Can enyone tell me why the rigging wires on some Bipes are crossed over as [Tiger Moth] where as on th D.H.60 the wire run parallel?.

The wires should always be "crossed over" because they perform two different functions. The wires running from the bottom at the inboard end to the top at the outboard end are "flying wires" which take the loads under normal (positive) G. The wires running from the top at the inboard end to the bottom at the outboard end are "landing wires" which take the loads under negative G - that is to say they take the loads whenever the lift developed by the wings is less than the weight of the wings. This would include the weight of the wings whilst taxying or standing still on the ground.

The wire bracing is there because the wing spars are not stiff enough to take the loads in pure bending, so the use of struts and wires converts these bending loads into tension and compression loads. Materials are much stronger in tension and compression that they are in stiffness (ie bending) so much smaller spars can be used where external bracing is used, with a huge saving in weight. The downside is that the struts & wires add a lot of drag - as a general rule on the full size the drag becomes a bigger penalty than the weight at a cruise speed of around 150mph, although this depends on a lot of other factors (desired runway length and desired wing loading to name but 2) so it's only a guideline.

PDR

just a guess, but as the Tiger, like the Bucker bipes, has sweepback, I would say that it uses landing and flying wires in a V shape in order to use the top rear cabane strut as a mounting for the landing wires and the front lower spar for the flying wires. This way the triangle formed in plan view is more evenly balanced for the relevant wing so that as  well as vertical forces, the V braces the wing against fore and aft forces.  take a look at

tiggie

 and

Moth

The DH 60 has noticably less stagger, so the parallel rigging in plan view can be used without a tendancy to pull the lower wingtips forward and the upper backards.

Ah, I see what you're getting at now. In this case it's a matter of design choices. The DH60 is the "classical" approach to bracing, where the front  and rear spars are braced to different points on the fuselage. As the bracing produces a resultant vertical compression load in the fuselage the DH60 will need two strong vertical frame members in the fuselage - one at each spar position. The Tiggie actually braces both spars to the same point on the fuselage, presumably so that only a single strong frame is needed. As to why this approach was chosen, it's impossible to say after all this time. It may have been an overall weight saving, or because it was particularly convenient to carry these loads at that location. I note that the fuselage rigging attachments are directly above the rear undercarriage members - a place where additional compression strength would have been needed anyway - so perhaps this was making the one heavy frame earn it's keep by doing something useful in the air as well as on the ground. It could equally have been that it was particularly  inconvenient to have a strong frame at the forward location (due to other requirements, or the need to put something else in the same place) and so the single attachment point was a clever way of addressing the competing requirements.

All aircraft are unique designs, with specific solutions to particular design requirements and conflicts - there are no "generic" solutions. All we can say is that there will have been a reason for each design choice.

Actually another thing has just occurred to me. I seem to remember that the Tiggie's wings can be folder back for storage and transport by road. This is done by hinging at the rear spar, and so it may be that this rigging layout removes the need to disconnect rigging wires when folding the wings. I have no idea whether this is true, but it's quite possible that this was the "other requirement" that led to the different design solution.

£0.02 supplied,

 PDR

The Moth (and Gipsy Moth) could have their wings folded along the fuselage (a jury strut was required at the front wing spar joint to keep the wings rigid when folded) but the Tiger Moth wings do not fold as the rear spar bolts are not in line due to the wing stagger. The Tiger was designed to a military spec and wing folding was not included.

There is this picture of Belgian surplus Tigers with their wings folded back but the concensus is that they were being stored prior to scrapping so the damage to their rear spar mountings did not matter!

Interesting thread, I part-own, maintain and fly a full size Tiger Moth as well as building flying models of them (have a look in my gallery). On the Flair 1/4 scale Tiger the wires are functional (silver soldered).

The flying and landing wires on the Tiger actually attach to the wing root ribs, this is a left-over from the earlier Moths with folding wings. I had a close look at a DH60 'Gipsy' Moth recently and was intrigued to see that de Havilland used the same wing fittings!  The quick release pins are replaced with a more permanent pin but the rear hinge points (upper and lower) are still there. As Simon says the wing assemblies can not be folded because of the geometry.

I've got some close up photos of the fittings if anyone is interested.

Often think about those wires when I'm floating along, they do have to be checked and looked after regularly.

Cheers

Gary 

 Hi, Gary. I would very much like to see your photo's of the wing fixing fittings of the Moth, to compare them with the one's I have made for mine, I have lots of pictures of the DH60 but no close ups of the actual fixings, I only hope mine are strong enough for the job!!  The flying wires are fully functional and running parallel to each other, unlike the Tiggy which are crossed, as you will know, part owning one [lucky you], always fancied a fly in on, have to make do with the model! Kind regards, Gerry.

Hi Gerry,

They are not as close up as I remember but I can take some more if you need them.

1. Lower wing rear hinge fitting and flying wire attachment:

Have not flown for a while (Tiger or models), weather is a lottery this time of year!

    Cheers

        Gary 

Gary

Nice pictures.

It always amazes me just how tiny all the fittings are and they take ALL the flying loads. As you say it a good idea to check them once in a while when that is all thats keeping you flying!

Yes, it is a bit 'thought provoking'  when you see what holds it all together, an incentive to do good pre-flight inspections and go easy on the 'G' forces.

Will do Gerry, won't be for a little while though (Sqn reunion this weekend and a visit to Duxford, never been).

Cheers

Gary 

The Tiger Moth introduced the staggered wing and change of rigging geometry as a result of the RAF's requirement that the front seat occupant can bail out as easily as the rear. The staggered wing allowed the centre-section wing struts to be moved ahead of the front cockpit. Both the lift and landing wires run to the forward spar position (at the fuselage) so as not to be in the way of the bale-out. 

 I'd be interested to hear Gary's thoughts of the difference/similarities of flying full size and large, quarter scale model Tigers.

 Steve 

Almost!

The centre section (cabane struts) went forward for the reason you describe ( a hacksaw and a cigarette packet drawing were involved allegedly!) then the wings had to be swept back to preserve CofG and centre of pressure (lift) relationship.

With the tail down this moved the lower rear wing tips quite close to the ground and they often touched on the prototype Tiger during taxiing, the answer was more dihedral on the lower wings (leaving the upper wings untouched)  to give more clearance, achieved with a hacksaw again to shorten the interplane struts!

The sweepback angle is slightly different on upper and lower wings and another 'fudge' left over from the redesign is that the wing ribs are in line with the leading edge and not the airflow. I've got a KeilKraft plan from the 1950's that has them in line (and a rolled up balsa cement tube shown for nose ballast, remember those tubes?!!)

Comparison between models and full size? Quite similar I think, both are very stable in flight and not particularly aerobatic. The full size controls are quite heavy in feel (especially compared to a Chipmunk) . The full size stall is quite benign with the slats out (about 35 knots) but with the slats in it is quite different and will drop a wing and spin quite rapidly if not recovered. Some Tiger's don't have slats (or anti-spin strakes) of course. Rudder needs to be used on both, I usually mix it in with the ailerons on a model.

Approaching the stall there is virtually no 'pre-stall buffet' warning which I found quite 'interesting' when I converted to the Tiger Moth, it might be the reason that quite a few have met the ground over the years with the pilot usually walking away wondering what happened!  I always watch the airspeed very carefully near the ground, being 'draggy' it is quite easy to slow down without noticing.

I think we fly TM models with a slightly forward CofG from the full size position for pitch stability, most of my Tiger models (I think I had five of different sizes at one stage) were very reluctant to stall or spin.

This Flair Tiger is very stable but a bit underpowered with an OS FS120, it originally had 2 lbs of lead in the nose, I gradually removed some (but not much) until  it  would just spin with the right 'provocation'.

It has working flying and landing wires which have silver soldered end fittings (standard metal RC servo clevises for adjustment).

Sorry about the ugly bloke! 

Cheers

Gary

This one was an experiment (rubber free-flight to GWS electric power and radio control conversion), suffered from 'glitching' interference and it is in semi-retirement (thought I'd better before it met a sticky end!)

Gary, Thanks for your quick reply and interesting comments re full-size and model Tigers. I've only managed to have one Tiger flight - that came as a complete surprise and was due to winning a raffle at Shuttleworth's several years ago. Best memory from the flight was turning at Cardington and seeing the airship sheds below. I'll be making a DB Tiger Moth over the winter (1/6th size) so it will be interesting to see how it goes together and flies.

Steve 

Old Warden is a very special place for me, been a visitor since the late 1960's. My dad was a regular on the free flight days, I met fantastic people like Ron Moulton, Howard Boys (a real character), 'Jack' Frost, John Blagg (superb peanut scale), Mick Staples (excellent control line scale builder and flyer) and many others.

I have some old cine film of RC Spitfires and a Beaufighter taking off (or trying to) on hardboard runways, there is also a Jet Provost formation team of four aircraft in silver which might date it. 

Been over in the Tiger a couple of times this year and always feel guilty for temporarily stopping the modellers from flying! Always get a cheery wave though.

I have a very distant memory of a pub near Cardington with a ride-on steam railway in the garden, possibly called 'the fox and hounds', does this ring any bells with anyone? 

Good luck with the DB build, I hope you are going to post a build thread.

Cheers

Gary