Wind tunnel

Discussion in 'Workshop Tips and Secrets / Tools' started by rtfm, Jan 20, 2012.

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  1. Feb 1, 2012 #21

    Aircar

    Aircar

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    Duncan -- I spent decades fighting the"Department" (DCA,DoT,CAA,CASA -who knows what next )to get relief from a degree of OVERregulation,OVERkill in terms of excessive and pedantic demands so that you and others never had to face it.
    (imagine if you can for EVERYTHING to be MANDATORY tested,documented,justified etc etc etc to the most utterly absurd lengths --far beyond even FAR 23 ( you would never have even seen that or know anything about it I expect --from 1956 till 1999 it was the ONLY option that an Australian designer of an aircraft -like yours - had and NOBODY was ever going to be able to comply -which was the INTENTION of the bureacrats . Even though the (now) SAAA had co operated in the writing of the legislation which opened the door to any US uncertified homebuilt design -possibly unairworthy or dangerous (as some were ) but definitely uncertified to FAR 23 -a US law - they slammed it shut absolutely to any Australian design and so betrayed their members and all Australians who might want to design something of their own.
    THEY DID NOT EVEN POSSESS a copy of the design standard(FAR 23) imposed on Australians --not in their library or by a member.

    I was the ONLY person who had it (outside of the department itself and a few professional engineering consultants ) --this shows just how uninterested in local design of any kind they were and confident that nobody would even attempt to challenge this unassailable barrier --I left Australia in 1973 to get a proper design oriented aeronautical engineering education in a place where aircraft were being designed and built _ Germany and Stuttgart university (the energy crisis and Yom Kippur war ended both the German post war 'economic miracle' and my plans to complete my education in Germany but I did get some training and knowledge to further my design ambitions.
    To cut a long story even shorter another year and a half working on the best sailplane ever built in the US --being responsible solely for the design and production of the fuselage and controls landing gear canopy etc also helped further some capability --I had already flown gliders for nearly eight years and won competitions by that time but still felt that I needed to LEARN from those who knew more and knew that there was more to learn.

    I returned to Australia because of work permit non renewal in an economy much like now and had no option but to fight the barriers in my own country if I had any hope of building an aircraft of any design of my own that could benefit others by bringing the low man hours of molded composite (NO other design anywhere was then using it )and -even then, targetted at doing something of real value to others rather than just to get a cheaper aircraft as a sort of self indulgence --eventually the mass produceable flying car.

    The first effect of the lowering of oppresive design regulation (ONLY in ultralights in 1976 ) was a wave of fatal accidents and bad publicity right up to "60minutes"
    that threatened to not hust shut the door to any future experimental category but weld it shut for good --poor behaviour by a few threatened everybody .

    I have seen too many people with little or no experience or capability kill themselves or others as a result of arrogant ignorance embodied in some creation or another --and almost without exception they never felt the need to do an 'apprenticeship' in effect --start by learning the ropes, do some in depth study,get their hands on aircraft by some means (help others build or repair,restore etc) and then progress to maybe building some modest aircraft from a kit or plans and find out how to build something before taking it on themselves to go right to the head of the queue and show that they know it all --words are not a substitute for something of substance.

    Both Steve Mitchell (formerly the technical rep for SAAA )feel some responsibility for removing the barrier that previously not only prevented any competent local design but also protected the incompetent from hurting themselves or others -- we thought that there would be an opening for less than professional level engineers and tradespeople to create worthwhile aircraft without being burdened with the cost and time delay of certification but NOT that it would be the signal for "flat Earth" design to run rampant as it proved to be (people forget that a US "backyard" designer might have a day job as an engineer for Lockheed or have such friends and have a respect for the engineering involved --and many 'homebuilt' designers in the US are fully a qualified engineers who just need the freedom from certification to blossom --not as an excuse for 'anything goes' even if in a way it did. end send
     
    Last edited: Feb 1, 2012
  2. Feb 1, 2012 #22

    Aircar

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    After seeing enough 'designers' kill themselves and trying to stop it beforehand you get to see a common pattern and some tell tale signs --that doesn't mean that you can then forestall the 'inevitable' outcome ,maybe even the reverse is true -- by all means go ahead with your plastic sheet wind tunnel etc I have nothing to gain by trying to tell you what will be the result and I don't guess you will get hurt from it either --I have lost too much time already in a fruitless exchange and can see nothing useful to come out of it and finishing here, so as not to waste anymore of it - I HAVE already given you what answers you need and heard enough to leave no doubt for me.

    And you are wasting your time and money using epoxy to make microballoon filler on a plug

    Ciaou.
     
  3. Feb 1, 2012 #23

    Aircar

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    Less than ten seconds to find www.nasa.central.cranfield.ac.uk/reports/1938/nac

    and scores of other hits on Fowler flap research with good solid data . Just google "NACA Fowler flap design" or other word string possibilities. Lack of data is NOT the problem --there is a general fixation on airfoil data on HBA as a whole which is itself curious
    (perhaps on Peter Garrison's site earlier or linked from it there can be found one of his earlier published columns where he addressed the matter of airfoil selection --with the proviso that it did not deal with canard airfoils or sailplanes where the difference can be appreciable -- he wrote " the pilot has not been born who can tell from flying the aircraft what wing section it has and the effect of one airfoil over another is swamped in the myriad other decisions the designer has made .." (quoted from memory but near to those words )

    He has since published software for doing CFD analysis and may have softened his views somewhat but the general point remains valid .
     
  4. Feb 1, 2012 #24

    addaon

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    Aircar, that link isn't to a specific report; it's generally easier to give the report / note number and let people get it from a local server (NTRS for most of us).

    In a quick NTRS search, I didn't find anything from 1938 that addresses the combination of Fowler flaps and spoilers. While I personally think that adding spoilers to Duncan's design is a mistake, I don't think that asking the question about the combination is unreasonable.

    While I confess that I have not read most of your posts (I have extreme difficulty with your grammar), nothing that I read makes me think that you understand the question Duncan is asking. If nothing else, a little courtesy would be appreciated.
     
  5. Feb 1, 2012 #25

    highspeed

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    I think the wind tunnel idea is a waste of time when the goal is producing a general aviation sport plane of conventional configuration. As an exercise in itself it may be an interesting curiosity, but getting meaningful data out of it will be very difficult without a background in aerodynamics. There are so many things that need to be accounted for (tunnel wall effects, reynolds number effects, noise in the data.) Unless you're looking at something novel, then a pen, paper, and calculator should suffice.

    Now that that's out of the way here are some references that I dug up in a search of the NASA Technical Reports Server.

    Paulson, John Jr.; Wind Tunnel Investigation of a Fowler Flap and Spoiler for an Advanced General Aviation Wing. NASA TN D-8236, June 1976.

    Wentz, W. H., Jr.; Wind Tunnel Tests of the GA(W)-2 Airfoil with 20% Aileron, 25% Slotted Flap, 30% Fowler Flap, and 10% Slot Lip Spoiler (Wichita State University). Aeronautical Report 76-2, 1976.

    This is only a small sample. A search of the server will yield a wealth of information. I think it prudent to stop work, do some research, get your planform and configuration frozen, do some detail design, THEN fabricate. You don't want to put the cart before the horse, as it were.
     
  6. Feb 1, 2012 #26

    Aircar

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    I think I gave the Google link as well ("Fowler flap design" or anything like it ) --any link that starts with http:// doesn't seem to 'highlight' or be accessible when I try to post and substituting www. doesn't always work either -- in any event it is not hard to find good data on fowler flap set ups and I could not see how Duncan found it apparently impossible.

    It may be clear to you and me or others that a pedestal fan is not going to even come close to generating enough velocity to get measurable forces even if you can measure them (itself a real job) --the thread I started to help amateurs actually get useable data --the rolling rig -- was either ignored or dismissed by Duncan . Many respondents have been a lot blunter than me in dealing with people who have just used the forum to do their own work or for less than valid reasons.

    If I come across as a little blunt then maybe it stems from having benn here before and having said "no he wouldn't do that ..." and not doing something before somone did kill themselves for utterly incomprehensibly stupis reasons --it is better to be frank than regretful afterwards ( an example;- a Mr Gordon Bedson --excellent maker of wooden propellers, trained at DeHavilland in the 30s etc --designed a two seat ultralight that was on display, uncovered (no fabric) at an airshow with a placard saying 'soon to be flown, stand by for exciting reports and leave your name here for ordering...' -- I was dumbfounded in looking closely at the strut fittings that appeared to be nothing but holes drilled in plywood across the (face) grain with no room for any tension straps or other material -- I could not find Gordon but I was sufficiently concerned to get the president of the Ultralight aircraft association to come with me and pointed out to him the obvious deficiency and asked if he could ASSURE himself that this was NOT how it was going to be left (it might have been a mock up or just cobbled together for the airshow despite the appearence of 'completion' -- I told the president that the best thing they could do if it WAS 'finished' would be to put a boot through it for him.

    Nobody DID anything and he (Gordon Bedson)died when the struts pulled out and the wings folded --one up luckily . Same deal with the Ligeti Stratos and -lets' see -five others that come to mind right off --they were all sure that they just knew about it all and several of them wrote chummy builder's reports with lots of banter as someone who is well versed in a thing might do because they know the thing so well --deceptive and for some disarming or reassuring .

    Others were clearly a bit flummoxed with Duncan's posted 'intentions' earlier and saw the need to be a bit frank despite the breezy way in which it was written (or because of it ) --I no longer 'overlook' things like this and even if nothing might ever come of it the consequences are fairly final --Duncan could very likely enjoy building a kit or plans aircraft and not have to learn design 'on the job' as it were. and have a good aircraft to fly at the end of it.

    And I am sure Duncan could probably buy and sell me many times over --I cannot afford to keep a car on the road now either and usually use a bicycle --and described a bicycle component built test rig that he could get useful data from . As I mentioned earlier I am tearing my hair out trying to help another --expat -Aussie who hasn't a clue about basic static moments let alone roadable aircraft design and likewise has a 'charming' writing style --particularly when talking about his own brilliance (but always lacking any reasoned,calculated or even anecdotally justified support --a writer owes it to his reader to give enough factual information for the reader to make a judgement as to veracity --and to be prepared to answer probing questions , rather than presuming his proclamations are gospel truth and unassailable .

    In the roadable aircraft field you ONLY get the welter of sarcastic or cocksure dismissal and at best luke warm (because also being uninformed) 'support' --Machiavelli put it best --'the proposer of something new has the established and self protective interests of those who stand to lose against him and only the vague and poorly formed
    support of those who might stand to benefit from the new and uncertain thing" (bad retelling of the basic saying but the concept is clear enough)

    If you can't take the heat -or stand your ground against vaild criticism then get out of the kitchen is the blunt way of putting it -- and others have even said 'stop wasting out time, spend some of yours in your own interest etc ' (NOT to DUNCAN I hasten to add but certainly you can find this sort of response --it is understandable and called for in certain cases. ) I will apologize happily when I am shown to be wrong -as I can be like anyone else but when the stakes call for it I will not mince words either. ( I got burgled a couple of days ago amongst other things and sometimes just get exasperated )
     
  7. Feb 1, 2012 #27

    addaon

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    Aircar, we understand how to design a Fowler flap.

    Do you understand that this is not what Duncan is investigating?
     
  8. Feb 1, 2012 #28

    rtfm

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    Hi Aircar,
    First, thanks for taking the time to write so comprehensively in response to my posts. I know it takes a long time to do so, and I appreciate both the concern and the time you spent.

    I will be getting a mentor from the local chapter of RA-Aus soon, who will be able to add a pinch of sanity to my sometimes fanciful ideas. I'll also be inviting the local chapter round to my workshop to see the plane thus far. I'd expect a fair degree of common sense opinion from these gentlemen. I don't want to build a dangerous plane, but I also don't want to ignore ideas simply because no-one has thought of or done it previously. Otherwise, what's the point.

    I'll try to get on to the wind tunnel soon, with photos. I'm looking forward to it...

    I have now covered the plug with Q-Cell/Epoxy (very nice to use, BTW) and last night sanded most of it back. I'm getting closer to what I'm looking for.

    Duncan
    PS Jeffco is hardly any more expensive than Polyester.
     
  9. Feb 1, 2012 #29

    Autodidact

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    Fantastic, Duncan! I had wanted to suggest something like that because the forum can only go so far, and also sometimes my posts are less than tactful and I have wanted to apologize for that "absurd" comment I made earlier. Sorry.
     
  10. Feb 2, 2012 #30

    rtfm

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    Hi guys,
    As usual, you guys on HBA continue to make this the best online forum - anywhere! My feelings may get hurt from time to time, and it is hard to put aside cherished ideas one has nurtured for months because of annoyingly sensible commentary from the forum, but I seldom take offense :) because there is no-one on HBA who sets out deliberately to cause offense (well, at least not towards me, anyway...)

    My problem with getting a mentor thus far has been that I am still tooling up, and haven't actually started building yet. But I've set the wheels in motion, and hope to be able to report back on this shortly.

    Regards,
    Duncan
     
  11. Feb 2, 2012 #31

    Aircar

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    Duncan --thanks for your tactful reply and the advice that you will seek some outside mentoring -that's reassuring . I hate writing on this forum actually because as soon as you take the time to correct any poor composition or typos or left out words that you might have thought but didn't type the bloody whole lot just evaporates --usually I am doing it after midnight and not particularly 'sanguine' to use your description (I am sure you meant why am I not sanguine too-- about the tunnel idea . The other option to get better data is a whirling arm --like an overgrown Hills hoist (a rotary clothes line like a maypole for US readers ) --you could hook up a 240 volt motor and get some reasonable airspeed and the bigger the forces involved mean you can use cruder measuring equipment like fish scales. Such things were used way back --the Wright brothers tested airfoils on the handlebars of a bicycle at first before building their tunnel and you can even drag a model through water and get the right ReNo and large forces --the aerodynamic forces decrease as the square root of the velocity and become next to nothing at low speeds ==friction etc will swamp anything .

    your design is not intended to uplift enough fuel to fly from the US to Japan as Peter Garrison's Melmoth was (and did) so he NEEDED a fowler flap (with fixed slat on the flap ) --needless complication is just that and I doubt you have any idea of what it entails --such things as synchronization of both sides and the complexities of flap load reaction etc ( I spoke to burt Rutan at Oshkosh in 98 and made him aware that his "three point flap support "patent was in fact anticipated - by Kurt Tank -designer of the FW 190 etc which actually pleased him --ther new 787 flaps (single slot and also quite uniquely supported were tested at DSTO while I was there --had to tip toe around during the max load tests and observe it all while eating lunch --just the loading of the flaps was needing dozens of frames(whiffle trees ) and hydraulic jacks etc etc
    Fowlers are complex in determining accirate loads as affected by the jet pod wakes and undercarriage wakes etc etc -- to do it properly is a full on job (just avoid the wake thing by putting the airbrake if any elsewhere than in front end send.
     
  12. Feb 2, 2012 #32

    Aircar

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    I checked my memory on theory of wing sections and sure enough there is quite a lot of design data in it on fowler flaps --it is not unusual to have the flap operate on a two phase system --out first then deflect ,-rather than the whole show rotating about a fixed pivot and the data available in TOWS and the NACA Cranfield or NTIS link n has copious examples of papers like "Pitching characteristics of a wing of aspect ratio 6 equipped with partial span fowler flaps" --I cannot wade through the maths on these sort of papers anymore but you can easily get the data you need from the test results of 'reduced' data to co efficient form and from the general form of the curves see how sensitive the forces are to various parameters --the slot configuration is quite sensitive on most fowler set ups -- for example one aircraft I did some testing on had a torque tube crossing the fuselage to the flaps that started outboard of a fixed centre section --the length of the torque tube was five feet on one side and three feet on the other --from the driver motor( 8ft wide centre section unflapped) so that extending flaps resulted in differential twisting of the, undersized, torque tubes so it wanted to roll over and even in level flight was 'listing' due to this )

    The effect of flap extension is to make a big step in the spanwise lift and almost certainly spin off vortices from the outer and inner ends which will very likely impinge on the horizontal tail,- both shaking and non linear trim changes would be likely and virtually impossible to calculate but reproducible by a WHOLE aircraft model --just testing a piece of wing section will tell you only what a wing of infinite span in isolation would do --and you get that by the barrow load for free from NACA and elsewhere (RAe papers,AGARD,OSTIV, AIAA,SAE, and others -- the co efficients need to be read carefully as mostly but not always the Cls are referred to the UN extended wing area and the Cm values possibly likewise .

    BTW check your design against the Venture ("flying egg") --designed by the same person as the Piper Meridian --someone said it might be called NuVenture now -- this is also a very truncated fuselage aircraft with quite comparable general layout --reading a couple of flight reports would be a good idea - it was very fast and so forth but a real handful --anyway that's the sermon for tonight ( I think I got the flap question covered --The other poster -off screen now )
     
  13. Feb 2, 2012 #33

    rtfm

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    Thanks Aircar.
    Strangely enough, I have never had posts go missing, even though they take quite long to write sometimes. But having said that, I have probably jinxed myself. :)

    As is quite evident, the Venture was a significant influence on my design. I have read a number of flight reports on the aircraft, but probably the most telling commentary on the plane came from Harry Riblett, who strongly criticised the wing, which had a much thinner tip foil than root, making it prone to tip stalls. I will definitely avoid that error. Other than that, the reports seem to suggest a very predictable aircraft, which was not at all pitch sensitive. I believe the Razorback will behave itself very nicely, with its generous ThC

    I can quite understand the torque tube issue. I plan to operate my Fowlers hydraulically, with a single linear actuator linked to a number of bellcranks for each flap.

    Nice background stories, thanks. You always seem to come up with little gems of aircraft lore, seldom found elsewhere.

    Cheers mate,
    Duncan
     

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