Heinkel He-162 Poor Interception Capabilities at High Altitude

[VSKYLABS Test-Pilot Notes] issued 22th September 2020

The main deal with the He-162 is (was) that actual high-altitude interception seems to be more of a wishful thinking...

Old school guns-interception of a target which is flying quite high, say above 20,000 and for sure at about 30,000 is a geometric and energy management challenge even for 5th generation jet fighters (intercepting a target which is flying with the same relative speed and altitude of the He-162 and the targets in the WWII area, and with guns as the selected weapon).

While a modern jet fighter has a thrust to weight ratio of over 1:1 and vertical interception path is possible even for guns...chasing the target is also an option. The He-162 could not do that. High altitude interception seems to be non-relevant, as any increase of turn rate got the He-162 back down into a descent, without any option to chase the target.

He-162 high altitude "Interception" seems to be a one-shot/chance shooting effort, in relative paths aspects which are close and for sure greater than 90 degrees (between 90 degrees and head-on). In such aspects, aiming for guns is almost impossible...and after passing the target, circling back to chase it was irrelevant.

The He-162 had poor handling and energy management while flying at altitudes of 8km...executing a 180 turn while maintaining flying altitude and speed was a challenge. Now imagine that you need to close on a flying target...the turn should be so wide (accompanied with excessive loss of altitude to maintain  maneuvering speed) so that you won't lose energy, making any kind of high altitude *interception* very short and lacking...

So the He-162 was capable of flying at 30,000 feet, however fighting in these heights was non-practical.

A more realistic interception profile may be considered of targets which are flying at around 20,000 feet, maybe a bit higher, or...flying high at about 25,000 feet, above lower-altitude targets and then intercepting the targets from above.

In these profiles, the on-board Oxygen would have been sufficient as well.

JMH

In the video: 
Calibrating the guns-sight and downing an AI aircraft in X-Plane 11.30. It was not a high altitude interception, yet the restricted energy of the He-162 during the turn is noticeable.

Heinkel He-162 High Altitude Pilot Notes (X-Plane 11)

[VSKYLABS Test-Pilot Notes] issued 21th September 2020

High Altitude Operations Pilot Notes (X-Plane 11):

Following an Oxygen system 'maintenance' updates, the following high-altitude profile was tested. It may be useful to who ever is interested to test this.

*Maintenance included: Oxygen regulator mode adjustments, which were previously set to supply 100% when the valve is opened, and now the regulator is set to deliver more Oxygen with increasing altitude (should be 1.0 liter/min per 10,000 of pressure altitude up to about 34,000 feet).

The following setup and flight profile have been verified:

*This is not a checklist. For actual operation checklists use the advised checklist to be found in the manual.

1. Fully loaded fuel-tanks.
2. Normal takeoff/JATO assisted takeoff, Nozzle in "S" position.
3. Climbed as advised (practical climbing speeds should vary between 350-400 km/h).
4. When crossing 4 km, Oxygen supply switched to ON.
5. Climbed as advised to 8 km (practical climbing speed may vary but should not get below 400 km/m).
6. Leveled off at 8km, set nozzle to "H" position.
7. Accelerated to 420 km/h.
8. Set climbing angle to maintain 400 km/h up to 10 km.
9. Once 10 km was exceeded, throttle went down to maintain 6000 rpm (flight idle).
10. Rapid descent within airspeed limitations (there are marking on the airspeed indicator which are helpful).
11. Got back to 4 km with a bit of Oxygen reserve.
12. Got back to base.

Pilot notes:

• In such profile, flight endurance is higher than the 20-30 minutes of low-altitude operations. This is due to the lower fuel consumption at high altitude, and also because the long descent is in low rpm (6000) setting.
• The He-162 is having a low thrust to weight ratio, and high wing loading. As altitude goes up, indicated airspeed reading gets lower for a given true airspeed (due to air density decrease). In modern aircraft, climbing to high altitude is done with climbing profiles that are following Mach number (which is not changing during the climb). The He-162 climb to 10 km can become a challenge, if a too-low airspeed is being maintained during the climb.
• From ~8 km, never let your indicated airspeed to get below 400 km/h, or else the aircraft will hit a climbing ceiling. Mach number during high-altitude climb should not get below 0.5 (in the He-162). There is no Mach number indicator in the aircraft, and keeping above 400 km/m will set you around the lower-safe side.
• The real He-162 did not have enough actual operational experience in such profiles, as it did not complete its development by the end of WWII. Testing this in X-Plane can give some fascinating insights.
• The He-162 (real and VSL) is not pressurized, meaning that above a certain flying altitude, breathing 100% Oxygen may not be sufficient to avoid other physiological concerns. (Oxygen carrying capacity of our blood reduces with the reduction of pressure). This can be a real operational limitation in an un-pressurized fighter jet designed to intercept high-altitude bombers.
• Rapid descent (or normal descent) may also become a challenge. Beware of exceeding airframe limitations!

JMH