15
votes
Why do newer engines have such wide fan blades?
The improvement in efficiency has two roots:
Higher turbine pressure ratios. While the very early turbojets managed just 3.14:1, the most recent civil turbofans run at 50:1.
Higher bypass ratios. The ...
- 228k
13
votes
Accepted
How to slow down while maintaining altitude
To maintain altitude, lift must be equal to weight. The first question is, does slowing down reduce the amount of lift we have?
We can look at the lift formula for the answer:
$$\mbox{Lift} = C_l \...
- 14k
11
votes
Is it feasible for an individual with limited current knowledge to undertake the development of an aircraft from scratch?
It's not possible to solo-develop a 9-12 seat airplane to a legally flyable condition. The authorities want passenger aircraft built by people who know what they're doing, then checked again by ...
- 22.6k
7
votes
Accepted
Why do newer engines have such wide fan blades?
Fan blade evolution
The historical fan blade had the same form as a compressor blade,
Figure 3 and 4. The weight of the solid titanium blade stopped a wider
cord design. The long and slender shape ...
- 2,765
6
votes
Why do newer engines have such wide fan blades?
Long, slender wings impart a small momentum change to a large volume of air. Short, stubby wings impart a large momentum change to a small volume of sir. Small momentum changes generate less ...
- 20.4k
6
votes
Why does Vx have a relationship with thrust but Vy has a relationship with power?
For the best climb speed, you need to maximize your vertical speed $\text{v}_z$.
For the best climb angle, you need to maximize the ratio $\frac{\text{v}_z}{\text{v}}$ of vertical speed $\text{v}_z$ ...
- 228k
5
votes
How does the Boeing TTBW reduce fuel consumption?
We have a question here concerning the Boeing TTBW study from the time it was called Sugar VOLT. In my answer I speculated that the cruise Mach number of that design is 0.75 or lower.
You are correct ...
- 228k
4
votes
Can vortex ring state (VRS) be solved by shaping the blades so that the vortexes they produce are weak enough not to form a vortex ring?
No. VRS isn't about the tip vortices you are thinking of.
VRS is a thing even if you had a pure actuator disk. I.e. it is a fundamental phenomena of powered lift. It has everything to do with disk ...
- 5,916
4
votes
Why do newer engines have such wide fan blades?
Gliders utilize the long, short span wing design to achieve high efficiency as you described. This design enables them to accelerate the necessary mass of air downwards with the least amount of ...
- 26.7k
4
votes
How to slow down while maintaining altitude
Consider the four forces acting on an aircraft in equilibrium:
Drag must exceed thrust in order to decelerate. Presuming that you don't have speed brakes to increase drag, the only way to slow down ...
- 24.1k
3
votes
Can the use of wide-chord supercritical airfoil blades in a helicopter with coaxial counter-rotating rotors solve retreating blade stall?
Counter-rotating rotating rotors is enough to effectively eliminate the retreating blade stall problem. Note that the CH-47 is considered the fastest helicopter in the US military.
Retreating blade ...
- 5,916
2
votes
Can vortex ring state (VRS) be solved by shaping the blades so that the vortexes they produce are weak enough not to form a vortex ring?
Vortex ring state (VRS) is a blade root stall phenomenon that occurs in rapid descents. In a normal rapid descent, there is a small amount of airflow UP through the center of the rotor disc right at ...
- 125k
2
votes
Are there fixed wing planes that have a Vne above their terminal velocity with the nose pointed straight down?
Dive bombers, such as the Ju-87 and SBD Dauntless have purpose built dive brakes.
Aircraft designed with an emphasis low drag for fuel economy, such as airliners, are susceptible to rapid airspeed ...
- 18.7k
2
votes
What open-loop control inputs can guarantee non-divergent descents in fixed-wing aircraft?
One possible solution may be to monitor airspeed/rate of descent. Lacking all other sensory input, this (aside from the parachute (for the the pilot or the aircraft)), may be one way to keep control ...
- 18.7k
2
votes
How to slow down while maintaining altitude
Is reducing throttle/power already enough? Or do I have to adjust the
pitch as well?
It depends on the aircraft. It also depends on whether you are flying on the "front side" or the "...
- 21.4k
2
votes
How to slow down while maintaining altitude
If you reduce forward thrust then you implicitly reduce the lift generated by the wing in its current configuration. So to maintain altitude you must pitch up or otherwise change the configuration of ...
- 31.1k
2
votes
Can the use of wide-chord supercritical airfoil blades in a helicopter with coaxial counter-rotating rotors solve retreating blade stall?
Supercritical airfoils are unsuitable for helicopter blades due to their high pitch moment coefficients.
The idea of a supercritical airfoil is to separate the effects of thickness and lift creation ...
- 228k
1
vote
Can the use of wide-chord supercritical airfoil blades in a helicopter with coaxial counter-rotating rotors solve retreating blade stall?
Supercritical airfoils are designed to operate at far higher speeds than conventional airfoils (thus can produce more lift), have a high maximum lift and docile stall behavior, and generally stall at ...
- 8,301
1
vote
Delta wing RC aircraft unstable
The center of gravity is too far back.
What angle do the elevons have when trimmed? Do their trailing edges point up or down? I guess they point down ... let us know more by adding to your question!
- 228k
1
vote
Delta wing RC aircraft unstable
pitch happy and tends to somersault when at high speed
The old saw is to move the weight, but the most time honored approach is to glide it unpowered first. Make weight adjustments here.
This helps ...
- 18.7k
1
vote
Wing incidence angle of tandem wing aircraft
I am less concerned about your wings than your lack of lateral stability. You can achieve lateral control by means of differential thrust, but not lateral stability. Please add a fin or winglets at ...
- 228k
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