Flutter can be a problem with any aircraft design and we prefer to predict and modify the critical flutter speed of an aircraft before an incident occurs. We can accurately predict flutter speed with finite element analysis programs and our SUBSONIC AERODYNAMIC FLUTTER,SAF, computer program which run on Windows 95/98/2000/XP.
To learn how to perform flutter analysis, attend one of our flutter classes. See details under Classes
Far left, ADI performs ground vibration testing using a Tek Oscilloscope to validate eigenvalues and mode shapes determined by finite element analysis.
Landing gear drop tests are also performed to determine loads on landing gears. These loads are checked against computer program loads.
A flutter analysis is performed by setting up a very detailed finite element analysis (fea) model of the structure to find the eigenvalues and mode shapes. The control surface weights and control stiffness of the fea model are matched to those of the actual aircraft.
The mode shapes from the fea are input into our Subsonic Aerodynamic Flutter (SAF) program to determine the critical flutter speeds. Balanced control surfaces, altitude and fuel load are some of the parameters that influence flutter speeds. We have made flutter analysis affordable. Be safe and fly safe. We do not want to perform a post crash flutter analysis on your aircraft, like we have on the Wheeler Express, BD-10, and Adventurer. Following is a partial list of aircraft for which Martin Hollmann has performed a flutter analysis on.
Adventurer (post crash)
Lancair 360 with big tail and small tail
Lancair 360 with big wing and small wing
Sadler Vampire (single place all metal)
Killdeer (four place all metal)
Cessna C337 with extended wing tips, STC’d (six places all metal)
Wheeler Express, (post crash)
BD-10 Jet, (post crash)
Rans S-7 Courier, FAA Certified
FAA Flutter Certification can be performed by analysis only. Flight testing is dangerous and not required to meet the flutter criteria of paragraph 23.629 Amdt 23-459a)(2) (b).
This is the animated fuselage bending mode of the original BD10 Jet which crashed. The fuselage bending occurs at a frequency of 27.3 Hz and couples with horizontal tail twisting. The flutter analysis predicted the exact critical flutter speed. ADI increased the critical flutter speed by rigidly fixing the horizontal tail and stiffening the tail and fuselage structures.
On Feb. 21, 2003, BD10 Serial #002 came apart in the air over San Clemente, CA killing the pilot. An acquaintance of the accident pilot claims that no fix was made to the tail since he could move the tail up and down by 3/8 inch. Flutter is most likely the cause of this accident which could have been avoided if the machined rib on the bottom, left had been installed to provide a stiff support for the horizontal stabilizer against the fuselage boom. A number of other BD10's are still flying and the modification is there for their benefit.
A closure machined rib as shown on the left was required to reinforce the horizontal stabilizer to increase the critical flutter speed of the BD10. The Peregrin (BD10) had crashed killing the CEO of the company because of a tail flutter problem. This fix prevented that from happening on the second Peregrin. However, a 1/8 in diameter flap shear pin failed at 35 lbs shear force causing a split flap which killed my good friend Joe Henderson, the second CEO of Peregrin. This pin had been installed by Jim Bede. Below, the BD10 video shows that it is flying again with the modifications made that are necessary to make this a safe and neat aircraft.
This is the finite element model for the Lancair 360 with the large tail. The back of the fuselage required stiffening to increase the critical flutter speed. Some builder have opted not to make this very simple modification.
Design and extensive finite element analysis and structural sizing was performed by ADI on the Lancair series of aircraft. As such, when built and operated to the design specifications and weight limits, they are one of the safest and best kit aircraft on the market today.