1
$\begingroup$

Assuming my full kit and I weigh 82kg total, I have estimated that I need 5hp. To calculate this, I used the formula:

weight force (W) is F = m g

W= 82kg*9.8 ms/2 =401.8 Newtons

Now, if the drag ratio is 9:1 that means that there is also 401.8 Newtons of Lift (L) and 45 Newtons of Drag (D): D= L / (L:D) 45= 401.8/9 So if 45 Newtons are required to be overcome drag, this is the thrust the engine must produce. Using a rule of thumb of 11 Newtons per Hp that equals 4.05 Hp. I rounded this up to 5hp for climbing.  Is my math correct? 5hp  seems low compared to paramotors on the market with 20+hp. I would also need approximately 10kg of thrust, 82/9=9.1 rounded up to 10

Improve this question
$\endgroup$
2
  • 2
    $\begingroup$ An easy way to calculate the power is to think in the 'gravitational power' of the aircraft in a glide. If the horizontal speed is S, and the glide ratio (L/D) is R, the vertical sink speed V = S/R. Now, the power P involved is the weight W of the aircraft times that sink speed => P = W * V. For a given mass and L/D, the 'gravitational' power involved in the glide is the same s the power you'd need for straight and level, unaccelerated flight... $\endgroup$
    – xxavier
    Dec 4, 2022 at 17:52
  • 1
    $\begingroup$ Make sure you have excess power to climb. You can figure ROC as a mirror image of glide ratio. So if you climb 1 to 9 @ 40 knots, climb vertical rate is around 4.5 knots or around 450 feet per minute. To provide safety margin, double hp required for level flight. $\endgroup$
    – Robert DiGiovanni
    Dec 4, 2022 at 18:16

1 Answer 1

Reset to default
1
$\begingroup$

With a ratio of 9:1 (rather high for a paramotor) and a mass of 82 kg, you have a 'gravitational power' (in a glide at 60 km/h = 16,7 m/s) of 82 * 9,8 * 16,7/9 = 1491 W = 2 HP. That, also for prop-driven s/l flight at that speed and L/D. Thrust would be 1491/16,7 = 89 newton.

But if you use an engine with a prop, you have to take into account the propeller losses. If the prop efficiency is 75%, you would need an engine power of 2/0,75 = 2,7 HP.

Probably, the L/D is not 9, but much less, so you might need more power...

Improve this answer
$\endgroup$
4
  • $\begingroup$ I plan on flying the Ozone Mojo Power 2 wing, I couldn’t find any data on the glide ratio. A quick google search told me that an average is around 9, but would 7 be better? I have heard it’s always better to be over than underpowered. Would a 3 blade ducted fan of 16x10” with a duct wall clearance of 1mm be enough? I plan on using the dle 55RA engine, as it can put out 5hp at 8500rpm $\endgroup$
    – Lelotz
    Dec 4, 2022 at 18:41
  • $\begingroup$ @Lelotz Let me suggest not to use the comments to make questions. Instead, you should put them in the Aviation SE... $\endgroup$
    – xxavier
    Dec 4, 2022 at 18:53
  • $\begingroup$ If the average speed of the wing is 40km/h would I change the 16.7 to a 11.1? $\endgroup$
    – Lelotz
    Dec 4, 2022 at 21:23
  • $\begingroup$ @Lelotz 1 m/s = 3,6 km/h $\endgroup$
    – xxavier
    Dec 4, 2022 at 22:08

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .