What are these things (old airplane content)

I'm at the Smithsonian Air and Space museum, and am looking at a De Havilland DH-4 airplane. I'm wondering what are these two little (electric?) propellers that are mounted on the landing gear for?

Air speed measuring devices?

Cool?

They're generators to power the radio and lights.

Since they are wired in, I would assume they are auxilliary power generators.

Airspeed and electrical generator. Many aDH-4s were mail planes, and were expected to fly in damn near any waether. Air speed and instrument lights proved to be benificial.

Thanks, that makes sense 

In reply to Appleseed :

I don’t know when pitot / static systems started being used to indicate airspeed, vertical speed, and altitude but even if this DH-4 predates these systems, placing the airspeed measuring instrument in the prop wash will, at times, give a dangerously overstated indication of speed…why in the hell wouldn’t it be placed out on the wing to indicate how much lift can be generated...much more important then knowing how furled the pilot’s scarf is wouldn’t you say.

The DH-4 dates from the end of the great war. Even then, they were still figuring it out. It's possible they took propwash into account. Many (often dead) pilots around that time disregarded instruments altogether. 

FWIW, I just looked at some internet pictures of the exhibit from other angles and there does appear to be an additional wind powered device. It appears to be attached to the bottom of the fuselage several feet behind the landing gear and has four, slightly smaller blades. Additionally, it has a thinker cable which runs up into the fuselage.  What I didn't see was any kind of pitot / static system...not even something like the simple clear tube and ball designs they use on ultralights.

RX Reven' said:

In reply to Appleseed :

I don’t know when pitot / static systems started being used to indicate airspeed, vertical speed, and altitude but even if this DH-4 predates these systems, placing the airspeed measuring instrument in the prop wash will, at times, give a dangerously overstated indication of speed…why in the hell wouldn’t it be placed out on the wing to indicate how much lift can be generated...much more important then knowing how furled the pilot’s scarf is wouldn’t you say.

it would seem to me, you would want to know the windspeed over the wings more than over the ground. I have seen biplanes actually fly backwards in a strong enough gust, but still have enough wind over the wings to generate controlled lift

The pitot tube was developed in the 18th century by Henri Pitot . I have never seen an airplane , no matter how old, with out an airspeed indicator mounted out of the prop wash . It may be as simple as a spring loaded lever  with down being slow and parallel with the horizon fast. 

Smokey yunick mouted a prop driven generator on a NASCAR car and the rules were changed immediately

Crap. I confused it with the location of typical venturi tubes for vacuum instruments. That DH-4 was used in over 2,600 expiriments before it was retired in 1919. I'd bet that is what we're looking at.