Maximum Maneuvering Speed 1

[mblackwolf]

Hey everyone! I am new here and was wondering if someone could help me out.

I went to school for mechanical and aerospace engineering (dual major) and have been working in the mechanical side for a while. I recently started working in the aerospace side and am working on a aircraft design. I need to find the maximum maneuvering speed of the aircraft to include in the pilot operating handbook to be sent to the FAA for approval. I can't for the life of me remember exactly how to calculate this speed and I can't seem to find my old aerodynamics book that included the formula. Any help in finding the formula would be greatly appreciated or any tips on deriving the formula. Thank guys!

 

[rb1957]

FAR 23 or 25 ?

look into the ACs

start with the FAA website, regulation requirements ...

is this a new airplane or a modification ? if modification, have you changed the Vmo ??

 

[mblackwolf]

Thanks for the info on which FAR it is in. It is a modification tachnically. They had a prototype model and brought me in to revamp the aircraft as they were having trouble with the old version. Turns out the old engineer didnt feel it neccesary to determine the stability of the aircraft. The air testing scale models at this point but they were having crashes due to uncontrollable spins. now that the issues have been resolved with the new model the full sized test plane is being constructed and they have me writing the operating handbook. Thanks again!

 

[mblackwolf]

rb1957 just wanted to say thanks again just took a look through those FARs and found exactly what I need VA = VS*sqrt. I truely appreciate your help I didnt even think that the formula would be in the FARs.

 

[rb1957]

OMG !

are you looking into max operating speed, or minimum manoeuvring speed ? ... minimum manoeuvring speed is determined mostly by lateral stability (spins sounds like this is a problem !?).

this sounds like a home-built project, which is a "simpler" set of requirements. I'd start with something like Dan Raymer's design book to size the fin properly.

you're test flying a model ... are you sure you're scaling the model properly ?

 

[btrueblood]

mblackwolf,

There is a button below rb's posts that reads "Thank rb1957
for this valuable post!"

It's a really good way to pay him back for good advice given. It's the only way to pay back on this site.

 

[mblackwolf]

Okay. The model is scaled properly and I hjave been able to fix all of the stability issues. It was due to mis-sized horizontal and vertical tails. I am currently just writing the POH for it and am trying to calculate the numbers required by the FAA. My new problem is the VNE and VNO which are the never exceed speed and the maximum structural cruise speed. I am not sure how the never excedd speed is calculated or even using a model how you could use flight tests to determine it. Any help on that would be great. The maximum structural cruise speed is based on the speed in sluf (straight,level,unaccelerated flight) where structural damage will not occur. If I am not mistaken this is based on things such as wing flutter and g load on the wings due to drag. However, The aircraft was designed for slow flight and the wings were a little over built. The problem I am having is the maximum speed the motor and prop combination can acheive is less than any speed that could cause structural damage. In this case how do you go about finding VNO. Thanks again!

 

[rb1957]

i think you're using FAA requirements as a guide (ie, do you Really apply ?).

Vd and Vc are designer selected (rather than FAA directed).

With Vd and Vc you can then determine Vne and Vmo (often = Vc).

have a look at FAR23 App A.

 

[mblackwolf]

So Vne and Vno typically equal Vc? Thanks again. I am using it as a guide but it is tricky because I am writing the POH that will be sent to get approval from the FAA. I am using FAR23 as a guide to what information I will need to include as there are no real guidelines for the actual application as it is a UAS. The problem is much of the design info disappeared along with the old engineer who I took over for. Thanks again.

I do have the Vc but from there how do I go about finding the Vne and Vno?

 

[rb1957]

ok, UAS makes crashes a little more acceptable !

Vne is related to flutter (i think) ... ie it's backed off from the onset of aero divergence.

This sounds like it's early days in your project, ie you haven't made it to market yet. I'd set Vne = Vmo = Vc and demonstrate with flight test, and change as suits.

 

[btrueblood]

"Vne is related to flutter (i think)"

Concur with that, but it's been a long while...

 

[rb1957]

this looked relevent ...

Sec. 23.629

Flutter.

[(a) The wings, tail, and control surfaces must be free from flutter, airfoil divergence, and control reversal from lack of rigidity for any condition of operation within the limit V-n envelope, including all speeds up to the lesser of 1.4 VC and 1.2 VD. but not less than VD except as provided in paragraph (b). In addition--
(1) Adequate wing torsional rigidity must be shown by tests or other approved methods:
(2) The mass balance of surfaces must be designed to prevent flutter; and
(3) The natural frequencies of main structural components must be determined by vibration tests or other approved methods.
(b) A smaller margin above VD than that permitted in paragraph (a) of this section may be used if flight flutter tests demonstrate that--
(1) A proper margin of damping exists at VD; and
(2) There is no large and rapid reduction in damping as VD is approached.
(c) Flight flutter tests are acceptable as proof of freedom from flutter if it is shown by these tests that proper and adequate attempts to induce flutter have been made within the speed range up to VD and that the vibratory response of the structure during the test indicates freedom from flutter.
(d) Compliance with the rigidity and mass balance criteria (pages 4-12), in Air Frame and Equipment Engineering Report No. 45 (as corrected) "Simplified Flutter Prevention Criteria" (published by the Federal Aviation Agency) is acceptable as proof of freedom from flutter, if--]
(1) The wing and aileron flutter prevention criteria, as represented by the wing torsional stiffness and aileron balance criteria, are limited to airplanes without large mass concentrations (such as engines, floats, or fuel tanks in outer wing panels) along the wing span; and
(2) The elevator and rudder balance criteria are used only for tail surface configurations that have fixed-fin and fixed-stabilizer surfaces.
[(e) For multiengine turbo-propeller powered airplanes, the dynamic evaluation must include--
(1) The significant elastic, inertia, and aerodynamic forces associated with the rotations and displacements of the plane of the propeller; and
(2) Engine-propeller-nacelle stiffness and damping variations appropriate to the particular configuration.]

 

[rb1957]

and ...
Sec. 23.1505

Airspeed limitations.

(a) The never-exceed speed VNE must be established so that it is--
(1) Not less than 0.9 times the minimum value of VD allowed under Sec. 23.335; and
(2) Not more than the lesser of--
(i) 0.9 VD established under Sec. 23.335; or
(ii) 0.9 times the maximum speed shown under Sec. 23.251.
(b) The maximum structural cruising speed VNO must be established so that it is--
(1) Not less than the minimum value of VC allowed under Sec. 23.335; and
(2) Not more than the lesser of--
(i) VC established under Sec. 23.335; or
(ii) 0.89 VNE established under paragraph (a) of this section.
[(c) Paragraphs (a) and (b) of this section do not apply to turbine airplanes or the airplanes for which a design diving speed VD/MD is established under Sec. 23.335(b)(4). For those airplanes, a maximum operating limit speed (VMO/MMO airspeed or Mach number, whichever is critical at a particular altitude) must be established as a speed that may not be deliberately exceeded in any regime of flight (climb, cruise, or descent) unless a higher speed is authorized for flight test or pilot training operations. VMO/MMO must be established so that it is not greater than the design cruising speed VC/MC and so that it is sufficiently below VD/MD and the maximum speed shown under Sec. 23.251 to make it highly improbable that the latter speeds will be inadvertently exceeded in operations. The speed margin between VMO/MMO and VD/MD or the maximum speed shown under Sec. 23.251 may not be less than the speed margin established between
VC/MC and VD/MD under Sec. 23.335(b), or the speed margin found necessary in the flight tests conducted under Sec. 23.253.]