Talk:Power-to-weight ratio

Untitled
Since we have the power/weight ratio of batteries and fuel cells, it would be interesting to compare this with petrol and diesel fuels, too. Also could add other common forms of transport such as motorbikes, trains, boats. Milliondead (talk) 23:15, 16 March 2009 (UTC)


 * Fuels don't have a power to weight ratio, since you can generate power from them at arbitrary rates by using them up at essentially arbitrary rates, it's the engine that has the power to weight ratio.- (User) Wolfkeeper (Talk) 01:47, 17 March 2009 (UTC)


 * For example, a fuel with 42 MJ/kg burnt in one second gives 42MW. If burnt in half a second it is 84MW.- (User) Wolfkeeper (Talk) 01:53, 17 March 2009 (UTC)


 * They have a fixed energy/weight ratio though.- (User) Wolfkeeper (Talk) 01:47, 17 March 2009 (UTC)

A lot of these could be also applied to cars.


 * Done. --Robert Merkel 01:11 Jan 6, 2003 (UTC)

Is square of the square a typo? If not, we can call it fourth power. Patrick 01:21 Jan 6, 2003 (UTC)


 * Yes, it's fourth power. I was in "keep it simple for the plebs" mode, which is probably inappropriate here. --Robert Merkel 01:34 Jan 6, 2003 (UTC)

I'm not so familiar with this term but let me ask. Is it correct that "power loading = weight / power"? (I found this on D.P.Raymer's "Aircraft Design") If so, it seems to me better to clarify this point. - Marsian // talk 14:20, 2005 Jun 17 (UTC)

Sukhoi T-50
According to russian wikipedia charachteristics of this plane are understated. It weights a tonn less and produces more thrust with the new engine.

Aircraft
The section about "in an aircraft it's more critical than in any other vehicle" could reworded a bit. As far as I can tell, much of the information there applies to other vehicles as well... "power-to-weight greatly affects top speed...  if two engines produce the same power, the lighter one will produce a better car". The basic premise isn't incorrect, but some of the explanations don't seem to clearly differentiate aircraft from other vehicles. --Interiot 13:00, 20 April 2006 (UTC)


 * Induced drag is proportional to weight, so a heavier aircraft will consume more power for the same airspeed compared to a lighter one. — Preceding unsigned comment added by 2.29.18.184 (talk) 09:44, 1 May 2015 (UTC)

flight power (hamish)
Can we go neculer with aircraft using less fuel. Or can we use the sun to harness the power for flight —The preceding unsigned comment was added by 68.154.210.39 (talk) 14:20, 23 February 2007 (UTC).

flight power (hamish)
Can we go neculer with aircraft using less fuel. Or can we use the sun to harness the power for flight. —The preceding unsigned comment was added by 68.154.210.39 (talk) 14:21, 23 February 2007 (UTC).

Table
If we're going to have a table to give people ideas of typical values, anyone else think it'd be more useful to have the power/weight ratio of the car rather than just an engine. Automotive mags often write about power/weight ratios of cars- I haven't seen them talk about it in reference to just the engine much. Also, anyone else think a sampling of typical cars is more informative than a bunch of exotic high-powered cars? Friday (talk) 15:11, 29 May 2007 (UTC)

Under the heading "Notable low marginal power", the tables list power-to-weight ratio in lb/hp. This should be hp/lb —Preceding unsigned comment added by 148.163.178.11 (talk) 22:19, 11 January 2010 (UTC)


 * Would someone be keen to fix the long standing anomaly of lb/hp rather than hp/lb in the lists (not just the notable low ratio one). It seems a heap of values need inverting? 124.170.53.76 (talk) 05:37, 14 May 2010 (UTC)

In the "Electric Motors/Electromotive Generators" section, the values in the table for the Prius 2004 are wrong. Just by intuition there's no way the Prius 2004 motor mass is 183 kg. Go to the link at http://www.magnets.bham.ac.uk/documents/Jewell.pdf. "Total active mass = 36.3kg; Power density = 1.37kW/kg" I'm too lazy to figure out how to edit the table, so somebody please fix it. 69.226.238.225 (talk) 05:58, 5 March 2010 (UTC) RWconsult

More cars to compare + powers/weights
Added some more cars to the list. More mainstream cars should make the comparisons more valid to most users. Also added the weights and powers for additional info. Keppelk (talk) 11:55, 31 August 2008 (UTC)

Ultima
The Ultima GTR 720 makes 720 bhp. —Preceding unsigned comment added by 99.59.26.101 (talk) 03:41, 19 July 2009 (UTC)

Torque?
This article makes no mention of torque, I know the industry standard (For motor vehicles at least) is power-to-weight ratio, but torque-to-weight ratio is at least as relevant. For example from the article:

Turbocharged V-8 diesel engine Power to weight ratio: 0.25 hp/lb / 410 W/kg Total Power Output: 250 hp / 186 kW

So the peak power is respectable but it isn't amazing for a V8, but being a) turbo charged, b) V8 and c) diesel, I'd hazard a guess that the torque is going to be quite impressive (I know this is probably a fictional engine and there are many other factors, but I'm grossly generalising here). It may even have a higher peak torque than the F1 car:

BMW P84/5 2005 (Formula 1) Power to weight ratio: 4.6 hp/lb / 7.5 kW/kg Total Power Output: 925 hp / 690 kW

Also no mention of power curves is made, for example a V8 may have a very shallow power curve but stays above 150 kW for half of it with a peak of 200 kW, but it will have a worse power-to-weight ratio of a same weight 4 cylinder with a large turbo, sharp peak power of 250kW and average power of say 50kW.

Anyway, sorry about the rant, my point is that I don't think this article mentions the other factors enough such as power curve, torque curve and even max rpm. Hullo exclamation mark (talk) 11:43, 14 September 2009 (UTC)

Hullo, yes, and for good reason. Power is torque * rpm. Torque is independent of power. With gears you can get as much torque as you want from any power. -Jason Arthur Taylor — Preceding unsigned comment added by 96.231.140.87 (talk) 14:42, 22 August 2015 (UTC)

Weight-to-power - Vandalism?
Power-to-weight ratio is commonly given in bhp/tonne or kW/tonne... Hence power divided by weight.

The tables in this article appear to quote weight-to-power ratios. Is this deliberate or has someone taken it upon themselves? —Preceding unsigned comment added by 80.6.35.235 (talk) 11:42, 8 May 2010 (UTC)


 * Looking at the logs, someone in the past pushed for weight-to-power ratio (as can be seen with the "power loading" mention). The United States customary units were at that time made weight-to-power.  This appears to have been maintained.  Should it be eliminated (it does seem wrong)?  The SI units appear correctly power-to-weight.  Anyone game to make all the conversions/inversions? 124.170.53.76 (talk) 05:50, 14 May 2010 (UTC)

'Flight vehicles'?
I've changed the table heading for 'Sports and Flight Vehicles' to read 'Sports vehicles and Aircraft', though really they need to be in separate tables. Can someone with the appropriate know-how do this?

I'm also unsure about the power specified for the Spitfire and Bf-109: these look like mid-war figures, not the figures for the prototypes as given. This needs confirmation elsewhere. AndyTheGrump (talk) 02:05, 6 November 2010 (UTC)

Jet Engines
Two problems with the jet engines in the power/weight table: 1) The engines (GE CF6-80C2 and GE90-115B) should not be referred to as "Brayton" jet engines. Just call them by the actual given name, e.g. GE90-115B turbofan. Drop the obscure, pedantic eponym. 2) The output of a jet engine is measured in thrust (units of force), not power (force*distance/time). If you look up the specs for any jet engine, the output will be given in lbf. or N. You cannot arbitrarily convert the thrust produced by a jet engine (or rocket engine) into horsepower or watts. Because the power output of a jet engine cannot be readily determined, but the thrust can easily be measured, the performance of a jet engine is given by thrust/weight, not power/weight. It is nonsensical to say that the GE90-115B produces 85,000 horsepower. A jet engine on a test stand, producing the maximum rated thrust, 513kN in the case of the GE90-115B, is producing no power because it is stationary. Zero power. When the airplane is in motion, then the engines are producing power, and it is theoretically possible to calculate the power, but you would have to somehow already know the thrust required for the given airspeed.157.182.105.1 (talk) 02:28, 7 March 2011 (UTC)


 * How about including some turboshaft engines instead? That sounds more reasonable. Martijn Meijering (talk) 13:28, 23 December 2012 (UTC)


 * It is mentioned in the article that "For jet engines there is often a cruise speed and power can be usefully calculated there, for rockets there is typically no cruise speed, so it is less meaningful.". This description could be expanded to better explain the problem with power/weight ratio as it applies to the broader set of jet propulsion engines (inc. rockets).  Elimination of obscure use of terms is also a good idea.   As for the power output from a jet engine on a test stand, the following analogy might be useful: A lithium ion battery at open circuit voltage is producing no power because it is not loaded.  Zero power.  When the battery is loaded, then it is producing power, and it is possible - given a known load and a current flow through an ammeter to calculate the power.  Would you need to know prior to the test the current flow?  No - it would be measured.  As for the GE90-115B and it's output power, look carefully at the listing for GE CF6-80C2 in the Boeing 747 which is also sold by General Electric as the aeroderivative LM6000.  The one of GE spec sheets cited (the LM6000 one) specifically describes the average output power of the turbine at rated mechanical load at sea level at 59°F.  Is it nonsensical to say that the LM6000 produces 59,900 hp?  Perhaps one could ask about the ratio of rotating power output to exhaust (jet) power output between the aeroderivative and aerotuned variants.  Just ask GE.  For the GE90-115B, based on the values at writing quoted for a  Boeing 777-200LR at "typical cruise speed" of 0.84 Mach, at 35000 ft, 512kN being the maximum loaded thrust (which is probably more than the thrust at typical cruise speed; thrust will vary with drag and reducing fuel load at cruise speed), -40°C being the prevailing temperature, my calculations suggest (a) speed of sound in surrounding air is 305.8 m/s and (b) thus, 132,000 kW ~ 176,000 hp maximum typical cruise power output (2 engines for redundancy, wear sharing and weight balancing, not power) so the original figure looks wrong. 124.149.47.244 (talk) 02:47, 16 April 2011 (UTC)


 *  More importantly, thrust varies with air density. The numbers in the table for the 747-300 at altitude are grossly over-estimated. Cruise power is only tens of thousands of hp. ( What is the drag? Answer: weight divided by lift/drag ratio!) 86.181.117.134 (talk) 05:25, 16 May 2012 (UTC)


 * Please note re: above comments that the L/D ratio of any object is not a fixed value but depends on it's relative velocity. The induced drag can be held constant with increasing aircraft weight by holding a constant angle of attack, but doing so requires an increase in speed.  This speed increase effects an increase in parasitic drag, which means that in general holding vehicle shape constant while increasing mass will affect a lower L/D ratio.


 * While a jet on a test stand remains stationary, the air around it does not. Since thrust specifications are typically quoted based on sea-level standard atmosphere (SLS) conditions, is there a formula to calculate the force applied to accelerate that SLS air from rest to the velocity needed for the given thrust? If so, could that be combined with the length of the engine (distance) to calculate power (F×d/t)? sn‾uǝɹɹɐʍɯ (talk) 23:03, 19 February 2013 (UTC)


 * To say that a stationary jet engine can have its thrust assessed (Newtons) but not its power (kilowatts) is nonsense. True, mechanically the jet engine is not moving and from that perspective does no work. As alluded above, the exhaust is moving and represents work even if not easily quantified. The most practical power assessment of any engine is its power consumption in terms of the fuel consumed!  The amount of fuel per second consumed represents the amount of chemical energy per second, thus power.  The tables should have a column to show this.

"Power" in this context refers to shaft power. So for a turbofan engine, that would be the shaft power available to the fan, torque times angular velocity in radians. That is non-zero even when the engine is bolted to a test stand. It is true that when looking at the larger system, the net mechanical power produced is zero as long as the test stand doesn't move, but this is irrelevant pedantry. The various diesel, electric and pneumatic motors listed on this page also produce zero power when spinning against a brake on a test stand, but their specifications show shaft power.--Yannick (talk) 22:53, 29 August 2015 (UTC)

power to weight ratio of one notable car – GM EV1
Consider adding electric car by General Motors – EV1. It's ratio equals 97.86 bhp/ton  — Preceding unsigned comment added by 83.26.66.28 (talk) 13:16, 26 March 2012 (UTC)

I think "Supersonic vehicles" should be deleted
I dont know what engineer wannabe wrote this table but its COMPLETE nonsense. Its obviously calculated by this simple formula : Power = (Engine Thrust in Newtons) x (Aircraft Mach number) x 1236 / 3.6 (km/h to m/s conversion).

1-In engine specifications, the engine thrust is stated as "uninstalled thrust". As soon as it is installed into airframe, it wont be giving its uninstalled thrust.

2-Even more importantly, intake design dictates how dynamic thrust of engines will be. A fixed inlet optimized for transonic regime wont be giving ANY thrust supersonic, no matter how powerful engine is(for example Su-25), but a optimized variable inlet can give even higher than uninstalled thrust at high supersonic speeds. To compare, a MiG-25 with 200kN total thrust 0.55 T/W, and a draggy airframe can reach M2.83 with 4 missiles, but a clean F-15C with 220kN total thrust, twice T/W and less draggy/lighter airframe cant. In short, its wrong to assume engine gives the same thrust at all speeds.

3-Engine thrust is also dependent on altitude, so its also wrong to assume sea level static thrust applies to all altitudes. (Obviously most aircraft reach their top speeds at 20000+ feet)

4-Mach number also changes with air altiude, so multiplying with 1236 is also wrong.

Most of these goes for rockets (space shuttle etc). In that case, thrust depends on altiude, airspeed, compressibility and nozzle design point. So unless anyone objects, I will be deleting all these aircraft relates bullshit from the article. Its a embarassing table for a site calles itself encyclopedia. Andraxxus (talk) 20:46, 3 June 2012 (UTC)


 * I wish to second the idea of deleting or significantly altering the "Supersonic Vehicles" section, jet engines and rockets because the link between power and weight for vehicles/engines in these classes is problematic towards meaningless. However I do see that ALL power plant forms have specific design considerations that prevent them delivering theoretical/uninstalled/laboratory performance specs.  It seems that this whole article needs a rethink.  An occasionally achieved peak power in a turbo small automobile is not directly comparable with the sustained power near peak of another multi-cylinder automobile designed to tow.  And then there is the aerodynamics of automobiles which are not even considered.  Comparing power-to-weight ratio seems only possible when comparing significantly similar vehicles under similar conditions.  In the aerospace arena, there are more variables that make significant effect on performance making comparisons virtually impossible and the power-to-weight ratio meaningless. 203.96.74.238 (talk) 05:39, 9 August 2012 (UTC)


 * I'd like to third the deletion...a quick unit conversion has the space shuttle producing 1 hp per 6 grams, which is patently absurd. The only way to squeeze that kind of energy out of that kind of mass is explosives.  I ran some more numbers, and it seems like whoever did the math is using the empty weight of the orbiter/boosters/external tank as the weight in the calculations.  This seems to be distorting the issue significantly, since at no point does the shuttle actually produce anywhere near that kind of power to weight ratio.  In a technical sense, it is correct in that fuel weight is not usually included in the power/weight formulas, but in this particular instance it leads to utterly nonsensical numbers.  One could easily argue that the SRB engine IS the fuel, and as the "engine" weight is changing during operation, the power/weight ratio becomes meaningless. It might make sense to run the calculations for a liquid fuel rocket, but for a solid fuel rocket it's like calculating the power to weight ratio of gasoline.  I vote for deletion on the simple basis that the numbers misrepresent reality, regardless of how they were calculated.  Or, for that matter, the "technical" correctness of the calculations. 66.42.152.225 (talk) 15:40, 8 November 2013 (UTC)


 * Actually the value for rockets depends on speed, and peaks at maximum thrust at maximum speed. Rockets are indeed insanely powerful. The power of a jet-propulsion engine is MAX(thrust x speed) where thrust is a function of speed, altitude. For a rocket thrust maximises in a vacuum as there's no aerostatic backpressure on the nozzle. Towards the end of the burn the space shuttle could accelerate at over 3g at a speed of 7.8km/s. That's over 30N per kg @ 7.8km/s, 234 kW/kg or ~300 horsepower/kg, 1 horsepower for every 3.2 grams, including (remaining) propellant, tanks, astronauts everything. So twice as good as 1 horsepower for every 6 grams. Hope this helps.GliderMaven (talk) 17:05, 4 December 2013 (UTC)


 * Concorde super-cruised across the Atlantic at Mach 2.0 on ~40,000lb of thrust, around the equivalent in power of a single early RB211. — Preceding unsigned comment added by 2.29.18.184 (talk) 09:37, 1 May 2015 (UTC)


 * This definition for "power" of a rocket is patently nonsense, as it depends on reference frame. How much power does the rocket produce relative to the surface of the sun?  How about relative to the center of the galaxy?  Does a simple model rocket produce nearly infinite power relative to red-shifted galaxies?  All accelerating vehicles push against something; in the case of a rocket, it is pushing against the fuel in it's tanks.  By calculating the power output of the space shuttle in the fashion used above, one ignores the power already delivered to the propellants in the fuel tanks earlier in the launch cycle to accelerate them to (nearly) orbital velocity.  A more reasonable definition of the power produced by a rocket is it's thrust multiplied by it's exhaust velocity.  — Preceding unsigned comment added by 71.174.93.74 (talk) 14:50, 22 March 2016 (UTC)

Ships?
Ships should be included in this article, as they are the most efficient movers of cargo, shown by the very low Power-to-weight ratio. I could not find references for the mass of an empty functional ship, but hopefully others have better luck. TGCP (talk) 14:37, 25 May 2014 (UTC)

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Formula 1 engine BMW M12
I checked the reference, there was no weight and the power was just 850 bhp. I did not find anything about 1400 bhp org weight inArrows A10 or BMW M12. --Fisch4Fun (talk) 06:35, 17 October 2017 (UTC)
 * I inserted a reference for 1400 hp --Fisch4Fun (talk) 07:12, 17 October 2017 (UTC)

Toshiba SCiB cell 4.2Ah Li2TiO3 Lithium-ion battery Comment
I've removed the C/12 rating for the Toshiba SciB cell. The math was wrong (50A at 2.4V is 120 W, not 600W), and the cited source doesn't mention a 50A discharge at all. What it does mention is charging at 50A:

More than 90 percent of the SCiBTM cell capacity can be charged in just 5 minutes using a large charging current (max. 50A). Dominik Honnef (talk) 20:27, 8 September 2020 (UTC)

Split
This article is now 78 pages long and has ~500 refs in it. How about we split the examples into another article for people who want to see the details and leave this article to explain the definition and interpretation of the concept? Lfstevens (talk) 19:12, 13 May 2021 (UTC)

Electric motors and electromotive generators : Data Problems
Hi, the section on electric motors appears poorly sourced and unreliable. When the links are followed, they don't go to specific product pages and the products that are there don't seem to match the claimed results for H3X and Integral. I was trying to verify claims and power levels and weights didn't seem to match up let alone Power/Weight ratios. Perhaps an Editor should assess wether this is [UNRELIABLE] and wether it should remain in the article? Patbahn (talk) 17:40, 8 July 2022 (UTC)

Point of the lists?
What's the point of the lists? I do not think it passes WP:NLIST. X750. Spin a yarn? Articles I've screwed over? 21:48, 5 April 2023 (UTC)

Humans Power
Remove any mention of any athletic achievement since most professional, if not all, cyclists are 'doped up to the eyeballs' and does not accurately portray their power but how well their team doctor can concoct something 'good' and undetectable to enbale them to cheat. The issue is that the cyclist mentioned was caught doping with asthma medication and collapsed from excessive use. 210.84.5.219 (talk) 14:04, 23 March 2024 (UTC)