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Author Topic: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)  (Read 3587 times)
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Konrad
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« Reply #25 on: April 27, 2020, 02:18:16 PM »

Some more setup details. I have to admit I never could get the tiller arm to work reliably with the stock nose strut. This was with both the FMS and Taft Super Scorpions and the other Taft models. My fix was to use the mounting plate itself as a guide (stop) keeping the pushrod from moving up rather than actually rotating the strut. To do that I swapped the spacer and tiller arm block on the strut pin. This brought the tiller arm block closer to the mounting plate but away from the anti-rotation ramp. I then moved this ramp as far forward as the mounting plate would allow. As a safety I added some ramps to the mounting plate to ensure that the tiller arm could not bind on the mounting plate should the rudders be commanded while the retracts were in motion. A weak point in this tiller are system in that there really are no stops to keep the tiller arm moving down. To minimize this issue I bias the “Z” bend so as to have the push rod pointing (biased) to the fuselage bottom at all times.

I was also fighting an elevator induced roll. This was traced to improper Ackermann effects as a result of servo arm geometries.  With odd spline count servo outputs the servo arms are NOT aligned at the same spot with the feed back pot when flipped between sides. One will need to use the "trim offset" in ones radio to make sure that the servo arm geometry is correct and that both surfaces move the same along the surface’s travel. More advance radios such as those running OpenTX can use curves. Also make sure that the end points allow for the same total deflection.  I like elevator differential to help with the feel for inverted flight. As one is working against the camber of the airfoil I find I need more “down” than “up” in my elevator response.

Much the same conditions apply for the ailerons. Make sure that the servo arms are point forward the same amount for the initial mechanical differential.

All the best,
Konrad

P.S.
I see that FMS has added a shelf to keep the stearing push rod in place. This would be more effective than my Z bend bias.
Attached files Thumbnail(s):
Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
« Last Edit: April 27, 2020, 02:45:29 PM by Konrad » Logged

Cut it twice and it's still too short!
Konrad
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« Reply #26 on: April 27, 2020, 04:53:25 PM »

Mainly for transport and storage reasons I’ve made the nose cone removable. I’ve found that magnets never are strong enough to keep the nose cone, on even when I on the rare occasion make a good landing. So I’ve added carbon rods to actually carry the flight and landing loads.

Another issue that I’ve always had with snap on canopies is that they come off in flight, particularly when in knife edge.  To stop that I’ve added a carbon rod that pins the  canopy to the fuselage. It is a bit of a pain having to pull back the nose cone to release this pin. But it is much better than spending most of the day looking for the canopy that is lost in the fields.

All the best,
Konrad
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Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
« Last Edit: April 27, 2020, 06:48:48 PM by Konrad » Logged

Cut it twice and it's still too short!
Konrad
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Measure twice cut once



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« Reply #27 on: April 30, 2020, 09:19:59 PM »

As I mentioned earlier I felt that the Taft Scorpion's inlet system might be lacking. Looking at the small inlets up front and the large cheater hole I was thinking that the air going past this cheater hole might actually be drawing air out of the duct at low or negative angles of attack.

As I had some SuperFil epoxy already mixed up for another project I thought I'd run an engineering exercise. Along with filling in some of the inlet grate periphery for (esthetic reasons) I built up a 2 to 3mm air dam. It was hoped that the dam would allow more air mass into the fan giving me added acceleration.

The jury is still out on this as I've only got 2 test flight in under this configuration. In a shallow dive I do think my top speed is a bit better. In level flight I think my acceleration is better but can't say as I'm seeing a lot of added speed. At low speed in the vertical I don't see any change.

Attached files Thumbnail(s):
Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
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Cut it twice and it's still too short!
Konrad
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« Reply #28 on: May 01, 2020, 02:52:25 PM »

I have to say I really liked how the FMS Super Scorpion was performing even on 6 cells. Like I said I think it can be traced to the inlet. The key is that there isn’t a cheater hole in the FMS inlet.

Here is what I think is going on with the inlet for the Taft Scorpion. The inlets are far too small. As this is a sport jet I don’t understand why they were made so small! The inlet duct gets larger towards the fan. This allows the air to slow down causing a pressure rise in the duct. Right before the fan we have a cheater hole. This cheater hole is in an area of low pressure from the narrowing of the fuselage contours and the high speed air in flight flowing past the opening. This is fighting against the fan’s efforts to draw air in.

At higher angles of attack this isn’t as bad as one might think as the rear of the opening is lower exposing the cheater hole to some ram air effect from the forward motion.  Unfortunately the Taft Scorpion has the wings set at a rather high angle of incidence. Meaning that for most of the flight profile the rear of the fuselage (cheater hole) is not exposed to the incoming air.

I hope that adding a little air dam will add pressure to the cheater hole area. I hope that what I gain in airflow going through the fan makes up for the added drag from the air dam for most of the flight profile.

If anybody has any input on this I’d like to learn what you think. Do I have a large enough air dam (2mm to 3mm high). Is this is a waste of drag? If so, I can sand the air dam off rather easily.

So what do you all think?

All the best,
Konrad
Attached files Thumbnail(s):
Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
« Last Edit: May 01, 2020, 03:35:39 PM by Konrad » Logged

Cut it twice and it's still too short!
Konrad
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« Reply #29 on: May 29, 2020, 02:35:46 PM »

I think I may have found the missing performance. The ESC Taft uses is a Flycolor ESC. This ESC has a thermal protection circuit. This is nice as it gradually cuts back the power to 40%.

I suspect that the flights flown with/against the FMS Super Scorpion were flown with the ESC cutting back on power.

The bad news is I'm flying this with a Spektrum radio and don't have telemetry. If I was flying FrSky it would be super easy for me to add some thermal sensors. (I'll need to look into this a bit more).

Next time out I'll change the ESC frequency from 12 kHz to 8kHz and maybe up the timing from 7.5° to 11.25°. I'll also see what I can do to get more airflow around the ESC.
(You might have noticed that I removed the OEM ESC mounting shelf and have the ESC tucked "nicely" into the turtle deck.

The good news is that at 40% power the Taft Super Scorpion didn't embarrass itself.

All the best,
Konrad
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Cut it twice and it's still too short!
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