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the bare bones of the High Performance Sportster. The 20″ span model looks a lot like a small Gollywock.<\/p><\/div>\n
That’s not to say it was “perfect” (there are always improvements that can be had) – it seemed wobble or roll quite a bit – maybe the CG was back to far and it was on the edge of a stall the entire time.\u00a0 Also, I had used a printed 8″ diameter prop with 13″ pitch.\u00a0 \u00a0Combined with two loops of 1\/8″, this created a slow climb – no zooming here.\u00a0 But the long duration of power, even in cruise, put it in a great position to just cruise around and wait for the little thermal and that rear CG created a model that was very susceptible to those thermals and it would just go up.<\/p>\n
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As I prepared for yesterday, I figured attendance would be low, so I took to “modifying” the HPS in preparation for testing.\u00a0 The main thing I wanted to do was to test a lower-pitch prop.\u00a0 The 8″x13″ prop has a P:D Ratio of 1\/6:1 – that’s quite high – but it does explain the slow climb-out and long motor run.\u00a0 A long motor run is great, but slow climb can result in short (not max) flights since the glide portion could be short due to low altitude.\u00a0 So I printed an 8″x11″ prop with a much more typical P:D of 1.3:1.\u00a0 I also made a new noseblock (printed) so I could just swap the entire front end (I made sure both prop & noseblock assemblies weighed the same).\u00a0 The idea here was to test with the original prop, then swap front ends and wind to the same torque and see how the flight differed.<\/p>\n
I also swapped out my BMK Band-burner DT for a BMK Remote Band-burner DT.\u00a0 This took a little work:\u00a0 I print little boxes to hold the DT and Battery so they can be moved from model to model.\u00a0 But I had set this DT “backwards” or in reverse so the leader line came in from the front (see the image above) instead of the rear.\u00a0 The box for the RDT unit is the same mounting size BUT due to the front entry of the leader line,the antenna pointed down.\u00a0 I had to re-run the line to come in from the rear.<\/p>\n
Note that the model has a pop-up wing DT system.\u00a0 I did this to keep excess structure and weight off of the tail and move that weight to much closer to the CG location.\u00a0 In fact, all of the DT system is well in front of the CG – and I still had to add nose weight.\u00a0 I did not want to slide the wing further aft as that compromises the model, making the tail moment shorter.\u00a0 Anyway, I got the RDT installed and working.\u00a0 AND – I discovered (maybe I already knew this?) that you do not have to put the DT on the timed count-down to activate the DT remotely; it just has to be plugged in and when you hit(and hold) the button, the DT burns through the rubber.\u00a0 This is ideal for testing.<\/p>\n
In four hours at the field yesterday, I probably put in close to 20 flights some short and some long.\u00a0 I started with the “known” condition – I used the original 13 pitch prop to verify that the setup hadn’t changed and things were relatively the same.\u00a0 Cold dense air is different than warm buoyant air and the model did act differently.\u00a0 But one of my first flights was a 1:56 – not bad for no thermals.\u00a0 (Oh, this demonstrates what I said before:\u00a0 it had a great motor duration, but never climbed high enough to allow for gliding over the 2-minute mark.)\u00a0 But the model was “less good” than it had been.\u00a0 I am pretty sure the lack of thermals and a slight breeze revealed that the model really was not trimmed the best – at least not trimmed for these new conditions.<\/p>\n
I swapped out the prop & noseblock and eased into trimming the thrust.\u00a0 This took several flights.\u00a0 It also revealed a great feature of the RDT.\u00a0 I could launch, watch the climb, see it wasn’t well trimmed and hit the RDT, bringing the model down after 30 seconds or so and move on.\u00a0 And more than once, I had high-torque launches that were going tight right and would have hit the ground hard, but I could push that button and save the model.\u00a0 These two uses saved much time and saved the model more than once, proving the RDT to be very useful and almost necessary.<\/p>\n
But the model was quite different in this weather, regardless of the prop used:\u00a0 it seemed to be more loopy than it had been, both under power and in the glide.\u00a0 in the glide, I decided that maybe the model had too much incidence and I sanded down the stop that holds the front of the wing up.\u00a0 Similarly, under power, it seemed to zoom, stall, recover, zoom again, etc, etc.\u00a0 I think this was a fault in my construction design.\u00a0 I think the front of the wing was not being held down firm enough and high speed would lift the front of the wing, increasing incidence.\u00a0 As it stalled, the force on the wing would allow it to re-seat and reset to normal incidence.<\/p>\n
Given all of this, I tested a lot.\u00a0 My last flight was with the 8″x11″ prop and a fully wound motor.\u00a0 The trim was just right and the plane climbed out very aggressively – the way one does when it has a little assistance from the air.\u00a0 I mean, it went up like it never had before, the prop and the air combining to carry it VERY high.\u00a0 I am glad I looked at my transmitter – it was OFF – the battery must be getting low!\u00a0 I quickly turned it on, checked the watch and it was just over 1 minute.\u00a0 The model was so high.\u00a0 I pushed the button and it DT’d .\u00a0 The model finally hit the ground at 2:06 just off the field – it took a MINUTE to come down.<\/p>\n
And learned a lot.\u00a0 Probably the primary thing I learned was that if I want to optimize this model, I probably need to build a new one, or at least a new fuselage.\u00a0 I would lock down the wing and move the DT to the tail, where all DTs should be.\u00a0 Then I’d probably move motor peg forward one bay to shift some of that motor weight forward.<\/p>\n
I learned that the RDT is a great tool for trimming – it will shorten your flights so you can move on to the next adjustment.\u00a0 I learned that you better keep that transmitter charged, just like all the rest of your equipment.\u00a0 I learned that testing can really help you improve a model’s performance – and it can reveal some of the bad choices you made during construction.\u00a0 I also learned that this little model is a performer – right up there with the best OT Sticks.<\/p>\n
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Ok, yesterday was our last outdoor contest of the year.\u00a0 The weather was cool (30s with frost on the ground when we started and 50s when we left), with light breezes blowing away from the pits, for once.\u00a0 However, only … Continue reading