Flight Design "Safety Box" & possible LSA Implications

Talk about airplanes! At last count, there are 39 (and growing) FAA certificated S-LSA (special light sport aircraft). These are factory-built ready to fly airplanes. If you can't afford a factory-built LSA, consider buying an E-LSA kit (experimental LSA - up to 99% complete).

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drseti
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Re: Flight Design "Safety Box" & possible LSA Implications

Post by drseti »

Andy, you're absolutely right that fatality rates go up logarithmically with speed. That's because of the (v^2) in the kinetic energy equation. And, you are entirely correct in saying that the 45 KCAS stall speed limit is what keeps LSAs relatively safe. What some might be missing here is that the stall speed figure is related to weight. Remember, when you overload an aircraft beyond maximum gross weight, the stall speed increases above that specified 45 knots (stall speed varies as the square root of load factor). So, yes, stall speed matters more than weight - except that stall speed is a function of weight.
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Re: Flight Design "Safety Box" & possible LSA Implications

Post by designrs »

Re: Andy's Post Above

Questions for the Physics professor... Impact forces of:
1) 1320# aircraft at 45kts (clean stall)
2) 1320# aircraft at 35kts (average LSA dirty stall)
3) 1750# aircraft at 45kts (RV 9-A approximate clean stall)
4) 2300# aircraft at 45kts (Cessna 172M dirty stall)
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Re: Flight Design "Safety Box" & possible LSA Implications

Post by MrMorden »

drseti wrote:Andy, you're absolutely right that fatality rates go up logarithmically with speed. That's because of the (v^2) in the kinetic energy equation. And, you are entirely correct in saying that the 45 KCAS stall speed limit is what keeps LSAs relatively safe. What some might be missing here is that the stall speed figure is related to weight. Remember, when you overload an aircraft beyond maximum gross weight, the stall speed increases above that specified 45 knots (stall speed varies as the square root of load factor). So, yes, stall speed matters more than weight - except that stall speed is a function of weight.
Absolutely true for loading a 45kt stall airplane beyond its normal gross weight. But for new designs, there is nothing to keep you from designing a 2000lb gross airplane that stalls at 45kt; you just need more wing area and/or a higher lift airfoil to support the additional weight. My point is that if the stall speed limitation was retained and the gross weight restriction removed, I don't think that safety would be compromised, even though much heavier airplanes would result.
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Re: Flight Design "Safety Box" & possible LSA Implications

Post by MrMorden »

designrs wrote:Re: Andy's Post Above

Questions for the Physics professor... Impact forces of:
1) 1320# aircraft at 45kts (clean stall)
2) 1320# aircraft at 35kts (average LSA dirty stall)
3) 1750# aircraft at 45kts (RV 9-A approximate clean stall)
4) 2300# aircraft at 45kts (Cessna 172M dirty stall)
Impact energy is simple mass times velocity squared. But the *effects* of those impacts on humans might be harder to gauge, because you have to take into account the rigidity/deformability of the aircraft structure, seat design, safety features like seat belts and airbags...there is a lot going on in a collision. When I was a police officer I worked a lot of accidents, and it's not easily predictable what will happen. Relatively mild impacts are sometimes fatal, and extremely violent impacts sometimes leave people unscathed.
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Re: Flight Design "Safety Box" & possible LSA Implications

Post by Jack Tyler »

"My point is that if the stall speed limitation was retained and the gross weight restriction removed..."

Well...would you settle for 'increased', Andy? Don't want to give designers too much rope to hang us with. <s>

Here's a Q worth mulling a bit, given this discussion: Which LSA a/c now being actively marketed can do what Andy suggests, i.e. have their MTOW increased by some reasonable factor (let's say 100#) while retaining a 45 kt or less 'clean' stall speed. Take that subgroup of LSA a/c and you might find some of them are rated for a higher MTOW in the EU or down in Oz. Those might be LSA a/c candidates for heavier SPL pilots or those needing to carry large loads who also want to maintain the kinetic energy-related safety we've been discussing. Alas, such a choice would not be in compliance...
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Re: Flight Design "Safety Box" & possible LSA Implications

Post by MrMorden »

Jack Tyler wrote:"My point is that if the stall speed limitation was retained and the gross weight restriction removed..."

Well...would you settle for 'increased', Andy? Don't want to give designers too much rope to hang us with. <s>

Here's a Q worth mulling a bit, given this discussion: Which LSA a/c now being actively marketed can do what Andy suggests, i.e. have their MTOW increased by some reasonable factor (let's say 100#) while retaining a 45 kt or less 'clean' stall speed. Take that subgroup of LSA a/c and you might find some of them are rated for a higher MTOW in the EU or down in Oz. Those might be LSA a/c candidates for heavier SPL pilots or those needing to carry large loads who also want to maintain the kinetic energy-related safety we've been discussing. Alas, such a choice would not be in compliance...
Well, the FAA doesn't listen much to my ideas anyway, so it's moot! :)

But yes, increased would be nicer than where it is now. And I guess it *would* be funny to see an AN-2 sized airplane with 90ft wingspan, two seats and 6000lb of baggage capacity as an "LSA"... ;) Presenting the New Antonov LSA-2:

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Re: Flight Design "Safety Box" & possible LSA Implications

Post by designrs »

Placard it a bit to ensure compliance in critical performance areas and it should clear any LSA criteria scrutiny! :lol:
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Re: Flight Design "Safety Box" & possible LSA Implications

Post by Merlinspop »

Jack Tyler wrote:"My point is that if the stall speed limitation was retained and the gross weight restriction removed..."

Well...would you settle for 'increased', Andy? Don't want to give designers too much rope to hang us with. <s>

Here's a Q worth mulling a bit, given this discussion: Which LSA a/c now being actively marketed can do what Andy suggests, i.e. have their MTOW increased by some reasonable factor (let's say 100#) while retaining a 45 kt or less 'clean' stall speed. Take that subgroup of LSA a/c and you might find some of them are rated for a higher MTOW in the EU or down in Oz. Those might be LSA a/c candidates for heavier SPL pilots or those needing to carry large loads who also want to maintain the kinetic energy-related safety we've been discussing. Alas, such a choice would not be in compliance...
The CarbonCub SS is an example. At the LSA weight of 1320 it stalls at a ridiculously low IAS (granted that at such an AOA the instrument error is probably significant). In it's identical kit form, it can be registered as an E-AB up to 1,865 and still stall at a very low speed, although I haven't seen published numbers at that weight. At that weight, stall might be over 45kts, but even at 1500 - 1600#, I'd be shocked if it wasn't below 45kts and you'd actually be able to get a modicum of utility out of it.
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Re: Flight Design "Safety Box" & possible LSA Implications

Post by drseti »

designrs wrote:Questions for the Physics professor... Impact forces of:
I'll run those numbers for you later, Richard (after my students are done for the day).
The opinions posted are those of one CFI, and do not necessarily represent the FAA or its lawyers.
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Re: Flight Design "Safety Box" & possible LSA Implications

Post by snaproll »

IFlyRC wrote:I came across this article and I thought I'd share. (http://www.aviationpros.com/press_relea ... evelopment)

It sounds like they're making the technology available to anyone. Maybe we'll see some LSAs with a "safety box" in the near future.

EDIT: Sorry this might've been better in the safety section.
Getting back to the original subject, is Flight Design duplicating or improving on the Remos high strength kevlar-reinforced passenger cage design? Good idea to remain intact and protect the pilot/passenger.
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Re: Flight Design "Safety Box" & possible LSA Implications

Post by CTLSi »

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Last edited by CTLSi on Sun Nov 30, 2014 12:13 pm, edited 1 time in total.
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Re: Flight Design "Safety Box" & possible LSA Implications

Post by 3Dreaming »

snaproll wrote:
IFlyRC wrote:I came across this article and I thought I'd share. (http://www.aviationpros.com/press_relea ... evelopment)

It sounds like they're making the technology available to anyone. Maybe we'll see some LSAs with a "safety box" in the near future.

EDIT: Sorry this might've been better in the safety section.
Getting back to the original subject, is Flight Design duplicating or improving on the Remos high strength kevlar-reinforced passenger cage design? Good idea to remain intact and protect the pilot/passenger.
I'm not sure when they started, but Flight Design has been using a Kevlar interior lay up for quite some time. That is what holds the Egg together in a mishap. The safety box is additional design improvements over what they were already doing.
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Re: Flight Design "Safety Box" & possible LSA Implications

Post by snaproll »

3Dreaming wrote:
snaproll wrote:
IFlyRC wrote:I came across this article and I thought I'd share. (http://www.aviationpros.com/press_relea ... evelopment)

It sounds like they're making the technology available to anyone. Maybe we'll see some LSAs with a "safety box" in the near future.

EDIT: Sorry this might've been better in the safety section.
Getting back to the original subject, is Flight Design duplicating or improving on the Remos high strength kevlar-reinforced passenger cage design? Good idea to remain intact and protect the pilot/passenger.
I'm not sure when they started, but Flight Design has been using a Kevlar interior lay up for quite some time. That is what holds the Egg together in a mishap. The safety box is additional design improvements over what they were already doing.
Did some checking and you are right. Remos and Flight Design actually did their prototypes the same year, both used the Kevlar reinforcement, and flew first flights the same year.. Guess great minds think alike.... Will be interesting to see the new improved safety box.
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Re: Flight Design "Safety Box" & possible LSA Implications

Post by zaitcev »

I saw the pictures of the second fatal of Remos, and it didn't look pretty. The airplane came apart like any plastic airplane - engine in front, tail in the back, the pilot rolling on the runway in the middle. The separation of front and back occured at the trailing edge of the wings down. Obviously the restraint system does nothing in such case.

Previously, I saw that happen to Jabiru, when an old lady landed a J-230 on top a hangar at Front Range. When the plane came apart, she fell into the gap between hangars and died there because professional first responders took their sweet time, and nobody else could fetch her. Pretty much what I expected from Australian plastic, honestly.

If CT has the same joke of survival cell that Remos has, then you're better off in a Cub's steel tube cage. Fortunately, CT comes with a chute and you should not test its survival cell unless you're suicidal.
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Re: Flight Design "Safety Box" & possible LSA Implications

Post by MrMorden »

zaitcev wrote: If CT has the same joke of survival cell that Remos has, then you're better off in a Cub's steel tube cage. Fortunately, CT comes with a chute and you should not test its survival cell unless you're suicidal.
The CT has had very good results on the survival of their safety cell. It's not 100% as no aircraft could be, but there are many very impressive crashes where it stays largly intact:

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This last one involved two people, one of whom was killed. But the accident was a high energy nose-on impact into the ground from a probable stall-spin. The structure is still largely intact, and in many other aircraft neither person would have survived:

Image
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