Vladimir,
I have made a Pennyplane but have never made a VP mechanism so the following is more comment than advice.
The shape of the unwinding torque curve does not vary greatly from motor to motor and I think the cruise torque could be expected to be about one fifth to one sixth of the maximum torque.
In the cruise part of the flight the diameter and blade angle will be very similar whether a VP mechanism is used or not so just start from your best fixed pitch propeller. The VP will increase blade angle considerably to absorb the very high initial torque and probably, but less importantly, reduce blade angle as the torque tails off at the end of the turns.
You mention spring tension but I have never seen a tension spring on a VP mechanism. The usual spring is a close coiled helical spring used in torsion. I think F1D springs are usually about 0.009” diameter wire so PP would probably use somewhat larger. Efficient springs, if I remember correctly, use an inside diameter about 6 to 8 times the wire diameter and the number of coils will depend on the torque required . The torsional stiffness of a close coiled helical spring (the torque required to twist the coils) is easy to calculate and the formulae required are on the Internet. However to apply the torque it is usual to have a straight piece of wire extending from the end coil and the length of straight wire affects the torque load. Also, of course, the straight wire is a cantilever in bending and will have a deflexion which must be included in the VP calculations.
John
From: Indoor_Construction_at_yahoogroups.com [mailto:Indoor_Construction_at_yahoogroups.com]
Sent: 23 November 2014 22:45
To: Indoor_Construction_at_yahoogroups.com
Subject: [Indoor_Construction] Pennyplane vp hub
Undergoing a dvelopment of new Open pennyplane hub. What are the experiences of those before me in terms of a average cruise torque on these models to determine a starting point for spring tension? With the cruise torque i would like to know the prop dia and pich as cruise torque is directly related to these variables. Those that have built vp props for open penny plane what are the spring specifications used (wire dia, number if turns and inside dia)
Vladimir Linardic
Received on Mon Nov 24 2014 - 10:05:31 CET
This archive was generated by Yannick on Sat Dec 14 2019 - 19:13:48 CET