1/84 iffy USS Tucumcari

[Rick Lowe]

'Foilborne'... entirely logical, and my vocabulary has been enhanced. 

Cheers, Jon 

[jcf]

If there's something that screams "This needs to be 1/35" it's military hydrofoils

Also, I think the Avenger turret from the the TWQ-1 Avenger SHORAD might make a useful modernization  for the aft battery.

The turret that replaced the original gun and mortar armament on the rear was the Emerlec EX-73 with twin 20mm cannon. The turret could be used for both anti-aircraft and anti-surface vessel purposes, the SHORAD wouldn't be of much use in the latter role.

Tucumcari with Emerlec turret, the port and stbd gunmounts are also twin 20mm.

[jcf]

The bulges are the water intakes when foilborne. The waterjet exhaust when hullborne is in the transom below the turbine exhaust, when foilborne the water jet exhausts through nozzles on the bottom of hull.

Why doesn't it say that anywhere where I can find it? grrrrrrrrrrrrrrrr.

Kit you'll probably find this of interest, from retired Boeing engineer Bob Bogash about his three years in Hawai'i supporting the commercial jetfoil operations.
He goes into detail about why it didn't work out.
Jetfoil in Hawai'i

Dead right Jon, that's fascinating and I've saved it away on disc. He goes into some length on the Jetfoil's pitch performance in rough seas, but doesn't mention the 'tilt' performance, which I found equally interesting of course and very well done on my tip to Ostend and back.

The Boeing Jetfoils have an automatic control system that controlled height, pitch, tilt and steering and it is all tied in with the throttle and wheel. The amount of tilt is automatically determined based on velocity, throttle setting and the degree of steering input. The concepts had been tested and worked out using Little Squirt. Tucumcari, the Jetfoil and the PHM all used the same basic system.

[PR19_Kit]

Here ya go Kit. 
Hullborne propulsion on Tucumcari was with a separate standard waterjet powered by a Detroit 6V53.
You cannot view this attachment.

That's brill Jon, thanks.

It makes sense they used a separate waterjet on the Tucumcari when hull-borne as the main jet intakes could be clear of the water with the foils up.

And they used BRIT turbines on all three of those ships/boats? I'm astonished, why so?

The Boeing Jetfoils had an automatic control system that controlled height, pitch, tilt and steering and it was all tied in with the throttle and wheel. The amount of tilt was automatically determined based on velocity, throttle setting and the degree of steering input. The concepts had been tested and worked out using Little Squirt. Tucumcari, the Jetfoil and the PHM all used the same basic system.

So they didn't use the lateral acceleration generated in the turn to roll the boat? I would have thought that would have saved quite a bit of computing power, we did exactly that on the APT-E with two lateral accelerometers and a wholly analogue control system.

There's another question, is such a size hydrofoil a ship or a boat?

[jcf]

The Jetfoil literally flies through the water, all control is done with moveable control surfaces
on the trailing edge of the foils. The same surfaces function as flaps, elevators and ailerons
depending on what is required. The vessel banks as it turns for the same reason that an
airplane does. The fwd strut also has a small degree of movement either side of the centreline
of the vessel.


Boeing and Grumman opted for the British engines because marinized versions were already
available and proven. Plus the Navy has never actually been quite as NIH as the Air Force.

The Jetfoil has Allison 501-KFs, a marinized version of the 501/T56, which didn't become 
available until the 1970s.

Kawasaki delivered their 16th 929 Jetfoil in 2020 and the 17th is under construction for delivery
in 2029. Kawasaki licensed it from Boeing in 1987 and although the license has technically lapsed
as far as Boeing is concerned Kawasaki is free to do whatever they like in regards to manufacture
and redesign. A digital control system and "glass cockpit" are amongst the upgrades already made
to the fleet. The 16 built, to date, by Kawasaki are all in service in Japan on multiple routes.

[PR19_Kit]

The Jetfoil literally flies through the water, all control is done with moveable control surfaces
on the trailing edge of the foils. The same surfaces function as flaps, elevators and ailerons
depending on what is required. The vessel banks as it turns for the same reason that an
airplane does. The fwd strut also has a small degree of movement either side of the centreline
of the vessel.

Yes, I figured that out from what I've read already.

When I 'rode/flew' aboard the Jetfoil to Ostend and back it felt EXACTLY like the APT-E did in a turn in that the ship/boat hesitated just a short while as the yaw came on and the it started to roll, catching up with itself and remaining stable during the turn before reverting to 'level flight' with the same hesitation.

We tried to eliminate that hesitation on the train by adding in some forward gain in the control loop and found that passengers didn't kike the higher vertical acceleration as it started to tilt faster, so we went back to the original system.

[Joe CalPo]

Nice work!  Not your typical battleship either!  Thanks for sharing. 

[killnoizer]

This is very good, great Job 

[Captain Canada]

I'm still confused as to how it stays foilborne when the jets are out of the water ?

[wacek85]

I'm still confused as to how it stays foilborne when the jets are out of the water ?

Jets are IN water wnen foilborne. Jets are this thicker elements on foils.

[PR19_Kit]

To be precise, the waterjet  INLETS are in the water when foilborne as they're at the forward end of the bulges at the  bottom off the foils.

The waterjet 'exhausts' are clear of the water as they shoot out through the transom of the ship/boat.

See post #33 where I quoted JCF's original drawing of the three  different hydrofoil systems.

[Weaver]

And they used BRIT turbines on all three of those ships/boats? I'm astonished, why so?

Just to add to what Jon said, the USN had sunk an awful lot of money and time into high-efficiency steam plants before and during WWII, and they were very successful, striking just the right balance between safe but inefficient low steam conditions (British approach) and powerful but unreliable high steam conditions (German approach). Because they were very invested in their steam plants, they developed them right through to the 1960s, and were relatively slow to take an interest in gas turbines. In the UK, by contrast, the existing steam plants were nothing to write home about and the country had a world lead in gas turbines, so naval designers and engine companies started looking at them very early. This is why there were developed and in-production British marine gas turbines available first.

[PR19_Kit]

I'm still not convinced that Boeing needed computer control for the roll commands on the Jetfoil.  At the time computers were THE thing of course and anyone  who was in engineering then were constantly asked 'Is it computer controlled?' and I  spent a lot of time saying 'No, we built the controls using Vero board and stuff rom the RS catalogue!' which we really did. 

Titling trains didn't use any computer based control systems until the late 1990s, and even then much of the input signal was derived from  gyros and accelerometers.

[Captain Canada]

So the jet stream hitting the surface of the water was enough to keep her foilborne ? That's the part I'm struggling to believe.

[PR19_Kit]

It's not just hitting the water, it acts just like the exhaust of a jet engine.

It's being propelled backwards at a hell of a lick by the waterjet pump, and Newton's 3rd Law says that something has to be propelled in the opposite direction as a result, and that's the ship, boat or whatever.