Who Says You Cannot Make your Own Airplane? Series #2: Understanding The Thrust Mechanism And How The Engine Works

Hey welcome back guys. That sweet nigga is here with his sugarcoated-mouth again and we are going to continue in our understanding of the mechanism behind airplane and eventually building one by ourselves. For the benefit of those who are just joining us, I am going to give you a brief recap of our previous lesson. Like I did on the previous post, I am going to break the concepts discussed on this post down into the absolute basics.

The mystery behind that heavier-than-air object flying at a speed faster than that of light despite having loads of several pounds aboard is SCIENCE. The principle behind flight is Sir Isaac Newton's laws of motion, especially the third. There are four forces of flight. Lift, being the most complicated among the four (happened to be the one we discussed) and then, others are weight, thrust and drag. The principle commonly taught, regarding lift is Bernoulli's theory but there are some misconceptions regarding what actually causes lift.

Mehn it is much more than what I can brief you right here. Want to check through the whole story? Click here.

---

---

Here on this post, we are going to resume from where we stopped the last time. Just like Newton proposed, the opposing force to lift is weight.

Like I stressed out earlier, lift and drag are opposite forces as are thrust and drag. Weight, the downward force is the total weight of the plane and its contents. Again, Sir Isaac Newton's laws of motion oversees the principle of weight. Weight creates problems during flight as the gravitational force pulling the aircraft downward must be overcome. Weight might be seen as a problem that must be overcome before lift can take place, however, we cannot write off its influence in aircraft's safe landing. When a device called spoilers is used when plane is landing, the gravitational force starts to gain more control of the plane. This is to ensure that the plane does not engage in lift while trying to land.

Thrust

Thrust is the forward force that propels the aircraft forward. Here, the propelling engine is at work. While thrust is taking place, a massive air is pushed backward and hence, the aircraft moves (in opposite direction like Newton proposed). When we talk about thrust, there is no way we can avoid talking about the engines (just like we do talk about wings when lift is concerned). This is because the engines, like I said earlier in the previous lesson is responsible for thrust; moving the airplane forward (horizontally). When the thrust force is acting, speed is actually at work. So before we discuss how the aircraft engines work, first let us take a look at take off speeds.

Basic take-off speed

There are three take-off speeds used in flight. Orderly, they are V1, Vr/"Rotate" and V2. Let us look at V1. Imagine yourself in your plane and applying take-off force through engines and as you gently accelerate down the runway, it comes to a point where you reach V1. So by the book:

V1 simply means the speed beyond which the take-off should no longer be aborted.

This means in case you experience any trouble with your plane before reaching V1, the classic example is engine failure, you would immediately abort your take-off and would apply all necessary matters to bring the aircraft to a stop. In as much we need to bring the plane to stop, that would be because of an engine failure and at this point, one of the reversals might be inoperative and therefore full reverse thrust can be added to the breaking measures.

Because V1 needs to be calculated prior every take-off taking into account; airplane weight, runway length, wing flap setting, engine first used, runway surface contamination and environmental factors and even the aircraft break, to ensure yourself that any given failure prior reaching V1, you have enough runway leftover to come to a complete stop. If it is a minor failure, you can continue to take-off (that we will discuss later in this series). This is why the captain keeps his hand on the throttle until the pilot monitoring crosses out V1 and then he moves his hand away from the throttle to know when to abort in case of failure. Oh I hope I am not getting you confused already. I strongly request you read these last two paragraphs again, this time slowly. I really need you to get this pretty well as that is the reason for this ehm, ehm (is it tutorial?) in the first place. Now you get it? Oh c'mon take a hug.

Okay, that is enough with the hug. So in case you experience any serious malfunction after V1, you will have to commit yourself to continue to take-off, otherwise a take-off abort would lead to a runway overrun and that could severely damage your plane.

The next speed to call out is Vr or better known as Rotate. By the book:

Vr is defined as the speed at whcih thee pilot begins to apply control inputs to cause the aircraft nose to pitch up, after which it will leave the ground.

Again, Vr is also calculated prior take-off in accordance with aircraft weight, environmental factors, etc, and it is the point where the generated lift over the wings becomes higher than the aircraft weight that keeps it on the ground. And the point where the main gear leaves the ground is the point where you have reached Vlof - the lift off speed.

Now V2. Some airliners still have the standard operating procedures to call out V2. By the book again:

V2 is defined as take-off speed. The speed at which the aircraft may safely climb with one engine inoperative.

Now let us go back to V2 and engine failure situation. In case one engine fails, you need to maintain the speed of V2 in order to leave the runway at screen height of 35ft or higher and maintain the climb rate at V2 to be clear of obstacles in the departure sector and you should be able to maintain that speed and climb rate until reaching acceleration altitude where you then gain speed and return the flaps and slat and continue with the emergency procedure. Wow! That is a hell long sentence. On your permission, I will be taking a sip from my coffee cup.

Oh, that coffee is amazing. Tastes good. Now we are back to where we were; talking about the aircraft engines as this cannot be avoided since they are responsible for thrust. I just felt we should check on the take-off speeds in order to keep our understanding at its best.

Engines

Oh yeah, of course we are going to discuss how the airplane engine is built and how we can build one by ourselves using the resources we could get around (of course those resources are not going to come cheaply). But right now, understanding the basis is more important. So, follow me.

I am sure that while you have been walking around the airport, you have seen that some of the aircrafts have their engines mounted under their wings while some have theirs mounted at the back of the body. Here, we are going to talk about the major reasons why some manufacturers prefer to mount their aircraft engines under the wings and why some mount the engines at the back.

To have the engine mounted under the wings have some really obvious beneficial things. For example, the engineers have easier access to the engines in case of maintenance. So it is easier doing maintaining stuffs like changing of oil and the like while standing on the ground. That is one thing. Another, which is the most important thing is that they can fit larger engine under the wings. You might have noticed that the bigger the aircraft is, the bigger the wings. That means the aircraft needs wings big enough to push the massive air backward, and that pushes it (the aircraft) forward in opposite direction. Those bigger engines can only be fitted under the wings of the aircraft and the only thing that is limiting the size of the engine is the size and height of the landing gear.

You can fit the bigger engine under the wings and you can at the back of the aircraft and that has to do with the structure, like how the aircraft is designed. You can also have more engines under the wings and so if you want to have a four-engine aircraft, you can have the four engines under the wings rather than at the back of the aircraft. Although you can see some aircraft having four engines or thereabout at the back, that will actually look irregular rather than regular. Having the engine on the wings also help stabilize the aircraft during the flight as the engine add more weight to the wings. It also have a beneficial effect when it comes to wing flutter.

Now, why would you have the engines mounted at the back of the aircraft rather than beneath the wings?

Well, there are some very good benefits to that as well. One of them is noise. Most of the noise that is coming out from the jet engines is coming from exhaust. So if you have engines mounted at the back, the exhaust will normally be coming out behind the cabin and that will of course help limit the amount of noise going into where the passengers are seated. Also, you would have noticed that most of these private jets have their engines mounted high up at the back. That is because this kind of aircraft is smaller compared to airbuses and if the engines are mounted below the wings, unwanted particles, refuses and the like might be sucked into the engines while running at the runway, thereby causing damages to the engines. So they are mounted at the back where they are farther away from the ground.

Another benefit to this is that with such aircraft having its engines mounted at the back, you can actually use reverses to back the aircraft out from stand. You would have seen that this is quite common in United States, for example Boeing 717 that could reverse out from the stand without the use of push back tractor. The thing is you could do this with an aircraft that has its engines below the wings as well, just that like I said, the engines would be sucking in particles from the ground and those particles could damage the engines.

However, the most important thing you need to realise when you have your aircraft engines mounted at the back is that those engines are going to be seated where the stabilizer normally is. That means such aircraft needs its stabilizer to be mounted at the top of the fin rather than at the bottom. Such tail is called a T-tail. What happens with that is that if you get into a stall situation, with a very high altitude, the wind might come straight over to the T-tail and that means when you need to push forward, like get out of the storm, you need to lower the nose of the aircraft to get airflow over the wings again. When you try to do that, the wake from the wings will be disturbing the air over the elevator so that the elevator does not have an authority anymore and then you can get into something called a super-stall/deep stall. That is a very very bad situation but is it particularly prone to happen on T-tail aircraft. This is why on T-tail aircraft, we have something called a stick pusher. This is a device that automatically pushes further to make sure that even if the pilot is not doing what he should be doing when there is going to be a potential stall, the aircraft is pushing its nose down before it gets to a super stall. Stick pusher is very common on T-tail aircraft while we have what we call a stick shaker on aircraft having its engines mounted below the wings.

Again, I am going to break this down into the absolute basics. Reverse thrust is used to slow down the aircraft on the runway as it touches down.

Conclusion

Now if you have been following this series with your absolute attention, you would understand that we have discussed the forces involved during take off (thrust and lift), during the flight and now we are going to take a look at some stuffs regarding when an airplane is landing. On our next meeting, we will be starting with something called reverse thrust. But for now, I believe we need to take a break.

The truth is I am enjoying this so badly already. I feel like continuing this non-stop but then, I need to consider my readers. And besides, the most important thing is I do not want my readers to get confused. So we really need to take a break here. We have lots of ground to cover and we will continue again shortly.

---

---

References

• Aircraft take-off speeds
• Take-off
• Stabilizer
• Stick pusher
• Podded engine

Previous Lessons In The Series

• Series #1: Understanding The Mechanism Behind Airplanes And The Misconceptions

Till we meet again on my next post, well I am not changing my name. I am @teekingtv and I write STEM!

Hey! Do you write posts that are related to Science, Technology, Engineering, and Mathematics (STEM)?

Then join #steemstem on on discord. Click here.
Check this blog post by @steemstem to understand the guidelines on how to become a member of @steemstem.
Also check on this post by @steemstem to understand the use of images so as to avoid copyright infringement.
And in case you are writing from Nigeria, you can include #stemng tag in your posts. Details on @stemng blog.

---

---

Thinking of delegating SP to @steemstem to support this great initiative? All you have to do is to use the links below:

50 SP | 100SP | 500SP | 1,000SP | 5,000SP | 10,000SP | 50,000SP

However, ensure you have at least 50 SP left in your wallet.

I know you don't give a crap, but I will tell you this:
I am @teekingtv, the no.1 Global Meetup analyst