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Old Oct 25, 2012, 01:06 AM
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Australia, NSW, Baulkham Hills
Joined May 2004
399 Posts
Help!
Thunder Tiger Sport 40L low wing trainer conversion

Hi guys,

Need your help here pleaseÖÖÖ.

I have been given a Thunder Tiger Sport 40L low wing trainer and want to set this up with an electric conversion.
Specs on this plane are:
Wing Span: 56"(1422mm)
Wing Area: 542 sq in
Length: 43"(1092mm)
Weight: 5.3 - 5.7 lbs.(2.4-2.6kg)

I have previously converted a Thunder Tiger Easy Trainer 40 high wing trainer.
Specs on this plane are:
Wing Span: 61" (1510mm)
Wing Area: 682 Sq. in.
Length: 50" (1274mm)
Weight: 6.5 lbs.

For this conversion I used the following combination based on recommendations from forum members: Turnigy G46 670kv motor, 741W with a 3000 mah 4S pack and a 12 x 8 prop

This setup has plenty of power for take off and cruises nicely (for a learner like myself) at half stick. I do notice however that if I increase to full power, it picks up nicely but isnít overly powerful at full throttle.

Iím thinking of using the exact motor / battery / prop setup for the Tiger Sport 40L conversion and given the slightly lower weight of this plane, am thinking that it should perform slightly better than my existing high wing plane setup.

Question is though, the Turnigy motors that they have as direct drop ins for .40 to .46 for glow conversions also come in other Kv ratings:
G46 550kv 925W
G46 420kv 925W

Iím still trying to understand the whole KV and watts thing but am wondering whether one of these other G46 motors would be better suited, given the weight difference between the 2 planes.

Any help appreciated!

Cheers,

Steve
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Old Oct 25, 2012, 07:26 AM
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Australia, NSW, Baulkham Hills
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I haven't got the plane yet but think I have hit my first issue. I only just have clearance on the Easy Trainer to spin a 12" prop. Given the Sport 40L is smaller all round, I'm thinking the 12" prop won't fit.

What are my options here please guys, apart from converting perhaps to a tail dragger?

Cheers,

Steve
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Old Oct 25, 2012, 03:25 PM
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jim e's Avatar
USA, MA, Northfield
Joined Sep 2005
633 Posts
3 blade prop

The lower kv motors you mention are meant to swing a larger prop. So the one you are using is probably best and you can go to a three blade prop and drop around 1" in diameter or go with a higher pitch/smaller diameter two blade prop. Here is where a watt meter really comes in handy. You can also increase the diameter of your "lite" wheels to increase prop clearance. Finally you can add a cell to your battery pack (figuratively) if you motor and esc will handle it and use a smaller prop and get higher rpm's. cheers jim
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Old Oct 25, 2012, 03:57 PM
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Australia, NSW, Baulkham Hills
Joined May 2004
399 Posts
Thanks Jim,

I should have the plane in my possession in the next few days so perhaps its best if I put the component order on hold until I can actually check out the clearance for the prop.

It's nice to know there are options re blade pitch etc - this is all new to me.

I do have a wattmeter though

Cheers,

Steve
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Old Oct 25, 2012, 09:20 PM
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Australia, ACT, Kambah
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Hi Steve, first thing, 741W on a G46-670, 4S 12x8 sounds very high - I'd have expected nearer to 440W, or about 530 with a 3 blade prop. 740W sounds right for 5S. Can you confirm your actual components in the trainer.

re Kv and Watts on a motor spec. The power is the maximum it can safely handle IF you put a big enough prop and enough cells on it. The ACTUAL power the motor uses from the battery is determined by the prop size, the voltage/cell count, and the motor Kv, and could/should be a fair bit less than the maximum.

Kv is not a direct measure of power as such - it's just how fast the motor wants to spin the prop in rpm per volt . Note "wants" not actually does - actual prop rpm will be a fair bit less than volkage x Kv. So higher Kv motors want to spin faster, and the faster a prop turns the more power it requires, and power goes up with rpm cubed. The trick is to choose the combination of Kv, prop and cell count that delivers the performance we need without exceeding the motor or ESC limit while using a pack that is be able to deliver the current for as long as we need.

The listed engines for the Sport 40L are a TT GP-42 and FS-54. The recommended props for the FS 54 include 11x8, so I'm going to work on the assumption that an 11" prop will fit comfortably. Easy enough to review/rework if 12" is possible.

Working on 6lbs flying weight, target power @ 100-120W/lb (which should be pretty generous given wingloading is not excessive) is 600-720W, so the goal is to achieve around that at reasonable motor efficiency and pitch speed, constrained by an 11" prop. It's worth noting that with prop similar in diameter to that used for a glow engine, it's going to need to turn at glow rpm. The max power for the FS-54 is .9hp (675W) at 12000rpm.

If 12000rpm is the loaded rpm at say 80% of unloaded rpm, unloaded rpm would be 15000 rpm. Fairly roughly, on 6S @24V (unloaded) 16000 rpm would need a Kv of about 625. On 5S @ 20V, rough Kv would be 750, and on 4S, Kv about 940Just ballpark figures, but helps to narrow the search.

Starting with the G46-670, it looks like it would have to run on 6S to be up around 12000rpm. The G46-670 on 6S should use about 770W to turn an APC 11x5.5 at aropund 12600rpm, for about 3kg static thrust and pitch speed of 66mph. Stepping up to 11x7E jumps power required to about 880W at and pitch speed to 81mph. But eCalc suggests the motor is going to be very hot, so this might not be an option.

A G32-770 might be a reasonable 5S candidate. A G32-770 on 5S should use about 770W to turn an 11x7 at 12000 rpm, about 4.3kg static and 80mph pitch speed. That would be a little over the peak current for the motor, but you'd only use full throttle in very brief bursts
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Old Oct 25, 2012, 10:33 PM
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Thanks Al...some great info which will assist.

Appreciate the detail of your reply.

Cheers,

Steve
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Old Oct 25, 2012, 11:30 PM
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Al,

I meant to mention the 741W is from the motor specs on the Hobbyking product page.

I now have a wattmeter so will hook it up tomorrow and see exactly what the Easy Trainer 40 is pulling with its current setup.

Cheers,

Steve
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Old Oct 26, 2012, 12:12 AM
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Australia, ACT, Kambah
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Quote:
Originally Posted by stevo1957 View Post
Al,

I meant to mention the 741W is from the motor specs on the Hobbyking product page.

I now have a wattmeter so will hook it up tomorrow and see exactly what the Easy Trainer 40 is pulling with its current setup.

Cheers,

Steve
I thought that might have been the case, although I couldn't find the actual 741W on the current HK specs.

So what it really means is it is an UP TO 741W motor, but with 4S, 12x8, it is part of a 440W system.

At 6.6lbs on 440W, I can see how the model might feel a little docile. You might be pleasantly surpised by the difference a 12x10 makes.
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Old Oct 26, 2012, 06:47 AM
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Commerce Township, MI
Joined Aug 2001
4,466 Posts
Steve,

Converting trike gear planes can sometimes be a PITA because of the prop diameter restriction.

I just did a conversion of a Sig LT-40 for one of my student pilots. Without a lot of modification, it was limited to a 12Ē diameter prop, and it is a much larger plane than the Thunder Tiger Sport 40L.

When you gave the specifications for the plane, you omitted an important piece of information, the recommended glow engine size. Here are the specs from
http://www.modelflight.com.au/rc_mod...er_sport40.htm
Tiger Sport 40
Wing Span: 56"(1422mm)
Wing Area: 542 sq in
Length: 43"(1092mm)
Weight: 5.3 - 5.7 lbs.(2.4-2.6kg)
Engine: .40-.46 2-stroke, .46-.60 4-stroke
Radio: 4 channel

I have an article on Glow to Electric conversions at:
http://www.theampeer.org/Glow2Electr...w2Electric.htm

Iíve posted a screen grab showing conversion data on a spreadsheet created for and available in the article.

I agree that an 11Ē diameter prop might be the largest diameter you can swing for decent prop clearance without modification. You can see that your Turnigy G46 670Kv motor should work for this conversion with an APC 11x8.5E prop, 5S 3500mAh LiPo and 45-amp or greater ESC.
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Old Oct 26, 2012, 07:08 AM
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Thanks Ken,

Some more great info for me to digest.

I'm actually going to wait until I have the Sport 40L so I can get an exact measurement re prop clearance and then I'll go from there.

Appreciate the level of info that you guys have gone to.

I was actually putting my current setup through the eCalc program tonight, now that I have an exact plane weight for my Easy Trainer 40.

All up, it is 4.1 kg so when I put this in the calc with the motor, lipo and prop particulars, it says "Prop may stall - static thrust may not be reached".

I don't know what this means but the model flies great, albeit a little underpowered at full throttle.

Cheers,

Steve
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Old Oct 26, 2012, 03:25 PM
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Australia, ACT, Kambah
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Quote:
Originally Posted by stevo1957 View Post
Thanks Ken,

Some more great info for me to digest.

I'm actually going to wait until I have the Sport 40L so I can get an exact measurement re prop clearance and then I'll go from there.

Appreciate the level of info that you guys have gone to.

I was actually putting my current setup through the eCalc program tonight, now that I have an exact plane weight for my Easy Trainer 40.

All up, it is 4.1 kg so when I put this in the calc with the motor, lipo and prop particulars, it says "Prop may stall - static thrust may not be reached".

I don't know what this means but the model flies great, albeit a little underpowered at full throttle.

Cheers,

Steve
4.1kg I can see why it feels a little relaxed. But you are successfully proving by getting good flights at 49W/lb that you don't need 100+W/lb for a trainer. But the weight does help to explain your short flight time - the poor little porker needs probably 75% most of the time.

I had similar experience with my Kadet. It flew surprisingly well on 54W/lb for the first few flights while I waited for the right packs.

Don't worry about the static thrust warning. Props with pitch to diameter ratio over about 55% generate that warning in eCalc as a matter of course. Even if the prop is stalled static, it still develops plenty of thrust, and it unstalls pretty early in the takeoff roll.

An off topic note: Earlier mark Spitfires had a 2 position prop - coarse and fine. Trying to takeoff in coarse cost plenty of aircraft and lives. The engine couldn't reach its rated power rpm and the prop was inefficient. Our electric motors are so relatively overpowered that we can afford to have a coarse pitch prop.
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Old Oct 27, 2012, 02:47 AM
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GUys,

I will continue the discussion re my Easy Trainer 40 in the separate thread I have running for that plane.

Cheers,

Steve
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Old Nov 06, 2012, 04:07 PM
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Australia, NSW, Baulkham Hills
Joined May 2004
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Hi guys,

The Tiger Sport 40L is now in my possession and following a repair to the landing gear, I am now ready to start the conversion to electric.

Unlike my high wing conversion, where I had the entire inside of the fuse to place battery,ESC and flight pack etc, with the low wing, I am restricted as to where I can place things.

I’m thinking that with the canopy and moulded cockpit piece removed, I can install a thin tray of ply/balsa, which will give me a perfect place to fit the components, however this will mean it is towards the top of the fuse, above the motor shaft line, instead of below as in my current high wing conversion setup.

So this leads me to a few questions:

- Will this cause any problems, with the weight “up top”?
I will still be able to get the correct CG given the battery can move towards the front / back as required to get the balance.

- With the battery and placement where I am proposing, I will be unable to re-install the cockpit moulding and canopy cover.
Will it be an issue if the battery and ESC are exposed. I’m thinking not and obviously will not be flying in wet weather.
Will the absence of the canopy create any issues with aerodynamics, drag etc?

- Servo choice – What standard size servos are recommended? I don’t want to spend a fortune and given for a trainer, would imagine I don’t need to go for fast and high performance units.

Any info appreciated.

Cheers,

Steve
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