As some of you have seen, I've recently purchased a -3 with Edo 2870 floats.

Does anyone know how hard it would be to get an STC for an increase in Max. Gross Weight? The -3 I bought has a useful load of 720 lbs. With the 2870's being 80 lbs (give or take) heavier than the 2425's that the -3's are normally put on, you would think that it could be easily justified to add this weight difference to the useful load.

I'm not an airplane expert but it seems to me that if the floats are rated for 2800 lbs, this would not be difficult to justify. I would not be asking the aircraft frame to carry any more than if it was on 2425's.

Any comments?

garth

Never happen on the south side of the border. You would have to spend a million dollars on flight testing etc. As you probably already know, the -3 goes from 2400 on wheels to 2500 on floats, and that's the top legal load limit. Maybe Canada has different rules, but never heard of any STC 337 etc on a Stinson to upgross beyond TC weights. Honestly Garth, you got a heck of a plane there, and it will haul whatever you need to haul. Stinson's are built like a brick Sh!thouse. Put in what you need to and go, that machine ain't gonna even begin to break a sweat at 2500 pounds. I know people who knew people that would leave the water at 3000. My -3 with the 220 Franklin just didn't care what you put in it, no wind, humid, hot, just didn't seem to matter. And I'll just leave it at that.

Per the TCDS a -3 on floats goes from 2400 to 2500lbs GW, so you get an extra 100lbs right there. Correspondingly, your VNE (normal) is reduced by 18mph, but I doubt that will affect you much. I've not heard of any upgross beyond that - you can always sign up on the Yahoo Stinson group and search the archives there.

TCDS here...
http://rgl.faa.gov/Regulatory_and_Guida ... /A-767.pdf

Rhyppa wrote:Never happen on the south side of the border. You would have to spend a million dollars on flight testing etc. As you probably already know, the -3 goes from 2400 on wheels to 2500 on floats, and that's the top legal load limit. Maybe Canada has different rules, but never heard of any STC 337 etc on a Stinson to upgross beyond TC weights. Honestly Garth, you got a heck of a plane there, and it will haul whatever you need to haul. Stinson's are built like a brick Sh!thouse. Put in what you need to and go, that machine ain't gonna even begin to break a sweat at 2500 pounds. I know people who knew people that would leave the water at 3000. My -3 with the 220 Franklin just didn't care what you put in it, no wind, humid, hot, just didn't seem to matter. And I'll just leave it at that.

Your right Russ - I guess I'm a little to focused on this. In any event - I'm pumped about flying it.

Garth, one other thing, two actually. First, go out and fly it and get the feel of things for awhile before you start going heavy. While I can honestly say my Stinson really didn't take any special technique to get off the water or fly heavy, it was a little different. Carry speed coming to land. Stinsons fall like a brick when the power is off. I never ran out of elevator, but your 470 has at least 80 pounds more out on the nose, so some airspeed for the flare could be important. Second, looked like you have hatches on those 2870s. Use em. put as much heavy stuff as you can in there. Learn to pack slimer bags to fit down in those narrow hatches. cases of beer, pop, heavy fishing gear, etc. Those soft side tall narrow coolers fit great. You might have to but the cooler in there first empty, then load it once its in. Since the Stinson only has a trim tab on the elevator, versus a trimable horizontal stab like a 180 or SC, you will find with heavy aft loads it will slow down quite a bit in cruise. Basically dragging the tail. Again, nothing scary about the flight characteristics when this happens, but trying not to get aft loaded helps in any floatplane, except maybe on amphibs. You'll find this plane to be one of the most user friendly out there, and it will make you look like a pro on landings and takeoffs. I'd own another Stinson in a heartbeat. Enjoy!

Not that I've ever tried in my stinson-3 but ....They will pull 2800 lbs off the water w/o breaking a sweat w/ that 470 . Mine w/ the 165 pulls 2400 pretty easy for the small engine on wheels. It just looses a lot of climb, no problem w/ the 470.

Mike

Rhyppa wrote:..... you will find with heavy aft loads it will slow down quite a bit in cruise. Basically dragging the tail.........

Not considering the aft loading on floats issues, I've always heard that aft loading generally makes an airplane faster in cruise flight. Most airplane tails have download on them in cruise flight, aft loading would make the tail heavier (duh!) thus reducing the need for as much down-loading by the elevator, making things cleaner aerodynamically resulting in higher speed. I do also hear that aft loading, while faster, also make the airplane squirrellier-- it will hunt around yaw-wise.

Eric

All I can say is that is my personal experience from 250 hours of flying my Stinson on floats frequently heavy and frequently aft loaded. You can see the pitch change looking out the window and the airspeed will drop close to 10mph.

Rhyppa wrote:All I can say is that is my personal experience from 250 hours of flying my Stinson on floats frequently heavy and frequently aft loaded. You can see the pitch change looking out the window and the airspeed will drop close to 10mph.

Russ,

The float hatches look like they's take a lot in there (like a few stringers of Walleye) so I think your right - I'll have to do some experimenting and see how it performs.

garth

Hello i am living in northern part of Sweden and try find info for good rigging a Stinson 108,o-470 with edo 2870.Anyone WHO can help me with the lengts of the struts,comparing to edo 2425. All info is very welcome !
Hkpjulle

Hkpjulle,

Do you have 2425's for you plane now?

Brian

hotrod180 wrote:

Rhyppa wrote:..... you will find with heavy aft loads it will slow down quite a bit in cruise. Basically dragging the tail.........

Not considering the aft loading on floats issues, I've always heard that aft loading generally makes an airplane faster in cruise flight. Most airplane tails have download on them in cruise flight, aft loading would make the tail heavier (duh!) thus reducing the need for as much down-loading by the elevator, making things cleaner aerodynamically resulting in higher speed. I do also hear that aft loading, while faster, also make the airplane squirrellier-- it will hunt around yaw-wise.

Eric

Ummm, he's talking about aft LOADING, not just loading.

MTV

gear wrote:As some of you have seen, I've recently purchased a -3 with Edo 2870 floats.

Does anyone know how hard it would be to get an STC for an increase in Max. Gross Weight? The -3 I bought has a useful load of 720 lbs. With the 2870's being 80 lbs (give or take) heavier than the 2425's that the -3's are normally put on, you would think that it could be easily justified to add this weight difference to the useful load.

I'm not an airplane expert but it seems to me that if the floats are rated for 2800 lbs, this would not be difficult to justify. I would not be asking the aircraft frame to carry any more than if it was on 2425's.

Any comments?

garth

Garth,

As often as not, max gross weight is dictated by performance, as opposed to structural strength. So, climb rate, stall speed, engine cooling at max temps, and all sorts of other performance criteria may in fact dictate max gross weight.

But, also, the limits can be dictated by many different structural issues. Things like wing struts, strut attach points, gear attach points, etc. Bear in mind that on floats there is NO cushioning of the airframe by the landing gear, as there is on wheels.

Anyway, the useful load you noted is pretty decent in any case. If you do choose to operate it heavier, go there VERY gently and with great caution. And, watch the Center of Gravity. Keeping that within the approved range is essential when operating "a little heavy".

MTV

Hello,still no floats it is easier to find 2870 vs 2425 or 2440.but my exp from Beavers C185 and also Single Otter is that big floats are Ok except payload on the paper.Of coarse with right rigging.
Hkpjulle

hotrod180 wrote:

Rhyppa wrote:..... you will find with heavy aft loads it will slow down quite a bit in cruise. Basically dragging the tail.........

Not considering the aft loading on floats issues, I've always heard that aft loading generally makes an airplane faster in cruise flight. Most airplane tails have download on them in cruise flight, aft loading would make the tail heavier (duh!) thus reducing the need for as much down-loading by the elevator, making things cleaner aerodynamically resulting in higher speed. I do also hear that aft loading, while faster, also make the airplane squirrellier-- it will hunt around yaw-wise.

Eric

Generally speaking, that's certainly true. Even in a 4 place airplane with a relatively short CG envelope, running close to the aft CG limits will make the airplane a tiny bit faster, regardless of whether the trim is by adjusting the tail or with a trim tab. Certainly, the pitch forces will be lighter, also. That's why when I was instructing, I always made sure that my students had the opportunity to fly the airplane both at gross and with an aft CG, since the handling compared to our usual training scenarios with just me and the student in it, both lighter and with a forward CG, was significantly different. 6 place airplanes are even more dramatically affected by CG placement.

Why the Stinson would slow down with an aft CG, I haven't any idea, other than this: It would be normal for it (or any airplane) to slow down as it is more heavily loaded, because it takes a steeper angle of attack to compensate for the heavier loading. So if the comparison is lightly loaded and forward CG vs heavily loaded and aft CG, the airplane would slow down. But if the comparison is just a change in the CG without a change in the load, the aft CG should result in a small speed gain.

Cary

In steady-state flight (including climbs and descents, so long as they're unaccelerated), lift equals weight. More weight requires more lift. A byproduct of lift production is induced drag. Make more lift and you'll make more induced drag.

Most horizontal tails provide down force to counter the wing's pitching moment. That down force has the same result as adding weight to the plane, as well as a small amount of the horizontal tail's own induced drag. The further aft your CG is, the less down force is required, reducing the amount of lift the wing is required to produce and reducing the drag.

CamTom12 wrote:In steady-state flight (including climbs and descents, so long as they're unaccelerated), lift equals weight. More weight requires more lift. A byproduct of lift production is induced drag. Make more lift and you'll make more induced drag.

Most horizontal tails provide down force to counter the wing's pitching moment. That down force has the same result as adding weight to the plane, as well as a small amount of the horizontal tail's own induced drag. The further aft your CG is, the less down force is required, reducing the amount of lift the wing is required to produce and reducing the drag.

Correct, but this is all assuming, as Cary noted, that you're operating at the same All Up Weight. Increase the weight, and that will increase the angle of attack of the wing, to create more lift, which creates more drag......etc.

But, assuming the same AUW, an aft CG will increase speed at least some compared to a forward CG.

MTV

mtv wrote:

CamTom12 wrote:In steady-state flight (including climbs and descents, so long as they're unaccelerated), lift equals weight. More weight requires more lift. A byproduct of lift production is induced drag. Make more lift and you'll make more induced drag.

Most horizontal tails provide down force to counter the wing's pitching moment. That down force has the same result as adding weight to the plane, as well as a small amount of the horizontal tail's own induced drag. The further aft your CG is, the less down force is required, reducing the amount of lift the wing is required to produce and reducing the drag.

Correct, but this is all assuming, as Cary noted, that you're operating at the same All Up Weight. Increase the weight, and that will increase the angle of attack of the wing, to create more lift, which creates more drag......etc.

But, assuming the same AUW, an aft CG will increase speed at least some compared to a forward CG.

MTV

We're saying saying the exact same thing. Just different words

CamTom12 wrote:

mtv wrote:

CamTom12 wrote:In steady-state flight (including climbs and descents, so long as they're unaccelerated), lift equals weight. More weight requires more lift. A byproduct of lift production is induced drag. Make more lift and you'll make more induced drag.

Most horizontal tails provide down force to counter the wing's pitching moment. That down force has the same result as adding weight to the plane, as well as a small amount of the horizontal tail's own induced drag. The further aft your CG is, the less down force is required, reducing the amount of lift the wing is required to produce and reducing the drag.

Correct, but this is all assuming, as Cary noted, that you're operating at the same All Up Weight. Increase the weight, and that will increase the angle of attack of the wing, to create more lift, which creates more drag......etc.

But, assuming the same AUW, an aft CG will increase speed at least some compared to a forward CG.

MTV

We're saying saying the exact same thing. Just different words

Yes, indeed. But, sometimes it's easy to be mistaken....

MTV

mtv wrote:
Yes, indeed. But, sometimes it's easy to be mistaken....

MTV

True. I've been called a lot of things, but an excellent communicator isn't one of them! hahaha