LSA, MTOW, VS0, Floats

[saintlfd]

There has been a lot of discussion on this forum regarding flying 'over gross' in LSA's (as well as other aircraft). I understand the points made regarding being safe, being legal, questioning the apparent arbitrariness of the 1320-lb limit, etc. The point that always makes me think twice is the effect on stall speed of extra weight. So it surprises me that so many pilots seem to have no hesitation to fly over gross.

Then I thought about all the LSA's that can be put on floats--with the blessing of the manufacturer (CTLS, Allegro, Kitfox, Highlander to name a few)--and instantly move up to a 1430-lb limit. I guess this proves the point, made by some forum members, that many of the airframes can support the extra weight.

Since I have never seen the general specs nor the POH for a float-LSA, can someone tell me what the 40-ish knot stall speed goes to when you add 110 high-drag pounds?

Thanks.
D

[3Dreaming]

For the CTLS the clean stall speed with -6 flaps is 44kts. On floats the FAA don't allow for an increase in stall speed, so it doesn't have room to go up much. I do know that the floats also add some lift.

[rab23us]

There has been a lot of discussion on this forum regarding flying 'over gross' in LSA's (as well as other aircraft). I understand the points made regarding being safe, being legal, questioning the apparent arbitrariness of the 1320-lb limit, etc. The point that always makes me think twice is the effect on stall speed of extra weight. So it surprises me that so many pilots seem to have no hesitation to fly over gross.

Then I thought about all the LSA's that can be put on floats--with the blessing of the manufacturer (CTLS, Allegro, Kitfox, Highlander to name a few)--and instantly move up to a 1430-lb limit. I guess this proves the point, made by some forum members, that many of the airframes can support the extra weight.

Since I have never seen the general specs nor the POH for a float-LSA, can someone tell me what the 40-ish knot stall speed goes to when you add 110 high-drag pounds?

Thanks.
D

After doing a lot of reading you are posting in the same vain I have been thinking the last couple of days. Especially on the 1320 pound MTOW. Going through a lot of threads here and reading on sportpilot.org and some plane owner sights I couldn't find any rhyme or reason behind the 1320 or the 1430 for amphibious craft.

I was reading the jabiru sight for Australia and I see that the plane we call j230 is a two or four place plane there and the MTOW definitely exceeds the 1320. Can one of the more knowledgable members give a reason behind the 1320 how it came to be.

Again looking at many of these planes in Europe they have higher gross expanding useable and still flying within speed specs here. Heck I read the entire thread on the sling go lsa it's limit 1320 but go EAB same frame but now it's over 1500 pounds.

Reading about choosing the right plane for the mission the one mission that a lot of people seem to want to accomplish is a good true long cross country flight. The one thing that seems to be the lacking part is either fuel or baggage weight when planning said flight sometimes it appears that if the FAA would extend the limit it would open up some these aircraft back to some of their outside the United States specs.

Not looking for MTOW of 2000 plus pounds but something that seems to be closer to. The planes actual specs sometimes. Great discussion all. I do enjoy the reading.

[zaitcev]

The answer is that the stall speed goes up by 7% or so. If the airplane is designed so that its stall speed bumps right against the legal limit of 45 knots, then it's impossible to add floats and keep it legal. But most LSAs have a margin. CTLS has VSo of only 39 knots, so adding floats is trivial.

[jnmeade]

The answer is that the stall speed goes up by 7% or so. If the airplane is designed so that its stall speed bumps right against the legal limit of 45 knots, then it's impossible to add floats and keep it legal. But most LSAs have a margin. CTLS has VSo of only 39 knots, so adding floats is trivial.

I think the stall speed must be with flaps retracted, which means -6°, in which case the stall speed is 45 kias.

[jnmeade]

The answer is that the stall speed goes up by 7% or so. If the airplane is designed so that its stall speed bumps right against the legal limit of 45 knots, then it's impossible to add floats and keep it legal. But most LSAs have a margin. CTLS has VSo of only 39 knots, so adding floats is trivial.

I think the stall speed must be with flaps retracted, which means -6°, in which case the stall speed is 45 kias.

[rab23us]

The answer is that the stall speed goes up by 7% or so. If the airplane is designed so that its stall speed bumps right against the legal limit of 45 knots, then it's impossible to add floats and keep it legal. But most LSAs have a margin. CTLS has VSo of only 39 knots, so adding floats is trivial.

Ok that I can understand a little so the weight limit has to do with stall speed, because one of the things that always made me wonder wasn't even float issue but, and I will use the jabiru j230 and j430 they are the same plane except one has 4 seats 430, and the 230.has them removed both run the 3300 120 hp engine but the two extra seats gives the same plane an extra 220 pounds or so on the MTOW specs appear to be similar in most respects.

Thanks for the answer.

[drseti]

Ron, the relationship is actually pretty simple. Stall speed varies with the square root of load factor. So, for example, if the stall speed at max gross (1320#, let's say) is 45 Knots, then if you were to double the weight to a ridiculous 2640#, that would represent a load factor of 2, or an increase in stall speed by a factor of the square root of 2, which is 1.41. Now 45 knots times 1.41 is 58 knots, which it so happens is pretty typical of GA aircraft weighing 2640 pounds!

Now, for a more realistic example, let's say you load up a 1320# LSA to 1510# (yes, I've seen people on this forum advocating flying 190 pounds over gross, on the basis that "the airframe can take it"). This represents a 14.5% weight increase, or a load factor of 1.145. The square root of 1.145 is 1.07, which means your stall speed goes up 7%, from 45 to 48 knots. No, that's not a huge difference, but it is a difference.

Where you really get in trouble with this is in steep, level turns. Crank that plane into a 60 degree bank. That in itself is a load factor of 2. So, stall speed goes up an additional 41% (remember, the square root of 2 is 1.41), to 69 knots. If you were even that little bit over gross, and were flying at 70 knots when you entered that steep turn, you just deprived yourself of all your safety margin.

[Jack Tyler]

...and lest we forget, one of the main causes of FATAL a/c accidents is loss of control while maneuvering. When we fly from Point A to B, we often only do maneuvering at one point in the flight: flying the pattern to land, when we are close to the ground. I personally don't think it's a big 'airframe issue' to overgross some of these LSAs - especially the ones that were built and certified at higher MTOW like the P1 and Jabiru 230. But what seems genuinely dangerous is to knowingly increase the stall speed when it is relevant to what we know is one of the biggest risk factors.

[jnmeade]

Where you really get in trouble with this is in steep, level turns. Crank that plane into a 60 degree bank. That in itself is a load factor of 2. So, stall speed goes up an additional 41% (remember, the square root of 2 is 1.41), to 69 knots. If you were even that little bit over gross, and were flying at 70 knots when you entered that steep turn, you just deprived yourself of all your safety margin.

Paul,

When is the last time you or anyone you knew flew an LSA at a 60° level bank at 70 kias? You know full well that most people start turning green when the bank exceeds 30° and very few are eager to look out the door of an LSA in a 45° bank. What was the power setting in the last 60° bank you performed? WOT, I bet, because you aren't going to hold level without it and a huge amount of up rudder.

The FAA says don't exceed 60°. I'm saying we routinely don't even get close. My point is that your example is unrealistic and that the 60° number only comes out of an FAA edict, not because of anything you ever intended to do. Your example verges on scare tactics.

[jnmeade]

...and lest we forget, one of the main causes of FATAL a/c accidents is loss of control while maneuvering.

What are we doing in the loss of control while maneuvering? The public consensus is we are in a cross controlled configuration because we have a tail wind on base and are blowing through final so we are afraid of the steep turn (hey, Paul, where is your 60° bank) so after about 30°, which is the max the FAA suggests in a pattern and even when we go to 45° (oh, horror!), we push the rudder over to skid the plane around and voile, the world ends.
The stall speed increase that Paul is worried about is in the load factor found in level flight and in the pattern we are in a descending turn, so the stall speed isn't raised nearly as much because we don't have the angle of attack up to generate the lift or load factor.
The situation is that, of course, if you are 10 or 20 or even more pounds overweight and nothing happens, nothing happens. But if you are 10 pounds overweight and you have an accident, it will be held against you by the FAA and the widow of the dead passenger (he said he'd never sue you but forgot to tell you that his widow would!) will take your farm. And, if there is any doubt, Paul, or an attorney who sounds even worse, will testify that you must have exceeded 60° degrees and the poor airplane just couldn't stay in the air.
So, when it comes to flying overweight, like the old Indian said, what you see depends on where you stand. The thing is, those who judge you will almost certainly be standing somewhere other than where you are.

[drseti]

My point is that your example is unrealistic and that the 60° number only comes out of an FAA edict, not because of anything you ever intended to do. Your example verges on scare tactics.

Jim, I know we've had this discussion before. For the benefit of those who may not have read those other threads, I have to respond.

First off, my concern is not at all hypothetical. It stems from over two dozen actual fatal stall-spin accidents I've studied over a period of 35 years. Some I researched in grad school, two I was involved with as an expert witness (yes, you're right, there are always lawyers involved), for two I wrote amicus briefs, one (sadly) involved a former student and her whole family, and one (even more sadly) I witnessed in person. So, I've studied not just NTSB briefs, but entire fat folders of NTSB files.

Yes, the scenario I describe is unrealistic. That doesn't mean pilots don't do unrealistic things, and all too frequently. In the case of all the accidents I researched, the planes were over gross. In all cases, the stall-spin happened only after some other factor contributed to pilot distraction. In other words, something else had gone wrong, and the situation spiraled out of control. Can we say that loading over gross caused the accident? Of course not. Can we say that being lighter would have prevented it? Again, of course not. All we can say is that these accident scenarios do happen, and are nearly always fatal.

Is it being an alarmist for me to want pilots to know that these things do occasionally happen, and why? I don't think so.

[CharlieTango]

I'm with Jim Meade on this.

Paul, look at your argument, you construct one that admits the probable stall speed increase is minimal and even at 1,500lbs its 3 kts clean.

Then the scare tactics where you argue that the real danger is in 60 degree banks, level. I recently demonstrated 60 degrees level and saw 1.9 on my g meter but I didn't do it close to the ground. My CT is great for steep banks even in the pattern but if I do that I am descending trimmed fro an approach speed and with no back pressure.

You re-but admitting that your 60 degree scenario is unrealistic.

To summarize I hear you saying
1) Stall speed increases a marginal amount, but it is an increase.
2) You really get into trouble in steep level turns
3) The steep level turn scenario is not realistic
4) I have studied stall/spin incidents so I know!


You have to resort to weak argument because your premise is unsupportable. If you want to have real impact your target should be training. Bring back spin recovery!

Simulating that base to final stall/spin entry at altitude is an eye opener and can provide real protection, by learning to avoid.

[KSCessnaDriver]

You have to resort to weak argument because your premise is unsupportable. If you want to have real impact your target should be training. Bring back spin recovery!

Simulating that base to final stall/spin entry at altitude is an eye opener and can provide real protection, by learning to avoid.

Yes, bring back training which will kill more people in training than in saves in practice. Sounds like sound logic to me.

[dstclair]

Assuming the airframe can handle the increased load (over MTOW) and ignoring SP regs, I can't see that a known 3kt increase in stall speed increases risk. As I said earlier, this would be the same as stating their is high risk due to increased stall speed if my normative flight is 180 lbs under gross and now I'm flying at 1320lbs.