The_Rocketeer Posted July 11, 2016 Share Posted July 11, 2016 1 hour ago, Chemp said: I love the way this looks, especially the cockpit placement. How do you deal with the asymmetric thrust? Did you angle the engines, or do you let the control surfaces handle the offset? Thanks! I'll try to answer as fully as I can and cover everything. Sorry for explaining in a roundabout way... I built the craft with 1 pair of Goliaths on top of the floats, plus 3 Wheesleys on the trailing nodes of the 3 'hulls'. There's no angle on the engines, they're just attached straight on the nodes/edge surfaces without rotation adjustment. During my first distance run, I made a pilot error that damaged the craft and bust the intake and Wheelsey off the port float. To keep thrust balanced, I shut down the opposite Wheelsey and ran on just the Goliaths and the centre Wheelsey. For unknown reasons, the starboard float intake has also since detached - it was there one moment and the next time I looked it was gone the latest design revision has replaced the intakes and engines on the floats with nose-cones for better durability. Running on 2 Goliaths and the centre Wheesley, initially I found the craft, while still planing, was about 30% slower. I perceive that the centre-of-thrust moved upwards when the lower engines shut down, so the boat was tending to pitch-down and drive into the water instead of skimming over it. However, after re-trimming the planes to give a little more lift forward and a little less aft, I found that it was still possible to reach the same 100m/s target speed. I could be wrong about this part, but my impression is that the 3 engine configuration is more efficient than the 5 engine configuration (but I have to allow that as the comparison was made on the same run and the craft mass was decreasing the whole time that could be a false impression). Nonetheless, assuming the change in mass is insignificant, and speed and throttle setting being the same (100m/s, 100% throttle), I think I must be using less fuel per distance with 2 fewer engines. The Goliaths also have higher ISP than the Wheesleys, so if a higher proportion of available fuel is ultimately consumed by Goliaths it should go further - i.e. more efficient. Also relevant is the fact that in both configurations, as the fuel mass decreases it's necessary to continally re-trim the planes inline with mass reduction to reduce lift. While in theory more engines means higher cruising speed, maximum speed is limited by the point at which aerodynamic lift force exceeds mass, because at that point the craft stops hydroplaning and starts aeroplaning. It's possible that as the tanks get dry, it might become impossible to stop the craft flying without reducing speed, either by cutting throttle or by setting the planes to negative pitch. Mastering the hydrofoil is an ongoing education! TL:DR, I think correcting the offset-thrust with more control surface pitch is more efficient than reducing it by adding engines lower down. ======= In other news, after one or two further mishaps, and having learned a lot from this attempt, I've decided to demote this adventure to a shake-down cruise. Hoping to return with a new and improved hydrofoil Elcano attempt in the coming days. Quote Link to comment Share on other sites More sharing options...
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.