RKAJFSAZ Posted July 19, 2018 Share Posted July 19, 2018 Does anyone repair Waltham Tesla air friction speedometers ?, application is a 1928 Franklin Link to comment Share on other sites More sharing options...
Mark Gregory Posted July 25, 2018 Share Posted July 25, 2018 I am not a Franklin owner but there is probably lots of advice from some of these Vendors on the Franklin site . http://www.franklincar.org/forsale/service.html Link to comment Share on other sites More sharing options...
Spinneyhill Posted July 25, 2018 Share Posted July 25, 2018 Sounds like something from the aeronautical world? Link to comment Share on other sites More sharing options...
C Carl Posted July 26, 2018 Share Posted July 26, 2018 It may have aeronautical provenance. Airspeed is essential information for flight, in general, FAR more important than ground speed. Relative headwind plays an important part, sometimes beneficial as when a tailwind reduces it, in the operation of our ancient crates with such high drag coefficients. Even more critical in the case of air cooled cars. Drivers of our beloved old junk should be particularly cautious when driving into headwinds. Operating at high intake manifold pressure (high torque output), under such conditions may lead to engine destruction. Slow way down driving into strong headwinds, and keep a close eye on temperature and oil pressure. Even on modern cars, maintaining EXCESSIVE speed into EXTREME headwinds can be detrimental to engine health. Hmmmm......... You know ? I think I want one of these air friction speedometers. Anybody have one for sale ? - Carl Link to comment Share on other sites More sharing options...
Spinneyhill Posted July 26, 2018 Share Posted July 26, 2018 Well I was wrong about that then. It is not a Pitot Tube. It relies on the friction of air between two metal surfaces in close proximity. Here is a bit of guff about it. 1 Link to comment Share on other sites More sharing options...
C Carl Posted July 26, 2018 Share Posted July 26, 2018 Very interesting, Professor Spinney', my friend. However, you have burst my bubble. All : please cancel my order for an air friction speedometer. ?, - Carl Link to comment Share on other sites More sharing options...
Friartuck Posted July 26, 2018 Share Posted July 26, 2018 If I'm correct, air friction speedometer was a Tesla invention. The inner drum is directly connected to the cable/gear assemblage and the outer drum is on a light spring The outer drum has the numbers around its circumference. The air between the two drums makes the connection between them. Calibration is made by either drum height or the spring. Link to comment Share on other sites More sharing options...
RKAJFSAZ Posted July 26, 2018 Author Share Posted July 26, 2018 If the delicate aluminum drum (with the speed printed on it) gets distorted in any way by improper handling, the thing won't work (I have three like this). Im surprised there's not an expert who repairs these, thought they were used in a lot of higher end cars, not just Franklins. I think 1928 was the last year they were used. Link to comment Share on other sites More sharing options...
ply33 Posted July 26, 2018 Share Posted July 26, 2018 4 hours ago, Friartuck said: If I'm correct, air friction speedometer was a Tesla invention. The inner drum is directly connected to the cable/gear assemblage and the outer drum is on a light spring The outer drum has the numbers around its circumference. The air between the two drums makes the connection between them. Calibration is made by either drum height or the spring. Interesting that Tesla, renowned for his work with electricity and magnetism, would invent a air coupled mechanism for a speedometer. Link to comment Share on other sites More sharing options...
Restorer32 Posted July 26, 2018 Share Posted July 26, 2018 Wouldn't the accuracy of such a device be dependent somewhat on barometric pressure i.e. air density? Link to comment Share on other sites More sharing options...
C Carl Posted July 26, 2018 Share Posted July 26, 2018 No. Read the 1916 Scientific American article which Dr. Spinneyhill links in response #5 above. Very clever, sensitive device, with remarkable accuracy, even down to less than one mph ! The thing does not lose function at high altitude either. It was tested up to 10,000'. - Carl Link to comment Share on other sites More sharing options...
Spinneyhill Posted July 26, 2018 Share Posted July 26, 2018 @RKAJFSAZ can you ring any instrument repairers and ask if they can do them and if not, do they know who does? Telephone calls are pretty cheap in the USA compared to many other places, e.g. here! If the cups are bent, a very good panel beater or jeweler should be able to put them back into shape. Link to comment Share on other sites More sharing options...
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