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Greyhead · 18-07-2008

As was shown in a previous post the theoretical top speed for my SE5a using the 16x4 prop is 26mph, this gave me some concerns, however, looking at a ”typical circuit” eased those concerns somewhat.

At 18% scale the speeds would be

Take off: not below 9mph
Climb out: 10.8mph
Level flight: 14.4mph
Touchdown: 8.1mph

The maximum speed is given as 123mph, it doesn’t say if this was obtainable on engine power alone but somehow I imagine this was the absolute maximum speed the airframe could withstand before the wings ripped themselves off or something equally terminal happened! At “scale” speed this equates to 22.14mph so my theoretical top speed of 26mph sounds reasonable.

Of course the theoretical top speed doesn’t take into account the drag factor and models always seem to fly faster than “scale” speed but in practice it has worked out OK so I’m happy to stick with the large prop even if it does mean that the engine is somewhat “over-propped”.

18-07-2008	#650 (permalink)
Greyhead Scale Model Member Join Date: Oct 2004 Location: County Durham Real Name: Grahame My Models: Preference for biplanes Visit Greyhead's Gallery Posts: 581 Images: 642	As was shown in a previous post the theoretical top speed for my SE5a using the 16x4 prop is 26mph, this gave me some concerns, however, looking at a ”typical circuit” eased those concerns somewhat. At 18% scale the speeds would be Take off: not below 9mph Climb out: 10.8mph Level flight: 14.4mph Touchdown: 8.1mph The maximum speed is given as 123mph, it doesn’t say if this was obtainable on engine power alone but somehow I imagine this was the absolute maximum speed the airframe could withstand before the wings ripped themselves off or something equally terminal happened! At “scale” speed this equates to 22.14mph so my theoretical top speed of 26mph sounds reasonable. Of course the theoretical top speed doesn’t take into account the drag factor and models always seem to fly faster than “scale” speed but in practice it has worked out OK so I’m happy to stick with the large prop even if it does mean that the engine is somewhat “over-propped”.