Altimeter & vent port diameters for a Blackhawk 54?

[lucanica]

Hi there, this Wildman Blackhawk-54 will fly on a K455. Max simulated speed is Mach1.1 and the bay is 7.5" long by 2" in diameter. As per the RRC3 manual, 3 x 0.034" holes (roughly 3 x 1/32") would be enough for the altimeter bay. However, I somehow find them too small... What do you guys think?

Since this is a dual deploy design I would also like to drill a vent hole in each parachute section in order to prevent drag separation. Which diameter would you recommend for this purpose?

Many thanks in advance!

 

[Titan II]

1. This is straight from the RRC3 quick start guide regarding the vent holes:
B. 54 mm by 7 in. 3 x 1/8" holes

2. 1/8"

 

[lucanica]

1. This is straight from the RRC3 quick start guide regarding the vent holes:
B. 54 mm by 7 in. 3 x 1/8" holes

2. 1/8"

Thank you Titan II,

Would you mind sharing your calculation for point 1? Mine goes as follows (also base on RRC3 manual):

Volume = L * pi * R^2 = 7.5 * pi * 1 In^2 = 23.6 in^3

Single Vent Diameter = Volume/400 = 0.059 In

Single Vent Area = pi * (Single Vent Diameter/2)^2 = 0.00273 In

Vent diameter (3 holes) = 2* SQRT(Single Vent Area/(3 * pi)) = 2 * SQRT( 0.00273 / (3 * 3.14 )) = 0.034 In ≈ 1/32 In

Kind regards

 

[Titan II]

I did not calculate.

This is straight out of the quick start manual, page 2. The link is below.

Vent Holes Vent holes in avionics bay allow the altimeter to sample air pressure. Here are some 3‐hole example sizes typically used for simplicity:

A. 38 mm by 6 in. 3 x 1/16” holes
B. 54 mm by 7 in. 3 x 1/8" holes
C. 3 in. by 9 in. 3 x 5/32” holes
D. 4 in. by 12 in. 3 x 3/16” holes
E. 6 in. by 18 in. 3 x 1/4"holes

link to manual:

file:///C:/Users/hobby/Downloads/RRC3%20Quick%20Start%20Guide%20(4).pdf

Your bay is close enough to the 54mm x 7" example.

 

[robopup]

If it helps, I almost always use three 9/64" holes in my ebays for 38mm - 75mm, flights > mach 2.5. Never had any issues. These are probably quite oversized, but I also arm my switches through them.

 

[DragonRocketry]

By VCT port calculator, port size would be .039" x 3. I would do .0625 x 3. This is what is in my 54mm ebay that is 8" long and has worked perfectly.

 

[sharkbait]

Hi there, this Wildman Blackhawk-54 will fly on a K455. Max simulated speed is Mach1.1 and the bay is 7.5" long by 2" in diameter. As per the RRC3 manual, 3 x 0.034" holes (roughly 3 x 1/32") would be enough for the altimeter bay. However, I somehow find them too small... What do you guys think?

Since this is a dual deploy design I would also like to drill a vent hole in each parachute section in order to prevent drag separation. Which diameter would you recommend for this purpose?

Many thanks in advance!

If you are asking for altimeter bay static port hole sizes then the answers you received are correct. If what I am reading is correct at the end of your post, you are asking for pressure vent holes in your upper and lower airframes, this would typically be a single 1/8” hole in each airframe. On a short 54mm airframe you could go even smaller like 3/32” or 1/16”. Shear pins would be highly recommended also

 

[Titan II]

I grabbed a few bays and they have the following measurements. All have been flown exclusively with RRC3s many times. I know none are the same as yours, but you can get some idea what works. As you can see by the various responses, you have a degree of latitude regarding the combined vent volume.

38mm x 5" 3 x .050

38mm x 6" 4 x .075

3" x 8" 4 x .134

4" x 8" 4 x .125 (two of them)

5" x 12" 3 x .225

 

[lucanica]

Your replies have been of great help. Thank you very much, guys!!!

 

[Cherrywaves89]

Your replies have been of great help. Thank you very much, guys!!!

May I ask what other altimeter you’re using along with RRC3?

 

[lucanica]

May I ask what other altimeter you’re using along with RRC3?

I've used a Featherweight Raven 3 as a backup. Both altimeters worked as expected firing all four charges. Apogee was around 19K feet, and calculated (i.e., derived from baro/accel) max speed around mach 1.5

Cheers!