How to calculate the loss of vertical thrust when motor is canted?

So I have built 3 rockets (working on 4th) that have the motors canted. Depending on the rocket, they are 15 or 20 degrees off parallel to the rocket body. Obviously, as I angle the motors, and the thrust is not straight down, I will loose some thrust in the up direction. I assume that since 0 deg. is no loss in the up direction, and 90 deg. would be 100% loss in the up direction, the 15 deg. would be 16.7% loss (15/90=.167).

Am I correct? Anyone know if this is right or do I need to geek it out more? If so, how?

I can't answer your question, and I have never tried to sim a canted motor in OR, but if it is possible, then perhaps you could sim the same bird with canted, and again with vertical, and see what the difference looks like.

If your motor is canted at 15 degrees off vertical, you would have ~96.6% of your vertical thrust. You can figure this out by: Total vertical thrust = motor thrust * sin(90 - cant angle). Make sure your calculator is in degrees mode.

Here is an online calculator: https://www.cleavebooks.co.uk/scol/calrtri.htm
If you image that Side 'a' is your vertical thrust and Side 'c' is your rocket motors actual thrust, simply type in your cant angle (B) and your average motor thrust (c), and (a) will be the thrust your rocket will experience. Of course, multiply that by however many motors you have for total thrust.

CZ Brat said:

So I have built 3 rockets (working on 4th) that have the motors canted. Depending on the rocket, they are 15 or 20 degrees off parallel to the rocket body. Obviously, as I angle the motors, and the thrust is not straight down, I will loose some thrust in the up direction. I assume that since 0 deg. is no loss in the up direction, and 90 deg. would be 100% loss in the up direction, the 15 deg. would be 16.7% loss (15/90=.167).

Am I correct? Anyone know if this is right or do I need to geek it out more? If so, how?

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No idea, likely more geeking out to be done, however I like your rockets the copper steampunked one is pretty cool@

Bat-mite said:

I can't answer your question, and I have never tried to sim a canted motor in OR, but if it is possible, then perhaps you could sim the same bird with canted, and again with vertical, and see what the difference looks like.

Click to expand...

I ask since OR does not have a cant function.

lkal32 said:

If your motor is canted at 15 degrees off vertical, you would have ~96.6% of your vertical thrust. You can figure this out by: Total vertical thrust = motor thrust * sin(90 - cant angle). Make sure your calculator is in degrees mode.

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96.6% seems very high. I would love that.

CZ Brat said:

96.6% seems very high. I would love that.

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cosine(angle from vertical). For example: 15 degree angle: cos(15) = 0.966.
The sideways thrust is: sin(15) = 0.259.
Check your answer by taking the sqrt of the sum of the squares (vector addition), answer should be 1: (0.966)^2 + (0.259)^2 = 0.933156 + 0.067081 = 1.000.

CZ Brat said:

I ask since OR does not have a cant function.

Click to expand...

You have to edit the eng file manually. Multiply every thrust point by cos(15)

Do some web searches on vector addition and trigonometry... two of the most useful subjects I learned in school and have used regularly in rocketry.

Basically, you use a right triangle to break the canted motor's thrust vector into vertical and horizontal components (the full-thrust of the motor forms the vector along the hypotenuse). Remember the Pythagorean theorem? Useful here also. Anyway, you can calculate the vertical and horizontal thrust components in this fashion.

Math. Don't leave home without it. And if you did, this is one worth turning around to go back and get it.

To visualize you can use something like this crosswind component graph. You can use it to see how much vertical and horizontal thrust you have depending on the cant angle.

https://1.bp.blogspot.com/-ToSRCKG_HVo/TaeRcchwOaI/AAAAAAAAAME/d78aq933_xA/s1600/CrosswindChart.jpg

Thanks a lot guys. I was assuming a much greater loss of vertical thrust than is actually occurring. I will use the sin/cos from now on.