Need suggestion on thrust required for fixed wing on during cruising

ArduPlane Plane 4.1
1

Hello everyone,

Am Making (Quad plane) Vtol using pixhawk 4.
Overall weight is around 3.5 kg.
Selected motor (Forward pusher) is giving 912g thrust at 50% throttle

My doubt is during the cruising

  1. Is that 912g thrust is enough to make my aircraft to stay in the air and move forward?
    (OR)
    I have to still increase thrust level?

Someone let me know on this.

Thanks.

2

Even commercial airplanes have at least a 0.3 thrust-to-weight ratio. I don’t have VTOL experience (mainly working on multi copters and planes, not at the same time :stuck_out_tongue:) but if I were you, I find a motor that provides at least 5kg of thrust (ideally 7kg would be best).

3

Hi Thanks for the reply.

For multi (quad)copter, minimum thrust to weight ratio is 2:1 and more than that.

That Means if the weight is 2 kg means thrust by all four motors is shuold be 4 kg at 100% throttle. So that above 50% throttle it can hover easily.

So, for fixed wing, what is the minimum thrust is required for cruising, not for take off?

Thanks.

4

Exactly, good.

Depends on your design’s wing loading and drag. But basically, most designs can be flyable with 0.5 ratio but cannot do aggressive maneuvers (could not be able to cope with bad atmospheric conditions) and this may result in weak cruise control in bad weather. 1 thrust ratio plane can do the vertical climb in good weather. I always equip my RC planes with a thrust-to-weight ratio of 2 to ensure they can cope with certain weather conditions and also use the motor at its efficient power level. Of course, these are just the basics that I recommend.

5

@Drone Cruise speed is a function of airspeed. Usually, I stay around 1.5 of stall airspeed. Stall speed is going to be determined, as @Mustafa_Gokce mentioned, on your design’s wing loading, drag, aspect ratio, etc… Having said that, with the VTOLs I’ve built, I start with at least a 0.75 thrust to weight ratio on FW motor. You can always pull back on the throttle to achieve a good cruise which in turn will help reduce amp load and consumption, subsequently increasing your efficiency. I also only go about 1.6 to 1.8 on MC motors keeping in mind that it just needs to get it air born and land with minimal time, 2-3 minutes for the most part with minimum maneuvering.

Keep in mind that you’re mainly going to be using full throttle during the MC-FW transition so drag is already at minimum, compared to taking off from the ground. You want enough thrust to get the aircraft past stall speed as quickly as possible to get it flying on its own and have your MC motors shut down. The sooner the MC motors stop, the quicker the drop in amp draw on your battery.

Just as a point of reference, you can see the differences in thrust ratios:

  • Ranger EX (Standard airplane) 4212g 1000kv 1006 prop 0.50 thrust ratio 20 mph stall 34 mph cruise at 60% throttle
  • RVJet (Flying Wing) 4444g 910kv 1308 prop 0.73 thrust ratio 25 mph stall, 40 mph cruise at 55% throttle.
  • Zephyr 3 (Flying wing) 3812g 900kv 1109 prop 0.96 thrust ratio 26 mph stall 43 mph cruise at 55% throttle.

Hope this helps. Good luck.

6

Yes, the average RC-trainer plane flies fine with thrust of one third of the takeoff weight. With some kinetic energy management you are still able to perform basic aerobatics. Back in the NiCad battery period we were happy with this amount of thrust. It was good enough for ground takeoffs (and slow climb outs).

The availability of Lipo batteries an BL motors make us believe in the need of higher minimum power to weight ratios.

Hope this helps.

7

Thanks for the brief.

Having a doubt.

0.73 thrust ratio means

Thrust to weight ratio of 0.730:1 (or ) 0.730g : 4444g?

Thanks

8

4444g x 0.73 = 3244.12 g of thrust at full throttle.

Good luck.

1 Like
9

Got it
Thanks a lot…

10

Thanks for your support