# Homework Help: Power question for aero class

1. Apr 2, 2006

### ranger1716

OK, I have a question regarding this homework that I have to complete about power and airspeed.

I have a beech bonanza v-tailed aircraft and I need to calculate rate of climb in ft/min with a True airspeed of 110 knots. (110 knots = 185.7 ft/s)

I am using R/C= (excess power)/weight My problem is that when I found the power required for level cruise at the same speed as above, I got a huge number because I did PR=Thrust required x Velocity (200.3 lbs x 185.7ft/s)

This going to give me a negative number for my excess power. The power plant is capable of 345 hp at sea level.

What am I doing wrong?

2. Apr 3, 2006

### FredGarvin

I'm calculating only 67.6 HP for cruise. Where did your huge number come from?

3. Apr 3, 2006

### ranger1716

I honestly don't know what I'm doing wrong. I used the equation I described above and multiplied by 60 in order to get ft lbs/min.

4. Apr 3, 2006

### FredGarvin

$$PR = TV$$
$$PR = (200.3 Lb_f)(187.5 \frac{ft}{sec})$$
$$PR = 37556.3 \frac{ft*Lb_f}{sec}$$

Use the relationship that $$1 HP = 550 \frac{ft Lbf}{sec}$$

That leaves $$PR = 68.3 HP$$

Why are you multiplying by 60?

5. Apr 3, 2006

### ranger1716

oh ok.....that makes total sense. I was multiplying by 60 to try and convert the units, but now I can see how to get the answer. I didn't use that relationship that you gave.

Thank you!