2009-03-11

Y-tail, V-tail or crusifix form ?

Here is a complete story of Bede-5b:

http://www.absoluteastronomy.com/topics/Bede_BD-5

Here is a pic of the very first Bede-5B with v-tail. No wonder it was unstable; the v -tail is way too small.

http://www.airport-data.com/aircraft/photo/040961.html



I have discussed this pusher V vs. Y tail issue several times with aeroengineer Eric Ahlstrom and the Y tail has been recognized as the valid form for this kinda pushers. His DART design had such and seen here; http://www.renaissance-research.com/projects/

I wonder why Bede did not put the rudder in the end of the fuselage and leave the V work as a rudder stabiliser and working elevator.

The safety record of BEDE-5B was terrible:

Insert from the link above,

Over the next few years the aircraft garnered what at first glance appears to be a terrible safety record. The earliest kits shipped with the short "A" wings (optionally), and all four examples completed with these wings crashed on their first flight, with three fatalities, largely a side effect of a 100 mph (160 km/h) landing speed combined with the tiny wheelbase. Nevertheless the current record holder of the FAI C-1a/0 (300 kg or less takeoff weight) class speed record over a 3k m course at restricted altitude is a BD-5A (listed as BD-5B but used -5A wings for the record attempt) with a Rotax 618UL 74 hp two-stroke, three-cylinder water-cooled engine..Most of the crashes of -5B models can be traced back to pilots who were not prepared to fly the aircraft. It is not uncommon for kit or plans-built aircraft builders to spend years on their projects and neglect their currency requirements to maintain their pilot skills. Many accidents took place because builders were in too much of a hurry to fly an aircraft that was not truly airworthy. Several crashes in the -5B models were found to have taken place due to engine failure on takeoff, both due to the mix of "oddball" engines as well as endemic cooling problems.The reason this is such an issue with the BD-5 is two-fold – the high line of thrust means an engine failure immediately results in an unexpected (for most pilots) nose-up attitude change. Pilots who fail to fly the aircraft first and then attempt to restart the engine inevitably stall, with the associated consequences. This was aggravated by the fact the original wing had a very sharp stall with little warning and a nasty tendency to "snap roll.". To make matters worse, a documented manufacturing error in some wing skins delivered to kit builders exacerbated the problem. A rather small center of gravity range also added to the problems of properly trimming the aircraft.

I think I have solved all problems stated above.

1. I don't have a small wing option ( like VmaxProbe..very little wing and no wash out )
2. Landing speed is normal ( 65-80 km/h ).
3. High line of thrust is now like centerline ( with wing that is shoulder level positioned ).
4. Wing foil will be studied to be ideal for a small plane.
5. Bigger tailfeather area will ease the small ( narrow ) CofG problem ( also the movable seat will help ).
6. Cooling problem is handled with a totally new system with ram-air effect.

Molton Taylors first big success the Taylor Aerocar inflight. http://www.youtube.com/watch?v=NQ_D22Me_4A http://www.youtube.com/watch?v=GUgJOnhXorc&feature=related

It has got the Y-tail as well.

6 comments:

  1. V-muotoisissa jää toinen komponentti jarruksi. ilmeesesti tässä v pyrstö hoitelee korkeusperäsimen hommat ja "kannuspyörän suoja" sivuvakaimen ja sivuperäsimen. potkuri piiskaa sivuperäsintä läheltä, jottanotta Kannattais tehä sivupersin sekä ylä- että alapuolelle niin potkurin aiheuttama sysäys olisi eripuolille tasapainos. (tietysti jäykkä tankovälitys sivuperäsimeen) Sitten ehdottaisin korkeusvakaaja deltamuotoon pyrstöä tukevaksi ilman peräsintä ja sen sijaan kokonaisuudessaan kääntyvä canardi eteen. Tällöön voimat menis oikeeseen suuntaan nostetta lisäten kun isolla? kohtauskulmalla tullaan laskuun. Jokatapaukses tämmöönen harrastekone tehään muuten hyvin vakaaksi jolloon siihen sopiis canard. Sauvan korkeusohjainvoimien välitys olis kans mahrollisimman lyhyt. Piirroksessa kannus on peräsimen ja vakaajan välissä, eihä se siinn voi olla, ilmeesesti se tulee sivuperäsimeen ja alin laakerointi päittäisvoimaa kestäväksi, nii on pyöräohjaus mukana polkimis. Kun kerran kuvan perusteella peräsin on täyskorkea vakaajan kanssa. Näin pienes ei varmaankaan kevittäjää tartte, mutta vois olla just tuon pyöränpuolikkaan verta saranalinjan etupuolella ja pyörä tasan saranalinjas nii ei iske kintuille ku maahan koskettaa peräsin sivussa. Tai sitten on ohjaamaton sivuvakaajan puolella. T:Pv

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  2. Niin siis kuvaa katsottuani ehotan kiinteää pientä korkeusvakaajaa perään pitkänä deltamuotoisena ja symmetristä sivuperäsintä pystysuoraan potkuriakseliin nähen. Korkeusohjain canardina eteen kokonaisuudessaan kääntyvänä, jolloin mielestäni sekä otsapinta-ala että ilmavirran häiriöt ennen potkuria olis mahdollisimman pienet.

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  3. Pienviljelijä !

    Kehoitan pysyttelemään tämän designin puitteissa kommenteissa.

    t. Jukka

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  4. Have a very good luck completing this project. It´s perfect. Don´t listen those morons who always try to restrict geniuses like you. You´ve figured everything out.

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  5. Kiitos Thanks for these kind words !

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