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Radio Control Forum => Jets => Topic started by: Konrad on September 11, 2017, 04:50:26 PM

Title: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
Post by: Konrad on September 11, 2017, 04:50:26 PM
Let me admit that I have this addiction. I as a modeler am ashamed to admit that I’m addicted to foam ARFs. True modeling to me is where one creates a representation of a subject or a simplified testing tool.
What I have here is a no bones example of check book modeling. For $260 (Labor Day sale)I found this Taft Super Scorpion 90mm 8 cell sport jet for the same price as the 80mm 6 cell Freewing.

This is exactly the type of model I like to get. That is one that has a bad reputation on the forums. For about 3 hours of hobby work and $50 to $100 dollars in replacement parts (if any fail my burn in) I’ll have a model that will out perform the $450 FMS 6 cell Super Scorpion. Here is a photo of the Super Scorpion next to the Dynam Meteor. I will say that transportation might be an issue!

Yes, this will become a detailed review of the Taft Super Scorpion. On first blush it looks to be a good value for the current asking price of $299. Everything worked straight out of the box. My JDPower's initial customer quality evaluation is that the Taft Super Scorpion is not up to par with the FMS offerings. Initial quality appears to be much better than what I've experienced with Dynam models. I'd place the quality right around what we might expect from say Freewing. That is good but in need of some work prior to first flight. To be brutally honest the quality we find in the  Taft Super Scorpion really is just half a step below the Freewing models. On balance the Taft Super Scorpion a great value for real modelers who have the skills and fortitude to put a little work into their models.

We shall see if at the end of this exercise I can hold my head up as a real modeler.

All the best,

Title: Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
Post by: Konrad on September 13, 2017, 12:29:14 PM
Keeping with my trust but verify approach to these mass market toy EPO models. I’ve inspected the power system. For the most part I’m pleasantly surprised at what I found. I was really happy to see that Taft added a cap pack to the battery side of the ESC to combat the issue of damaged MOSFETs as a result of the long battery leads. ALL OEMs should ad these if the anticipated battery leads are to be longer than 6” to 8” long! I was also surprised to find dual switch ESC’s included in the power system. Very nice touch.

I was a little disappointed in that I found a mis-marked motor. The sales brochure and the kit manual clearly state that the motor is a 1300KV motor. Unfortunately the motor in labeled as a 1500KV motor. Modeling the fan on 8 cells would indicate that the motor is close to a 1300KV motor the current draw measured of 66 amps closely matched that of a 1300KV motor.

What little I could find about the X-team motor is that this 3674-1300KV has a current limit of 48 amps yet has a power limit of 2.4KW. This isn’t as bad as one would first think. The motor really is designed for “buggy” use. Being as this is in an EDF it is in the cooling blast of the efflux which allows for huge over amping. As measured I’m getting 66 amps but at a voltage of 32V the power output is well below the 2.4KW limit as it is only 2.1KW. That being said the 309g mass of the motor really is a bit on the light side. One really needs to add a finned heat sink to the motor.

I was a bit shocked to find that I could not remove the EDF unit from the airframe without taking it apart. One needs to remove the inlet lip to draw the EDF unit through the hole provided by Taft to service the EDF unit. This cause some issues at the point of manufacture as glue was dripped onto the rotor blades when trying to glue on the inlet ring. This might account for some of the rough running I noticed in my testing.  I’ll try to balance the rotor to see if this smooths things out.

Edit: Current limit is 48 amps per X-Team.

Title: Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
Post by: Konrad on September 14, 2017, 06:18:06 PM
Plugging away at the Taft Super Scorpion I’ve found some Good Bad and Ugly points.

What I really like is the look of the anhedral stab. This combined with the splayed out vertical fins make this a great looking model yes even better than the MD F-18 E/F US fighter! On a more practical note I hope it addresses an issue I’ve notice with the other offering of the Scorpion. Having flown the Freewing 80mm Scorpion and the 70mm ROC/FMS Scorpion I notice that the elevator response was a bit lethargic with the straight stabilizers. I suspected that this might be due to some separation bubble on the stab or wake turbulence from the wing. With the anhedral stab Taft is insuring that some part of the stab is working in clean air regardless of the plane’s attitude.
I have to admit that seeing this stab anhedral gave me concern about the attachment points to the fuselage. Clearly Taft is NOT using a through spar (rod) to mount the stab and its associated pivots. Taft has give the stab a nice wide bearing area inside some large plastic load spreaders. What I do have are some grave concerns about the length  of the stub to which the stab is bolted.

I did notice a no fly item and that is the stab push rods. Taft (and most other toy EPO vendors) is using a low grade 1.2 mm wire with stamped thread. This wire is so flexible that Taft added a carbon tube to try to stiffen it from flexing mid span.  This weak wire and the poor quality spherical end combined with the gross course 0.75 mm thread pitch necessitated a full rework of the push rod. I’m using Dubro 2mm Swivel Ball Links Cat# 368. I’ve threaded a 2 x 0.4 pitch thread onto a 0.078” (nominal 2mm) music wire. You might have noticed this means that you will end up with the rod that allows for twice as fine a length adjustment! The wire is 110mm long with [email protected] 14mm long threads. (To thread music wire you need to anneal the wire otherwise you are likely to break you 2mm die).

I do have a concern with the stab elevator servos. Not with the brand or quality of the servo. If Quique Somenzini is willing to put the reputation of his new venture “Flex Innovation” on the line with Potenza, I’m sure he has vetted them well. My issue is with the size/power a 19 gram 2.9 Kg-cm sounds rather weak for this weight and speed of aircraft. With proper geometry it might work. But I read far too many folks are crippling the servo’s performance by limiting the motion of the servo to 50% or less. You should alway try to set up your servo/surface throw so that you are using 100% to 120% of the servo’s normal rotational throw. This keeps the power torque up and improves the surface resolution. MOVE THE PUSH ROD CLOSER TO THE SERVO CENTER LINE!

The battery area appears to be huge, at least 87mm wide and 56mm tall. This space goes all the way 30mm past the wing’s carbon through spar! I can’t understand why so many folks claim to have issue making the CofG with the appropriate batteries.

The ESC mount, well that is just a bad idea!

All the best,

Title: Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
Post by: Konrad on September 14, 2017, 06:20:07 PM
Flight is all about fluid flow.

Over all I’m NOT impressed with the flow ducting on ether end with this large model. The upthrust really has me concerned. I recall having a horrible time with changes in flight trim with changes in power setting with the Multiplex twister (it had down thrust in the thrust tube). I fear that Taft is using upthrust to over come some concerns about being nose heavy. Upthrust is the wrong trim variable to adjust for being nose heavy!

All the best,

Title: Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
Post by: Konrad on September 15, 2017, 01:43:41 PM
Some corrections are needed.
While Taft does provide 2 SBEC they are not redundant. One is a set for 5.5V. I assume this is to power the radio and servos. The other is set at 7.45V with a 2 pin JST connector on the output. I assume this is to drive some other accessories, such as brakes (No brakes are provided on the wheels).

I was in error saying that the FreeWing 80mm Super Scorpion was a flat tail ship. She does have a slight anhedral stab. This is much like this Taft Super Scorpion but at what appears to a lesser angle. (I'd like to make note that the stab pin purchase area appears on the Freewing 80mm Super Scorpion to be twice as large as the area on this Taft 90mm Super Scorpion.)

Title: Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
Post by: Konrad on September 15, 2017, 11:11:38 PM
Cleaned off the glue from the Taft rotor and rebalanced the rotor. Wouldn’t you know it, the glue (weight) was almost 180° away from where I needed to add weight to get a smooth running EDF unit.

I performed my 5 minute burn in on the Potenza DS19 servos and they past with no issues. But looking at the size of the stabilators I wasn’t comfortable driving them with a 2.6 Kg-cm servo. As I had a few HS5085 laying around I felt these were more suitable. Luck would have it that removing the plastic pocket, Taft uses as a screw pad to mount the servo, leaves a foam pocket that fits the HS5085 perfectly. Keeping with my belt and suspenders approach to flight safety I glued in the HS5085 with both Welders contact cement and hot glue. The bond area is close to the same as with plastic pocket. The only down side with this is that it will take some effort to replace the servo should the need arise.

I will reuse these Potenza DS19 servos to replace the 13 gram aileron servos.

Something to be aware of is that regardless of the level of modeling good mechanical protocols need to be adhered to. In the case of these metal servos there needs to be some form of lock washer added. Without the lock washer (star washer) the servo arm screw WILL vibrate out, with the result being total loss of control from that servo.

Title: Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
Post by: Konrad on September 18, 2017, 06:45:05 PM
More correction/clarification!
This is the price of doing these builds live.

The power from the stock EDF unit just jumped from a current draw off 66 amps to that of 107 amps with a steady draw of 98 after 30 seconds.
I can only attribute this to better batteries; 25C for the 66amp reading and on the bench, 55C (TP Lightning series) for 107amp and with the EDF in the fuselage.
Will definitely be adding that finned heat sink!!! And limiting the flights to 3 an hour to keep the duty cycle (heat build up) in check.

Well, Taft isn’t making it easy for me to up grade this ship. I wanted to move the Potenza DS19 from their location as stabilator servos aileron servos. While the aileron servo cover/mount will hide the larger Potenza DS19 the aileron pocket and liner Taft provides to hold the cover/mount will not allow an easy upgrade.

It has to be more that the battery impedance! I was messing around with the ESC programing this weekend. Maybe I released some hidden monster in the ESC programing. Re-running the numbers in the predictive programs it is looking like the motor may in fact be a 1550Kv motor (I owe X-Team an apology the motor may not be mis-marked). If it is indeed a 1500Kv to 1600Kv motor the nominal amp limit rose from 48 amps for the 1300Kv to 70 amps the motor 1500Kv labeled)

Not sure I trust any of these EDF simulators. I should just remove the fan and measure the Kv directly. Unfortunately I can't safely remove the fan as there is no motor hold feature on the Taft adaptor and the nut appears to be held on with a very strong thread locker.

Title: Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
Post by: Konrad on September 19, 2017, 01:27:54 PM
Well, just incurred my first of what I’m sure will be the first of many added expenses, spare parts.

This has nothing to do with Taft or any quality issues. I just like to have replacement parts on hand for all the models I have in flying condition. And the things that first hit the ground, spinner and landing gear, are high replacement items for me. So I got some retracts.

Again luck would have it that Horizon Hobbies (HH)is closing out their inventory of Taft parts. While HH carried the Viper jet but not the Super Scorpion.
Many of the components are the same between the Viper and the Super Scorpion.

Title: Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
Post by: Konrad on September 20, 2017, 02:30:03 PM
Just got back from the machine shop where I fitted a 28mm long (actually the fins are 24mm) finned heat sink to the motor.  I’m using “Arctic Silver Thermal Adhesive” both as the heat transfer compound and as the adhesive to attach the heat sink. I took the opportunity to machine a 4mm long pilot diameter into the finned heat sink. Lacking any other data I machined this pilot diameter to have a wall thickness of 1mm. In hindsight it might have been better to make the wall 0.5mm or 0.7mm thick. The purpose of the pilot diameter is to give added support to the rear of the stators and to add some rear support to the long motor.

I find it odd that most heat sinks are supplied with an anodized finish. This is odd for a heat sink as aluminum oxide (the anodize without dye)is an insulator! I did grit bast the ID of the heat sink to get improved thermal transfer from the motor case to the heat sink. I’m ashamed to say that I kept the blue anodize as it looks good against the red fuselage of the Super Scorpion.

Title: Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
Post by: Hank G B Z on September 26, 2017, 05:20:36 PM
" I’m ashamed to say that I kept the blue anodize as it looks good against the red fuselage of the Super Scorpion. "

  I am aghast.  The Konrad I flew with would never let form over function go.  I always heard from you "Form follows function..."  To sad! I hand down the following punishment.

   You must go finish your Guillows Beachcraft Privateer/ Dutchess conversion and end this check book modeling which is clearly affecting your engineering judgement.  I'm supposed to be the one picking a pretty color over something that works right...

  The scorpion is cool thoguh.  Speaking of Scorpions did you ever fix that Cox one i used to fly? 


Title: Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
Post by: Konrad on September 27, 2017, 12:45:46 PM
LOL; (head down in shame)

Lets see if I can recover from this. As aluminum is very susceptible to oxidation the grit blast surface would have been covered in oxides soon enough. So I choose to keep some color as it might aid in the resale of the jet. Now if I had access to alodine I might have grit blasted the outside of the heat sink and applied the alodine treatment to protect the aluminum from oxidation. I think I recovered from the shame of allowing function to follow form. (Alodine is an acid etching process that protects aluminum from corrosion and oxidation.)

The wife is asking much the same question about the Guillow type models. Her opinion is that these foamies are the antithesis of what modeling is, that is the creation on a smaller scale. They maybe fun and challenging to fly and even small, but not really modeling, as one does little creating.

That little Cox Scorpion is being used for templates and as a parts queen for the second Scorpion. (The Cox Scorpion is a small 1/2A pattern ship of old.)

Back to the Taft Supper Scorpion.
A major manufacturing issue has shown up. That is the flaps are badly bowed (warped). I’m not sure if this is a problem with the cooling of the EPO parts after release from the mold. Or as a result of paint shrinkage as it looks like only one side of the flaps has paint (the red side).

I will have to remove the flaps and add stainless steel stiffeners to control this warp (ALA the Multiplex Heron). I might even add some carbon to the trailing edge.


Title: Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
Post by: Hank G B Z on September 27, 2017, 01:08:32 PM

    You are forgiven for keeping the blue anodize.  I used alodine once, i was not a fan.  We have stopped clear anodizing parts at work for the most part as it doesn't do much.  Hard coat anodize for wear purposes we still do. 

    Your wife is right we should do more modeling.  I haven't done much modeling this year and none of it has been balsa kit.  Well that one Flying flea from bang good, but that was more assembly than building.  Anywhoo. 

    The scorpion looks good, that warp is odd.  Your fix sounds good to me.  Looking forward to hearing about test flights. 


Title: Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
Post by: Konrad on October 16, 2017, 07:24:17 PM
Some annoying quality/assembly issues.

I was flabbergasted that anyone would try to glue a structural component to paint! How difficult would it really be to make a mask for this area prior to painting? It is omissions like this in the assembly process to costs one, one reputation!  Taft you knew better than to try this!

It looks like the pocket for the flap hinges on the wing side are a little too shallow. Easy enough to fix, shave the pad area with a utility knife 0.3mm. I suspect this was a mis-judgement as to the shrinkage rate of the foam when making the molds.

I can confirm that the warped flaps are as a result on uneven painting of the flaps (and ailerons). Taft needs to apply a clear coat to the opposite side (top of the control surfaces).  

Title: Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
Post by: Konrad on October 17, 2017, 05:57:25 PM
The severe warps on the flaps has required that a stiffening rod be added to the flap full span. I chose to use a 1/8 (not 3/16) stainless steel tube (K&S # 87111) much like what we see with the Multiplex Heron. This and the addition of some 0.014” carbon to the trailing edge of both the flap and aileron result in a trailing edge that looks to be rather straight. We will see what the flight trim dictates. But I’m sure the control surfaces will now respond much better than if I had left the warp in place. With the Taft Super Scorpion the flaps are a bit more than your standard flap. This is because the manual has you mix in snap flap as a function of up elevator. This is to give the small wings a boost in their lift coefficient (added camber) and to gain some much needed rigged washout at higher angles of attack. With warped trailing edges I’m sure the low and high speed (high “G’s”) flight characteristics would have been compromised.

Title: Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
Post by: Konrad on March 23, 2018, 02:04:26 PM
After a 6 month hiatus I decided to throw some money at this and buy some wheels. The wheels that Taft supplies are horrible, they are hard and HEAVY. I found a set of wheels sold by Maxx Products that fit the bill perfectly ( P/N AW225). These are foam with a hard rubber like center line compound. I think these will become my standard wheels for my light to mid sized models.

Note: That the plastic bearing that come with the wheels are NOT adequate for the weight of this model. Maxx products sells a set of brass bushing for these higher weight models (P/N AWB04). ( I never understood the need of desire for ball bearing wheels on our models. My roll out distance is already far too long!)

The Dave Brown style of lite wheel while they work often don’t provide enough lateral support, and wear far too fast with my style of landing.

With the 2.25” wheel I had the make some clearance by beveling the rear of the landing gear strut yoke.
Even with the stock wheel there wasn’t adequate clearance in the wheel well. I opened up the wheel well biased towards the rear, after all this is the direction most struts move as the aircraft ages.

Title: Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
Post by: Konrad on January 25, 2020, 03:40:08 PM
I’ve been stalled on this project mainly because of transport issues, I have a first gen. Prius. Also I’ve ben focused of FAI F3F racing. And now that the FAA has given us a drop dead date for our hobby I thought I'd try to fly this model befor that date.

Now I’ve heard that there are some concerns with the Taft Scorpion in that she hunts in pitch. I found this a bit odd with that huge stabilizer. Looking closely at the control linkage I found a gross engineering oversight. Taft is using a large set screw as a drive pin to connect the control horn to the stabilizer axle. This results in a horrible amount of slop between the control arm and axle (shaft) as one can’t torque down on the set screw. I’ve read that some guys are trying to use teflon tape and or loctite to take up the clearance. The fix is to allow the arm to clamp down on the shaft. I’ve decided to change the drive mechanism with a cap screw verses the drive pin. To do this one needs to make 2 modification to the arm. First is the drill out the threaded holes to clear the 3mm threads of the cap screw. And then make a trough in the control arm to allow clearance for the cap screw head. Keeping the thread in the shaft allows the head of the cap screw to clamp the arm onto the shaft. This also allow one to add torque to the threads taking up any clearance in the threads. I still add loctite for stability but with the clamping force from the cap screw there in no slop to allow the stabilizers to move.

All the best,

Title: Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
Post by: Konrad on February 06, 2020, 03:34:44 PM
Well, finally after close the 2.5 years I performed the maiden flight on my Taft 90mm Scorpion. It was surprisingly uneventful. I’m posting a proof of life photo take after the maiden.

So a few minor issues did come to light. First is that the decalage is way off. I had to add 8mm of up trim to fly neutral (level). Also I’m experiencing some throttle to pitch coupling. That is I have far too much down thrust, when I cut power the Scorpion climbs up. You might have noticed that from the OEM Taft does point the tail pipe for a lot of up thrust. When I added the Viper tail cone I took most of this out, even adding some down thrust. It looks like I’ll need to reevaluate this.  with some up thrust this decalage might come in line looking more normal.

In the air she feels real honest, if not a bit heavy. The manual has you set up the flaps to add 5° to 10° snap flap with the elevator up movement. This is to give the wing some wash out at high coefficients of lift, to keep the wing from tip stalling. I set mine for 7° and found that this resulted in the Scorpion feeling like she was pushing through the turns rather than a nicely pulling through the turns. I will work on cutting down the snap flap.  Now I have to say that per the manual’s snap flap settings the Scorpion did not snap out of a hard loop.

The only real down side I found was that the main landing gear is far too close the balance point, making it real light on the nose gear. It is so light on the nose gear that she weather vanes into the wind  just taxiing. I will need to see about raking the main gear aft. With the CG at 186mm (measured from the wing to fuse LE part line. The manual sketch is in error) this place the CG on the front of the landing gear trunnion block. I can’t move the CG aft and still hope to have any use of the nose gear.

There is another gross error in the manual. Don’t set up the stabilizers for 30° movement! I don’t know why so many of the Chinese models have you set up the control so fast. Are they try to brag about how good their test pilots are!

My control set up is as follows:
Elevator UP 27mm DOWN 32mm (at the TE at the root)
Aileron   UP 17mm DOWN 15mm
Snap flap less than 8mm
Flaps One 19mm, Flaps 2  65°+
Flap comp 9 and 12 on a Spektrum radio
Rudder All I can get
Nose gear 1/2 throw, mix in the radio
CG 186mm

My power system is drawing 110 amps with the Flycolor ESC set at 7.5° advanced. I’m using 8 cell 5000 to 5500 mAh battery that weights 1020g to 1050g.

For $269 the Taft Scorpion was a very good value, even adding another $100 or so in upgrades (2 Servos, 2 wheels and a Castle Creation BEC.).  While there were a lot of engineering and quality issues that really pushed this model outside what one would normally think of as an ARF. As a typical model, her issues were well within the capabilities that a pilot who has the skills to fly her should have as a modeler. It is a little bit bigger than the FMS Super Scorpion. I like the classic red far better than than the Hot Rod day glow orange of the FMS. I also like the full flying stab.  For a real modeler the Taft Scorpion is the better model. For the plug and play crowd where they are looking for a model with most of the issues properly vetted, the FMS is the better model.

Now that I think about it a bit longer, the $100 to $150 premium for the FMS really does make the FMS Super Scorpion a better value, if you value your time.

All the best,

Title: Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
Post by: Konrad on February 08, 2020, 11:40:49 AM
On my third outing with the Taft Scorpion I flew with/against an FMS Super Scorpion. As much as I hate to say this the FMS is looking to be the better ship in the air. I attribute this to the better inlet ducting. The FMS Super Scorpion has larger inlets and no cheater hole. This makes feeding the fan much more efficient. This shows in speed and battery life.  The Taft Scorpion does hold her own. But she needs an 8 cell battery, with the associated cost of more cells. I was really surprised at how much more efficient the FMS was, as measured by how much battery capacity was left at the end of the flight. I was expecting the Taft Scorpion to have more capacity as I was using 8 cells (larger battery = larger gas tank).

As I had solved most of the known issues with the Taft Scorpion I was thinking of getting another as a back up. But having seen the FMS Super Scorpion if I need a replacement I’ll get the FMS Super Scorpion. The FMS is well worth the $150 premium! I should hope so, there is about 4 years development between the 2 models. I honestly thought that the 8 cell power system would make up for the advancement. This is a classic example that raw power can’t mask all ills.

Please don’t get me wrong I enjoy the Taft Scorpion a lot. I just think the modern FMS Super Scorpion is the superior ship. I’d like the see Horizon Hobbies import the subdued red FMS Super Scorpion

I had noticed that the FMS Super Scorpion drifted more in a cross wind landing. I think this was caused by the huge front gear door. I think a dual door might help. I noticed this same issue with my FreeWing 80mm F-5.

On trimming the Taft Scorpion the change from 1.5° down thrust to about 1.5° up thrust from the added viper tail cone did improve the throttle coupling. I could probably add another 1.5° of up thrust. But the tail tube is looking a bit weak with all the cutting it has been subject too. Also the Taft Scorpion need very little flap to elevator compensation, like a 9 (Is this a % value?) on the Spektrum radio with 80° flaps.

All the best,

Title: Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
Post by: USch on February 09, 2020, 05:35:32 AM

as measured by how much battery capacity was left at the end of the flight. I was expecting the Taft Scorpion to have more capacity as I was using 8 cells (larger battery = larger gas tank).

Correction: numbers of cell does not mean a bigger tank, translated crudely it could mean something like how high above the carburettor the tank is placed.

Capacity is a different thing and is measured in Ampere per hours (Ah) and determines how long the tank will  feed the motor till its empty.

Sorry, but I could not do without noting this often heard (wrongly) statement about numbers of cells and capacity.


Title: Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
Post by: Konrad on February 09, 2020, 12:09:47 PM
Correct, if looking at amp hours.

Or, as I was meaning the amount of energy, watt hours available.

Using a nominal voltage of 3.7 V per cell;
In my Taft Scorpion I'm running 8 5500 mAh cells, for 163 watt hours of energy in the "tank"
The guy with the FMS Scorpion was using 6 5000 mAh cells, for 111 watt hours of energy in the "tank".

Now I was drawing approx. 110 amps on the ground at full throttle, for take off power 3.25 KW. For a 3 minutes run time

He thought he was drawing 112 amp on the ground at full throttle, for take off power of 2.48 KW. For a 2.69 minutes run time

Now in the real world he had what looked like more energy left in his tank at the end of a 3 minute flight, than I had in my tank. (His cells had a higher voltage at the end of the flight). This means he is better with the throttle management, and or the model/power system is more efficient in the air. I suspect both! The Taft fan looks to be based on the dated Changsun EDF unit. While FMS has developed theirs EDF from some modern CFD programs for ducted fans developed by Dr Drela.

Subjectively (we did not fly at the same time) it looked like the FMS Super Scorpion was faster and had better acceleration. While the Taft Scorpion works and works well the FMS Super Scorpion is just a better aircraft.

All the best,

Title: Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
Post by: Konrad on February 11, 2020, 01:17:44 PM
After seeing how poorly my Taft Scorpion is performing when looked at against the FMS Super Scorpion has me rethinking the inlet.

Taft is using a cheese grater style cheater hole. By my measurement these gills are blocking just under 1290 square mm of area. They also allow large FOD objects to inter the fan.

I changed over to a wire grid that blocks just over 774 square mm. 500 square mm isn’t much of a change.

My question, to those that have experience with this kind of thing, is how does the round wire perform verses the rectangular cross section gills. Despite the added 500 square mm of inlet area, have I actually cut down on the inlet’s flow? We all know how much drag (resistance) a piece of wire has! I know I should just make a flow bench (box) with a simple U-tube manometer.

BTW, I set the wire grid so that all wire elements are taking some of the vibratory load from the spinning fan.

All the best,

Title: Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
Post by: Heron pilot on April 14, 2020, 03:22:10 PM
Did you keep the distribution board or eliminate it and wire the servos directly to the rx.. (asking for someone on RCG).. I always enjoy your build threads, thoughts and opinions. It's refreshing to read things written on a higher plane of understanding that what is typically posted on RCG.

Title: Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
Post by: Konrad on April 14, 2020, 04:13:53 PM
I'm happy to help our fellow modeler, even if he is part of RCG's membership.

I removed the board. Not for any reliability issues, but to allow me to place the batteries further aft. I have no idea why the board really is there. I also removed the retract control board. In my jet it was causing all sorts of reliability issues. Again I don't know why Taft supplied these controller as there are no doors that need to be synchronized. Now I did replace the Taft supplied BEC with a larger Castle Creations BEC pro.

All the best,

I did use a set of Multiplex 6 pin connectors at the wing and fuselage joint to aid in making the wings removable.

Title: Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
Post by: Konrad on April 14, 2020, 04:16:21 PM
Prior to the shelter in place orders I did get in some sport flying. It became painfully obvious that there isn’t enough weight on the nose gear if the center of gravity is properly set for neutral flight characteristics. With the landing gear placed at the OEM location one might be able to control the ground handling by aerodynamic forces (rudder and elevator).  But as the Scorpion slowed down these became less and less effective. The landing gear geometry is so poor that even in a slight cross wind the Super Scorpion would weather vane into the wind on the slightest bump. This made taxing all but impossible.  But even worse this lack of weight on the nose wheel would allow the aircraft to flip inverted on the landing roll out. This made grass landing very dangerous.

The solution to this is to move the main landing gear axle aft to but more weight on the nose gear. I tried to rake the gear aft by shimming the retract mounts with little noticeable improvement. I’ve been forced to rework the landing gear struts to incorporate trailing linkage. This did place the axle about 12mm aft in the unsprung condition. Also the the unsprung landing gear length it longer that the OEM rear landing gear. This helps point the nose down minimizing nose pop ups as the aircraft goes over bumps. As the trailing arm strut compresses the wheel axle moves aft adding more weight to the nose gear. Again helping keep the nose planted on the ground.

So far so good. Now for the bad news. To get this new landing gear I had to make the struts and trailing arm from various struts. For these Frankenstein mains, I ended up using a set of trailing arms from the FMS Super Scorpion. I couldn’t use the struts as they were too short. I choose to use a set of Hobby King for the struts (PN91007000310-0). These were a bit of a let down as the spring couldn’t support the weight of the Taft Super Scorpion.

To get the proper spring rates I had to hand wind my own springs. I now have my main gears, set that fully loaded with batteries the struts just come off the fully extended stops. And when fully compressed the springs are coil bound. I bind the coils so as to not put any stress on the anti rotation pins or up stops should I land a bit hard. This has worked out just fine. The only real down side is that the cost is a bit high as I actually had to buy two sets of struts to get all the needed parts.

I am now rewarded with some of the best landings I’ve seen with an EDF jet. There is one operational thing. As the struts are sprung they will compress should the model swing one way or the other on the take off roll. To control this I’ve cut down the tiller servo arm to minimize the nose wheel steering movement.

An annoying thing I’ve noticed is that in neutral trim the stabs don’t align with the fairing on the fuselage.

All the best,


The BEC is in the tunnel just above the batteries. Not the best location as to air flow, but it has worked well.

Title: Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
Post by: Konrad on April 15, 2020, 03:51:40 PM
Some more photos that might help.

What I like about the Taft Scorpion is that this jet really makes it clear when our flight instructors said; elevator controls speed and throttle controls height when on a landing approach!

To land my Taft Scorpion I line up on the the runway drop to full flaps. Keeping the nose level (on the horizon) I let the model drop. On final I do carry 20% to 30% power. Full flap (80°+) does keep the model from gaining too much speed. If I think I’m going to over shoot I add some up to slow down. If it looks like I’m a bit slow and I fear a snap I speed up by pushing the nose down. If I’m sinking too fast I add more power. With full flaps this has worked great. As the model gets knee high to the ground I feed in full up to flair. The result is a very nice nose high landing The Super Scorpion lands like a butterfly with sore feet. With the dual rudders yaw control is very effective, even in the deep stall of the flair.

All the best,


With the flaps out I've yet to get her to snap. Hard straight ahead stalls yes, but snaps no.

Title: Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
Post by: Konrad 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,

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.

Title: Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
Post by: Konrad 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,

Title: Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
Post by: Konrad 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.

Title: Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
Post by: Konrad 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,

Title: Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
Post by: Konrad 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,

Title: Re: Taft Super Scorpion 90mm 8 cell, Sport Jet (Banana Hobby, Thanks Alex)
Post by: Konrad on June 03, 2020, 04:05:39 PM
That was it! Th ESC was cutting back as a result of over temp.

With the ESC frequency lowered to 8kHz, the motor timing increased to 11.25° and the ESC lifted 10mm into the inlet duct slip stream. I actually allowed some air to flow around the ESC by cutting some air paths into the foam. This was opposed to just relying on the heat sink to carry away the heat.

With the ambient temp being 33°C I was able to run at full power (107 amps, 3 kilowatts) for about 135 seconds. I was also able to fly using energy management for 4 minutes with no thermal cut backs in the motor/ESC power.

I didn't fly against any other FMS 90mm Super Scorpions, but the verticals are now a joy to behold.