Lavi - An Engineer's Perspective

[@wombat3455]

An outstanding lecture, extremely interesting!

[@pedroprietofuertes7147]

Brilliant presentation. Thank you very much

[@squishface80085]

John, How do you think the turning and specific excess power performance of the Jas-39 Gripen compare to the Lavi?

[@JohnGolan]

Good question. I believe it was essentially answered on Slides 12 and 13 of the chart deck (time stamp 15:36 to 19:01 in the video). For a first order approximation, neglecting differences in aerodynamic performance, lower wing loading (W/S) will lead to higher turn rates, and a higher thrust-to-weight ratio (T/W) will lead to superior acceleration. As illustrated under the chart on Slide 13, the Lavi has slightly lower wing loading and a slightly higher thrust-to-weight ratio as compared to the Gripen in a point air defence configuration (full cannon, two air-to-air missiles and 50% internal fuel). The difference in performance between the two platforms, however, would be less than between either of them and say, the F-16 (higher wing loading but higher thrust-to-weight ratio). A pilot flying the Lavi or Gripen would have been trained with similar strategies for engaging dissimilar opponents in a maneuvering engagement.

[@squishface80085]

@@JohnGolan Thank you for the reply. That is more or less the conclusion I reached by watching the video but wanted to know whether or not my understanding was at least close to correct. My next question is what is the relationship between thrust to weight...wing loading...and specific excess power? Specifically as it relates to bleed rates at the maximum allowed turn rate. For instance the publically available EM diagrams for the F-16A and Mirage 2000 show bleed rates -1000ft/sec for roughly a 20 degree per second turn at 15,000 feet in the same configuration as your chart does for the Lavi. How much more engine power or how much less wing loading would these fighters have to have in order to cut that bleed rate to -500 feet per second? I am trying to understand the scale; for example would it require something a minor upgrade in engine power...or would it be the equivalent of strapping an F-22 engine into the Lavi airframe while also making it weigh the same as the engine it originally had.

[@JohnGolan]

@@squishface80085 If you're looking to understand energy bleed rates and trade factors, I'd point you to the series of videos that I published previously on aircraft peformance. The third video in that series includes the equation for specific excess power on Slide 4 of the chart deck. Specific excess power is directly proportional to the thrust-to-weight ratio, and is inversely proportional to the lift-to-drag ratio. kzbin.info/www/bejne/d4qqaYCheZ2csMU The sensitivity of specific excess power to thrust-to-weight should be obvious. The sensitivity to wing loading, however, is buried in the lift-to-drag ratio. To fully quantify the relationship, you really need to know the drag polar - including the effects of Mach number and g-loading. I'll used the drag polar calculations behind the Lavi as an example to perform a quick sensitivity study. At 15k ft altitude and a turn rate of 20 deg/sec, the Lavi is projected to achieve a bleed rate of -1000 ft/sec at roughly Mach 0.70 (438 knots). Increasing the thrust by 10% would decrease this bleed rate to around -935 ft/sec at these same conditions. Reducing the wing loading by 10% would decrease the bleed rate to around -875 ft/sec.

[@sailorssilence1983]

hi squish

[@bob-wo3ir]

Great content !

[@RAWtiercel]

Hi, I just bought your book, and have been perusing your videos. I have a question about the close-coupled canard configuration. How does the canard-wing interaction improve lift to drag ratio? I had been under the impression that the vortex spilling off the canard was useful because it could delay boundary layer separation over the main wing, which allows for higher alpha and thus higher lift and more Gs to be pulled. But I was also under the impression that in cruise flight this vortex interaction would impair the efficiency of the main wing, so much so that designing canard-configured fighters is a balancing act between making the vortex interact a lot with the main wing at high alpha, but barely at all during cruise. But as you say, the Lavi was designed for maximum cruising range and it has absolutely enormous canards that are very close to the wing. So how does this actually work? Thanks in advance.

[@JohnGolan]

The subject of canard-wing interactions is covered under Appendix 1 in the book. In a close-coupled canard configuration, the influence of the canard is intentionally maximized. This changes the distribution of lift over the wing. The downwash from the canard will decrease wing lift, while the upwash from the wing will increase the lift from the canard. If done properly, the result is a net increase in the overall lift produced by the wing-canard system, and a more optimal spanwise lift distribution - even at transonic conditions. If you're still seeking additional details, I'd refer you to the end notes in Appendix 1. The published literature has documented this effect extensively, with the study published by Tu being among the most comprehensive, although further test data is also presented by Rom, et. al.

[@RAWtiercel]

Aha! Thank you.

[@teorinolagamba]

Excelente explicación.

[@AeroSail727]

This was a very informative video. Would you be doing more case studies? Also could you include more about the E-M diagram and mathematics of flight theory? Nice job on the video!

[@JohnGolan]

Thanks. If you look on my KZbin channel, you'll find a series of videos covering the subject of aircraft performance. Part 4 deals with Energy Maneuverability Theory: kzbin.info/www/bejne/enaXaWd-qLOSmsk The material is also covered in my blog: john-golan.blogspot.com/2015/08/aircraft-performance-part-4-energy.html In addition, the subject of E-M theory is also covered in Appendix 7 of the book.

[@bradhartliep879]

It would be interesting to know why they chose the PW1120 over the PW F100 .. At that time [ late 70s - early 80s and well into the 1990s ] the PW F100-100 was powering F15s and the PW F100-200 was powering F-16s - two aircraft / engines Israel was flying .. They even upgraded their F-16 A/Bs to F16 C/D capability but retained the PW F100s over the GE F110s .. The F100 has a higher thrust to weight ratio , higher max take off weight and a larger combat radius than the PW1120 and all of the Jet Mechs were trained on and experienced in repairing the PW F100 .. As an F100 Mechanic on F15s and F16s, I was one of the first 5 AF Mechanics trained, by GE Engineers, on the GE F110 and spent the next three years maintaining F110 powered F16s and training AF Jet Mechs how to maintain the F110 on the Flight Line, Phase Docks and Intermediate Maintenance Shops .. In Combat, in the field, parts commonality is extremely important .. I'm surprised the Israelis didn't choose the F100 over the 1120 ..

[@muhammadfahadzahid7202]

It is said in the video that the F-16 like intake was chosen because of lower weight. My question is why didn't all the aircraft after that employed the same design feature ? (like the JAS-39 Gripen with its side mounted air intakes). This efficient configuration of air intake should freeze for similar role aircrafts (like we have been watching the tube and wing configuration for commercial aircrafts for the past sixty years).

[@JohnGolan]

The major disadvantage to the ventral inlet is its proximity to the runway during takeoff. It requires that the runway be regularly swept to remove debris. For a modern air force that expects to operate from major air bases - such as the U.S. Air Force or the IDF - this is expected practice. Debris can damage tires or puncture fuel tanks as well as risk ingestion to the inlet (remember the Concorde?). Sweden's air force, however, is expected to operate from remote, dispersed facilities, including roadways with minimal preparation. For them, the threat of ingesting snow or other debris outweighed the structural weight penalties from the side-mounted inlet design. Russian developers have tended to take a similar attitude towards inlet configurations.

[@muhammadfahadzahid7202]

I got it ! Thanks

[@yohl6538]

could you provide a short analysis of the F35 dynamic characteristics? there is only one main public source on the topic that I could find, and much controversy and PR noise. would be much appreciated!

[@JohnGolan]

Unfortunately, there are certain aircraft that, for professional reasons, I cannot publish an analysis of.

[@yohl6538]

Thank you john. That's really unfortunate -- the F35 project is shrouded in smoke screens, and the public is not getting the information it deserves.I personally believe it is a complete and utter fiasco. the gadgetry and sensors could have been retrofitted on current generation fighters. knocking down radar stations is not a good enough reason to billions in expenditure on inferior platforms

[@aaresale]

Thank you so much for your information. It would have been a great fighter program for Israeli. US was monster of world pressured to shut down.

[@JohnGolan]

You are most welcome. It was a privilege to reveal this story and little known history to a wider audience.

[@aaresale]

Full of Respect to Jewish People and their capabilities and achievements. They should have completed Lavi Fighter Program at any cost. I do believe that Lavi can match easily with Rafael and Gripen Ng.

[@Tzipora_Azoulai]

The United States financed this project to its own detriment. No one wants to lose income there's no point to blame them.

[@moisesbuja8698]

I would appreciate a video by Mr Golan of the IAI nammer/ Kfir. Kfir r. Iai nammer is quite the gripen ng, by a fraction of price. Nammer had one prototype. Comparing with rafale, latest f16 would be great.

[@scottwolf1131]

With respect to the high instantaneous turn capability of the Lavi, was this the result of the input of the combat experience and gun kill culture of Israel's Aviators of that era?

[@JohnGolan]

The Lavi was the product of numerous design trades, so finding a single, one-for-one causal link for its net performance attributes can therefore be difficult to achieve. Such attempts will naturally wander into areas speculation. It should nonetheless be acknowledged, however, that the compromise that the Lavi developers arrived at - with its relatively low wing loading and high instantaneous turn rate - would have naturally appealed to the pilots that were closely involved in the development effort, and who had accumulated much of their combat experience flying the Mirage III during the 1960s and early 1970s. Even those pilots that later went on to fly the F-4 Phantom, universally preferred the handling qualities of the earlier Mirage. Again, it can only be speculated as to how much those individual preferences influenced the requirements and design trades that later went into developing the Lavi. So unfortunately, there is no direct answer to your question. Only observations that can be made, and speculation stemming from those observations.

[@scottwolf1131]

Thanks.

[@edwinortega433]

Colombia debería comprar los derechos del LAVI para fabricarlo bajo licencia. La "CIAC" Corporación de Industria Aérea Colombiana, esta en la capacidad de fabricarlos.

[@oc101289]

its was finished at 1982, when israel shut down the program under US pressure and lack of funds for self demand, it first flew publically at 1986

[@Sithvulcan76]

We could use an airplane just like this right now! The F22 has ended production and the F35 is too expensive and not as capable when it comes to pure flight performance. This aircraft would round out an air force's need for an economical aircraft with good flight performance and would work well in a hi-low mixed fleet.

[@көрбүөччүуолатүргэн]

Еврофайтер это почти лави с двумя двигателями но лави универсальное

[@Tzipora_Azoulai]

EF-2000 Typhoon is a completely different aircraft. Lavi is an analogue of JAS-39, as well as Yugoslavian Novi Avion that didnt go into production and Tejas from India.

[@көрбүөччүуолатүргэн]

Лави мог бы затмить Ф-16 своей многофункциональностью

[@SoumyadipMondalsoumya16]

China copied Lavi fighter jet design and made j10.....

[@abhrajitdhar4628]

evidence?

[@SoumyadipMondalsoumya16]

@@abhrajitdhar4628 what type of evidence you want??

[@Tzipora_Azoulai]

They're redesigned the engine, avionics and tail of the airframe

[@chrisewing8407]

"No single airplane can be all things for all roles" ?!?!? But doesn't that undermine the whole rationale of the F-35???

[@gsopoagmle]

F35 is designed to be a generic on all level except on stealth and radar.

[@kaitang1700]

It matured into J-10C hahaha

[@bob-wo3ir]

"matured" 40 yr old jet.