Not mass balanced & cable failure
Not mass balanced & cable failure
(OP)
I found that many certified LSA aircrafts and some standard FAR 23 certified don't have mass-balanced surfaces. I'm interested in how they are designed to show freedom from flutter, especially control surface flutter and if these aircrafts can handle a disconnected freefloating surface emergency (due to cable failure, for example).
If they are not prone to develop flutter in normal operation, how things may change if, for example, the aileron cable fails?
If they are not prone to develop flutter in normal operation, how things may change if, for example, the aileron cable fails?





RE: Not mass balanced & cable failure
As for FAR 23 types, can you offer an example? I can't think of one without mass-balanced ailerons/stab/rudder right now. I admit that I've only flown 172's and DA-20's, and my work on FAR 23 types includes only a handful of twin-engine models.
I remember getting into a "advanced ultralight" (Canadian equivalent to LSA) and accompanying the pilot on the walk-around. THAT was an eye-opener on what is and is not important when you can't fly faster than 80 miles per hour.
STF
RE: Not mass balanced & cable failure
However, the question is, how things change in a cable failure in these aircrafts? Even if it's a very rare occurence, from time to time cables may fail. I'm wondering especially about an aileron cable failure, when the aileron is disconnected and freefloating, how prone is to flutter? Is this scenario, is it at risk to (violently) flutter?
As about FAR 23 aircraft, for example, American Champion series (Scout, Citabria..) have no mass-balanced surfaces, especially ailerons.
Also, about the "advanced ultralight" (Canadian equivalent to LSA), one of the airplane I use to fly was designed and certified on these standards and I can say that the speed limit is not that low as you said 80 mph. The cruise speed is 110 mph and the max cruise speed, Vno, is about 120 mph and in other LSAs it may be even a bit higher.
RE: Not mass balanced & cable failure
The ultralights I was in simply could not go any faster. It was physically not possible with a 80 hp engine. It wasn't rules limiting the speed, it was Thrust/Drag ratio. Diving didn't help much.
In your research, have you figured out if the LSA's on the market tend to be just "book limited" to 120 knots, or similarly limited by power and drag, so they can't go faster even if you try?
STF
RE: Not mass balanced & cable failure
RE: Not mass balanced & cable failure
NOTE. a large-enough overhang with heavy mass [forward] might be a sneaky way to add booth aero and mass balance.
My Dad built a Thorp T-18 as I was growing-up. One thing I never understood was why the stabilator and ailerons required heavy lead masses for balance, but the rudder had NO added mass for balance. I finally asked the designer John Thorp. He smiled and said it was aero and mass balanced: look at the design! I reviewed the drawings and finally realized the surface aft of the hinge line was all made from O-too-thin-0.016 skins, ribs and bent stiffener-angles. The spar, nose-ribs and the forward [nose] skins were all made from thick [0.062?] sheet metal and protruded quite-a-bit ahead of the hinge-line. This design not only provided a rigid/strong rudder: it was elegantly balanced “by cleaver design”.
Regards, Wil Taylor
Trust - But Verify!
We believe to be true what we prefer to be true.
For those who believe, no proof is required; for those who cannot believe, no proof is possible.
RE: Not mass balanced & cable failure
There was an incident with the Glasflugel Libelle sailplane, where after a pilot took off and landed again quite quickly with one aileron disconnected,( he experienced the wing flapping up and down with gust loads while the aileron was free floating), the manufacturer later issued a service bulletin calling for the surfaces to be balanced with lead strips along the leading edge of the control so that if somebody else did it, it would be a little safer. I also owned and flew a Dutch built sailplane that flew for close to 15 years with no problems with a redline of 146kts with unbalanced ailerons ,however the Dutch government issued a service bulletin requiring Mass balance weights be added, following an incident with one machine in 1985.
B.E.
RE: Not mass balanced & cable failure
Well, it got fluter, right? Thanks God it was not fatal.
RE: Not mass balanced & cable failure
B.E.