Washout on Thruster wings

[Tony]

Hi Guys,

 

I am nearly completing restoration of my Thruster 85SG 'clipped wing' 25'6''.

 

I am looking for answer to the question: How is washout achieved on Thruster wing ?

 

More specifically, is there any structural washout, if yes, what is the value to change the angle of the incidence on the tips.

 

Thanks in advance to your inputs.

 

Tony

 

 

[pudestcon]

Hi Guys,I am nearly completing restoration of my Thruster 85SG 'clipped wing' 25'6''.

I am looking for answer to the question: How is washout achieved on Thruster wing ?

 

More specifically, is there any structural washout, if yes, what is the value to change the angle of the incidence on the tips.

 

Thanks in advance to your inputs.

 

Tony

I'm far from being any sort of a person whose opinion you should value, but to my knowledge there is no washout on Thruster wings.

Certainly, my T500(yes I know its not a 85SG) does not have washout.

 

Pud.

 

 

[Peter G]

My Thruster has washout in it for sure, much like the R/C models I build but as to how many deg it is I would have to measure with my digital incidence meter,

 

Mine is the T83 ELF with 29'6" wing and has flapperons..

 

How it is achieved I would gather in the wing strut lengths, eg the rear strut is longer than the leading edge strut to lift the trailing edge spar upwards giving a - deg washout of the wing tip to increase the low speed stability, about 2deg but can check it for you if you like.

 

Cheers Pete

 

 

[Head in the clouds]

I've looked into this for a couple of different folks. The single seat Thruster has quite a large amount of washout and I've done a bit of research on it to try and find out why because I can't imagine that there's any real reason for it and it seemed to be significantly degrading the performance. Washout is generally needed on tapered wings which have a reasonable degree of taper but designers will avoid the use of geometric washout as far as possible because it's such an efficiency killer. A more efficient form of washout is aerodynamic washout which involves the use of a different airfoil section and/or thickness ratio at the tip, compared with the root section i.e. using a tip section that has a more positive zero lift angle and/or is proportionately thicker than the root section (aerodynamic washout) means that you don't have to physically twist the wing (geometric washout) to get the same effect of having the tips still flying when the root is stalling, and not having the wing twisted is a lot less draggy at any given angle of attack (alpha).

 

Unless there is something very unconventional about their airfoil section or the aircraft's general configuration, rectangular wings will generally stall at the root end first even when the whole wing is set at the same incidence and has the same airfoil section and thickness throughout the span (i.e. no geometric washout) and so experienced designers very rarely use geometric washout on a rectangular wing, and these days most don't use it on a tapered wing either, choosing aerodynamic washout instead.

 

On the T300 (and earlier models) the wings' set incidence is achieved by the front spar being attached well above the boom tube and the rear spar is attached on the boom centreline, this sets the wing root at more than 4* which is a bit higher than is conventional (3* is more commonly seen) and that may have caused the early Thrusters to fly nose down in the cruise, so it is possible that Steve Cohen corrected that tendency by adding more geometric washout. Back in the 1980s most of us used 2-3* of geometric washout even on rectangular wings (so the root was set at 3* and the tip was at 0*), partly as a safety factor for the inexperienced flyers since most of us taught ourselves to fly in our own single seat designs, and partly because we were amateur designers who didn't know better so we erred on the safe side.

 

The washout rigging on the T300s do seem to vary between individual examples, I've seen one with 7* of washout, so the tip is at about 2.5* negative incidence and understandably that machine's glide was breathtakingly bad. I suggested making up a new pair of shorter rear struts to try but the owner was so fed up with the poor glide that he went straight ahead and modified the existing struts, and seemed to be very happy with the handling and improved performance after that.

 

Anyone who does modify their plane should do so with a great deal of thought and careful measurement. It's not something you want to get wrong, and as a disclaimer I'm making it clear that I'm not suggesting that anyone should change their wing rigging themselves. If they know what they're doing and how catastrophic the results of getting it wrong could be then they can make up their own minds ...

 

I don't know much about the T500/600/Sprint washout. The earlier two seat Gemini did have some washout but it wasn't all that much. I tried reducing the washout on a friend's Gemini in around 1986, trying to make it glide better, but it didn't make much difference so I put it back as the factory had it.

 

 

[facthunter]

Your wing tip area will always ( when providing lift), spill air over from the bottom to the top creating vortices (drag) I dispute the no washout concept for this reason, apart from the spinning tendency being increased. On a plane that is designed to fly inverted it is not good for obvious reasons. There are better ways, but a plank wing needs it and I would argue that SOME amount would increase efficiency. ( experiment would find that out). You aim to make the inboard wing stall first and washout helps. Most Light aircraft seem to have it and some quite perceptibly large amounts. Nev

 

 

[Head in the clouds]

Your wing tip area will always ( when providing lift), spill air over from the bottom to the top creating vortices (drag) I dispute the no washout concept for this reason, apart from the spinning tendency being increased. On a plane that is designed to fly inverted it is not good for obvious reasons. There are better ways, but a plank wing needs it and I would argue that SOME amount would increase efficiency. ( experiment would find that out). You aim to make the inboard wing stall first and washout helps. Most Light aircraft seem to have it and some quite perceptibly large amounts. Nev

Ohhh Facty.... Your rather categorical response reflects very dated beliefs, or perhaps you could offer some modern publication to support your statements?

 

A "plank wing" that you mention, among designers refers to an unswept tailless aircraft (flying wing), so for clarity in the discussion I think you mean a rectangular wing, often referred to as a Hershey Bar by our American friends, in recognition of their chocolate bar of similar planform?

 

The "experiment would find that out" that you refer to has, of course, been taking place since 1917 at Langley (NACA) and at the NASA facilities since 1958 and is certainly no mystery, is well understood and fully documented in fact, although many light aircraft designers are still catching up. Your comment "many light aircraft have it etc" is correct but doesn't mean it's the right way to go. Do keep in mind that the 'many light aircraft' you refer to were, for the most part, designed between 1930 and 1950 when many of their designers didn't understand the effects of Reynolds' numbers and so hadn't considered the use of aerodynamic washout or thickness ratio variation, and were using tapered wings of taper ratio greater than 1:7, above which some form of washout is desirable/required (and these days we know that aerodynamic is vastly better than geometric).

 

The drag you refer to from wingtip vortices is a much maligned feature because it is also poorly understood. In the cruise the loss of lift caused by geometric washout and which results in half the wing causing parasitic drag (when it should be causing induced drag instead, due to the lift it should be contributing), and the inboard half of the wing is flying at an inefficiently high alpha and causing unnecessarily high induced drag. The only time that the tip vortex (induced) drag is of any real significance on a light aircraft is when it is flying very slowly, usually in the landing phase, and at that time the extra drag is a benefit rather than a hindrance. Keep in mind we're talking about lightly wing loaded aircraft here, tip vortices on heavy airliners are quite a different matter hence the good reason to fit winglets on an airliner and not much benefit on a lighty.

 

I have the entire set of NACA Reports from the Langley Research Centre 1917 to 1958 on file, all 7640 Reports, Technical Notes and Research Memoranda of every wind tunnel and laboratory test ever conducted, and I can't find anything that supports your view, in fact it's quite clear that a rectangular wing does not need washout (geometric or aerodynamic) to cause it to stall inboard first.

 

I'm certainly no expert on the matter but Karl Bergey is Emeritus Professor of Aerospace Engineering at the University of Oklahoma, and John Thorpe shouldn't need any introduction here. This article from Flying magazine on Rectangular Wings is an interesting discussion between those two experts covering the relative merits of tapered and rectangular wings from both structural and aerodynamic viewpoints and also discusses the tip losses you refer to which happily result in a rectangular wing producing something very close to the 'ideal' elliptical lift distribution which we all strive for. Note that Mr Thorpe's reference to 'a couple of degrees of twist' doesn't, in this case, refer to physical (geometric) twist, the Flying article is a shortened version of a much longer paper where aerodynamic twist was the main subject of discussion, and is suggested to achieve the tapered wings' elliptical lift distribution, not for the benefit of its stalling characteristics, although it's agreed that it does make them even more benign in the stall.

 

 

[pudestcon]

Hang on guys, we are talking about Thrusters here. Low performance grass roots flyers, not high end. The OP wants some answers on washout on his Thruster - can we help him?

 

Pud

 

 

[facthunter]

I would never to get my point of view past you HITC, but most of our aircraft are pretty basic and I try to keep my arguments simple and easily understood. Don't read into that that I am from some past and PASSE era that might be considered irrelevant because of the way I present things. You have your special interests and I have mine. I try to speak to the majority here and I don't go into great technical depth where I feel it will lose interest rather than generate it. I will still stick to what I have written on this matter in principle. I have seen people remove washout from planes and I don't consider them better for it. They will always be safer with it, and can be quite dangerous without it. The C-172 is so docile at low speed due in no small part to the wing wash out "effect" and not tip stalling first. The Cessna highwing family of planes are also among the best aircraft for lifting weight on hot days (High density altitude) when you might be technically overloaded, and flying near stall. which is where most pilots get into strife..Nev

 

 

[Head in the clouds]

Hang on guys, we are talking about Thrusters here. Low performance grass roots flyers, not high end. The OP wants some answers on washout on his Thruster - can we help him?Pud

That's what my post #4 is all about - Thrusters ... but even so post no.6 is also completely relevant, grass roots and/or other lightly wing-loaded planes all have the same requirements, the only real differences between them being whether they have tapered wings or not, and if they do, how you will apply the roll stability, by either of two kinds of washout (geometric or aerodynamic) or by using a foil that is suited to the lower Reynolds number at which the tip will be operating (thickness ratio mostly). For the specific answer for the constant chord, constant section Thruster wing, see Post #4, paras 4 and 5.

 

If it were mine I'd set the Thruster wing at the same incidence from the root to the tip, it'll fly best that way but the stall propagation from root to tip will be more rapid than with some geometric washout (twist). The amount of washout you give it will affect the rate of stall propagation but also the efficiency. I.e. more washout = kinder stall (slower/less likely to drop a wing) + less efficient (slower cruise, poorer glide) and v.v.

 

So if one wanted to go for the 'middle of the road' one might give the wing, say, 2* twist between root and tip. That was the figure many cautious amateur designers used in the 1980s. Very cautious designers used 3*. Sander Veenstra never used any washout at all and tufted his wings on a few occasions to demonstrate that it wasn't needed. One memorable occasion was when he was accused by the old Dept of Aviation of not knowing his stuff because "he should be using washout in his wings". For those who don't know of Sander he was a prolific builder of the SV range of ultralights and motorgliders and they were by far the most efficient of the time, he used to get 90kts out of his planes and he always used the same engines - 18hp Fuji Robins direct drive with a 32" prop at 7000rpm.

 

 

[Tony]

Hi Guys,

 

I am very gratefull for all your inputs from every each of you.

 

I think I have to disclose a bit more about this particular one seater Thruster 'T85SG' I am reconstructing.

 

It has the dihedral 50mm at the leading edge. (Only.)

 

What is alarming to me, it has got a NEGATIVE (!) washout so bad so the ailreons appear to have NEGATIVE dihedral by 50mm.

 

It still was flying, but not by me.

 

Now, everybody on this post would agree this is absolutely wrong and I have to do something about it.

 

It is very easy to extend the rear struts only if I know by how much exactly.

 

Talking degrees, one degree represents a shift up of trailing edge by 22.5mm.

 

Measured as cross section as a difference in Angle of Incidence that is.

 

If Peter G can measure that in degrees please do so.

 

Thanks, please keep going here.

 

Never assuming anything Tony

 

 

[facthunter]

I would set it up using trammels and levels check it all out. unless the planform of each wing is identical (at least the location of the strut attach points are accurate), going by strut length change may not achieve equal washout figures. Nev

 

 

[Head in the clouds]

Hi Guys,I am very gratefull for all your inputs from every each of you.

 

I think I have to disclose a bit more about this particular one seater Thruster 'T85SG' I am reconstructing.

 

It has the dihedral 50mm at the leading edge. (Only.)

 

What is alarming to me, it has got a NEGATIVE (!) washout so bad so the ailreons appear to have NEGATIVE dihedral by 50mm.

 

It still was flying, but not by me.

 

Now, everybody on this post would agree this is absolutely wrong and I have to do something about it.

 

It is very easy to extend the rear struts only if I know by how much exactly.

 

Talking degrees, one degree represents a shift up of trailing edge by 22.5mm.

 

Measured as cross section as a difference in Angle of Incidence that is.

 

If Peter G can measure that in degrees please do so.

 

Thanks, please keep going here.

 

Never assuming anything Tony

What you describe sounds nasty Tony, if I'm following you correctly you're saying that the tips have more set angle of incidence than the wing root?

 

If that's so, and if (with the aircraft set level in the flying attitude) the front spar has 50mm of dihedral AND that 22.5mm at a spar end represents a change of wing incidence of 1*, then, if you decided to set 2* of geometric washout you'd need the rear spar to have 50+(2x22.5)mm = 95mm of dihedral. It's an odd way of achieving it but should work ... Important thing is to be certain both wings get set up the same, you can usually lay a board over the spar ends of each wingtip and sight across them to check.

 

 

[Head in the clouds]

...I will still stick to what I have written on this matter in principle. I have seen people remove washout from planes and I don't consider them better for it. They will always be safer with it, and can be quite dangerous without it.

I can't agree with this FH. A plane that's properly rigged will be safer, not one that's got washout just because some people may believe washout makes them safer. The safer plane is the one that aerodynamically performs best. Since a rectangular wing stalls inboard before the tips stall (which they always do because the spanwise flow caused by the spill around the tips effectively increases the chord the further you go outboard, so the wing is operating at a higher Reynolds number the closer you get to the tip) then the tips are still flying and it has roll control at the onset of the stall, and that is all that is needed. The safest plane is one which has the greatest range between the zero lift angle of attack and the stall angle. Every degree of washout that you add is one degree that you have reduced that range and thus reduced the performance envelope of the wing, and resulted in a plane that must fly faster to remain airborne which means it has a reduced glide ability and an increased stall speed. That is another reason why rectangular wings are aerodynamically superior to tapered wings, because you can have the maximum possible aerodynamic performance envelope with a rectangular wing, and you cannot have that with a tapered wing.

 

It's one thing to describe things in a simple way for the benefit of the masses, but quite another if it has the effect of being misleading on what is safest. To take the example to extremes, it might be implied that the more washout you have the safer the plane becomes? In the example I gave of the Thruster with 7* of washout, well 7* doesn't sound much but when you bear in mind that it's half the stall angle you can quickly see why that particular aircraft was a real dog to fly, and damned dangerous too. Because at any time when the outer part of the wing reached an efficient cruise angle of attack, the inner portion was beginning to stall, so when the power was reduced it just fell out of the air.

 

The C-172 is so docile at low speed due in no small part to the wing wash out "effect" and not tip stalling first. The Cessna highwing family of planes are also among the best aircraft for lifting weight on hot days (High density altitude) when you might be technically overloaded, and flying near stall. which is where most pilots get into strife..Nev

I quite agree with what you say about the characteristics of the C172 but what you describe as washout "effect" is actually washout on the outer (tapered) panel of each wing only. The majority of the 172's wing area is rectangular (they only taper outboard of the strut attachment) and does not have any washout, so they are a great compromise by having a non-twisted rectangular wing doing most of the work and with washed-out tapered tips for tip-stall resistance. It's notable though, that all the newer generations of Cessnas do not have geometric washout, instead having changed over to using a different airfoil section at the tips with a greater thickness ratio.

 

 

[facthunter]

You debate to win an argument. When you imply things and suggest going to extremes, that is just verballing and makes discussion without point. Let's not bother Eh!. Nev

 

 

[corky450]

Hi Tony,I am also rebuilding a clipped wing single seat(1984 ),and need to make the wing struts(lost by previous owner),so will be very interested in the strut measurements and if there was any washout ,I'm yet to source the tubing though.

 

Cheers Corky

 

 

[pudestcon]

On further digging through the documentation I have, I have found in the Tony Hayes (may he RIP) publication "Thruster Two Seater Identification Guide For Owners and Inspectors Second Edition 2003", some information on washout. I offer this as information only as it does not specifically relate to single seat Thrusters, such as the T85SG that the OP here, Tony, is rebuilding.

 

On page 42 under the section GEMINI SPECIFIC TECHNICAL INFORMATION, Pitch Instability Contributing Factors, 5. Changed Wing Wash-out. I quote "The Thruster wing has neutral wash-out when static(i.e. the under surface of the wing root and wing tip should be at the same angle). However wash-out is built into the wing support design and is adopted when under flight loads." end of quote. The section goes on to explain that changing the lengths of rear lift struts, and incorrectly tensioned flying and brace wires can deform the wing from prime design under flight loads. No mention is made about degrees of wash-out or other specific measurements.

 

This information doesn't bring Tony any closer to the answer he seeks, but is extra information on washout design on the Thrusters.

 

Perhaps contacting Kay Hayes, Tony's wife, may uncover some specific documentation on this.

 

Pud

 

 

[Peter G]

Hi Guys,I am very gratefull for all your inputs from every each of you.

 

I think I have to disclose a bit more about this particular one seater Thruster 'T85SG' I am reconstructing.

 

It has the dihedral 50mm at the leading edge. (Only.)

 

What is alarming to me, it has got a NEGATIVE (!) washout so bad so the ailreons appear to have NEGATIVE dihedral by 50mm.

 

It still was flying, but not by me.

 

Now, everybody on this post would agree this is absolutely wrong and I have to do something about it.

 

It is very easy to extend the rear struts only if I know by how much exactly.

 

Talking degrees, one degree represents a shift up of trailing edge by 22.5mm.

 

Measured as cross section as a difference in Angle of Incidence that is.

 

If Peter G can measure that in degrees please do so.

 

Thanks, please keep going here.

 

Never assuming anything Tony

Hi again Tony,

 

I will measure the fr & re wing struts from bolt to bolt as well as check the wing washout with my digital incidence meter.

 

I can see if I can get some side on pics looking down the spars to get a idea of washout..

 

After working in the morning I am heading out there in the arvo and will post tomorrow evening :)

 

I was told my Thruster is a one off so things may be built different on my T83 EHF than yours to give you a idea of the changes on my plane were,

 

T500 Landing gear which gives a wider more stable track for ground handling,

 

Enclosed cabin with wide doors and rear pod to streamline,

 

Aerofoil wing struts,

 

flaperons,

 

The wing and cabin are more forward to give a more smoother pitch control having a longer tail length (also reduces the issue of ground looping).

 

Fiberglass airfoil shape farings covering all the box tubes on the lower fuselage..

 

I have the Technical Data Manual which states on the cover "THRUSTER '84" by ULTRALIGHT AVIATION PTY LTD which is a little different to my plane but has lots of the detailed info on the single seater Thruster anyway if you want other close up pics let me know before midday :)

 

Pete

 

 

[facthunter]

You might be reduced to considering a "generic" solution in the absence of specific figures. I thought the Tony Hayes thing was taken over by someone...... Daffyd Llewellin? Nev

 

 

[pudestcon]

You might be reduced to considering a "generic" solution in the absence of specific figures. I thought the Tony Hayes thing was taken over by someone...... Daffyd Llewellin? Nev

Bob Llewellin, but that's a brick wall.

Pud

 

 

[facthunter]

No comment there. Tony and I used to communicate extensively but there is nothing in that material I have which is helpful on this issue. In the absence of anything else I would try neutral on the ground. Having a reduced wingspan complicates it for me. They are not a speed machine and I have never felt they would improve from a smaller wing. Not the two seat one anyhow. I haven't flown a single seat, to comment on that.Nev

 

 

[Peter G]

HI Tony,

 

My wing has 3.5 deg washout between the inner first wing rib out to the outside rib, dihedral is the thickness of the ribs at the wing tip.

 

The Wing strut lengths will be what you set both washout and dihedral with...

 

I hope this helps your setup and if you need more details let me know.....

 

Pete

 

 

[Tony]

Hi Guys,

 

We have scored 204 views and 20 replies in this problem and we got some answers - thanks to everybody !

 

In conclusion, it appers to me the Thruster wing may be rigged to 0+ (zero plus) geometrical washout.

 

How much the value of PLUS is ? It is rather a matter of a taste and experience.

 

At this stage I am going for 1 and 3/4 of a degree which is 40mm measured vertically.

 

Peter G,

 

thank you for taking the measurement from your machine.

 

Gorky450,

 

the length of the struts is affected by the exact position of the predrilled holes for the top brackets and the bottom ones, which can be different type to type. Your position of your brackets may not be the same as on my type.

 

Never the less, just to get a picture for the material needed as it goes as follows on mine:

 

Front:

 

1)Top solid round alum plug 80mm long x 40mm Dia, 35mm Dia inserted into

 

2) Alum round pipe 35mm inside 300mm long with inside rectangular timber inset, alum wall 1.5mm.

 

The bottom end flatten to oval inserted into eliptic strut

 

3) Alum strut eliptic 2mm wall 25mm x 70mm - circumference 165mm at 2125mm Length accomodates at the bottom the:

 

4) As Item 2) but Length 450 with STEEL insert of 1.5mm wall, all that goes into bottom bracket.

 

Rear:

 

1)Top solid round alum plug 80mm long x 40mm Dia, 35mm Dia inserted into

 

2) Alum round pipe 35mm inside 400mm long with inside rectangular timber inset, alum wall 1.5mm.

 

The bottom end flatten to oval inserted into eliptic strut

 

3) Alum strut eliptic 2mm wall 25mm x 70mm - circumference 165mm at 2500mm Length accomodates at the bottom the:

 

4) As Item 2) but Length 350 with STEEL insert of 1.5mm wall, all that goes into bottom bracket.

 

Precise rigging occurs by shifting all members of this whole set inside of each other.

 

Brackets set first, holes drilled last.

 

I have no 'jury struts'.

 

 

[facthunter]

The jury is still out then? nev

 

 

[corky450]

Tony

 

Thanks 4 the info,time to do some measurements & get it flying.

 

Cheers Corky

 

 

[Guest ozzie]

Ok from memory.

 

this thruster sounds like the one that Dave Belton had us build for him for demo flights at airshows. He wanted one with a bit more snappy manoeuvring. So we clipped the wings and removed all the dihedral and zero washout.

 

Normal washout was 3deg.

 

Can't remember the dihedral.

 

Best way to measure this is run a string wing tip to wing tip on top of leading edge and measure from string to top of fuse tube.

 

Ozzie