifter45]

Yes David, Wittman was a bit of a genius all right. Dave Thatcher uses his wing tip design on the CX4 and that cruises at 110kts on 65hp. The Buttercup would be a good project except it might be a long one.

 

John

 

 

[Yenn]

Some of the old aircraft had control of wing geometry by way of slats and slots, modern aircraft have flaps to do the same thing. The pitch as you call it I assume is angle of attack and that is controlled hy the elevator and horizontal stabiliser. These can be made adjustable in flight, as was done by the Lysander, so there is plenty of experience, but modern aircraft are usuallu configured to comply with most pilots needs. If you have real good STOL performance, you are not going to get very high speeds without very complex mechanisms.

 

 

[sain]

rather than stuffing about with the wing, why not use a in-flight adjustable prop?

 

You could also look at using devices that improve your wing's performance near the stall, such as leading edge slats and vortex generators. Both have a slight negative impact on cruise speed, but can (if done correctly) significantly reduce stall speed and low end performance. To reduce the cruise speed impact there are devices that allow you to extend and retract the leading edge slats. Wouldn't be hard to do the same for vortex generators, although probably not worth the effort. Pegastol used to make retractable leading edge wings for the CH701, but I think they went out of business.

 

 

[sain]

Oh, I forgot to mentiont that the reason why Hornets, CH701s and Savannahs are all only-their-owner-could-love-them ugly is because they are built to be draggy as all hell so they'll slow down fast. This allows them a steeper approach angle and shorter run-out on landing.

 

If your just after Short Take Off performance you can do away with a lot of that and go for a lower drag fuselage.

 

Take a look at some of the really small single seat low wing aircraft (hummelbird, CriCri etc etc). Take off distance can be suprisingly short, given they are not designed specifically for it. Cruise speed is pretty decent on those as well. Its amazing how fast you can get off the deck with a decent power-to-weight ratio.

 

 

[Guest Andys@coffs]

Actually if I understand what Bones is asking NASA did research on this some time ago for military aircraft I believe it was called MAWS for Mission Adaptive Wing System. Fundamentally it change the wing profile (not just its chordline) depending on what part of the mission timeline/profile called for, for example take off close to or at MTOW and the wing profile maximised lift at the expense of speed so that useful reductions in airfield length and quality was achievable and then later in the flight the profile changed again to provide high speed low drag cruise etc.

 

If you google +NASA +"Mission Adaptive Wing" there will be plenty to see. In the first iterations they expect to see flaps and leading edge slats incorporated in the design in such a way athat they can be called on, and the wing surface skin is unbroken, but ultimately the entire wing profile is up for inflight change.......Now when that trickles down to RAA style limitations...maybe my kids, or their kids, unlikely in my lifetime due to current materiel limitations and an aircraft regulatory regeme in Australia that makes conservatives look down right radical

 

Andy

 

 

[Guest Maj Millard]

 

The thinking is not too bad Bones, but just impractable to engineer, when really the same wing adjustment is easily achieved by simply pulling back on the stick. Most wing airfoils only operate in a small aoa area any way, generally in the region of say 2deg to 12-14 deg. The problem with pulling the stick back, is that is it is only temporary, for as you raise the aoa you create big drag, and pretty soon you've got to push the stick foward again.

 

So you need a clean wing for a fast cruise, and then lift producing devices such as large flaps, LE slats or VGs that come into play as you raise the aoa of the wing (pull back on the stick), to slow right down. This is very well demonstrated on say a Storch where the difference between a clean wing, and one with huge flaps out and the LE slats working, is very noticable both in speed and feel of the wing.

 

When using these hi-lift producing devices, you actually are changing both the camber, and aspect ratio of the wing, by altering the airfoil, chord, and often also effective wing area. So really it's two different wings in one, just by altering /deploying a few things.

 

One recreational aircraft that achieves the best of both worlds is the VG equipped Savanah. The relativly short clean wing achieves a pretty respectable cruise speed with the small fixed VGs creating only a minsicule amount of drag in cruise mode. However deploy some flap (full span incorporating the ailerons, ala Caribou) and the wing achieves pretty spectacular low-speed capabilities with the VGs now coming into play as the aoa increases, to keep airflow firmly attached to the top of the wing. It all works very well, and is safe, and predictable. A great easily achieved compromise, to achieve two totally different flight profiles...........................................................Maj...

 

 

 

 

[David Isaac]

Oh, I forgot to mentiont that the reason why Hornets, CH701s and Savannahs are all only-their-owner-could-love-them ugly is because they are built to be draggy as all hell so they'll slow down fast. This allows them a steeper approach angle and shorter run-out on landing.If your just after Short Take Off performance you can do away with a lot of that and go for a lower drag fuselage.

Take a look at some of the really small single seat low wing aircraft (hummelbird, CriCri etc etc). Take off distance can be suprisingly short, given they are not designed specifically for it. Cruise speed is pretty decent on those as well. Its amazing how fast you can get off the deck with a decent power-to-weight ratio.

Not quite that simple Sain,

Removing the draggy bits off a Hornet, or Savannah, wont make it go any faster. Most of the ugliness that you refer to is built in for strength because STOL aircraft typically land in rugged country and land on surfaces that would destroy a Jabiru, Tectnam etc.

 

The maximum speed of a STOL aircraft is limited by a combination of drag and loading; of far more importance is the loading at speed. What many don't realise is that a high lift low speed wing suffers much higher loads at speed than a low lift high speed wing. Most of the STOL RAA aircraft due to impractical weight limitations cannot build in enough strength to allow cruise speed more than 90 to 95 knots, but these same aircraft can safely do a landing approach at 40 knots or less under a properly controlled short field technique.

 

Adding power will certainly decrease takeoff distance simply from the aspect of greater acceleration. Higher power will allow you to overcome the drag at low speed to have a very impressive climb rate, but it will NOT increase your cruise speed without exceeding the load limitations of the wing.

 

Yanking the stick back on any aircraft to take off earlier than normal is a very dangerous technique unless you really know what you are doing. Plenty of people have met their maker doing just that.

 

 

[lark]

Never found that negative flap made all that much difference to cruise speed either.

 

 

[Guest Maj Millard]

Lark, Negative or reflex flap as it is more often called, is one of the easiest free rides in aircraft design. It does work, and works well, and the reason why is well understood. The air as it departs a normal wing wants to follow the downward curve of the wings airfoil (upper surface)....this air is reflected downwards and at cruise speed is simply drag..A reflexed wing (flaps/ailerons) plus some aerofoils that have reflex built in to their standard section, instead reflex the departing air upwards, and back instead of downwards, thus reducing the drag producing effect of the departing air.

 

The sailplane designers are very familiar with this, and some European aircraft have up to 14 degrees of reflex built in.............Maj...