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Old 01-16-2012, 08:05 AM   #1
gc737ng
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need Help!

I've just bought the Steen Aero Pitts S1-C Plans, CAD Version.
I'm looking the constructions photos that relate to the Pitts on the website, and i saw that there are some differences between plans and photo.

example:
in sheets 3 and 4 which are shown the the basic truss compared to the picture some tube are missing others are reiforced,




someone can tell me why?

Thanks[img]smileys/smiley9.gif[/img]


Edited by: gc737ng


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Old 01-16-2012, 08:55 AM   #2
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Hi,

These bits are for the spring gear fitting rather than the standard bungee gear. (the spring gear is green in these pictures) There is another sheet in the steen plans that details these changes if you want to fit spring gear.

I have been building from the steen plans and although they are good, there are a few small errors. (The torque tube is one that springs to mind).
There are lots of people on this forum who can help clarify things.

Have fun building!
Chris



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Old 01-16-2012, 10:43 PM   #3
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You should have a landing gear page in the plans (7A of 33) Called
"Landing Gear Spring Gear Conversion" That should help un-muddy the
waters.

The previous post is exactly right. The extra tube is a common way to support the lower longeron when the spring gear is mounted there. Also they add a doubler the "reinforced part of the first picture" to the longeron as well since the longeron was is only 3/4" 0.035 tubing and the spring gear if not re-enforced properly can have horrible effects. I had a friend that had to replace most of landing gear area becuase someone didn't re-enforce it properly. He only found in preflight after pushing it out of the hangar and noticed the gear wobbled back and forth (really not good). He found several broken tubes. If you are going with the stock landing gear (bungee) then these re-reinforcements DON'T need to be added if you are then they DO need to be added.






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Old 01-18-2012, 07:54 AM   #4
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Thanks guys i solved !

other errors that you know are on the plans?

Before starting to built, i'am taking time to put togheter more information available.

Thanks.


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Old 01-19-2012, 04:49 PM   #5
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The gear setup on this Pitts shown in the pictures is not ideal and can/will lead to cracking of the lower longeron. The recommendation now is to make the connection at the bolts rounded (in the longitudinal axis) so the gear can flex, without also flexing the longeron. Grove sells radius blocks for this purpose. Or the equivalent can be built into the frame at the mounting points. The pictures of this Pitts show flat mounting surfaces which will transmit the flexing of the gear to the longeron.
FWIW

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Old 01-19-2012, 04:55 PM   #6
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I found with the steen plans you just need to check some of the measurements. On the torque tube (unless they have changed it) when you add up the seperate small distances, they don't equal the overall dimension given. The steen plans also don't have the drawings for the tailplane leading edge support structure. I have access to aviat drawings via friends and have had to use them on a couple of occasions to fill bits in.
The other thing to note is the steen ss wing drawings are designed for their kit, i'm fairly sure you couldn't actually build a set of wings with just the drawings they send you.

Chris

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Old 01-19-2012, 04:57 PM   #7
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Regarding the spring gear, I was told once that if you buy it from grove they supply drawings with the reinforcement required. Not sure if anyone can confirm that or not.

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Old 01-28-2012, 09:54 AM   #8
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Hallo Boys!

As i said, i'm trying to built a S1-C, with a spring gear installed.

I'm studing the Steen drawings, and looking at some photos as backup.
SteenAero says that the plans they provide are the same for the Pitts S1-C and S1-SS, exept for the wings.

So the basic structure is the same.

But i found some photos about a S1-SS which show some differences in the basic structures. I dont know what plans have been used for these S1-SS, but these tube in my plans is not shown, as you can see from the pictures i posted first.




is these the connection at the bolt rounded mentioned by Pitts1flyer ?

Eventually,wath is its exact location and size?

I contacted GROOVE about it, and they told me that they need my plans to tell me how to better adapt the spring gear.


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Old 01-28-2012, 12:46 PM   #9
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fwiw, it looks in the first pic as if the sheet metal template used to hold the mounting lugs in place during welding was left on when they attached the gear.
there are at least four installation schemes that I know of, the S1 drawings, Model 12, Christen Eagle mod drawings from Aviat, and the drawings that Grove provides.
As someone said, the most important parts are the radius blocks as they allow the gear to flex across the bottom of the fuselage which in the process minimizes the twisting of the longerons. If the part of the gear that goes acrosss the bottom doesn't have the freedom to move up and down as the gear flexes then the longerons will end up cracking eventually.
Bart

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Old 01-28-2012, 05:22 PM   #10
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Hi g7, that last picture is of my gear setup. I installed an extra cross tube here to provide more rigidity against flexing and also to provide extra strength to the rear bolt spring gear bolt holes which looked a bit fragile just being welded to the longeron.
I recall discussing the mod in detail with a number of builders who had built spring gear Pitts, and this was the consensus on how to eliminate any danger of cracking. Don't recall the details but there may be some commentary on it in my blog.
CheersStuart

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Old 02-04-2012, 01:00 PM   #11
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Hallo MCWOLF!

Excuse me if i continue to use your photos as reference, but i guess that you, like many other in this forum, have done a nice job!!

As i said im trying to realyze my little dream......S1-C Version...with all the improvements available. So i am here again to ask you something new!!

Always about the basic structure...
What is the reason for this tube??





I sow your site....and is very nice.

Gaetano C.

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Old 02-04-2012, 05:49 PM   #12
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Hello Gaetano,


That tube at the top of the cabane struts is to reduce a little bit of twist that happenes to the top wing when pulling Gs. Some people have found the internal corner blocks where the drag/anti-drag wires attach pulled loose after several hundred hours of hard flying.


It came from a S-1S factory service bulletin. Many S-1C builders have added it, however the original S-1C plans do not show it.


I hope this helps.
Best wishes,
WallyEdited by: wally

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Old 02-04-2012, 07:31 PM   #13
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What Wally said.

I would add that the damage was usually traced to very aggressive snap type manuvers.

If I were building or re-building I would include the brace. If I had a flying airplane that showed no signs of distress in the upper wing and I weren't doing high speed or multiple snaps I wouldn't take it apart just to add this tube.

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Old 02-05-2012, 04:22 PM   #14
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hallo evryone!

someone knows the section and the axact position of this tube?
I can't find the relative service bulletin.

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Old 02-05-2012, 06:20 PM   #15
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Quote:
Originally Posted by wally
Hello Gaetano,

That tube at the top of the cabane struts is to reduce a little bit of twist that happenes to the top wing when pulling Gs. Some people have found the internal corner blocks where the drag/anti-drag wires attach pulled loose after several hundred hours of hard flying.

It came from a S-1S factory service bulletin. Many S-1C builders have added it, however the original S-1C plans do not show it.

I hope this helps.
Best wishes,
Wally
This modification is NOT a service bulletin. Its just an assumed structural enhancement Not sure I'm convinced that it is completely necessary. One way to keep from pulling your blocks NOT snap your aircraft above maneuvering speed.



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Old 02-05-2012, 07:01 PM   #16
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I always understood the brace tube as a way to complete the structure in such a way as to take much of the bending load off the front mounting plates. The flanged plates were a band-aid fix to make those fittings stiffer but they do not address the problem directly.

The rear cabanes are not supported against fore and aft movement except through the wing's center section. When G increases the forward lift vector of the airfoil tries to move the wings forward. This load bends the rear cabanes as the wing moves forward and also bends the forward wing fitting plates. In effect the front wing fittings and the rear cabanes are all there is to resolve this load. The brace brings the rear fitting plates in as an additional structural member to resolve the load. These plates are much more substantial than the front ones and the structure is much more robust as a result.

I'm not sure how snaps (asymmetrical lift loads) load this area any higher than large lift loads across both wings.

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Old 02-05-2012, 09:15 PM   #17
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"I'm not sure how snaps (asymmetrical lift loads) load this area any higher than large lift loads across both wings."

I guess I don't either but that is what I was told by a guy I respect. It could be that the people that do multiple snaps from high speed push the airplane hard in straight Gs as well.


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Old 02-05-2012, 09:28 PM   #18
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Bill,

What you've written is the conventional wisdom that I learned many years ago and didn't question. However, looking at the photo, I'm no longer sure it's correct. It seems to me that the main resistance to the forward component of lift comes from the rigid, triangulated structure of the front cabanes. The rear cabanes are unsupported fore/aft so can't contribute much resistance to the pull of the wing. Without the tube in question, when the front cabanes flex forward the movement is transmitted to the rear cabanes through the wood centre section. This probably causes a bit of twisting of the spars, which might be what Wally meant. Adding the tube sends the load directly to the rear cabanes and takes that stress off the centre section. (Since the tube can't stretch as much as the centre section, the rear cabanes probably bend a bit farther with the tube in place and so take up a bit more of the fore/aft load, but I'd be surprised if that is appreciable.)

Edit: More thinking has me seeing the conventional wisdom more clearly. If the plates that connect the front spar to the cabanes are the most flexible component, then Bill's description seems correct to me. What I wrote above was based on the assumption that the wood centre section is the most flexible component, which is probably wrong.

I share your skepticism about the role of snaps in breaking off corner blocks.



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Old 02-06-2012, 05:26 AM   #19
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Think of a snap roll, how much drag is being induced on one wing just at the break. The rapid increase in G load coupled with the much larger increase in drag onthe stalled tip, even if momentarily, prior to the recovery.As the snap is a very violent acceleration in a particular direction, and coupled with a substantial twisting due to the drag loads on one wing much more than another, there is massive strain placed on the rear cabane (and front but it is braced better) as the fuselage lags behind and tries to catch up.The rear cabane is not particularly resistive to forward and rearward bending but is also poor at resisting twisting movements whichI think are more harmful than those outlined above.By tying the two together there is shared load baring, resistance to the twisting (more importantlyI think)and also any fore and aft movement. The flanged plates will also assist in resisting this torsional load.Drag wire blocks cracking is again something I think is associated to snapping at too high speed, the resulting massive increase in drag loads imposed on one wing more than another results in cupping of the washers or cracked blocks. Again refering to the loads imposed during a snap with undeven drag forces, the wing has to give somewhere and in relation to drag forces these are imposed on the drag wires, washers and blocks.Yes, no, maybe..........
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Old 02-07-2012, 12:32 PM   #20
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[img]smileys/smiley14.gif[/img]
Thanks to all for the explanations

If i wanted to install it....

someone can tell me the size and tichkness?

Bye
Gaetano C.


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Old 02-08-2012, 02:01 AM   #21
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Gaetano, let me know when you begin wing construction (if you have not already) and I can enlighten you on some things.


I'm 20 hours in on the project and there are a few items that have surfaced. Nothing big, it's likea puzzle where the pieces fit nicely but not as shown in the plans...






Quote:
Originally Posted by gc737ng
[img]smileys/smiley14.gif[/img]
Thanks to all for the explanations

If i wanted to install it....

someone can tell me the size and tichkness?

Bye
Gaetano C.
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Old 02-08-2012, 03:36 PM   #22
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Hallo !

At this time i'm studing the fuselage.
Verifyng all the mesurament.
And i'm cataloging all the hardware. Then i will do the same thing with wings.

After this work... i will start building.

Have you already assembled the basic fuselage?














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Old 02-08-2012, 04:43 PM   #23
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Hopefully I'm addressing your points as you meant them to be taken. If not, please clarify.

Quote:
Originally Posted by DragonflyDH90


Think of a snap roll, how much drag is being induced on one wing just at the break.
The airplane is being yawed by the rudder input more than anything else. The last 2 or 3 feet of one tip is stalled, the rest of the wings are at high angles of attack so there's drag everywhere, a bit more at the stalled tip but I wouldn't think there's a huge force.

Quote:
The rapid increase in G load coupled with the much larger increase in drag onthe stalled tip, even if momentarily, prior to the recovery.
I don't believe the speed at which a load is applied has any effect on the structure, only the magnitude of the load. I suppose the CLmax of the airfoil could be momentarily exceeded with a quick AOA change but I'm not sure.

Quote:
As the snap is a very violent acceleration in a particular direction, and coupled with a substantial twisting due to the drag loads on one wing much more than another, there is massive strain placed on the rear cabane (and front but it is braced better) as the fuselage lags behind and tries to catch up.
The rear cabane is not particularly resistive to forward and rearward bending but is also poor at resisting twisting movements whichI think are more harmful than those outlined above.
Hmm. I'm seeing the rear cabane has being very well designed to resolve
any differential drag loads but relatively poor resolving fore and aft loads. The front cabane can resolve fore and aft loads because it has diagonal bracing. I
don't look at a Pitts and think it is a non-rigid structure where large
strains occur. It's pretty well tied together and the whole thing moves
as one with only minor deflections.

Quote:
By tying the two together there is shared load baring, resistance to the twisting (more importantlyI think)and also any fore and aft movement. The flanged plates will also assist in resisting this torsional load.
I think the plates are not loaded fore and aft from differential drag loads, that load is from lift loads.

Quote:
Drag wire blocks cracking is again something I think is associated to snapping at too high speed, the resulting massive increase in drag loads imposed on one wing more than another results in cupping of the washers or cracked blocks. Again referring to the loads imposed during a snap with uneven drag forces, the wing has to give somewhere and in relation to drag forces these are imposed on the drag wires, washers and blocks.
I have had a drag wire block fail and I did not do snaps at high speeds (level snaps @ around 110mph). That's not to say higher speeds wouldn't cause more problems, I'm just not sure how fast is too fast.

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Old 02-08-2012, 06:36 PM   #24
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Thanks for that Bill.I certainly wasnt meaning that the other ideas were wrong butI feel there is more going on here than just theforces in pitch. It would be very interesting to do a structural analysis of whats going on here. I know knothing about how thats done or if its possible but the I would certainly find the information interesting.
Quote:
The airplane is being yawed by the rudder input more than anything else. The last 2 or 3 feet of one tip is stalled, the rest of the wings are at high angles of attack so there's drag everywhere, a bit more at the stalled tip but I wouldn't think there's a huge force.
Just wonder how much twisting force on the rear cabane is enough, maybe huge is exageration but some. Is some enough to cause damage? I know with my top wing off it is very easy to move the rear cabanes (beforeI put the brace in).

Quote:
I don't believe the speed at which a load is applied has any effect on the structure, only the magnitude of the load. I suppose the CLmax of the airfoil could be momentarily exceeded with a quick AOA change but I'm not sure.
Poorly written on my part, brain not in gear with fingers. You are quite right, the rate of increase of load isn't of importance, magnitude is. Im not sure either.As the snap is a very violent acceleration in a particular direction, and coupled with a substantial twisting due to the drag loads on one wing much more than another, there is massive strain placed on the rear cabane (and front but it is braced better) as the fuselage lags behind and tries to catch up.
Quote:
Hmm. I'm seeing the rear cabane has being very well designed to resolve
any differential drag loads but relatively poor resolving fore and aft loads. The front cabane can resolve fore and aft loads because it has diagonal bracing. I
don't look at a Pitts and think it is a non-rigid structure where large
strains occur. It's pretty well tied together and the whole thing moves
as one with only minor deflections.
I think we may have to agree to disagree here in relation to the rear cabane. It is certainly not good fore and aft but it certainly isnt stunning in a twisting capacity either. Im certainly not saying that the Pitts is notrigid, it certainly is, there is obviously something going here that has prompted some to fit both the brace and also flanged attach fittings. Admittedly most are probably done due to the 'everyone else has done it soI will too' mentality but surely there was some truth to the idea when it was first done way back when. It may or may not have any relationship to my thoughts or yours but maybe there is something there.
Quote:
By tying the two together there is shared load baring, resistance to the twisting (more importantlyI think)and also any fore and aft movement. The flanged plates will also assist in resisting this torsional load. I think the plates are not loaded fore and aft from differential drag loads, that load is from lift loads.
I wasnt really think of fore and aft loads on these fittings, more twisting loads.
Quote:
Drag wire blocks cracking is again something I think is associated to snapping at too high speed, the resulting massive increase in drag loads imposed on one wing more than another results in cupping of the washers or cracked blocks. Again referring to the loads imposed during a snap with uneven drag forces, the wing has to give somewhere and in relation to drag forces these are imposed on the drag wires, washers and blocks.
I have had a drag wire block fail and I did not do snaps at high speeds (level snaps @ around 110mph). That's not to say higher speeds wouldn't cause more problems, I'm just not sure how fast is too fast.
Its interesting you mention this, im not sure how fast is to fast either. Perhaps the speeds we have been snapping at up until now are to fast.How was, or is, this figure determined. Was it an 'plucked from the air' figure or is it based on some formula? Is 5mph faster enough to cause problems? is 1mph? Inetresting....I certainly dont think Im 100% right, probably not even 50%, but I think some of my points are potentially valid as are yours. Its an interesting area.Just as a last note. in recent times I have seen on 3 different Pitts' (2 x S2A and 1 S2B) cracked top wing attach fittings both front and rear, top longeron cracking at the cabane junctions and a drag wire bolt almost sheared clean in half (blocks undamaged - this may have been caused by a wire that was a little too lose and freeting however). There are some pretty impressive loads going on up there, even with such an amazingly rigid structure with all the wires, bracing etc etc.I would be interested in comments from some of the structural engineers on the forum, maybe Chopmo would care to comment?
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Old 02-08-2012, 06:50 PM   #25
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I don't see how you could twist the rear cabanes unless you remove the front cabane bolt or the front fittings are loose, etc. Under normal conditions it can't happen. The load should be entirely left and right in reaction to the wingtips moving fore and aft.

I too hope Jim joins the discussion. He does this stuff every day.



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