Does anybody know anything about the HS-121 Airfoil?

It makes the plane fly.
There’s pieces of metal and plastic.
It’s attached to the Hs-121.

hawker34892312 wrote:

Does anybody know anything about the HS-121 Airfoil?

The Trident was one of the fastest subsonic commercial airliners, cruising at over 610 mph (980 km/h). At introduction into service its cruise Mach Number was 0.88/ 380 kn IAS. Designed for high speed, with a critical Mach number of 0.93,[43] the wing produced relatively limited lift at lower speeds. This, and the aircraft's low thrust-to-weight ratio, called for prolonged takeoff runs. Nevertheless, the Trident fulfilled BEA's 6,000 ft (1,800 m) field length criterion and its relatively staid airfield performance was deemed adequate before the arrival into service of the Boeing 727 and later jet airliners built to 4,500 ft (1,400 m) field length criteria.[44] The aerodynamics and wing was developed by a team led by Richard Clarkson, who would later use the Trident wing design as the basis for the wing of the Airbus A300; for the Trident he won the Mullard Award in 1969.

stratclub wrote:

hawker34892312 wrote:

Does anybody know anything about the HS-121 Airfoil?

The Trident was one of the fastest subsonic commercial airliners, cruising at over 610 mph (980 km/h). At introduction into service its cruise Mach Number was 0.88/ 380 kn IAS. Designed for high speed, with a critical Mach number of 0.93,[43] the wing produced relatively limited lift at lower speeds. This, and the aircraft's low thrust-to-weight ratio, called for prolonged takeoff runs. Nevertheless, the Trident fulfilled BEA's 6,000 ft (1,800 m) field length criterion and its relatively staid airfield performance was deemed adequate before the arrival into service of the Boeing 727 and later jet airliners built to 4,500 ft (1,400 m) field length criteria.[44] The aerodynamics and wing was developed by a team led by Richard Clarkson, who would later use the Trident wing design as the basis for the wing of the Airbus A300; for the Trident he won the Mullard Award in 1969.

Didn´t they install a fourth booster engine to achieve the takeoff criteria?

First300 wrote:

Didn´t they install a fourth booster engine to achieve the takeoff criteria?

Yes, but on the stretched Trident 3 only.

I've read a lot about various aircraft being the fastest, or among the fastest, commercial airliners- the VC10, Trident and CV990 are the ones most mentioned. However it's not clear whether operations at these supposed high speeds were standard practice or were they a capability achieved in flight-testing only? I suspect that once the oil crisis of the early 1970s hit, the most economical speed would have been preferred in any case.

iRISH251 wrote:

I've read a lot about various aircraft being the fastest, or among the fastest, commercial airliners- the VC10, Trident and CV990 are the ones most mentioned. However it's not clear whether operations at these supposed high speeds were standard practice or were they a capability achieved in flight-testing only? I suspect that once the oil crisis of the early 1970s hit, the most economical speed would have been preferred in any case.

All things being equal, the most economic cruise speeds of the aircraft you mentioned (and maximum speeds) were designed to be faster than the competition. As you touched on though... This was back when fuel was cheap. Producing the "fastest" aircraft seemed to be purely marketing. Case in point, the CV990's name is strictly derived from its max cruise speed (990 kph). Reality set in when gas prices shot up. Shaving a few minutes of a transcon flight suddenly wasn't worth the 15%+ increase in fuel burn. The difference between Mach .88 vs .80 wouldn't really register with the flying public as would say, Concorde.

stratclub wrote:

The aerodynamics and wing was developed by a team led by Richard Clarkson, who would later use the Trident wing design as the basis for the wing of the Airbus A300; for the Trident he won the Mullard Award in 1969.

Wow strat, what a fascinating post! Thank you so much for that information.

...inevitably of course I'm now curious: How does the Trident performance and airfoil compare to the 727? When operating at cruise speed: Did the 727's wing have that level of (then) bleeding-edge tech that Mr. Clarkson designed into the Trident, and future Airbus aircraft?

Sadly, any discussion of the Trident wing has to acknowledge the critical leading edge retractable droop element on the Trident 1s and that it was possible for flight crews to retract it prematurely with a catastrophic result. Trident 2s and 3s were produced with leading edge slats, plus other refinements/changes to the wing.

CrewBunk wrote:

Something to consider with regard to the Trident wing is that the Trident 3B could carry about the same payload as a 727-200 but with a gross weight about 50,000 lbs less! Amazing.

accentra wrote:

Sadly, any discussion of the Trident wing has to acknowledge the critical leading edge retractable droop element on the Trident 1s and that it was possible for flight crews to retract it prematurely with a catastrophic result. Trident 2s and 3s were produced with leading edge slats, plus other refinements/changes to the wing.

The leading edge devices of the Tridents Two and Three were more refined than the Trident One, as you state, but, they too could be retracted prematurely with the same disastrous results. In fact, that is true with most early generation jet transport aircraft.

The first aircraft I flew where there were safeguards was the A300B with “alpha lock”. Below certain speeds, or above a certain angle of attack, flaps could not be selected from 15/0 to 0/0. (Retracting the leading edge devices).

Thank you for the clarification and the additional information. Much appreciated. For some reason I mistakenly believed that there was some 'interlock-esque' function on the Two and Three that would either stop or warn against premature retraction of the leading edge slats.

I don't think it was usual for aircraft of that era to have protections against the premature (too slow) retraction of the high lift devices.

A mechanical interlock was retrofitted to the control stand after the Papa India crash. You could then only move the slat lever if the flap lever was at Zero.

It was also designed to make one hell of a lot of noise on takeoff, as anyone working on the LHR northern perimiter road will tell you.

rjsampson wrote:

iRISH251 wrote:

I've read a lot about various aircraft being the fastest, or among the fastest, commercial airliners- the VC10, Trident and CV990 are the ones most mentioned. However it's not clear whether operations at these supposed high speeds were standard practice or were they a capability achieved in flight-testing only? I suspect that once the oil crisis of the early 1970s hit, the most economical speed would have been preferred in any case.

All things being equal, the most economic cruise speeds of the aircraft you mentioned (and maximum speeds) were designed to be faster than the competition. As you touched on though... This was back when fuel was cheap. Producing the "fastest" aircraft seemed to be purely marketing. Case in point, the CV990's name is strictly derived from its max cruise speed (990 kph). Reality set in when gas prices shot up. Shaving a few minutes of a transcon flight suddenly wasn't worth the 15%+ increase in fuel burn. The difference between Mach .88 vs .80 wouldn't really register with the flying public as would say, Concorde.

stratclub wrote:

The aerodynamics and wing was developed by a team led by Richard Clarkson, who would later use the Trident wing design as the basis for the wing of the Airbus A300; for the Trident he won the Mullard Award in 1969.

Wow strat, what a fascinating post! Thank you so much for that information.

...inevitably of course I'm now curious: How does the Trident performance and airfoil compare to the 727? When operating at cruise speed: Did the 727's wing have that level of (then) bleeding-edge tech that Mr. Clarkson designed into the Trident, and future Airbus aircraft?

Copied and pasted from WIKI. Oh your welcome.

accentra wrote:

Sadly, any discussion of the Trident wing has to acknowledge the critical leading edge retractable droop element on the Trident 1s and that it was possible for flight crews to retract it prematurely with a catastrophic result. Trident 2s and 3s were produced with leading edge slats, plus other refinements/changes to the wing.

Somethin similar had been done had been done on a 727 with disasterous result. What the crew did was with flap at zero pulled the C/Bs for the L/E devices and then put the flaps at flaps 2. Viola! the plane was on a more fuel efficient step as it were.

It worked great until the F/E noticed the L/E flap breakers out at cruise and pushed them back in.

https://en.wikipedia.org/wiki/TWA_Flight_841_(1979)

stratclub wrote:

accentra wrote:

Sadly, any discussion of the Trident wing has to acknowledge the critical leading edge retractable droop element on the Trident 1s and that it was possible for flight crews to retract it prematurely with a catastrophic result. Trident 2s and 3s were produced with leading edge slats, plus other refinements/changes to the wing.

Somethin similar had been done had been done on a 727 with disasterous result. What the crew did was with flap at zero pulled the C/Bs for the L/E devices and then put the flaps at flaps 2. Viola! the plane was on a more fuel efficient step as it were.

It worked great until the F/E noticed the L/E flap breakers out at cruise and pushed them back in.

https://en.wikipedia.org/wiki/TWA_Flight_841_(1979)

Today the A350 does something similar, but intentionally. The flaps automatically extend in the cruise to move the CoL. Way less complex than moving the CoG by means of the trim tank as on the A330 and A380l

CrewBunk wrote:

Something to consider with regard to the Trident wing is that the Trident 3B could carry about the same payload as a 727-200 but with a gross weight about 50,000 lbs less! Amazing.

).

Indeed. The fuselage was almost 6 metres shorter (approx 40m vs 46m of the 72S), and also to consider the fact the Trident had no integral ventral airstairs at the back.

stratclub wrote:

accentra wrote:

Sadly, any discussion of the Trident wing has to acknowledge the critical leading edge retractable droop element on the Trident 1s and that it was possible for flight crews to retract it prematurely with a catastrophic result. Trident 2s and 3s were produced with leading edge slats, plus other refinements/changes to the wing.

Somethin similar had been done had been done on a 727 with disasterous result. What the crew did was with flap at zero pulled the C/Bs for the L/E devices and then put the flaps at flaps 2. Viola! the plane was on a more fuel efficient step as it were.

It worked great until the F/E noticed the L/E flap breakers out at cruise and pushed them back in.

https://en.wikipedia.org/wiki/TWA_Flight_841_(1979)

There’s actually nothing substantive to prove the crew took that action

The entire story is based on rumor

No disciplinary action was taken by the FAA or airline against the captain or the other two pilots


The particular aircraft involved in that incident had a history of significant, uncommanded roll inputs, an affidavit was filed by a TWA test pilot attesting to that
on a previous flight

Suggest you read the book ‘scapegoat’

Does anybody have some engineer drawing of the wing cross section perhaps?

hawker34892312 wrote:

Does anybody have some engineer drawing of the wing cross section perhaps?

No.

But I found a place where you can get them for $10!



Here's the link to grab what you want: https://www.ebay.com/itm/403594460972

I hope this is what you're looking for, and if you do end up getting it... after you read, digest, and enjoy.. share the information with us!

EDIT: You better hurry up and get this within the next few days. and report to us that you did. If you don't: I'll get it for myself.

CrewBunk wrote:

Something to consider with regard to the Trident wing is that the Trident 3B could carry about the same payload as a 727-200 but with a gross weight about 50,000 lbs less! Amazing.

.

Well the 727 had bigger fuel tanks and higher MTOW so it needed to be able to lift and have a structure to support a heavier weight. Its all relative. I'm sure the 727 wing was much heavier too with it's triple slotted flap system. That's why it could use shorter runways than the HS121.
https://www.youtube.com/watch?v=qDs7haZK7Go

Clydenairways wrote:

CrewBunk wrote:

Something to consider with regard to the Trident wing is that the Trident 3B could carry about the same payload as a 727-200 but with a gross weight about 50,000 lbs less! Amazing.

.

Well the 727 had bigger fuel tanks and higher MTOW so it needed to be able to lift and have a structure to support a heavier weight. Its all relative. I'm sure the 727 wing was much heavier too with it's triple slotted flap system. That's why it could use shorter runways than the HS121.
https://www.youtube.com/watch?v=qDs7haZK7Go

Incredibly, the Trident, then the DH-121, was stymied by lead customer and effective sponsor of the design, BEA, having a dip in loads in just one winter season, so they wanted the design shrunk.
RR stopped early work on what would have been the RR Medway, in the JT8D class, the DH, now HS-121, would use the smaller Spey engine.

In hindsight, HS should have built BEA the aircraft they wanted, what we call the Trident 1, RR should have proceeded with Medway development for a Trident 2, which would have been nearer in size to the T3, without that booster engine.
Since BEA soon regretted their call to shrink the design and wanted more capacity, this by the time the T1's were coming off the line.

Would have made the BAC 1-11 more easily to stretch and compete too.

https://en.wikipedia.org/wiki/Rolls-Royce_Medway

rjsampson wrote:

hawker34892312 wrote:

Does anybody have some engineer drawing of the wing cross section perhaps?

No.

But I found a place where you can get them for $10!

[...]

Those are great cutaway drawings, but I suspect that @hawker34892312 is looking for a drawing of sufficient accuracy that it is possible to measure the coordinates of the profile of the airfoil(s). Such a drawing is very unlikely to be in the public domain, and I would not be surprised if it was lost. I would try to follow the history of HS to this day. Let's say it somehow ended up in Airbus. Then I would write to Airbus, perhaps Airbus is big enough that it has a company historian, who may have some idea of where the big boxes of engineering data might be, and if they exist in the first place. I would also try with one of the aviation historical societies.

Ideally, the airfoil would be a NACA airfoil, so the coordinates could be computed using Abbott and von Doenhoff's "Theory of Wing Sections" or the UIUC Airfoil Coordinate Database web site: https://m-selig.ae.illinois.edu/ads/coord_database.html, or similar sources.

Short of that, the only possibility I can think of is to find a real Trident in some museum, or at least a wing, and physically measure the coordinates.

Here is the best I have:

dlednicer wrote:

Here is the best I have:

This is a very interesting drawing. Take a look at the obvious wing twist from the root to the tip. The angle of attack is significantly higher at the root.
Would this design feature induce a stall behavior where the root stalls first, moving the center of lift backwards, thus creating a nose-down pitch input to assist the recovery from the stall?

Best regards,
Hendric

hitower3 wrote:

dlednicer wrote:

Here is the best I have:

This is a very interesting drawing. Take a look at the obvious wing twist from the root to the tip. The angle of attack is significantly higher at the root.
Would this design feature induce a stall behavior where the root stalls first, moving the center of lift backwards, thus creating a nose-down pitch input to assist the recovery from the stall?

Best regards,
Hendric

If I remember correctly, root stall first was a design requirement mentioned in discussion of A380 wing. Probably impossible to find that link by now, the reason I remembered was designer's comments on how tricky that design was overall.
But such twist makes perfect sense as a passive safety feature for swept wing. I wouldn't be surprised if that twist is actually smaller in flight, though.

kalvado wrote:

hitower3 wrote:

dlednicer wrote:

Here is the best I have:

This is a very interesting drawing. Take a look at the obvious wing twist from the root to the tip. The angle of attack is significantly higher at the root.
Would this design feature induce a stall behavior where the root stalls first, moving the center of lift backwards, thus creating a nose-down pitch input to assist the recovery from the stall?

Best regards,
Hendric

If I remember correctly, root stall first was a design requirement mentioned in discussion of A380 wing. Probably impossible to find that link by now, the reason I remembered was designer's comments on how tricky that design was overall.
But such twist makes perfect sense as a passive safety feature for swept wing. I wouldn't be surprised if that twist is actually smaller in flight, though.

Probably trivial thing for those in the field, but may be a good starting point for those like me:
https://en.wikipedia.org/wiki/Washout_%28aeronautics%29

hitower3 wrote:

This is a very interesting drawing. Take a look at the obvious wing twist from the root to the tip. The angle of attack is significantly higher at the root.
Would this design feature induce a stall behavior where the root stalls first, moving the center of lift backwards, thus creating a nose-down pitch input to assist the recovery from the stall?

Best regards,
Hendric

For swept wing aircraft it's always desirable for the root to stall first for the reason you give plus the minimising roll tendency if the stall is somewhat asymmetric.
Some designs e.g. 727, 737 have outboard leading edge slats, but inboard krueger flaps to promote this root stalling first behaviour. Others use a mix of section and twist to achieve the same.

hitower3 wrote:

dlednicer wrote:

Here is the best I have:

This is a very interesting drawing. Take a look at the obvious wing twist from the root to the tip. The angle of attack is significantly higher at the root.
Would this design feature induce a stall behavior where the root stalls first, moving the center of lift backwards, thus creating a nose-down pitch input to assist the recovery from the stall?

Best regards,
Hendric

Yes exactly. If the root stalls first on a swept-wing aircraft there is a pitch down tendency, which is a requirement. Additionally, this means the ailerons remain unstalled at stall onset, so you retain roll authority. You can counter-roll and avoid a stall turning into, worst case, a wing drop and a spin.

If the tips stall first, there is a pitch-up tendency, which of course makes things worse.

Pitch down moment at high angles of attack is a certification requirement, which is why you see features like wing twist, section differences, additional pylon control surfaces on some of the MD-8x series, MCAS...

You might notice that the root airfoil also has negative camber and camber increases as you go spanwise.

On swept wings, the isobars cross the centerline with no sweep. This causes an unsweeping of the isobars in the wing root region, as they curve to go from one side to another on centerline. This is called the "middle effect" and results in increased wave drag. To counter this, airfoil camber is reduced in the wing root area and incidence is used to load up the forward portion of the airfoil, which moved the isobars forward.

I believe this treatment was first used in the design of the wing of the HP Victor. It was definitely used in the design of the wings of the DC-8, Trident and VC-10. Boeing didn't initially incorporate this into the 707 wing design and later added it with the glove added to the 720 wing.
.

Dear all,

Thank you very much for these insights. I definitely learned something.
Now I'd like to ask, how do they design the "automatic pitch down in a developing stall" in a straight wing, e.g. for the Q400 or ATR? A higher pitch angle at the wing root wouldn't change the center of lift in such a design.

hitower3 wrote:

Dear all,

Thank you very much for these insights. I definitely learned something.
Now I'd like to ask, how do they design the "automatic pitch down in a developing stall" in a straight wing, e.g. for the Q400 or ATR? A higher pitch angle at the wing root wouldn't change the center of lift in such a design.

You answered your own question.

Since it is a straight wing, the CoL won't move like with a swept wing, so you don't have to get all fancy. At stall onset, the is a natural pitch-down moment. In general, though, the wing is still designed to stall root first in order to maintain aileron authority.

Starlionblue wrote:

hitower3 wrote:

Dear all,

Thank you very much for these insights. I definitely learned something.
Now I'd like to ask, how do they design the "automatic pitch down in a developing stall" in a straight wing, e.g. for the Q400 or ATR? A higher pitch angle at the wing root wouldn't change the center of lift in such a design.

You answered your own question.

Since it is a straight wing, the CoL won't move like with a swept wing, so you don't have to get all fancy. At stall onset, the is a natural pitch-down moment. In general, though, the wing is still designed to stall root first in order to maintain aileron authority.

Looks like there are still tricks involved. Quite a few images like this:

Elliptical wing is beneficial for L/D ratio, but root stall first is preferred for roll authority...

Max Q wrote:

stratclub wrote:

accentra wrote:

Sadly, any discussion of the Trident wing has to acknowledge the critical leading edge retractable droop element on the Trident 1s and that it was possible for flight crews to retract it prematurely with a catastrophic result. Trident 2s and 3s were produced with leading edge slats, plus other refinements/changes to the wing.

Somethin similar had been done had been done on a 727 with disasterous result. What the crew did was with flap at zero pulled the C/Bs for the L/E devices and then put the flaps at flaps 2. Viola! the plane was on a more fuel efficient step as it were.

It worked great until the F/E noticed the L/E flap breakers out at cruise and pushed them back in.

https://en.wikipedia.org/wiki/TWA_Flight_841_(1979)

There’s actually nothing substantive to prove the crew took that action

The entire story is based on rumor

No disciplinary action was taken by the FAA or airline against the captain or the other two pilots


The particular aircraft involved in that incident had a history of significant, uncommanded roll inputs, an affidavit was filed by a TWA test pilot attesting to that
on a previous flight

Suggest you read the book ‘scapegoat’

You make a good point. Their downfall was erasing the CVR so it left a lot of room for doubt. I read that "hoot" Gibson the Captain was blackballed within the airline. There were crews that refused to fly with him after that, One thing is for certain that was a true feat of airmanship.

stratosphere wrote:

Max Q wrote:

stratclub wrote:

Somethin similar had been done had been done on a 727 with disasterous result. What the crew did was with flap at zero pulled the C/Bs for the L/E devices and then put the flaps at flaps 2. Viola! the plane was on a more fuel efficient step as it were.

It worked great until the F/E noticed the L/E flap breakers out at cruise and pushed them back in.

https://en.wikipedia.org/wiki/TWA_Flight_841_(1979)

There’s actually nothing substantive to prove the crew took that action

The entire story is based on rumor

No disciplinary action was taken by the FAA or airline against the captain or the other two pilots


The particular aircraft involved in that incident had a history of significant, uncommanded roll inputs, an affidavit was filed by a TWA test pilot attesting to that
on a previous flight

Suggest you read the book ‘scapegoat’

You make a good point. Their downfall was erasing the CVR so it left a lot of room for doubt. I read that "hoot" Gibson the Captain was blackballed within the airline. There were crews that refused to fly with him after that, One thing is for certain that was a true feat of airmanship.

In that era when CVR’s were first introduced they were distrusted by the vast majority of airline pilots


In fact ALPA’s recommendation was to erase the tape after each flight regardless of the circumstances


Gibson was just doing what he always did and following recommendations

rjsampson wrote:

hawker34892312 wrote:

Does anybody have some engineer drawing of the wing cross section perhaps?

No.

But I found a place where you can get them for $10!



Here's the link to grab what you want: https://www.ebay.com/itm/403594460972

I hope this is what you're looking for, and if you do end up getting it... after you read, digest, and enjoy.. share the information with us!

EDIT: You better hurry up and get this within the next few days. and report to us that you did. If you don't: I'll get it for myself.

Ha sorry for for very late reply, I am looking into getting this in the next day or so for sure! It will definitely help me and be nice to my collection

IADFCO wrote:

rjsampson wrote:

hawker34892312 wrote:

Does anybody have some engineer drawing of the wing cross section perhaps?

No.

But I found a place where you can get them for $10!

[...]

Those are great cutaway drawings, but I suspect that @hawker34892312 is looking for a drawing of sufficient accuracy that it is possible to measure the coordinates of the profile of the airfoil(s). Such a drawing is very unlikely to be in the public domain, and I would not be surprised if it was lost. I would try to follow the history of HS to this day. Let's say it somehow ended up in Airbus. Then I would write to Airbus, perhaps Airbus is big enough that it has a company historian, who may have some idea of where the big boxes of engineering data might be, and if they exist in the first place. I would also try with one of the aviation historical societies.

Ideally, the airfoil would be a NACA airfoil, so the coordinates could be computed using Abbott and von Doenhoff's "Theory of Wing Sections" or the UIUC Airfoil Coordinate Database web site: https://m-selig.ae.illinois.edu/ads/coord_database.html, or similar sources.

Short of that, the only possibility I can think of is to find a real Trident in some museum, or at least a wing, and physically measure the coordinates.

Yep, pretty much on point. It might be a good idea to get some hawker siddeley archives rotting away. I am looking into visting ZK for some detailed pictures perhaps.

dlednicer wrote:

Here is the best I have:

Ha this are perfect! where did you find this?

This will help a lot. I will be visiting ZK probably and I am going to ask around perhaps anybody has more info or manuals.

And honestly, thank you for everyone who shared information especially about the performance of aircraft. Definitely will help me building a flight model as accurately as possible

I do have another question though, how different is the trident 1e to 3b in terms of cockpit instruments

The upper figure is from Ed Obert's book "Aerodynamic Design of Transport Aircraft". The second figure is from a Royal Aeronautical Society paper "The Development of the Trident Series" by J.P. Smith

I've been a follower/contributor to this technical forum for nearly 25 years. This thread has been one of the best technical threads in those 25 years. Well done, participants. I'm not worthy to participate, only to learn!

hawker34892312 wrote:

rjsampson wrote:

hawker34892312 wrote:

Does anybody have some engineer drawing of the wing cross section perhaps?

No.

But I found a place where you can get them for $10!



Here's the link to grab what you want: https://www.ebay.com/itm/403594460972

I hope this is what you're looking for, and if you do end up getting it... after you read, digest, and enjoy.. share the information with us!

EDIT: You better hurry up and get this within the next few days. and report to us that you did. If you don't: I'll get it for myself.

Ha sorry for for very late reply, I am looking into getting this in the next day or so for sure! It will definitely help me and be nice to my collection

My pleasure, Hawk! Here's something else that's perhaps worth a purchase. The technical manual for the Trident for $10:



http://www.aircraft-manuals.com/dehahasihstr2.html

Their website sucks, and they don't even have their SSL installed (ie, their website says "not secure"). Having said that, I've made 2 successful purchases from them.

rjsampson wrote:

hawker34892312 wrote:

rjsampson wrote:

No.

But I found a place where you can get them for $10!



Here's the link to grab what you want: https://www.ebay.com/itm/403594460972

I hope this is what you're looking for, and if you do end up getting it... after you read, digest, and enjoy.. share the information with us!

EDIT: You better hurry up and get this within the next few days. and report to us that you did. If you don't: I'll get it for myself.

Ha sorry for for very late reply, I am looking into getting this in the next day or so for sure! It will definitely help me and be nice to my collection

My pleasure, Hawk! Here's something else that's perhaps worth a purchase. The technical manual for the Trident for $10:



http://www.aircraft-manuals.com/dehahasihstr2.html

Their website sucks, and they don't even have their SSL installed (ie, their website says "not secure"). Having said that, I've made 2 successful purchases from them.

Would you mind me asking, do you have any scans relating to the Hs - 121?