(rewritten article from Letectví + kosmonautika magazine 6/1998)

In the world market there is not the main HOW, but WHY. To design some product according to order, to make some strength analyzis, and - with acceptable quality to produce that - enough cheap - is normal around whole world . But there is the problem - to find the right order . The right goal. Every manual for starting manager  will explain You, the success of company is connected from 70% with pre-manufacturing stages of development . The most valuable is an IDEA  .

The base of success is connected in pre-project stages - in correct marketing , technical study and preliminary project, finding correct need of investitions, correct money  for correct target in correct time.

what - why - what time

From the reasons, world producers employ in marketing and preliminary design departments great teams of top specialists, creating studies and prelimianry designs - from which the very small part will be realized in the future. This chosem project has to be the perfect hit "to the black pole".  

To start development and production without perfect preliminary design and marketing analyzis is self-murder. - and a lot of world companies brought themself to the border of bankruptcy this way.

Take examples of not-typical aircraft concepts ,  in the time of their start evaluated by magazines around all the world - compozite Learfan I bankrupted afte very long development, CBA 123 Vektor project was stopped, production of composite canard bussiness-prop aircraft  Beechcraft Starship was stopped by No. 53. Problems are with  avantgard "three-areas" Piaggio Avanti, long time You cannot hear nothing about business aircraft OMAC 1, Gulfstream Peregrine, AJI Hustler...

In the same time , their successors - more conzervative planes of companies, survived their extravagant  trials, won the success  (Beechcraft 1900 D, Embraer 145).

Market is - looks like- strongly conzervative  and does not accept too great steps.  Ant that is valid including business airplanes - although a lot of people think , potential owner will want to have something not so much usuall ....

Although of that, some vell known world companies still prefere to touch "first line".  As if they do not understand, that the many part of medals are awarded to  killed soldiers...

So - progressive concept of design does not mean - aircraft has to be succesfull from the side of sales.

Succesfull project means to find the right levelling between performances, ergonomy, aestetic look and cost of serial aircraft - and interest of market about this way developed product   (resp. acceptability of chosen conception , technology and  design by real market )

Design offices  Tupolev, Suchoj, Mjasičev and next companies , created on the rests of soviet "OKB bureaus", show another using of extravagant projects.  their oreliminary design teams creates a lot of studies - not to be realized, but to be interesting mainly. Between studies of sport and business planes of not typical concept, monster cargoo machines and ekranoplans there are not missing  supersonic business jets, or machines, powered by adapted engines, using hydrogen fuel .

Looks like, the reason is not to be realized, but to show what is possible - to find some capital from rich companies abroad.  And for that - to be not typical can be perfect value .

Without view to the future - it is no way

Company, which will not look to its future is prepared to be canceled , or to change to supplier or assembly workshop for others.

And to look to the future is good to do without  blinders.  It is needed to try more ways, to find the right one. So studies and projects of not typical concepts are needed to try too...

Ability to prepare that, and real evaluation of its perspectives is perfect presentation of company potential, saving opposite to competitors and opposite to own ont inteligent steps.

The idea, there is possible to prepare some project on the background of specific order is not the best - as a first you are losing the time ( so abilities to prepare more alternative solutions) and as a second - somebody has to give You that order . And that is usually done according to preliminary studies.  To ignore this is prospective way to the hell, and from that reason Project department of LET Kunovice is all the time preparing a lot of studies and projects, which - ane time - could be moved to its next serial production .

So, in the archive of LET development departmen, You can find great line of studies and projects, which were not realized. Till now, there was not usuall to publish that only. So, forgot the time, when magazine Flight was marked by stample of TOP SECRET - and let me to introduce some of them :

 If we return to the history, the most succesfull aircraft - developed in LET  - is L410. Before L410 was moved to the serial production, preliminary design department prepared after L200 Morava aircraft a long line of studies and projects, sometimes not so much usual. On the background of them, good marketing and project of L410 was built.

Original design of L-420. First designs with Astazou engines were not so much similar like final   L-410 Turbolet .

And there were not small amount . sixties was full of creating invention. After turboprop version of a little bit bigger "aerotaxi" L-300, stopped in very prepared stage, there was followed L-400 project for till 12 passengers, conceptually similar like some that time old designs  (like Handley Page Herald).

Not so many people know, there were developed projects of other Czech companies competitors .  Not only project of military trainer L-39K (kunovice's oponent of L39 Albatros).

By my personal preference of planes "for people" there was really interesting for me project of sport aircraft family project XL-500, competitor of Zlín-line , from which, only Z-42 and Z-43 were produced.

XL-500

Original study from  1962  shown buidling of more aircraft types , using the same subassemblies and parts, including twin-engine aircraft called XL-542.  Mode detailed project from year 1965 calculated with four types only .

XL-500, original design from year 1962.

XL-510 would be elementary school plane, fully aerobatic with two persons on the board.  Focus of that plane was small cost, and from that reason was equipped by fixed landing gear and cheap engine M-132 without compressor  (120 HP).  From the reason of aerobatics preference , one-piece canopy was used, openable to the front, control system was standard one. With dividing of canopy in the symetrical area, with type of undercarriage and summarized geometry - this aircraft looked like family from today Sova ( Skyleader) LSA plane.

XL-500 (left) a XL-540 (right) - the most performancced from line  XL-500, four-seat all-metal aircraft with retractable gear.

XL-520 was the same aircraft of higher level - with more powerfull M-137 (180 HP) engine, equipped by IFR avionics , able to do towing and with one pilot crew able to do higher aerobatics  (in that years scale of course).

XL-540 was four-seat aircraft "for turist purposes and business traffic ".        Basic type of line was equipped with retractable undercarriage and powerfull engine M-338 with 235 HP. Roomy cabin with side doors was fully upholstered , with heating and air intakes, isolation opposite to noise and winter conditions, and large baggage compartment  ... and was designed in collaboration with art stylists and offered in that time not usual comfort.

XL-550 was coming from XL-540, but for cheaper price with fixed landing gear, engine M-137 without compressor and basic VFR instrumentation only.

Opposite to Zlin Z-40line focus to be maximally simple (finally not so much succesful ),  all Let projects were aerodynamically clean , with trapeze wings and empenages , and with streamline-designed fuselages. There were used art-stylist in that projects, so vizual feeling from that line was perfectly prepared, together with interior styling. All planes used riveted aluminum alloy semi-monocoque design , which gave them long life and acceptation ...

In this study, there were shown all abilities and skills of LET Kunovice development team, after which next designs were even better.

XL-600 and XL-1000

- were projects of jet planes , in eyes of their designers planes, coming to change  Il-14 and An-24 in the air, including similar western" aircraft types.  

Cut of aircraft XL-1000 Smaragd (top) and laircraft XL-600 (bottom)

More ambices XL-1000 Smaragd from 1963 should carry 40 to 48 passengers by speed  860 km/h in the lines 850 to 1200 km. Aircraft with swept wing, T-tail and widebody pressurized fuselage  , powered by 2 jet engines  RD-22DP with "take-off thrust 2845 kg", placed on the rear part of fuselage sides , used from airports with length untill 2000 m. Optimization for shorter range would give in average range till 800 km better economic parameters, opposite to competitors.  During first works, designers calculated with help of Soviet Union companies, but after L-200 develoment it was trying to do tooo big step...

A year after there was created project  XL-600, which was shown as replacing of DC-3 and Li-2.

Smaller  "600" was coming from Smaragd design, for using from shorter airports till 1000 m and for smaller speeds was designed with simpler straight wings . Two engines "with static thrust  1850 kg" was giving to aircraft with MTOW 10 000 kg speed around 740 km/h.  24 passengers in roomy cabin  with seat pitch  850 mm could use range 600 km, with 30 passengers   was range limited to  450 km.

Study calculated with luxury reprezentative verzion for 16 passengers, with range 1100 km. Typical solution of that types was rear cargo/passenger doors, between engines, under fuselage . Solution, used then in Russian Yak-40 design

Among of that - still relatively normal projects - You can find sometimes really unique studies : For example, study of VTOL flying car , prepared by  Ing. Janík, which solved not only that time very popular problems of engine and propeller folding and closing in horizontal flight, but in the same time general focus of that kind of flying vehicle... starting with very good done styling, closed to car industry access.

Because it was personal activity of its author mainly, people called that designs "Janikoplan" (airplane from Janík design).

Personal VTOL lairplanes "Janíioplan" were in the time of its creating really masterpieces  .

Both designs have "tunel powerplants" (propeller in ring) for vertical take-off , installed in front and rear part of flat fuselage, creating something like lift-body with V-empenage and cockpit for passengers in the middle .

Engines should be placed inside of fuselage body in both sides of rear part, with air-intakes on the sides of front part.  Short , slowly swept wings was equipped with fuel tanks on its ends ( like Morava aircraft) - which was possible to leave during the flight ( ?) Variant  with   turboprops Turboméca Marboré II should have two tunel- powerplants , secondary powered from jet engine ,  during horizontal flight covered inside by the system of  jalousies and covers . Variant with turboprops  Turboméca Astazou á 442 HP used identical front powerplant , with rear foldable propeller in the ring.

Airplanes should carry 6 passengers by the speed of 510 (400) km/h with range 1000 km , by the 1/2 of service expenses opposite to - that time popular business jet  M.S. 760 Paris.

Study wa of course too much avantgard - to be -  in czechoslovakia conditions during sixties ( although during "Prague Spring", still in communist system) - realized . But it can be typical example of abilities and range of goals of that time LET Kunovice development team - to be able "to see over the horizon".

During that time,  Let brought to the air  (together with Moravan) agricultural Čmelák aircraft, and around 1965 returned to design of more modern  "replacement of An-2". But either first study of L-410 still did not have all perfectly prepared.

To be dateless,  L410 receive during long development, with a lot of family studies and projects, so with day-by-dat increasing of developmnet team skills  .

Projects from the last years

No so during last year  we passed away the mode of not tradicional conceptions. For example - in the time of 19-passenger carrying project L-510 preparing, we prepared alternatives of pusher engines on the pylons  in the rear part of the fuselage , or with "three-areas alternative in the style of Piaggio Avanti . Both was that time very evaluated as new access ....

But after detailed analyzis of performances and aerodynamic calculations, we left that - as something what is bringing problems only, without some real advantages, without increasign of performances.

It is not so much nice to hear that for funs of not typical conception ( like I am too ) - but that is it  .  For not military  aeronautics  is much better to use technologies and solutions, solved from "other" money. Not typical conception stay to be acceptable for  military purposes , or for fun designing of sport airplanes.  Only that, what is accepted by  community as existing and functioned speciality - and after that they accepted that, can be used for massive sales.

L-510

L-510 is just now really the most finished project of brand new aircraft from LET Kunovice design .

Drawing of L-510 final look .

L-510  was projected as  "wide-body",  so, solution of large passengers cabin was the main item of its design. Chosen system of undercarriage retracting is creating possibility to minimalize undercarriage pod - and summarized fuselage crossection.

L510 development was started on the background of Soviet-Union specification for L-410 and An-28 airplanes replacement,  but step by step , and after destroying of Russian market , L510 focus was changed more to world-wide market needs and trends.

Aircraft was from the beginning prepared in not-typical conception look, but after large analyzis, final conception was more classic - wide body allmetal highwing, with T-empenage.  After some time, our result was confirmed - because all not typical concept aircraft of more companies was left. Some of them brought their producer to bankruptcy  .

19-passenger, pressurized  L-510 wit range to 2000 km is designed to competite to all aeroplanes in his class in the whole world, but to offer more large interior and the best performances - and in the same time was giving  ability of using in very hard service conditions.

Extremely focus was into ergonomy of passenger cabin, together with perfect shapes of fuselage, what bribgs more detailed design of front fuselage part, and undercarriage retracting system, created very good fluent shape and minimal crossection of undercarriage pod.

L-510 is from this reason able to offer much more , then every today existing commuter and in the same time, creates together with   Turbolet (L410)  and L-610 G perspective of closed offer of small LET civil aeroplanes .

L-510P, variant , the most closed with original look of  "L-410 replacement" , called so L-450.

FL-710 FX Freighter

FL-710 FX Freighter was project of airplane for air-transport of standard airplane containers .

Fairchild-LET FL-710 6FXT - variant called  "Boxplane" for delivery of six containers LD-3. In the basic version for  containers LD-3 (FL-710 6FX) there was calculated with maximal using of design subassemblies from L-610 G - wings including powerplants , empenage, main part of undercarriage , control and other systems. Not pressurized fuselage with square crosssection should be brand new, epřetlakovaný , with fixed undercarriage and large cargo doors. 8-container alternative  (FL-710 8FX), especially with rear cargo ramp ,  calculated with much more changes...

Project was prepared on the background of wishies and comments of Fairchild company in the year  1993.

Family Air

There is not so much known in the public,  project of  Family Air aircraft was after first introducing designed by Let development team as an order of LOK Praha  during 1993 and 1994 .  Idea of ing.  Smrček was dramatically redesigned by Letu design team.  Stopping of payments from the side of orderer brought this project  - in that times in relatively defined stage - to be "frozen".

L-110

After stopping of works in  Family Air project, there was prepared study of idea to prepare own four-seat design called  L-110, designed fully according to own ideas, using all skills , received from Family Air development - including using of parts, subassemblies, and sulutions, originally prepared for Family Air...

Followers of L-410

After wishes of Soviet - side to reduce take-off and landings , there were prepared studies of  Turbolet with fixed gear and tapered fuselage for 12 passengers, with engine TV-10 and T - empenage. There was prepare three-engine alternative too called that time UVP.  After skills with L-410UVP-E , during eightees (1986) there was prepared longer version of aircraft, to increase economy of traffic . TThat time , by  Ing. Smrček prepared study   L-410UVP-V sghould - with more powerful engines M-601F carry 22 passengers.

Team of Ing. Píštěk and Ing. Fridrich prepared then study of one-engine alternative  zpracovával  L-410 with tapered fuselage and fixed undercarriage (alternative of   Ae-270 project ). These works did not receive any interest from waited customers.  During last years  there was prepared study of installation of more powerfull engines from Pratt and Whitney PT6. Project L-430 offers not only better performances, but - thanks of bigger redesigning - better passenger and traffic comfort . Studiy L-410/420 Cargo solves till now not solved problems of cargo transport in L410 - without limits of cargo compartment . Maybe directly that realization can make L410 family still interesting for 21st century market.

L-410UVP-V ("Vstavka") - enlarged version of L-410  aircraft was not moved to production...

To the end?

It is nice, although of continuing financial problems of technical inteligence in Czech republic and its removing to other kind of business - management of Letu still understands, the true value of company is based on stabilized team of top experienced specialists  , able to offer to tradicional aircraft producer from south Moravia - the Future.

(this was something like joke - after a year, i left Kunovice factory from position of Head of preliminary design to small company for two-times higher salary. The main part of my friends left LET before myself)

Ing. Jaroslav Dostál, head of preliminary Design Department a. s. Let
Letectví + kosmonautika 6/1998