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Title: Low Thrust to weight ratio? Post by: AL HAM SHARI on March 15, 2018, 04:05:11 PM Has anyone flown a plane with 25% thrust to weight ?
Edit: Moved to a new topic here, to avoid diverting Sreekumar's build thread. Title: Re: Low Thrust to weight ratio? Post by: K K Iyer on March 15, 2018, 05:58:52 PM In my Sunbird, at the throttle setting we use for just cruising along maintaining height, the power drawn is only 25 watts. Since the prop is only 6" dia, it probably gives only about 4gms thrust per watt. Or say ~100gms. AUW is 450gms. Or under 25% t/w ratio.
Somewhere in the thread I'd mentioned 60watts during climb. Or under 50% t/w. Many of us think 1:1 t/w is required to be able to fly. Not true. Is it a heli or VTOL? ;D For more you can see this if you like: http://www.rcindia.org/electric-planes/sunbird/msg239836/#msg239836 Regards Title: Re: Low Thrust to weight ratio? Post by: AL HAM SHARI on March 15, 2018, 06:41:13 PM If it is that way , could we fly a plane which weighs 45 kg with 10-15 kg thrust motor 😁😂
Title: Re: Low Thrust to weight ratio? Post by: K K Iyer on March 15, 2018, 07:31:24 PM If it is that way , could we fly a plane which weighs 45 kg with 10-15 kg thrust motor 😁😂 Asking as a joke or seriously? So I'm not sure whether a proper answer is expected... Title: Re: Low Thrust to weight ratio? Post by: AL HAM SHARI on March 15, 2018, 07:33:57 PM Seriously , Is it possible? Given that the takeoff run should not be too long
Title: Re: Low Thrust to weight ratio? Post by: K K Iyer on March 15, 2018, 08:07:24 PM Seriously , Is it possible? Given that the takeoff run should not be too long Let's not add new conditions like short take off run etc just yet. The basic issue is whether 45kg will fly at 15kg thrust. Means whether it can maintain level flight. An associated question is whether this is enough for take off. There exists an airplane that weighs 2000kg. Has 4 motors of 7500watts max power each. Or 30,000watts total. Or 15watts/kg. This much power is only used for takeoff. The average power consumption in a flight is only 6000watts. Or 3 watts/kg. Which plane is it? I know I've given an extreme example. That's just to prove the point. BTW, usually only jets quote thrust, prop planes usually hp or watts. I'm not sure if you are considering building a 45kg model, and really want to know the power reqd. If you are really building a 45kg model (knowing the legal implications) I'm sure lots of members will follow your thread. Unless of course, your query, if not jocular, was only theoretical. In which case the answer is Yes. ;D Title: Re: Low Thrust to weight ratio? Post by: Aravind298 on March 15, 2018, 08:14:16 PM Here's a more practical example. I've listed the thrust-weight data of a few of the four-engine aircrafts.
I'm not sure if the data given is the for one single engine or for all the four of them combined. A340-300: 605 kN / 2696 kN = 0.22 A340-600: 997 kN / 3579 kN = 0.28 A380-800: 1247 kN / 5494 kN = 0.23 B747-400: 1126 kN / 3894 kN = 0.29 Source: http://www.airliners.net/forum/viewtopic.php?t=728395 The topic of this post was if the A380 was underpowered. Hope, now you get it. Edit: The numbers denote to the thrust produced by all the four engines combined. Title: Re: Low Thrust to weight ratio? Post by: K K Iyer on March 15, 2018, 08:29:53 PM @al ham shari,
I think I better be quiet! No point in discussing stuff no one is going o build. Leave theory discussions to those more qualified. Bye |