Sgian Dubh

[SGIAN DUBH]

yes, Iolaire flew.there is a video which details hugh lorimer reports and shows the tests of all flights.

Yes it has flown....... I have watched the video & spoken with Hugh on the subject...... I think it needs a bit of redesigning according to my Aerodynamicists.

 

The BMAA should have copies still on file of any structural reports that Hugh submitted - I honestly can't remember if it complied or not to Section S. Clearly I also need to find a competent test pilot prepared to take on a flight test evaluation and iron out any handling bugs - and I think it's likely some will exist. In particular I have been very strongly recommended that I test a wind tunnel or radio control model with the same all flying canard geometry to evaluate stall and stall recovery related handling characteristics before any attempt to fly the aeroplane. Specifically my Aerodynamicist was very concerned that the canard could adopt a lower incidence than the mainplane, so there was potential to achieve a condition where the canard was unstalled and the mainplane stalled, leading to a tailslide from which it was not possible to show by analysis that it would recover.

 

However, it's clearly flown at least once without killing anybody, which is a start. Nonetheless, I'd personally treat flying the Iolaire initially as a high risk flight test programme, with all that implies, as a matter of basic survival. Vaughan Askew's book "Flight testing homebuilt aircraft" and the FAA's flight test guide AC90-89 are useful guides to those processes, but ultimately you need it test flown by somebody who is a trained test pilot backed up by some robust preparation and planning - I don't want to make it up as I go along or I probably will die.

 

 

[Head in the clouds]

SD, I can't quite agree with your 'order of magnitude' for the three projects. I'd say the Iolaire is likely to be the most benign of the three, probably closely followed by the Quaiche. That said, I'd want to check the Quaiche CG carefully because unless it has a disproportionately heavy engine it looks a bit stubby in the nose so the CG might be a bit aft - that all depends on the weight of the aft fuselage structure of course.

 

I'd think that the real challenge will be the Sgian Dubh. With the weight in it's ends (pilot up front and engine down the back) it's likely to be very nasty if it ever entered a spin (would possibly want to go flat) and will probably have very limited pitch and directional stabilities since it appears to lack any effective sweep in the mainplane. It's not very clear in the photos, but from the little you can see it doesn't appear to have much, if any, reflex in the airfoil section either, if that's the case it could even be pitch unstable.

 

I hope I'm shown to be wrong, but the only plane I'm aware of that got away with similar design features was the Pelican, and you can see how much effort has gone into getting the major weights as close to the CG as possible, and it has a lot of reflex -

 

 

Yes it has flown....... ........ Specifically my Aerodynamicist was very concerned that the canard could adopt a lower incidence than the mainplane, so there was potential to achieve a condition where the canard was unstalled and the mainplane stalled, leading to a tailslide from which it was not possible to show by analysis that it would recover.

Though I've not seen a true planform view of it, the Iolaire would appear to be a very conventional canard design albeit rather difficult to access the rear seat.

 

I question the opinions of your 'aerodynamicist'. If you have doubts about the design I wonder whether you might do better to get the opinion of an aeronautical engineer. Aerodynamicists rarely know much about 'whole aircraft'. I'm not talking out of my ass, I know two of them very well, one is my nephew. Both were trained in Universities in England and whilst they are exceptionally knowledgeable about fluid flow around and over specific shapes, neither of them has any knowledge whatsoever about aircraft. My nephew read for his Degree because he was fanatical about the McLaren F1 team and wanted to work for them, he can tell you the most precise details about the fluid dynamics of the flow into or out of the radiator ducts for instance, but wouldn't know much about a canard's overall design requirements.

 

Referring to your aerodynamicist's comment above - well of course the canard could adopt a lower incidence than the mainplane - it's a control surface, and when you want to put the aircraft into a dive the canard will have a much lower incidence than the mainplane, but so what? In a dive the mainplane's not going to stall is it? Going back to basics you will recall that the best indicator of the potential to be approaching a stall is the stick position, when the stick is back you may stall, right? So when the stick is back the canard is at a high incidence compared with the mainplane isn't it? So the canard will stall first provided the CG is in the right position for a canard-style aircraft.

 

As long as the CG is well forward of the mainplane, and consequently the canard is much more heavily loaded than the mainplane then the canard MUST stall before the mainplane, if the plane is capable of flight at all, and I don't see any reason why it wouldn't be capable.

 

The underlined items previous are the critical factors for safe canard operation. Many people don't understand canard dynamics properly and consequently make quite erroneous comment about them, on occasions.

 

Of all the aircraft I've flown, the one I found to be the easiest, most forgiving and what I would describe as 'completely docile' is of very similar fundamental design to the Iolaire, the American Aircraft Falcon, even Chuck Yeager liked it -

 

 

 

 

 

[SGIAN DUBH]

SD, I can't quite agree with your 'order of magnitude' for the three projects. I'd say the Iolaire is likely to be the most benign of the three, probably closely followed by the Quaiche. That said, I'd want to check the Quaiche CG carefully because unless it has a disproportionately heavy engine it looks a bit stubby in the nose so the CG might be a bit aft - that all depends on the weight of the aft fuselage structure of course.

Whilst I am open to your opinion on which one you think would be most benign I am going to stick to what my Aerodynamicist has implied..... As he is regarded as the best aircraft engineer currently in the UK.

 

I'd think that the real challenge will be the Sgian Dubh. With the weight in it's ends (pilot up front and engine down the back) it's likely to be very nasty if it ever entered a spin (would possibly want to go flat) and will probably have very limited pitch and directional stabilities since it appears to lack any effective sweep in the mainplane. It's not very clear in the photos, but from the little you can see it doesn't appear to have much, if any, reflex in the airfoil section either, if that's the case it could even be pitch unstable.

I am glad that I am not the Test Pilot for the Sgian Dubh, it needs either a better pilot than I am or a more adventurous pilot than I am ;-) I have every faith in my choice of pilot & am pleased that he is also involved in the final checking before flight...... his enthusiasm for Flying Wings is second to none ;-)

 

I hope I'm shown to be wrong, but the only plane I'm aware of that got away with similar design features was the Pelican, and you can see how much effort has gone into getting the major weights as close to the CG as possible, and it has a lot of reflex -

[ATTACH]42900[/ATTACH] [ATTACH]42901[/ATTACH]

 

Hugh Lorimer has done so many calculations on the Sgian Dubh that it has the CofG marked on the side of the fuselage & also the aerodynamic CofG marked for reference ( weight & balance calcs show an inbuilt stability )

 

Though I've not seen a true planform view of it, the Iolaire would appear to be a very conventional canard design albeit rather difficult to access the rear seat.

If we succeed in getting the Iolaire into the SSDR ( single seat de-regulated ) category access to the rear will be disregarded ( it will be a baggage locker )

 

I question the opinions of your 'aerodynamicist'. If you have doubts about the design I wonder whether you might do better to get the opinion of an aeronautical engineer. Aerodynamicists rarely know much about 'whole aircraft'. I'm not talking out of my ass, I know two of them very well, one is my nephew. Both were trained in Universities in England and whilst they are exceptionally knowledgeable about fluid flow around and over specific shapes, neither of them has any knowledge whatsoever about aircraft. My nephew read for his Degree because he was fanatical about the McLaren F1 team and wanted to work for them, he can tell you the most precise details about the fluid dynamics of the flow into or out of the radiator ducts for instance, but wouldn't know much about a canard's overall design requirements.

My Aerodynamicist is probably better qualified to answer my queries than someone who studied fluid dynamics for McLaren F1 ;-) I think McLaren F1 need to go back to the drawing board with regards to their streamlining & fluid dynamics theorum ( or steal the Mercedes blueprints )

 

Referring to your aerodynamicist's comment above - well of course the canard could adopt a lower incidence than the mainplane - it's a control surface, and when you want to put the aircraft into a dive the canard will have a much lower incidence than the mainplane, but so what? In a dive the mainplane's not going to stall is it? Going back to basics you will recall that the best indicator of the potential to be approaching a stall is the stick position, when the stick is back you may stall, right? So when the stick is back the canard is at a high incidence compared with the mainplane isn't it? So the canard will stall first provided the CG is in the right position for a canard-style aircraft.

The concern with regards the Iolaire is the Canard is an all moving Canard..... My aerodynamicist 'thinks' we should make the Canard a 75% solid structure with some positive incidence and have a 25% movable elevator integrated into it.

 

As long as the CG is well forward of the mainplane, and consequently the canard is much more heavily loaded than the mainplane then the canard MUST stall before the mainplane, if the plane is capable of flight at all, and I don't see any reason why it wouldn't be capable.The underlined items previous are the critical factors for safe canard operation. Many people don't understand canard dynamics properly and consequently make quite erroneous comment about them, on occasions.

The Iolaire is the only one of Hugh's designs that has previously flown, having watched the video & got a miniscule bit of feedback on it I am inclined to think that the canard needs to be structurally secured with an elevator section

 

Of all the aircraft I've flown, the one I found to be the easiest, most forgiving and what I would describe as 'completely docile' is of very similar fundamental design to the Iolaire, the American Aircraft Falcon, even Chuck Yeager liked it -[ATTACH]42903[/ATTACH] [ATTACH]42904[/ATTACH]

I too have flown a Falcon XP as well as the Vari Viggen & Varieze..... I had a quick flight of a Rutan Defiant as well so used to Canard types.

I think I will just set my goals on me doing the Quaich Flight Testing & leave the Sgian Dubh to my assigned team & then build another team to fettle the Iolaire when Project 3 comes along.

 

I have no control over the way we get the projects..... Hugh wants the Sgian Dubh to take to the air before we start flight testing the Quaich, then as the SWANSONG the Iolaire will be restored to flying capability and tested fully.

 

 

[SGIAN DUBH]

Having asked the BMAA ( BRITISH MICROLIGHT AIRCRAFT ASSOCIATION ) if they still have access to the submissions for the Iolaire I received the following response from them ( Not sure why the Sgian Dubh came into the content as it wasn't a concern before getting their email :

 

Ben Syson via gmail.com

 

10 May

 

 

to PJK

 

 

Dear Peter,

 

Iolaire

 

We have an historic file on the Iolaire.

 

It has not been opened since I have been at the BMAA (2006), and I am unaware of its contents.

 

An ‘experimental’ 2-seat Microlight can now be test flown on E Conditions.

 

Details are on the CAA website: http://www.caa.co.uk/General-aviation/Aircraft-ownership-and-maintenance/Experimental-aircraft/

 

Although an ‘experimental’ single-seat Microlight can be legally flown without any airworthiness ‘approval’, it doesn’t mean it’s necessarily a good idea.

 

It is legal solely because the risk to third parties is very low; it is not a judgement in any way on the risks posed to the pilot by this activity.

 

I would strongly recommend using an E Conditions Competent Person - and with careful consideration of the E Conditions guidance - even if the aircraft is SSDR.

 

Sgian Dubh

 

I have noticed that you have also become the registered owner of the Sgian Dubh G-CJPK.

 

Some sample drawings of this type are available on the internet: http://www.hughlorimer.co.uk/sd_drg.pdf

 

There are some very questionable design features in these drawings.

 

For example, drawing L2-W4 shows a very unconventional wing root joint in which the spar caps are effectively discontinuous, and the load is transferred purely through the ‘tenon’.

 

The stress calculation at the end of the document raises more questions than it answers, and leaves me unconvinced that this design feature is in anyway satisfactory.

 

Again, I would strongly recommend using an E Conditions Competent Person and the E Conditions guidance, even though this aircraft is SSDR.

 

Regards,

 

Ben

 

Ben Syson

 

Chief Technical Officer

 

British Microlight Aircraft Association

 

01869 336 006

 

[email protected]

 

I am now looking for opinions on the Wing Loading Calculations on Page 21&22 of the PDF.

 

Obviously under our SSDR Category I/we can just go ahead & do our own flight testing, however I am now considering the E Conditions Test Pilot process if I get enough plausible reasons to follow that mindset.

 

 

[SGIAN DUBH]

Today seemed to be a Lucky Day for me.

 

I was a little bit concerned by the remark

 

 

 

"There are some very questionable design features in these drawings. For example, drawing L2-W4 shows a very unconventional wing root joint in which the spar caps are effectively discontinuous, and the load is transferred purely through the ‘tenon’.

 

The stress calculation at the end of the document raises more questions than it answers, and leaves me unconvinced that this design feature is in anyway satisfactory. "

 

 

 

so I had a Trusted Aircraft Builder/Restorer look over the Wing Loading Calculations & this was their informed response :

 

 

 

(PJK)Hiya, do you understand wing loading calcs?

 

 

 

Try me.

 

(PJK) Your friend BEN SYSON has queried the wing integrity of the Sgian Dubh......he says he is concerned by the calcs

 

 

 

Give me the chord,the length of the wings,the all up weight of the aircraft with fuel,the aerofoil section and the deepest part of the aerofoil ie the centre of pressure.

 

 

 

 

Let me study it later.

 

(PJK) http://www.hughlorimer.co.uk/sd_drg.pdf

 

www.hughlorimer.co.uk

 

hughlorimer.co.uk

 

 

 

I would very much doubt if the wing loading is too high.

 

(PJK) that is the PDF for Sgian Dubh calcs ( everything is there in B&W )

 

 

 

Is that the idiot who does not know the difference between a rib co-ordinate and a GPS ?

 

(PJK) yes wink emoticon

 

 

 

Sounds like someone is playing a blinder,mind you they are all blind there ?

 

Canards have higher wing loadings anyway.

 

(PJK) I am only looking for an opinion......I won't hold you to what you say.....just a man is going to fly the SD & I don't want him to fold a wing wink emoticon

 

 

 

Thats ok I will give you an honest opinion.

 

(PJK) The Sgian Dubh is not a Canard..... it is a Flying Wing.

 

 

 

Same but different,lots of wing area.

 

 

 

They are just trying to place obstacles in front of you.

 

Look at the flying bricks like Dykes Delta.

 

I cannot open that strange file Peter ?

 

It says file association unknown,drat.

 

(PJK) open the pdf

 

page 21 &22

 

 

 

OK got it.

 

 

 

 

Never mind the pdf will do,let me take a quick glance now.

 

(PJK) thanks wink emoticon

 

 

 

Its built like a tank,basically 137 square feet total + 41= 178 = 1.37 lbs sq feet at 300lbs all up weight at a 1g loading,its stressed at 1.68 /ton inch for 6 g,whats the problem ?

 

And that is just the spars,with the torsion box construction its well in.

 

(PJK) OK Thanks wink emoticon

 

 

 

I am very impressed with his drafting and designing skills,he has stressed at a level well below what is actually needed for safety,given the deep wing section and slow flying characteristics even in a severe buffet its a safe machine,I really think they are trying to hoodwink you Peter.

 

 

 

They said the Quickie was a high wing loading in the early days and look at the thickness of that wing by comparison.

 

yes I know

 

 

 

I would get back to him and query why he thinks the wing loading is high ? especially given the data supplied and that the designer has stressed at 6 g in his calculations.

 

(PJK) I know........over-engineered into the build

 

 

 

Yep.

 

I would be happy operating a delta with those specs.

 

(PJK) me too

 

 

 

That is going to leap into the air.

 

(PJK) yes

 

 

 

And you know what to do if the worst comes to the worst ?

 

(PJK) what?

 

 

 

Place the machine in flying position,load the wing up with sandbags at strategic points across the span and chord and do a static test,just like they did in the early days of flying,that way you can prove they are very wrong.

 

(PJK) We are going to do the inverted wing loading

 

 

 

Good idea,if they break they break,but I doubt if they will.

 

(PJK) I DOUBT IT AS WELL

 

 

 

Invite his lordship to be the observer when you do it,they have the facts well recorded what more do they want ?

 

 

So now I am more than happy that the Sgian Dubh Wings are substantial enough for the safety of the aircraft ;-)

 

 

 

Then the day got even better when I also received this reply to an email I sent to another Aircraft Collector :

 

 

 

Yahoo! Mail

 

17:02 (3 hours ago)

 

 

 

 

 

 

to me

 

 

Peter,

 

I have a 503 that you would be more than welcome to borrow for your testing.

 

It has been sitting in my workshop for some time and would probably need checking over.

 

I,m not too sure if I have a 447 to loan I would have to check, it could be a 377.

 

I may be able to arrange something with regard to St Austell, it is a pity as I delivered a Tiger Cub to my friends son at St Blazey last week.

 

I spend 4 days each week at St Mawgan which may be a better pick-up point if convenient for you.

 

Let me know what suits.

 

Regards,

 

Ian

 

All in all, everything is coming together...... I have also been given clearance to start on the Quaich Project now...... That will be flying within a Month.

 

 

 

[Head in the clouds]

I am now looking for opinions on the Wing Loading Calculations on Page 21&22 of the PDF.

Obviously under our SSDR Category I/we can just go ahead & do our own flight testing, however I am now considering the E Conditions Test Pilot process if I get enough plausible reasons to follow that mindset.

Well ... if you want another opinion I'd say there's some considerable degree of confusion in the discussion above, caused by lack of correct terminology SD.

 

The fella from BMAA expressed his concern about the transfer of the lifting load carried by the wing outer panels to the wing centre section - his assertion is that he doesn't like the discontinuous spar caps and considers the ability of the 'tenons' to carry the load to the centre section to be suspect.

 

He may, or may not be right, it all depends on the connection between the tenons and the spar caps in the outer wing sections, and for how far they overlap internally, and how they actually connect to the centre section. Based on the very limited (read 'quite insufficient') information in the sketches in the pdf, I concur with his concerns. It's not the prettiest way to hold wings on ...

 

Then you wrote to your mate asking him what he knew about 'wing loading calcs' and he completely missed the point you seem to have thought you were asking about, because wing loading has nothing at all to do with the transfer of flight loads from outer wing spars to the centre section. Wing loading tells you about how heavily the wing is loaded in weight per unit area, in simple terms it tells you how slowly the aircraft will fly. Your mate responds with comments like "heaps of wing area", that it will "leap into the air", "thick wing section" (they produce more lift), compares it contrarily with "flying bricks like the Dyke Delta (and canards)" - all these things show he is talking about the wing loading being low, NOT that the outer wing/centre section connection is sufficient.

 

AND - Hugh's calcs don't properly address all of the considerations either. The only proof he shows is a calc for the tensile loading in the tenon. At 1.23 tons/sq in it's not high but he doesn't specify the material or the material's properties. From the sketches the tenons appear to be 'mini box section spars' - they certainly seem to have caps and either a void or a filler of some kind between them. If that is the case it's not the way to do it because there's more bend than pure tensile and compression loading on the caps of tenons of that kind, so the tenon should be solid and of sufficiently hard material that it will resist surface crushing where it bears. As shown in the sketch the tenons would fail in buckling way before they reached the tensile and compression loading indicated in Hugh's calc.

 

Also - tenons like that usually join to the centre section via tapered pins through the locally reinforced web of the centre section, and that reinforcement carries the load back to the caps of the centre section. In this case there is no indication of any pins so it would appear that the tenon simply bears on the outer end of the upper centre section cap (in upright flight, the lower one if flying inverted). If that is the case, what is the arrangement to prevent crushing of the upper cap or its breakout from the webs?

 

Sorry to be a wet blanket but I think the BMAA CTO's concerns are perfectly valid based on what information is available. Of course the 'as built' may address a lot of the concerns that the sketches raise.

 

If I was in your shoes I'd be conducting a static load test to prove the whole structure's integrity, it's not difficult, only takes a day and allows you to proceed with flight testing without concerns about the wings clapping hands. If you approach the static load testing imaginatively you can test the drag/antidrag and torsional (think flutter) aspects at the same time.

 

 

[SGIAN DUBH]

Well ... if you want another opinion I'd say there's some considerable degree of confusion in the discussion above, caused by lack of correct terminology SD.The fella from BMAA expressed his concern about the transfer of the lifting load carried by the wing outer panels to the wing centre section - his assertion is that he doesn't like the discontinuous spar caps and considers the ability of the 'tenons' to carry the load to the centre section to be suspect.

 

He may, or may not be right, it all depends on the connection between the tenons and the spar caps in the outer wing sections, and for how far they overlap internally, and how they actually connect to the centre section. Based on the very limited (read 'quite insufficient') information in the sketches in the pdf, I concur with his concerns. It's not the prettiest way to hold wings on ...

I am always open to another opinion....... I am putting a lot of faith in Hugh's build quality & being face to face with him, everything he says seems plausible ( it is a bit like Rocket Science to me )

I have some very knowledgeable engineers around me who understand the flying wing concept , so I am letting them move this forward from a flight testing aspect.... I do have to consider that I will be putting a flying friend into the HOT SEAT & it could be a load on my shoulders if anything goes wrong. I think the messages in my previous post are not seen in full context as I was also discussing it by phone at the same time so that in reality is only 60% of the story ;-)

 

The Quaich which I will be playing a more active role in the Flight Testing seems like a conventional 3 axis microlight so I am fairly chilled out by this project.

 

I am looking at every single detail of the Quaich documents etc so that it is engraved in my brain what everything is on this SSDR microlight.

 

I am keen for Hugh to see his Sgian Dubh design & his Quaich design take to the air...... Thankfully the Iolaire has already flown so I don't have the pressure of getting that into the air ( Our CAA are not keen to allow that into SSDR as it is a big microlight that I doubt we can lighten down to 178kg safely )

 

 

[Deskpilot]

My interpretation of Hugh's wing joint. A single pin locks the joint.

 

 

 

 

 

[SGIAN DUBH]

The Sgian Dubh will be getting fitted with a Mid-Life Rotax 503 very soon ( just having the engine checked for serviceability ). The Sgian Dubh is going to Newquay St Mawgan for hangaring.

 

The Quaich is ready for test flying, just waiting for a UK registration to be assigned & then it will commence the flight testing.

 

 

[bexrbetter]

The Sgian Dubh (愚蠢的名字) looks surprisingly good in real life with people and other things to reference it against.

 

 

[SGIAN DUBH]

Hi Everyone, All going well but a bit slow with the Sgian Dubh. The Driving Force behind getting the Sgian Dubh ready for flight has made some major changes to the Aircraft : The Rudder pedals have all been moved and a ' tiller bar' now steers the nose wheel. The Rotax Engine is all in the right place but he had to do some glass work and make up new metal mounts for the engine. He currently needs to find place for fuel pump.He now has a full set of instruments and just need to be mounted. A new loom has been made and all the wiring is now in. It's taken hours of work to get this far and nearly £2000 ! Well, Anyway I hope you ALL have a superb new year. All the best from the SD Campus ;-)

 

 

[SGIAN DUBH]

The Sgian Dubh now has a low time Rotax 462 fitted and has been mentioned in the Royal Aeronautical Society newsletter January 2017

 

 

 

[Deskpilot]

I understood the Sgian Dohb translated to Hidden Knife as it was worn or hidden in the long socks worn by the Scots.

 

In answer to an earlier question, the tenon length is 24inches. My model images are to scale.

 

 

[SGIAN DUBH]

The name comes from the Gaelic sgian-dubh. Although the primary meaning of dubh is "black", the secondary meaning of "hidden" is at the root of sgian-dubh, based on the stories and theories surrounding the knife's origin, in particular those associated with the Highland custom of depositing weapons at the entrance to a house prior to entering as a guest. Compare also other Gaelic word-formations such as dubh-sgeir "underwater skerry" (lit. black skerry), dubh-fhacal "riddle" (lit. hidden word), dubh-cheist "enigma" (lit. hidden question).

 

 

[altair]

hi,good morning.

 

sgyan dubh flying now????