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Help! will it be unstable?

JasonK

Elite member
#2
Will it make the plane unstable in logitudinal axis if the nose is long?
what matters for stability is the Neutral point, CG, vertical stabilizer size. Generally the amount of fuselage in front of the nose is related to the mass distribution of the craft. IE some have very short 'noses' and some have longer ones.
 

quorneng

Elite member
#3
Juice
Assuming the CofG is in the right place the length of the nose, both its area and shape, does have an aerodynamic effect both laterally and vertically. How significant it will be depends on the area and shape of the rear fuselage and tail assembly.
Stability is only maintained if the centre of pressure (CofP) (the point through which the aerodynamic forces can be considered to act) must never be in front of the CofG. The problem is the CofP moves depending on the angle of the airflow. It is possible to have a plane stable when pointing directly into the air flow but becomes unstable beyond a certain angle and is then likely 'fall out of the sky' out of control.
Notice that airliners with long noses tend to have generous tail planes and fins. ;)
So first you have to get the CofG in the right plane so the wing is stable then you worry about the effect of a long nose and/or a short tail.
 

Monte.C

Legendary member
#4
Will it make the plane unstable in logitudinal axis if the nose is long?
Everybody always gives such complicated answers to simple newbie questions! Are you trying to pass an aeronautical engineering exam?

Short answer: No.
Battery placement directly affects CG location, and that's critical. I sometimes design my nose kinda long to make sure I have enough space to move the battery as far forward as I need to get the CG right. Then before I build I wind up adding another 1/2". ;)
 

BATTLEAXE

Legendary member
#5
You can use the length of the nose to help with your CG. Case in point...
737 jet, mid mount motors,
Boeing_737-85R,_Jet_Airways_JP7013193.jpg

Average nose and tail length

717 with rear engine mount
200-jet-aircraft.jpg

Much shorter tail moment and the nose is long to get the weighted leverage to balance the wing.
 

quorneng

Elite member
#6
Monte.C
It is wise to say the length of the nose does not effect the aerodynamic stability?
The area of the fuselage ahead of even a sound CofG position most definitely can.
 

L Edge

Elite member
#7
An example of dealing with the area in front of the CG is the SR-71. One of the problems is landing it. If the pilot pulls a too much nose up approach, the plane will go into a stall and crash. Also in flight, if you apply too much elevator in the turn, you are looking at it rolling over with that large area in the nose section. It flies just like the real one.

Stability in the yaw axis was also a big problem I had to solve as well due to the large nose area.


.
 

Monte.C

Legendary member
#8
Monte.C
It is wise to say the length of the nose does not effect the aerodynamic stability?
The area of the fuselage ahead of even a sound CofG position most definitely can.
I'll bet you ANYTHING this is not a situation where the designer is trying to create a giraffe plane. Based on the nature of his question - slightly new to the idea (that's why he asked) - if he has any sense at all he's modifying an existing design, or basing his design on previously designed models or full-sized planes. Complicating the answers with an in-depth dissertation on flight stability helps nothing, and only makes it sound like you're trying to prove how smart you are. Within ANY reasonable parameters my answer still holds.
 

Monte.C

Legendary member
#10
This is a tough one.
Argue, or stay on topic? :unsure:
Sorry @Addicted but I've seen it time and time again. A very young and very green member (which this poster may or may not be) asks a very basic and innocent question, and there is a short handful of members who like to reply with lengthy chunks of information about aerodynamic theory or whatever may apply. Nobody asked "What are you trying to build?" I know all the things these members do, but I don't show it off as often as possible without consideration for who asked the question. Too much, too soon. Have you no empathy? Are you not able to judge what's really happening here, and what response may be most helpful? Have you no ability to judge how your response may be received? It happens over & over, but the only real mistake I see is that I snapped when I could have walked away.

If you have a good reason to make your fuse longer then go ahead. Just don't make the mistake of making your tail surfaces too small. Sorted.
 

sprzout

Knower of useless information
Mentor
#11
I'm going to say "Maybe". Case in point, look at all the people trying to build X-Wings. The guys at FT did it a while back, and were fighting with it wanting to nose down as soon as they powered down, despite having it balanced across the CG. The Air Hogs X-Wing fighter has the same issue, and was remedied with a clear plastic canard.

I won't say it won't work, because as others have mentioned, it's a possibility that it will work, but you may need some additional lift at the nose depending on how things are balancing out..