I will resurrect this topic to avoid opening a new one. I have been reading on the He 177 development and my impression is that there are many grey areas. Perhaps other members can share their opinions, or contribute with new references.
I am reading the book by Griehl and Dressel, which contains appendices on the specifications and modifications of different prototypes. However, there is no clear explanation on why the empty weight goes from 13.72 ton in prototype V1 to 18.74 on V15.
Now, you could claim that the weight went up because the He 177 was required to perform dive bombing, but the He 177 A-5/R-2 empty weight is 16.8 tons, similar to other WW2 4 engine bombers:
- B-17G: 16.3
- B-24J: 16.5
- Stailing I: 22.4
- Halifx III: 17.1
- Lancaster I: 16.7
- Pe 8: 18.5
- P.108: 17.3
Extra armour and armament could add weight, but do no explain a 35% increase in empty weight.
Heinkel He 177 prototypes listed in the graph.
V1 (CB+RP/Wk-Nr 00 0001):
Flight characteristics and performance tests; evaluation of Fowler flaps. Severely damaged as result of crash-landing (3 October 1941).
V2 (CB+RQ/Wk-Nr 00 0002):
Stability tests and evaluation of new horizontal tailplane. Destroyed in crash 27 June 1940.
V3 (D-AGIG/Wk-Nr 00 0003):
Stability tests and evaluation of new horizontal tailplane. Destroyed in crash 24 April 1940 due to tailplane failure.
V4 (Wk-Nr 00 0004):
Performance and inclined flight tests; evaluation of brake flaps. Destroyed in crash 8 June 1941.
V5 (PM+OD/Wk-Nr 00 0005):
Performance and inclined flight tests; tailplane experiments. To Heinkel works 23 June 1943.
V6 (BC+BP/Wk-Nr 00 0006):
First armament pattern aircraft. Assigned to KG 40 as training aircraft 23 June 1943.
V7 (SF+TB/Wk-Nr 00 0007):
Second armament pattern aircraft. Assigned to KG 40 as training aircraft 23 June 1943.
V8 (SF+TC/Wk-Nr 00 0008):
Evaluation of flaps, radiators, shortened Fowler flaps, powerplants. At Heinkel works 26 June 1943.
V9 (GA+QQ/Wk-Nr 00 0023):
A-08 rebuilt to B-5 standard. Evaluation of four separate engines, twin fin/rudder assembly and K-12 automatic flight control system. Handed over to E-Stelle Rechlin 15 August 1944.
V14 (GI+BM/Wk-Nr 15152):
A-1 experimental aircraft for Kehl III equipment. Final whereabouts unknown.
V15 (Wk-Nr 355001):
A-3 fitted with new cockpit and used for inclined flight trials with brake parachute. Crashed 24 June 1944.
V19 (VF+QA/Wk-Nr 332101):
A-3 used for DB 610 powerplant tests. Destroyed as result of engine fire 13 November 1943.