The I.A.R. 80/81 propeller (part II)

The electric pitch adjustment motor (VDM 9-9500.12) was produced by Bosch, being the same type of motor that equipped the Messerschmitt aircraft from the initial series.

The electric pitch adjustment motor (VDM 9-9500.12)

The VDM 9-9500.12 motor was a 24V, two-way, reversible direct current motor to allow adaptation to the direction of rotation of the propeller and with a rated power of 80W at 2500 rpm. The connection with the blade drive gear and the VDM pitch-limit controller 9-9500.52 was made through a flexible shaft compliant to DIN Kr 5532.

The propeller pitch-limit controller was of the H&B VDM 9-9500.52 type (C-3210-E2 in the I.A.R. nomenclature). The figure below shows a drawing from the I.A.R. catalogue and a photo of the same controller installed on the Messerschmitt.

propeller pitch-limit controller: IAR 80 / Bf-109

All electro-mechanical components in the propeller assembly were connected by flexible shafts manufactured at I.A.R. according to DIN Kr. 5532

I.A.R. manufactured flexible shafts
original VDM flexible shafts

The rest of the components in the propeller assembly (main gear, motor gear and propeller hub) were identical to those that equipped the Bf 109E as can be seen from the images below.

Propeller main gear (VDM 9-11014.56)

Motor gear (VDM 9-0142.62)

Angrenajul motor VDM 9-0142.62: IAR80 / Bf-109E

Propeller Hub (VDM 9-081.25)

The figure below shows the blade bearing type VDM 9-11 081.40 compatible with the hub VDM 9-081.25., most likely the same type used by the I.A.R. 80/81.

The VDM propeller blades

We do not have precise information on the VDM 9-11 131 propeller blades but we can assume with a high degree of certainty that they were a mirror copy of the blades mounted on Bf 109E given that both aircraft used common VDM components, the propeller dimensions were the same (3 m diameter) and the power of the DB601A and IAR engines 14K similar. The similarity can be seen in the illustrations below.

Bf-109E propeller (VDM 9-11.081 A, year 1941) – VDM classical triangle logo

The first photo depicts one of the propeller blades of the IAR 80 C aircraft Nr. 264 piloted by NCO Olaru Aurel shot down on the 4th of February 1944 over the Black Sea as a result of an error by the German air defense and recovered by Ukrainian divers in the 90s. [14]

The second shows a modern replica of the VDM propeller for the Fw-190

VDM propeller geometry

The propeller blades mounted on Bf 109 E with manual VDM system (VDM 9-11 081 A) were of the type 9-11 073.10 illustrated in cross section in the figure below (excerpt from the catalog of VDM parts Ed. 1944 [8]). The diameter of the propeller was 3 m and the diameter of the blade fitting was 107 mm.

The same type of propeller was equipping the Jumo 211 A engines of the Heinkel He-111 H1, H-2 bombers. The image on the right shows the developed planform of the blade surface, the angle distribution and the blade profile of the Heinkel 111 propeller [4]. Note: due to the projection, the blade looks wider compared to the cross section.

The propeller blades were made of Duralumin with the following composition: 3.30% Copper, 0.46% Iron, 0.43% Silicon, 0.68% Manganese, 0.70% Magnesium, 0.02% Titanium and the rest Aluminum.

The propeller spinner

The propeller spinner of the I.A.R. 80/81 had two shapes, a more common rounded one and a variant with a more elongated tip. These variations do not seem to be related to a particular type but rather driven by logistical considerations. Assuming that they complied with the VDM models for propeller main gear compatibility, the most likely types appear to be those used on the Bf-109E for the elongated tip variant (VDM 11 081.30) and the VDM -11 257.32 type for the rounded tip variant.

P.S: special thanks to Franciszek Strzelczyk, who’s valuable feedback allowed us to improve the quality of this article

Author: Răzvan Mărgăuan

Bibliography:

1. Notița tehnică a avionului de vânătoare I.A.R. 80 cu motor I.A.R. 14 K. IV. C. 32, Brașov 1941

2. Notița tehnică a avionului I.A.R. 80 Ediția II-a, Brașov 1943

3. Catalog piese de schimb I.A.R. 80/81

4. Notița tehnică a motorului IAR-14K IV c32, Brașov 1942

5. John D. Waugh, Particulars of the German VDM, SAE Journal Vol. 52, No. 8, 1944

6. Bedienungs und Wartungs­Vorschrift für die VDM-Verstelluftschraube, 1939

7. VDM-Verstelluftschrauben Geräte-Handbuch Beschreibung und Wirkungsweise sowie Bedienung und Wartung für elektr. Drehzahlregelanlagen, 1941

8. Ersatzteilliste für die VDM-Verstelluftschraube, 1939, 1941, 1944

9. Marco Fernandez-Sommerau, Messerschmitt Bf 109 Recognition Manual, Ian Allan Publishing, 2004

10. P. Blackah & M.V. Lowe, Messerschmitt Bf 109 Owners’ Workshop Manual, Haynes Publishing 2009

11. Principiile zborului, Aeroclubul României, București 2011

12. https://digital.deutsches-museum.de/item/73585/

13. ME109 Bf109 DB605 Engine Propeller pitch demonstration from a Luftwaffe Messersschmitt (https://www.youtube.com/watch?v=qIpZAu61OM8)

14. https://www.facebook.com/rww2aa/posts/iar-80-c-nr-264-esc49-gr-4-vtpilot-adj-av-olaru-aurel-shot-down-on-04021944-by-g/2454965397911586/

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