[NSRCA-discussion] Fwd: Electric Weight Proposal Logic andRationale

Thu Jun 21 12:30:48 AKDT 2007

Fred,

And they have quit improving glow engines?
********Certainly glow continues to improve, but as a well established medium, it is not improving at the same rate as electric.

Didn't they just come out with a 2.0 ci glow engine thats light enough to stick on a Pattern plane?
********Yes.

Saying we can't  do something because technology wil advance means you must want to go back to the days when the Sig King Kobra was a top of the line plane.  Anything with higher performance than thhat had using 1975 technology is not allowed.
********That was not my statement.  My statement was that a rules change for an intended purpose needs be additionally evaluated for unintended consequences (pattern has a long history of unintended consequences from short sighted rules).

Glow planes DO bennefit from carrying more weight... you can bolt on that 2.0 ci engine and carry a 30 oz fuel tank to feed it.... and because you weigh empty you gain the bennefits of added power making the added fuel weight inconsequential.  Glow can compensate for the higher fuel consumption that comes with higher power and not blink.
********Fair enough.  However, the intended context/framework was the comparison of additional weight in the form of fuel to a glow plane with no other changes, and the addition of weight (in the form of battery) to an electric plane with no other changes.  The intended context aside, there are also several other complicating factors such as wingloading, noise, structural considerations, etc.

The basic conclusions I made remain unchanged.

Regards,

Dave

----- Original Message ----- 
From: Davel322 at comcast.net 
To: NSRCA Mailing List 
Sent: Thursday, June 21, 2007 12:09 PM
Subject: Re: [NSRCA-discussion] Fwd: Electric Weight Proposal Logic andRationale

Not a good proposal.

The fatal flaw is this - Glow planes receive no benefit from carrying additional weight.  Adding weight to glow reduces the power to weight ratio, carrying un-needed fuel detracts from performance.  Adding more battery weight to an electric could substantially increase the power output AND power to weight ratio.

Additionally, the proposal fails to acknowledge the inherent benefits of electrics over glow (reduced structure is possible with reduced vibration, reduced finish is possible with lack of oil...and many more).

An additional flaw (conceptually) is that this idea is very shortsighted.  Electrics are still in their infancy.  The motors, batteries, and ESCs will all get lighter and more efficient (and cheaper) with future develepment.  Airframes tailored for electric will continue to improve further reducing weight.  Within the existing rules structure, a very solid arguement could be made that electrics can already achieve equal performance to glow, and a very solid arguement could also be made that a cutting edge electric has better performance than a cutting edge glow.  Electrics do not need any additional advantages at this time and will be dominant in the near future within the existing rules structure.

An average flying weight for glow of 11.5 lbs assumes the average dry weight is 11 lbs.  11 lbs is not the average dry weight.

The assumption that 20 fluid oz is the average tank size needed for completion of a pattern flight assumes a Masters or FAI preliminary flight.  Not all flights are for Masters and FAI.  Substantially less fuel is needed for Adv, Int, and Sportsman.  Further, the assumption would also seem to be based on a glow engine with a very high fuel consumption ratio.  Plenty of 2C setups complete Masters and FAI on 12 oz.....well managed 4Cs do almost as well.  Perhaps 14 fluid oz would be a better average (~11 oz actual weight).

The past few years, I've been fortunate to be flying some very high quality composite models (glow Vivats and electric Prestiges).  The Vivats were 9 lbs 14 oz + 12 oz of fuel (more than enough for the Webra 160MC to get through 1.5 PO7s) for an average flight weight of 10 lbs 4 oz.  My electric Prestige with TP5300s was 10 lbs even on the 2006 NATs scale.....current configuration puts it at 10 lbs 3 oz.  At ~$1900 USD per copy, the Vivat and Prestige are not cheap, but hardly the most expensive option.  On the lower end of the price scale, there are plenty of options from UltraRC, Fliton, etc, that can be well under weight electric or glow.  The Black Magic series is among the biggest planes currently and recently available and can be built at 10 lbs electric and well under 10 lbs glow.

Applicable to this proposal (and others past, current, future) is that the proposal should be evaluated from the perspective of a competitor looking for a competitive advantage - ie, not how the proposal will effect current equipment/desigsn, but what higher levels of performance could potentially be achieved by a competitor looking to exploit the new rules.  Historically, any increase in size, weight, or displacement has resulted in larger and more expensive airframes.

Regards,

Dave Lockhart
DaveL322 at comcast.net

-------------- Original message -------------- 
From: Ron Van Putte <vanputte at cox.net> 
I got the following from John Fuqua. He is going to submit a proposal to increase the weight limit for electric-powered airplanes to 11.5 lbs. I suggested to him that he "float" his rationale by the NSRCA Discussion List, to get some feedback. Here is his response. 

Ron Van Putte

Begin forwarded message:

Date: June 21, 2007 10:40:36 AM CDT
To: "Ron Van Putte" <vanputte at cox.net>
Subject: Electric Weight Proposal Logic and Rationale

Now that I am flying electrics I have come to realize the penalty that electric planes have when being built that gas planes to not have. That building penalty is significant under the current rules. Electrics must be built lighter, to include paranoid attention to everything used - wood, paint, fittings, etc., - all to make weight. Much more of a concern than gas planes. Also I remember many instances at the NATs when we were weighing airplanes, when the contestant was doing all he could do to meet weight with a gas plane to include cleaning the fuel residue inside and out. A lot of gas planes were weighing in at 10lb 11oz, 10lb 11.9 oz, even one that was only a few grams under 5 kilos. Then they get to add a minimum of 16 to 20 ozs of weight by fueling up (and there is no limit to fuel capacity). Takeoff weights are 12 lbs or more. This situation seems bizarre and illogical when you put some thought into it. Electrics have a finite weight and gas! planes are open ended at Takeoff
. Even though the 2005 NSRCA survey did not support an electric weight increase it occurred to me that the survey did not offer any logic or rationale as to why some increase would be justified or not. I have attempted below to come up with a reasonable compromise on electric weight allowance. I believe the rationale supports an increase but it would be nice to have NSRCA membership look at it to find the fatal flaw in the rationale before it gets submitted. The two paras below are taken from the proposed change. Lets put it out and see what the discussion list comes up with.
John 
Change paragraph 4.3 Weight and Size page RCA-2 to read: No model may weigh more than 5 kilograms (11 pounds) gross, but excluding fuel, ready for takeoff. Electric models are weighed with batteries and are allowed an additional 8 ounces for a total of 11.5 pounds ready for takeoff. No model may have a wingspan or total length longer than two (2) meters (78.74 inches).

Logic behind proposed change, including alleged shortcomings of the present rules. State intent for future reference. 
Today’s 2 meter RC Aerobatics fuel powered aircraft typically use fuel tanks with a 20 fluid ounce capacity. A 20 fluid ounce Crank Tank containing 25% Cool Power Pro Pattern fuel was tested. The fuel weighed 17.3 ounces. Allowing for variation in tank sizes and fuel type a conservative weight of 16 ounces of fuel on average seems appropriate. This means that an allowable takeoff weight for fuel powered aircraft is at least 12 pounds. Assuming that all fuel is consumed during the flight, the average weight for the aircraft is 11.5 pounds. By restricting electric powered aircraft to the takeoff weight of unfueled aircraft an unfair weight penalty is being arbitrarily imposed against the electric model. By allowing electric aircraft an AVERAGE flying weight of the fuel powered aircraft, flying weight equity is restored.

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