WWI Replica Safety

Jim Bruton · 29 March 2009, 03:31 PM

This sounds a lot like the envelope which defines a Short Field Landing. You come in a little over stall speed though, versus the stall mush, and it is like coming down in an elevator. You can be more high on Final than you are used to but sure enough, you eat up more height than distance when you land this way. You can always drop the nose, pick up a little airspeed and extend your glide, which is what you will do anyway before landing in order to have some control speed and enough umph to flare with. Because I have the luxury, I make all of my landings short field landings. Let's face it, especially as regards this particular safety thread, just ask yourself the question, "what landing experience will I definitely need?" Short field landing is the answer- if you can land Short Field, you have a lot on your side.

I'm sure someone will think of a million exceptions, but that's my 2 cents.

Jim

Joe Perkel · 29 March 2009, 03:51 PM

Quote:

Originally Posted by Jim Bruton

Because I have the luxury, I make all of my landings short field landings. Let's face it, especially as regards this particular safety thread, just ask yourself the question, "what landing experience will I definitely need?" Short field landing is the answer- if you can land Short Field, you have a lot on your side.
Jim

Jim,

Even though years away from completion, as a result of the discussions here I have been "mentally" flying this aircraft for a while now. You've hit the nail on the head here, this power off approach angle is foremost on my mind.

I can only imagine just how steep it would be with the floats. Still, there is much documentation as to power off landings during operations and waiting for the ship to come get them.

The comment that you have the "luxury" to make all short filed landings,..what and where do you fly? A private strip perhaps?

There can be no argument against your logic regards this technique as a norm, it is solidly founded.

Ever fly a shuttle simulation?,...it's a lot of fun.

Flysafe · 29 March 2009, 05:05 PM

Read back a few posts and I commented in detail on the GWFM triplane stall characteristics. They are not exactly like this. Our triplanes both will break at the stall.

Our triplanes do not fly noticeably tail low either.

I am not sure I agree with the pitch up with speed increase explanation and to be honest this is normal for most any aircraft. The pitch up is a function of lift not drag. Let me try and resurrect from my memory the explanation. As speed increases, lift increases and creates a moment around the C of G. Given the location of the lift vector on the triplane relative to the C of G (forward) this creates the pitch up effect that must be countered with forward stick. Again this is considered "normal" and in modern GA aircraft is countered with the use of nose-down pitch trim.

j ferguson · 29 March 2009, 05:22 PM

Quote:

Originally Posted by Flysafe

Read back a few posts and I commented in detail on the GWFM triplane stall characteristics. They are not exactly like this. Our triplanes both will break at the stall.

Richard, Do you suppose the mushing was made possible by unusual rigging? That plane was built quite a while ago and they may have happened on this condition through combination of incidence on wings, stabilizer and perhaps limits on the elevator stops.

Somehow, not getting a break on stall seemed attractive, but there must be some other cost for this. It was intentional on the Antonov, though.

Sounds like nothing you flew behaved like this.

best, jf

Jim Bruton · 29 March 2009, 05:40 PM

Rearding the mushing stall Triplane, it would be interesting to confirm it's exact CG location, its angle of incidence and tail weight (put the tailwheel on some scales), and compare that data to the Triplane which doesn't have those exact stall characteristics...

Jim

Jeff Brooks · 29 March 2009, 05:48 PM

the vertical CG has a lot to do with this effect too.

Flysafe · 29 March 2009, 05:50 PM

JF, there are lots of potential reasons for the differences. Rigging is one. It also depends on the stall test methodology. I employed what is considered the accepted test for a stall. If you use another method the results will be different.

There are also a lot of complex relationships between C of G, and the wing/stab incidence. Changes to any of these items requires carful analysis. I have seen insufficient thought applied to a handling/trim problem and the resultant "fix" creating a bigger problem.

A good example was the GWFM N28. The C of G was calculated and found to be towards the aft limit. I test flew it from initial through the first few hours and noted that in-flight characteristics were quite acceptable. We were having lots of problems during taxi, with the tail being far too light and lifting with even slight braking. This was bad enough that we needed to make a change. changing the C of G was problematic and despite incremental weight increases to the tail, the ground handling improvement was minimal.

The whole issue came to a head on a takeoff with a light and variable wind that became a tailwind. On power up I started with the stick full aft, as I released the pressure the tail came up very rapidly. Despite returning to full back stick I was unable to control the tail and the aircraft nosed over and then on to its back. No serious injuries, other than to my provide. Lots of damage. During the rebuild we noted that when lifting the tail that at just a couple of inches above horizontal the aircraft would nose over.

The problem was not C of G, rather it was the static balance point of the aircraft. Without getting into long explanations the best solution was to move the axle aft, by literally reversing the gear. Since then the problems is very minor. The aircraft is slightly light in the tail on the ground and requires that you pay attention, but nowhere near as sporting as it was.

j ferguson · 29 March 2009, 06:00 PM

Quote:

Originally Posted by Flysafe

The problem was not C of G, rather it was the static balance point of the aircraft. Without getting into long explanations the best solution was to move the axle aft, by literally reversing the gear. Since then the problems is very minor. The aircraft is slightly light in the tail on the ground and requires that you pay attention, but nowhere near as sporting as it was.

This really seems counter-intuitive. I would think moving the axle aft would make the tail even lighter.

My C-120 had plates which moved the wheels maybe 4 inches forward from where they would have been if they had been attached directly to the struts. I flew other people's 140s and couldn't tell the difference, but then I may have not known how to test for a difference.

john

Flysafe · 29 March 2009, 06:12 PM

I was just going to edit the post, thanks for noticing the error. You are correct, we reversed the undercarriage and the axle moved about 4-5 inches forward.

Note to self: Don't hit submit when phone rings.....

Machinbird · 29 March 2009, 06:58 PM

The most probable reason for a mush instead of a stall (but not the only reason) is mis-rigging of the elevator. If the elevator stop results in a decrease of elevator up travel by as little as a degree from optimum, this kind of thing can result. When I rebuilt my Luscombe, I noticed that there were two elevator up travels in the type certificate and mine was set for the lower one. After two turns of a spin, it would fall out of the spin and accelerate. I set the higher up travel and the spin would then do 2 turns of flopping around and settle into a stable (semi-flat) spin which was still easily recovered. The difference between elevator travels was something like 1.2 degrees. Not really very much when you are trying to read angles. Things like stabilizer incidence and wing incidence as well as cg location can factor into things here. Set those things as accurately as possible, then wear a parachute on your test flights so you are ready for a surprise.
Sid