IMPBA FE Scale Rules Proposal #23-008

[RaceMechaniX]

Reading through the recent Roostertail I see the rules proposal for modifying the motors allowed in FE scale. Previously, there were three official motors from Neu, Lehner and Plettenberg and a list of non-record trials motors from TP, HET, Turnigy and Leopard. Although the diameter was defined the overall length of the motor was free for the three original motors. The new rules are proposing a 41mm diameter limit and a 108mm length limit. If the new rule passes it would ban the use of the Lehner 22 series and Plett 370 as both are larger in diameter than 41mm. Although I have rarely seen a scale FE racer run a Lehner or Plett in the last decade it would exclude them outright.

Is the new diameter and length rule applicable to all sanctioned racing including US1 and record trials or just heat racing?

 

[LohringMiller]

Well, let's take a look at what diameter and length rules has done to the P limited class. From my article in the to be published Propwash:

Under the previous rules, the class’s power seemed suitable for 3.5 cc nitro boats. Setups pulled around 80 amps at 16 volts or 1280 watts. That’s around 1.7 hp. K&B 21 engines were rated at 1.25 to 1.3 hp at 25,000 rpm. The OS VZRM is rated at 2.25 hp at 33,000 rpm. Some Picco RC car engines were rated at 2.75 hp at 36,500 rpm.

Let’s look at reality. The maximum brake mean effective pressure for the best small racing engines is between 85 psi (about 6 Bar) and 100 psi (about 7.5 Bar). A long time ago Marty Davis and Brian Calahan dyno tested a BMEP of 92 psi on a Picco 11 cc engine developing a little over 4 hp at 20,000 rpm. At these more realistic BMEP levels that means a 3.5 cc engine would develop between 1.12 hp and 1.3 hp at 25,000 rpm. At 35.000 rpm these figures would be between 1.6 and 1.8 hp.

New motors like the TenShock motor above are RATED at 3000 watts or 4 hp. The best K&B 45 was rated at 3 hp. A realistic rating would be more like 2.8 hp.

Lohring Miller

 

[LohringMiller]

PS: No KV rule? Why no outrunners?

Lohring Miller

 

[Dave Gilles]

has anyone ever brought up just limiting the ESC size? keep amps below 150A for example.

 

[Don Ferrette]

Reading through the recent Roostertail I see the rules proposal for modifying the motors allowed in FE scale. Previously, there were three official motors from Neu, Lehner and Plettenberg and a list of non-record trials motors from TP, HET, Turnigy and Leopard. Although the diameter was defined the overall length of the motor was free for the three original motors. The new rules are proposing a 41mm diameter limit and a 108mm length limit. If the new rule passes it would ban the use of the Lehner 22 series and Plett 370 as both are larger in diameter than 41mm. Although I have rarely seen a scale FE racer run a Lehner or Plett in the last decade it would exclude them outright.

Is the new diameter and length rule applicable to all sanctioned racing including US1 and record trials or just heat racing?

It applies across the board- heat racing, US-1 and record trials. Yes the Lehner 22s and Plett are now excluded but as you yourself said they are rarely if ever run anymore. Not to mention back when the original "motor list" was created the lipo technology was not yet available. Now that they are the Plett's power potential can be fully utilized and is far superior in the output it can produce, like allowing a 90 to run with the 67s in nitro scale. This is a much needed rule change in my opinion and personally I'm all for it.

 

[RaceMechaniX]

Well, let's take a look at what diameter and length rules has done to the P limited class. From my article in the to be published Propwash:

Under the previous rules, the class’s power seemed suitable for 3.5 cc nitro boats. Setups pulled around 80 amps at 16 volts or 1280 watts. That’s around 1.7 hp. K&B 21 engines were rated at 1.25 to 1.3 hp at 25,000 rpm. The OS VZRM is rated at 2.25 hp at 33,000 rpm. Some Picco RC car engines were rated at 2.75 hp at 36,500 rpm.

Let’s look at reality. The maximum brake mean effective pressure for the best small racing engines is between 85 psi (about 6 Bar) and 100 psi (about 7.5 Bar). A long time ago Marty Davis and Brian Calahan dyno tested a BMEP of 92 psi on a Picco 11 cc engine developing a little over 4 hp at 20,000 rpm. At these more realistic BMEP levels that means a 3.5 cc engine would develop between 1.12 hp and 1.3 hp at 25,000 rpm. At 35.000 rpm these figures would be between 1.6 and 1.8 hp.

New motors like the TenShock motor above are RATED at 3000 watts or 4 hp. The best K&B 45 was rated at 3 hp. A realistic rating would be more like 2.8 hp.

Lohring Miller

Lohring,

99% of the sticker ratings on electric motors and nitro engines are 100% marketing BS. Fortunately with today's data logging ESC's with reasonably accurate current measurement we know close enough what the motors are outputting minus their efficiency. The 2700kv 2240 6-pole Tenshock can run about 2300-2500W continuously in race conditions for a 1min before they are too hot. However for a 5 second burst I have measured 5800W.

I would agree it is a shame outrunners are not allowed. They have a lot better likeness to a turbine sound.

 

[RaceMechaniX]

has anyone ever brought up just limiting the ESC size? keep amps below 150A for example.

The nameplate rating on ESC's is BS. I have ESC's with a 160A rating that will push 400A all day long. If everyone agreed to using electronic limiters inside an ESC to 150A then it would be a different story.

 

[RaceMechaniX]

It applies across the board- heat racing, US-1 and record trials. Yes the Lehner 22s and Plett are now excluded but as you yourself said they are rarely if ever run anymore. Not to mention back when the original "motor list" was created the lipo technology was not yet available. Now that they are the Plett's power potential can be fully utilized and is far superior in the output it can produce, like allowing a 90 to run with the 67s in nitro scale. This is a much needed rule change in my opinion and personally I'm all for it.

Will previous records stand and be grandfathered in?

No arguing from me that with today's FE power it is an unfair advantage if done properly. However running a TP4070 on 10S is still bringing a gun to a knife fight. Prop diameter limits, capacity limits, reducing cell count or reducing the motor length further would be needed to reach parity to a nitro.

 

[Don Ferrette]

Will previous records stand and be grandfathered in?

No arguing from me that with today's FE power it is an unfair advantage if done properly. However running a TP4070 on 10S is still bringing a gun to a knife fight. Prop diameter limits, capacity limits, reducing cell count or reducing the motor length further would be needed to reach parity to a nitro.

Not trying to reach parity with nitro, this is to allow boaters more legal choices for motor/ESC combos for FE. The records still stand they were set with NEU 1527 motors that meet the new length/diameter limits. (I had all 3 until John Finch got the 1/3 mile oval recently)

 

[longballlumber]

In addition to Don’s comments; we started down this path roughly 5 years ago when the IMPBA Board released a technical bulletin to help encourage 1/8 FE Scale racing across districts. The objective was to get feedback from those actually racing/running the boats. It was an effort to see if “the shoe fits” sorta speak. We received little to no feedback on our tech bulletin.

Fast forward to today. We’ve seen increased participation in the 1/8 Scale FE class over the last couple of years. Albeit, local clubs started running their “own” rules. While this isn’t usually an issue and we always encourage local clubs provide an avenue for boaters to boat, these rules started to creep into multiple districts with the current IMPBA 1/8 Scale power rules (and tech bulletin) being disregarded all together.

It was time to propose an update our IMBPA 1/8 Scale rules. I think what has been proposed provides a better compromise on motor availability, practical wattage output, and existing boats past/present. All while maintaining the core integrity of our current IMPBA records and not eliminating a majority of boats that currently exist. Did we keep everyone happy – probably not, but I do think a big step in the right direction can be made. Additionally, I think we have left ourselves some room for adjustment over the next several years if necessary.
It's now in the hands of the organization to determine if we proceed down this path or not.

 

[LohringMiller]

To regulate power you need to limit voltage and current. It's easy to limit voltage by limiting the cell count. Current is harder. As Tyler pointed out, there are current limiters commercially available. At one time the propeller diameter was used as the current limiter. Since power varies as the 5th power of propeller diameter and the cube of the rpm, a KV and propeller diameter limit is pretty effective in regulating maximum current. For reference below is the data log trace on our NAMBA two lap record holding 1/8 scale. We ran 8S with a Scorpion 800 KV outrunner and a 1657 prop. The record of 25.88 seconds still stands. The same boat holds the NAMBA T sport hydro two lap record at 25.780 seconds.

Lohring Miller

 

[Don Ferrette]

We really are not interested in doing what NAMBA did Lohring. The short sighted rule change your org. made screwed the guys with previously legal 10S boats, something we in IMPBA will not do. Not to mention you all didn't even include your own national FE director in doing it, bypassing one of the most experienced FE guys in the US.

 

[Jeremy Linney]

Just my opinion but if you are going to allow a span of voltage ratings, there should be a max Kv limit for each voltage being utilized.

 

[LohringMiller]

The IMPBA two lap record set on 10S is 24.908 seconds. Higher voltages are always better since current is what burns things up. Over 8S just takes more expensive equipment. You pay your money and take your choice.

Lohring Miller

 

[Dave Gilles]

The IMPBA two lap record set on 10S is 24.908 seconds. Higher voltages are always better since current is what burns things up. Over 8S just takes more expensive equipment. You pay your money and take your choice.

Lohring Miller

why is it so slow? The gas and nitro riggers do like 18-20 second 2 laps at my club every week.

 

[Samuel Hagan JR]

why is it so slow? The gas and nitro riggers do like 18-20 second 2 laps at my club every week.

These aren’t riggers. Two totally different boats and weights.

 

[Samuel Hagan JR]

I like the new change. Hope it passes the BOD.

 

[Don Ferrette]

I like the new change. Hope it passes the BOD.

The BOD unanimously accepted the proposal and it will be voted on by membership. From the August Roostertail issue-

 

[Hydro Junkie]

why is it so slow? The gas and nitro riggers do like 18-20 second 2 laps at my club every week.

These aren’t riggers. Two totally different boats and weights.

I have to agree with Sam on this one. A scale nitro boat normally weighs 12-16 pounds. That's at least double the weight on a 60 rigger. An electric scale will normally fall into the low end of that range as well. A rigger also has the sponsons further apart, allowing faster and sharper corners, and has no hard bottom between the sponsons to add lift to the equation. Something else that the electric boats have to contend with(at least at NAMBA events) is prop limitations. I know NAMBA limits the prop on an electric scale to 57mm, not sure about IMPBA.

 

[Dave Gilles]

I have to agree with Sam on this one. A scale nitro boat normally weighs 12-16 pounds. That's at least double the weight on a 60 rigger. An electric scale will normally fall into the low end of that range as well. A rigger also has the sponsons further apart, allowing faster and sharper corners, and has no hard bottom between the sponsons to add lift to the equation. Something else that the electric boats have to contend with(at least at NAMBA events) is prop limitations. I know NAMBA limits the prop on an electric scale to 57mm, not sure about IMPBA.

dang i must be doing really good running like 12 second laps with my sprintcat FE. I didnt know that was considered fast. Most of the club crew blow me away.