Hello, everyone. After being PRO-less for a couple months, I’m finally back online. Last time I made a topic, I put my focus on a safety aspect: OEI. What is OEI you may ask? OEI stands for One Engine Inoperative. It describes a scenario where you lose one of you engines such as on takeoff.
With OEI, airplanes lose out on some of their flight performance, so we need safeguards to ensure we don’t…fall out of the sky. This is the biggest reason why we have V2 as one of the takeoff speeds. V2 is a speed where your airplane can successfully climb to 35 feet above the runway, and sustain a specific climb gradient to 400 feet AGL. Climb gradients can be classified as two things: gross climb gradients and net climb gradients. Gross climb gradient is the maximum theoretical gradient you can achieve at that speed. For twinjets, trijets, and quadjets, they have gross climb gradients of 2.4%, 2.7%, and 3.0% respectively. Net climb gradients are more practical and account for penalties such as pilot handling, small changes in atmospheric conditions, and other things. They reduce performance by 0.8%, 0.9%, and 1.0% respectively, putting jets at net gradients of 1.6%, 1.8%, and 2.0% respectively (wow I said respectively 3 times).
To account for these gradients, we need to chose V2 speeds that will generate enough lift to satisfy conditions. We will measure this with climb rate in fpm. To do this, we multiply our ground speed by the gradient (e.g. 100 knots GS × 2.4 = 240 fpm). Don’t worry about the net gradient (it’s an error margin essentially). Focus on the gross gradient. Finding the speeds involve trial-and-error as well as precise control over rudder else we’re forced slightly sideways, not creating smooth airflow.
Here’s a few links to help you understand what I’m talking about:
(Idea’s there, but he meant to say GS not TAS)
https://youtu.be/wMsk_FjKjeU?si=9CSOyZrPPH3A69mK
https://youtu.be/D0qIYHnzIDY?si=ir6EEwu7LnutbHcr
I ask anyone who likes or wants to experiment to share their findings here.
Important notes: Don’t bother testing the climb to 35 feet because the majority of aircraft will fail that test (excessive drag). Just worry about the climb gradient past that. Additionally, I decided to use MTOW tests at 100% THR for my tests because I found it easier for me and speeds get egregiously bigger using less power. This would be like a minimum V2 that works better if you have a runway length constraint. Ideally, you’d hit an altitude limit where you can’t satsify the gradient. I notice how aircraft manufacturers publish their v2 as a set number for all conditions under a certain weight. I feel like this number is taken from the worst case scenario (highest height) so a normal scenario would be a guarantee. I haven’t done that…not yet.
My findings on the 737-700 @ ISA, MTOW, flaps 1°, calm conditions:
My notes from Simbrief:
B752 flaps 5°, MTOW ISA MSL: 148 KIAS
B739 flaps 1°, MTOW ISA MSL: 182 KIAS
CRJ2 flaps 8, MTOW ISA MSL: 145 KIAS
A321 flaps 1, MTOW ISA MSL: 183 KIAS
MD-11 flaps 15, MTOW ISA MSL: 179 KIAS
F18? flaps half, MTOW ISA MSL: 117 KIAS? (Don’t ask me how I did this. DON’T)
Additional Info: Vmd (Minimum Drag Speed) is also being tested. Vmd is the speed at which the total drag of an aircraft is at its minimum. Because drag is at its minimum, fuel burn will be at its minimum, and you can maximize your flight time. Your engine isn’t working too much or too little.
Feel free to share any thoughts.
(Nerf that plane ASAP)
! My gift to you may not seem significant, but it’s the gift of knowledge. I’ve done testing on the A321 and provided a more extensive case. Take it as you will.
