Speed Impact of Levil BOM?

spatsch · #1 09-01-2019, 08:01 AM

I was wondering what speed impact one might expect from installing a Levil BOM (self powered instrument pod).

They say in the FAQ:

Question: What is the drag coefficient of the BOM?
Answer: This aerodynamic design only produces 0.175 lbs of force at 100 knots and 0.7 Lbs of force at 200 knots.

How does that translate to speed in an RV-8?

Seems like a really simple way to get a truly independent secondary system.

Thx

Oliver

Ironflight · #2 09-01-2019, 10:03 AM

I couldn’t tell any difference at all flying with the BOM on our airplanes Oliver - physics says that there is an impact, but it is going to be in the noise (1 or 2 knots at most I’d think) unless you are flying at Rocket racing speeds....

Paul

BobTurner · #3 09-01-2019, 04:24 PM

Quote:

Originally Posted by spatsch

Answer: This aerodynamic design only produces 0.175 lbs of force at 100 knots and 0.7 Lbs of force at 200 knots.

How does that translate to speed in an RV-8
Oliver

If we take 200 knots to be about 300 ft/sec (really 337) then the power needed is just V*F = 300*0.7 ft lbs/sec. = 210 ft lbs/sec.
1 HP = 550 ft lbs/sec, so it costs you the same as lowering your power by about 1/2 HP. Round numbers: if you?re cruising with 120 HP, then 1/2 HP is 1/240. Power is proportional to velocity cubed, so the velocity will change by about (1/3)*(1/240), or about 1/720. If you?re doing 200 knots, 200/720 is about 0.3 knots. e.g., you won?t notice it.

SmilingJack · #4 09-01-2019, 04:48 PM

OP is a PHD
2nd post is ex Nasa
3rd post is a Physicist

But.... as a pilot I can?t resist urge to say ?yeah! What they said!?

GalinHdz · #5 09-02-2019, 05:38 AM

Quote:

Originally Posted by SmilingJack

OP is a PHD
2nd post is ex Nasa
3rd post is a Physicist

But.... as a pilot I can’t resist urge to say “yeah! What they said!”

And as an engineer I can't resist the urge to say "OK, close enough for what I want to do."

RONSIM · #6 09-02-2019, 06:03 AM

I would be uncomfortable telling people I had a "BOM(B)" on my wing!

Ironflight · #7 09-02-2019, 08:37 AM

Quote:

Originally Posted by RONSIM

I would be uncomfortable telling people I had a "BOM(B)" on my wing!

You should try carrying one home on the airliner from SnF! No way I was taking it through security, and I was even nervous about putting it in my checked bag, figuring they?d see a mortar round on the X-Ray and blow up my luggage.....