How much trim control do LEVCONs provide?

element1loop · by **element1loop** » 20 Aug 2018, 02:01

vilters wrote:First you ask a question, then you don't mike the answer, and start insulting. N I C E ... Stay off the booze and drugs man..

Believe me when I say I'm being really nice.

As for your crap about "booze and drugs man", I use neither, but you really should have a look at your comments and ponder what a rolling train-wreck they are. :doh:

vilters · by **vilters** » 20 Aug 2018, 13:07

Ok, finally back to a more or less normal tone.

Waiting for 3 answers:
a) What surfaces does the Trejas use for pitch trim? => You say it is not the TEF, so what surfaces are used for pitch trim?
b) During the flare at landing, just before touch down? In what position are the TEF?
c) What pure Delta uses its TEF as flaps in landing configuration?

Best regards, Tony.

element1loop · by **element1loop** » 20 Aug 2018, 14:18

https://i.imgur.com/8e2pL3P.jpg

sprstdlyscottsmn · by **sprstdlyscottsmn** » 20 Aug 2018, 20:04

I don't put any stock into that picture because it is sitting on the ground unpowered. You can find pictures of F-16s the same way, with tails all the way down. Does that mean that is their landing position? I would look only at pictures of deltas landing or taking off. All your picture proves is that the trailing edge can go down. If the Levcon was up like that on final it would be stalled.
https://www.f-106deltadart.com/piwigo/u ... ac9d4e.jpg
The above image shows how the Elevons are deflected up to hold the nose up.

madrat · by **madrat** » 21 Aug 2018, 04:05

The missing ingredient is the stability of the design.

Typhoon fights the canard to constantly pitch nose up.

F-106A is a stable design.

vilters · by **vilters** » 21 Aug 2018, 10:54

element1loop wrote:https://i.imgur.com/8e2pL3P.jpg

That is a static picture with no hydr pressure on the TEF and they fell Down under their own weight.
Look at any static picture of the tails of an F-16, F-18 and so on.

In the flare, one foot before touch-down (30cm), they are UP, to crank the nose UP.

F-16ADF · by **F-16ADF** » 21 Aug 2018, 14:37

Old stable Deltas like the Mirage III, F-106, F-102 were known for having a very long landing run, because they cannot use their elevons as flaps. (Flaps lower the approach speed, and increase the angle of descent). I think the same applies to the Mirage 2000, yet its roll out is a bit shorter and lands a bit slower due to RSS (I believe). Old stable deltas also beat up their tires because of the high landing speeds.

Here is a vid of Rafale M carrier ops. It seems that approach to the carrier (due to the high up deflection of the canard), the pilot has both elevons down (i.e. acting as flaps, though only maybe set to 15-20 degrees max). But I'm guessing that he can only use his elevons like flaps once again due to the up deflection of the canard. Carrier Rafale lands at a pretty steep angle. Yet on the CAT launch, he has his elevons "UP".

https://www.youtube.com/watch?v=duL_95-OLug

Here is a Gripen landing. With high up canard deflection, minor elevon down input (I guess you can say acting like 15 degree flaps).

https://www.youtube.com/watch?v=AZUN3Tyl-PQ

I have never seen Eurofighter Typhoon do the like. Maybe it's all in the FCS laws?

element1loop · by **element1loop** » 21 Aug 2018, 15:12

Exactly.

And I also pointed out already (in detail) that less flap is required when the flap surface is further away from the pitch rotation axis, thus delta TEFs have more leverage on the air, so need less flap deployed deflection to achieve strong flap effect. The same leverage relationship of course applies to the canards on delta's too.

But this is all beside the point, and vilters is again derailing the topic question, which is about:

Whether LEVCONs can counter deflect enough air to trim out the induced pitching of flap deployment on approach--it's not about landing.

He wants to warble about anything but the topic--it's looking a bit pathalogical at this point.

F-16ADF · by **F-16ADF** » 21 Aug 2018, 15:26

I am not taking sides in this discussion. I have zero knowledge on LEVCONS and their associated FCS laws.

Here is a Mirage 2000 landing:

https://www.youtube.com/watch?v=FdMmjboX0J0

and

https://www.youtube.com/watch?v=ARj6YqfSXGs

sprstdlyscottsmn · by **sprstdlyscottsmn** » 21 Aug 2018, 15:37

madrat wrote:The missing ingredient is the stability of the design.

Typhoon fights the canard to constantly pitch nose up.

F-106A is a stable design.

You are right, but in these three pictures it still shows a Tiffy trailing edge up.
https://theaviationgeekclub.com/wp-cont ... yphoon.jpg
https://c8.alamy.com/comp/FX15M4/raf-eu ... FX15M4.jpg
http://www.freemages.com/album/aeronaut ... anding.jpg

sprstdlyscottsmn · by **sprstdlyscottsmn** » 21 Aug 2018, 15:39

element1loop wrote:Whether LEVCONs can counter deflect enough air to trim out the induced pitching of flap deployment on approach--it's not about landing.

For my part, I don't see LEVCONs as suitable for this because while they could pitch up to hold the nose up, countering the flap moment, they would likely be producing a stall under landing conditions as, unlike canards, the airflow cannot rejoin behind it to flow over the wing.

element1loop · by **element1loop** » 21 Aug 2018, 16:17

Yeah, that makes sense to me too spurts, I obliquely mentioned that effect and undesireable outcome of luffing the inner-wing skin earlier.

Seems to me the EF images are set to negate ground-effect, not because they would stall or land hard, but because they would tend to float too long in it. If you reduce flap they can spill/vent the compressed air cushion faster, and can sink through it more smoothly/progressively, imo.