[V.Narayan]

Originally Posted by Jeroen

Could you elaborate? I recall problems with longitudinal stability at high AoA.
Some problems with Mach Tuck? Maybe I am mixing up stuff here?

I'll draw out some hand drawings, a little later, to explain. Didn't find any drawings on the net that fully explain what happens.

[V.Narayan]

^^^^^^^
My attempt to answer the point about why T-tails get locked into a stall. I'll explain why the stall occurs as was discovered, tragically, through the BAC 111's flight testing at the prototype stage in 1963. After the deep stall occurs why an aircraft stays locked into the deep stall or swivels into tailspin is a whole different story -- (a) beyond by ken; and (b) with far too many variables and combinations.

Wing tips generate very powerful vortices i.e. spinning mass of air {separately they are also the cause of a lot of drag which winglets attempt to dampen}. Vortices are more powerful as speed slows or weight increases. Vortices are caused by more than one point on the aircraft but the wing tip or trailing vortex is relevant to this discussion and by far the most powerful.

In a conventional tail plane layout, in level flight, the vortices flow beyond the tail plane thus not significantly affecting the authority of the tail plane. See diagrammes A and B below. The wing and tail plane are in red and the vortices in purple. Vortices {or mini horizontal tornados} flow behind and slightly below the wing tips. In a typical mid-sized 60 tonne aircraft like a 737 the wing tip vortex would be felt even ~40 odd kms behind.

At a high AoA the vortices drift inwards away from the wing tip and are thus when seen from above roughly flowing in line with the tail plane - see diagramme D. However when viewed from the side the vortex is still flowing above the fuselage mounted tail plane leaving its authority largely undisturbed - diagramme C. With a T-plane configuration at high AoA the inward drifting vortex ends up flowing over the tailplane -- diagrammes E and F. This leads to a T-tail suffering from both being in the aerodynamic shadow of the main wing plus suffering the turbulence of the vortex. BTW these vortices even in a medium sized aircraft at 300 knots are very very powerful. This reduces the authority of the T-tail to zero causing the aircraft to enter a deep stall with zero lift from the main wing, the tail plane {or horizontal stabilizer} no longer able to stabilize and the machine plummets to earth, pointing upwards and with less and less forward speed.

From this discovery by the British came the stick shaker to warn of a stall. Prior to the BAC 111 incident the Tupolev Tu-104 had faced similar situations in commercial service. The new solutions helped the Boeing 727, Trident, DC-9, VC-10 and IL-62 all of which were under development in 1963

This explanation applies to commercial airliners with their moderate sweep, moderate aspect ratio wings. For deltas, low aspect ratio wings the concept is the same but the situation is different.

[Jeroen]

^^^^Thanks for the elaborate explanation. I remember now, love the drawings, very illustrative!

Jeroen

[V.Narayan]

Thank you for your insightful questions, Sutripta. I've moved them to the main forum for the benefit of all readers. I'm not an aeronautical engineer just a retired business wallah but I'll write what I know.

Originally Posted by Sutripta

Thanks.
I had asked this sometime back in another thread, when someone very authoritatively quoted verbatim from Wikipedia. And I did not feel like carrying on the discussion, to be fed answers from Wikipedia!

I did the drawings because the .com sites do not explain the inward drift of the vortex along the wing which is what brings it seriously in conflict with the T-tail's horizontal stabilizers. T-tails are not bad guys. Every configuration, as you know, has its plus and minus factors. That a T-Tail can get into an unrecoverable stall at a high AoA was discovered only in 1963. That BAC-111 prototype was testing how high an AoA was safe. Today's stick shaker and other cockpit/flight control surfaces come into play before that AoA is ever reached {a commercial pilot could explain more on that}.

The actual question I then wanted to ask was why do smaller planes like ATR42, Dash8, Whisperjet, and the business jets have T Tails. Understand that rear mounted engines don't leave much of an option, but then how are the problems overcome.

Great question. Interestingly a T-tail is more effective, than a conventionally positioned tail wing, in almost all flight regimes of an airliner or other non-aerobatic aircraft -like military transports or maritime recce planes. The clear air around the T-tail's top, largely undisturbed by the flow disturbances of the wing, in level flight, actually make a T-tail aircraft have much sharper control in pitch and roll, especially pitch. So for a commercial airliner which does not do Mig-29 maneuvers the T-tail, versus fuselage mounted conventional tail, actually gives better control especially while landing. Also T-tails now tend to be mated with taller vertical stabilizers. This puts the tail wings so high that except in an unusually high AoA the tail wings stay out of the shadow & {more or less the} vortices of the main wings. Most commercial airliner wing aerofoil sections typically stall at or below 20 degrees AoA. An ATR's wing shadows the horizontal stabilizer at close to 40 or 45 degrees which puts that risk beyond the flight envelope for an ATR. Similarly for other T-tail designs.

In conventional low wing configuration you must have noticed the tail plane is usually mounted higher than the wing {Boeing 737}. In small single engine planes with shoulder wings the tail wings are mounted below the height of the wing {Cessna 172} -- all in the interests of giving the tail wings clear air {or as clear air as practical, really}. At the lower speeds of say an ATR, of say 250 knots, the vortex doesn't drift in much. It drifts in further only with higher speeds say 400 knots.

Beyond a point it is six of one and half dozen of another -- it all boils down to what the aircraft's main role is and hence what aerodynamics it needs. For shoulder mounted wings T-tails are superior as they keep the horizontal stabilizers clear of the wing. Regional aircraft like shoulder wings as it enables them sit closer to the ground for collapsible door fitted air stairs, or to permit manual loading of pax luggage or in its freighter version create a rear ramp {e.g. CN-235 or An-26}. Military transports like T-tails as it gives them an unobstructed exit for air dropping of material or men.

Should the Caravelle be called a T Tail or Cruciform tail design?

Yes, cruciform.

Hope this helps.

[Jeroen]

^^^^^ Thank you, well explained. I have often seen it mentioned that T configuration makes for better STOL capabilities. There is certainly a large number of big and small military and civilian aircraft that sport a T-tail. So is it this better landing control the main contributor to STOL or are there other contributing factors too?

Jeroen

[Sutripta]

Originally Posted by V.Narayan

Great question. Interestingly a T-tail is more effective, than a conventionally positioned tail wing, in almost all flight regimes of an airliner or other non-aerobatic aircraft -like military transports or maritime recce planes.

Thanks. Saved yourself questions on the Globemasters and Galaxys! Which would have been the next item, after the small planes had been dealt with.

Suggest you edit the Wiki page.

Sutripta

[basuroy]

DeHavilland Devon( the only model of this type in India in Indian Air Force marking and most likely in entire world too).

Sukhoi su-7

Some French jet no one has heard about ��

[V.Narayan]

Originally Posted by basuroy

DeHavilland Devon( the only model of this type in India in Indian Air Force marking and most likely in entire world too).

Sukhoi su-7

Some French jet no one has heard about ��

Wow. WOW. WOW. Beautiful. As always I assume you have assembled these yourself and done the paint job too. I concur that Devon must be the only Devon in IAF markings in the world. That Su-7 colour schema is perfectly realistic.

[basuroy]

Originally Posted by V.Narayan

Wow. WOW. WOW. Beautiful. As always I assume you have assembled these yourself and done the paint job too. I concur that Devon must be the only Devon in IAF markings in the world. That Su-7 colour schema is perfectly realistic.

Yes all assembled and built by me. These were all done during the last few homestruck months. Flanker and then Apache are next

[Foxbat]

Originally Posted by basuroy

DeHavilland Devon( the only model of this type in India in Indian Air Force marking and most likely in entire world too).

Sukhoi su-7

Some French jet no one has heard about ��

Those models are just

The Su-7 picture looks like the actual aircraft rather than a model. Are the decals available for this in IAF colors ? Is the Shark mouth a decal or you have painted it. I remember in my childhood I put a lot of shark mouth decals on A-10s and some WWII aircraft.

Also is Apache the name of some weapon on the Rafale ?

[skanchan95]

Originally Posted by basuroy

DeHavilland Devon( the only model of this type in India in Indian Air Force marking and most likely in entire world too).

Sukhoi su-7

Some French jet no one has heard about ��

Fantastic work basuroy!!! The Su-7 looks almost real and the Rafale is just . Look forward to your Flanker and Apache.

IAF Su-7s, like MiG-21s from that era, were painted in some fascinating paint schemes. There was an IAF Vampire too that was also painted with a shark mouth.

Originally Posted by Foxbat

Also is Apache the name of some weapon on the Rafale ?

The Apache is an anti-runway missile that looks very similar to the SCALP/Storm Shadow cruise missile.

[basuroy]

Originally Posted by Foxbat

The Su-7 picture looks like the actual aircraft rather than a model. Are the decals available for this in IAF colors ? Is the Shark mouth a decal or you have painted it.

Also is Apache the name of some weapon on the Rafale ?

The Sukhoi 7 kit came with IAF decals( including shark mouth) in box. The other two I used aftermarket decals.

Apache is a cruise missiles yes.

Originally Posted by skanchan95

IAF Su-7s, like MiG-21s from that era, were painted in some fascinating paint schemes. There was an IAF Vampire too that was also painted with a shark mouth.
.

Same here; I don’t like the current gen bland Tipnis Grey airplanes at all. I mostly make modern jets as commission job, I myself prefer older airplanes for my personal collection.

[basuroy]

These two were made in 2018. The Moth has the original Chakra marking that was the standard between 47-48.

[Foxbat]

Originally Posted by basuroy

These two were made in 2018. The Moth has the original Chakra marking that was the standard between 47-48.

Breathtaking quality and attention to detail

The IAF should hire you as their official model maker !

[skanchan95]

Originally Posted by basuroy

Same here; I don’t like the current gen bland Tipnis Grey airplanes at all.
.

Agreed. Just imagine how bland the Mirage 2000s would have looked had they been repainted in Tipnis Grey shade at the beginning of the century. If anyone wants to visualize, just have a look at how boring Peruvian and Egyptian Mirage 2000s are to look.

Originally Posted by basuroy

I mostly make modern jets as commission job

To earn by doing what one loves is an opportunity very few in this world get. You are not only lucky but very talented as well. Loved the Vampire FB.52- lovely and realistic finish.

Originally Posted by Foxbat

IAF should hire you as their official model maker !

I concur. Truly oustanding works of art!!!