The YF-75D rocket engine nozzle features a strong spiral pattern for structural or manufacturing reasons.
the verdict
INSUFFICIENT LEANING
refutedsupported
the weight of evidence
2 sources for · 0 against
AS REPORTEDno primary record reached; this is what the reporting says
Retrieved sources acknowledge the existence of the YF-75D engine and pose questions regarding its spiral pattern, but do not provide definitive evidence establishing the specific structural or manufacturing reasons behind it.
# Why does the YF-75D nozzle have such a strong spiral pattern?
Tags: engine-design, design, engineering, nozzle, long-march
- Score: 13
- Views: 2049
- Answers: 2
- Answered: yes
- Asked by: user12102
- Asked: 2016-11-04
- Edited: 2019-08-09
- Site: space
## Question
Why does the YF-75D nozzle material have such a strong spiral pattern?
Is it a result/biproduct of a manufacturing process only, or does it have some specific function?
edit: The last, cropped images that have enhanced contrast and sharpening show a bead-like appearance around the bottom edge of the nozzle. This gives the impression that the nozzles is fabricated from fused rods or "ropes" of metal. This is consistent with them being nearly vertical at the top, and increasingly spiraled as the bell shape widens.
Could these have been made by some additive process?
above: YF-75D engine cropped from here.
above: YF-75D engine cropped from Chinaspaceflight. (In Chinese)
above: YF-75D engine from Chinaspaceflight. (In Chinese)
above: YF-75D engine nozzle detail, cropped from Chinaspaceflight. (In Chinese)
## Answers
### Answer by Jan van Oort (score: 6 [ACCEPTED])
According to the paper from the 64rd I
YF-75D
The YF-75D is a cryogenic rocket engine burning liquid hydrogen and liquid oxygen in a closed expander cycle. It is China's third generation of upper stage cryogenic propellant engine, after the YF-73 and the YF-75. It is used in a dual engine mount in the H5-2 second stage of the Long March 5 launch vehicles. Within the mount, each engine can gimbal individually to enable thrust vectoring control. As with its predecessor YF-75, the YF-75D can adjust its mixture ratio to optimize propellant consumption. As an additional improvement it can do multiple restarts, against the single one of its predecessor.
The combustion chamber required a redesign to keep the power balance. Since the expander cycle uses the heat extracted from the cooling circuits to drive the turbines, the chamber had to be lengthened and the cooling passages redesigned. The engine uses a redesigned hydrogen turbine. It uses an axial two-staged low pressure ratio subsonic turbine that operates at 65,000 rpm, which is between the second and third critical speed. It rests on dual elastic support dampers around the ceramic ball bearings.
| Country of origin | China |
| --- | --- |
| First flight | Long March 5
Everything we examined (2)
This check searched the claim as stated. It did not run a separate search for evidence against it.