Supermotive
Member
Hi Jean Claude. Can you help me understand what you mean? Whenever you say something, I really want to understand. I think you are very knowledgeable, and I like to learn from you.
A new tractor design
- Thread starter Supermotive
- Start date
JEFF TIPTON
Senior Member
Apply spar varnish to the wood before installation
Available most hardware stores
Available most hardware stores
Alan_Cheatham
Member
Don't be in a hurry to begin construction, on a new design much of your initial time will be spent in analyzing and refining. If you were to base your build on a tried and tested gyro that has shown in many hours of operation that it is a successful design and you only made cosmetic changes that would be one thing but an all new structure demands proper engineering to be safe.
I asked in a previous post if you had considered how to mount the rotor, that is very important as it will determine load paths within the structure and tubing sizes to carry that load. Also be aware that load paths can be much different in a fuselage that is designed as a strut braced high wing vs a gyro fuselage, depending on how the mast is mounted.
As an example the mast on the LW-5 is attached to the center of a 1"x .049" wall steel tube that crosses the forward cabin roof. The mast is triangulated to the roof sides at four points, the two forward of which attach to plugs which are welded into the ends of the 1" tube and threaded for a bolt. This is one area of concern I have about the LW if one considers that most of the aircraft is hanging on this one welded-in tube, if it fails...........
Now consider what would happen if someone wanted to make a side-by-side LW version and simply widened the fuselage from 26" to 43" without any additional consideration, imagine the resulting tube bending loads.
While tandem seating limits what you can do with mast placement on a tractor given that most of the cabin is filled with occupants and may require mounting the mast to the roof structure on a SxS design there is the possibility of running the mast between the occupants and attaching in other ways, have a look at Mishka's mast mounting.
Design decisions like this must be made first and the structure properly designed around those decisions.
I asked in a previous post if you had considered how to mount the rotor, that is very important as it will determine load paths within the structure and tubing sizes to carry that load. Also be aware that load paths can be much different in a fuselage that is designed as a strut braced high wing vs a gyro fuselage, depending on how the mast is mounted.
As an example the mast on the LW-5 is attached to the center of a 1"x .049" wall steel tube that crosses the forward cabin roof. The mast is triangulated to the roof sides at four points, the two forward of which attach to plugs which are welded into the ends of the 1" tube and threaded for a bolt. This is one area of concern I have about the LW if one considers that most of the aircraft is hanging on this one welded-in tube, if it fails...........
Now consider what would happen if someone wanted to make a side-by-side LW version and simply widened the fuselage from 26" to 43" without any additional consideration, imagine the resulting tube bending loads.
While tandem seating limits what you can do with mast placement on a tractor given that most of the cabin is filled with occupants and may require mounting the mast to the roof structure on a SxS design there is the possibility of running the mast between the occupants and attaching in other ways, have a look at Mishka's mast mounting.
Design decisions like this must be made first and the structure properly designed around those decisions.
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Supermotive
Member
Alan, I completely agree. I think, in excitement, I jumped the gun. Originally, the Mishka was my inspiration, and I am now thinking of just taking the Misha 2 design, lengthening the tail, and using stringers for shaping.
By the way, is that your LW? Do you have any more pics?
Alan_Cheatham
Member
Yes, that's from our build thread, additional picture there.
https://www.rotaryforum.com/threads/lw-5.2924/page-2
Brian Jackson
Platinum Member
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It did seem like you were moving pretty fast into production for the number of unanswered questions you had. Whenever I have let excitement govern an engineering endeavor, I have regretted it. I am learning that, especially with aircraft, it's good to think like a chess player and plan several moves ahead of the one you're about to make. I can definitely relate with your eagerness, but I bring this same gung-ho enthusiasm to my gyro CAD models before a tool ever touches metal. There may be tweaks in your design as you build for various reasons, but I would advocate spending considerable time learning and asking questions (which you are doing) and delving deep into the design you plan to build before laying out steel. A project like this is really worth obsessing over at an OCD level.
kolibri282
Super Member
Quote: For this long tubes, the buckling limit is reach far before the elastic limit /Quote
I wrote the same thing in post #124: You will have to design for maximum compression load on the members because in a truss compression buckling is the limiting factor
What JC means is that the maximum compression load for a column before buckling is
K=pi^2*E*I/s^2
where:
pi =3.14
E modulus of elasticity of the material
I second moment of inertia of the cross section
s free length of the member considering the way it is clamped at the end.
In an airframe you can consider s to be the length of the member unless you have an unusually large gusset plate and a Finit Element Program to calculate the bending moment at the attachment point.
Note that the tensile strength of the material does not appear anywhere in the buckling formula, so it is not relevant. Since buckling depends on unknown imperfections of the cross section one usually divides K by some suitable margin of safety.
I wrote the same thing in post #124: You will have to design for maximum compression load on the members because in a truss compression buckling is the limiting factor
What JC means is that the maximum compression load for a column before buckling is
K=pi^2*E*I/s^2
where:
pi =3.14
E modulus of elasticity of the material
I second moment of inertia of the cross section
s free length of the member considering the way it is clamped at the end.
In an airframe you can consider s to be the length of the member unless you have an unusually large gusset plate and a Finit Element Program to calculate the bending moment at the attachment point.
Note that the tensile strength of the material does not appear anywhere in the buckling formula, so it is not relevant. Since buckling depends on unknown imperfections of the cross section one usually divides K by some suitable margin of safety.
Jean Claude
Junior Member
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- I piloted gliders C800, Bijave, C 310, airplanes Piper J3 , PA 28, Jodel D117, DR 220, Cessna 150, C
- Total Flight Time
- About 500 h (FW + ultra light)
Maybe with this sketch ?:
This is not intuitive, because it is due to the instability of buckling, only linked to the ratio Strength / Stretch of the material
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Supermotive
Member
Thank you both. I understand better now. 
Douglas fir does well with water and is rot resistant, It is used in ship planking and masts, It tends to splinter more than spruce.
Alan_Cheatham
Member
Supermotive, you do get around, the forum that is. You are going to find that kit or scratch built side-by-side designs that will meet your needs very scarce.
Personally I feel you need evaluate what you really need in the way of performance and select an aircraft that will meet those needs, and don't limit your choice to only gyroplanes.
You mentioned in post #13 "To tell you the truth, I would be satisfied with a 100 foot takeoff. I am trying to make it shorter so I can safely take off on a small piece of land rather than someone else's airfield." This would be a tall order if not impractical for a gyroplane with two adults and fuel and if you really need to operate in this short of a distance one of the STOL fixed wing sportplanes might be a better choice. Your other requirements for 100 mph cruise, cross country range and rough field capability is also better served by a fixed wing.
Select a machine that has proven to meet your requirements rather than hoping a machine will.
Personally I feel you need evaluate what you really need in the way of performance and select an aircraft that will meet those needs, and don't limit your choice to only gyroplanes.
You mentioned in post #13 "To tell you the truth, I would be satisfied with a 100 foot takeoff. I am trying to make it shorter so I can safely take off on a small piece of land rather than someone else's airfield." This would be a tall order if not impractical for a gyroplane with two adults and fuel and if you really need to operate in this short of a distance one of the STOL fixed wing sportplanes might be a better choice. Your other requirements for 100 mph cruise, cross country range and rough field capability is also better served by a fixed wing.
Select a machine that has proven to meet your requirements rather than hoping a machine will.
kolibri282
Super Member
Nordic boat builders have used floor wax to seal fir spars for a long time. The surface becomes sealed against liquids and also gets much harder. My wife treated our elevated bed, made of glued fir boards, with floor wax for several years and now the surface feels as if we had sheathed it with a cover of lightweight GRP.
Supermotive
Member
Thank you for your reply
wolfy
Gold Supporter
If you still want to build why not just go with a little wing, you have an engine and the tubing. It is a proven design there will be no guess work.
Ticks most of your boxes, the tandem can be made to solo from either seat. Or modify the design into side by side (back to some guess work).
Technical support avaliable.
wolfy
Supermotive
Member
Some good points. I talked to Ron about that. Considering my needs, the biggest drawback, of the tail dragger tractor, seems to be the potential for a rollover when a ground loop occurs during landing or taxi. I personally believe good training coupled with pushing the landing gear as far forward as possible, could all but eliminate this threat, but I can guaranty it. Most of this second questioning after CFIs continually warned me if the rollover potential. The fact that they are CFIs gives their comments a little more clout. I really do like the rag and tube side by side tractor though.
wolfy
Gold Supporter
Pushing the gear further forward will increase the potential for a ground loop not reduce it.
Much less chance of a ground loop in a gyro than a fixed wing because landing speeds are very slow/nil.
There are not that many little wings around, are all these CFIs experienced in little wing flying?
wolfy
Alan_Cheatham
Member
Some points.
As Wolfy stated moving the main gear further forward of the CG will increase the potential for a ground loop and reduces the "overturning angle" further contributing to a roll over. On a gyro without elevator control some degree of forward main gear mounting is warranted to help prevent a nose over. While the potential of a ground loop or roll over is increased with the conventional gear it is doable with extra cautions.
Hon Herron himself has had a roll over in his LW, NTSB report here: https://www.ntsb.gov/_layouts/ntsb.aviation/brief.aspx?ev_id=20001206X02451
If you're into modifications modify the LW into a tricycle, proper engineering is required.
There are many problems with converting a LW into a SxS design, the engineering required to produce a safe design is the same as required in an all new design, one that would be better optimized.
One major deciding factor in any gyro that is going to be used for cross country flight is comfort and range. The LW's are based on the N3 Pup fuselage with modifications to accommodate a second person, as such the fit with two is very tight and not comfortable long term for the front passenger (have a look at my LW5 build thread linked previously for some idea as to pilot/passenger fit).
Fuel is also a limiting factor, since it's normally carried in tanks within the fuselage tank size would be limited when carrying a passenger, for any type of range a belly tank would be required (there are two LW with belly tanks FYI).
As Wolfy stated moving the main gear further forward of the CG will increase the potential for a ground loop and reduces the "overturning angle" further contributing to a roll over. On a gyro without elevator control some degree of forward main gear mounting is warranted to help prevent a nose over. While the potential of a ground loop or roll over is increased with the conventional gear it is doable with extra cautions.
Hon Herron himself has had a roll over in his LW, NTSB report here: https://www.ntsb.gov/_layouts/ntsb.aviation/brief.aspx?ev_id=20001206X02451
If you're into modifications modify the LW into a tricycle, proper engineering is required.
There are many problems with converting a LW into a SxS design, the engineering required to produce a safe design is the same as required in an all new design, one that would be better optimized.
One major deciding factor in any gyro that is going to be used for cross country flight is comfort and range. The LW's are based on the N3 Pup fuselage with modifications to accommodate a second person, as such the fit with two is very tight and not comfortable long term for the front passenger (have a look at my LW5 build thread linked previously for some idea as to pilot/passenger fit).
Fuel is also a limiting factor, since it's normally carried in tanks within the fuselage tank size would be limited when carrying a passenger, for any type of range a belly tank would be required (there are two LW with belly tanks FYI).
Alan_Cheatham
Member
One other consideration.
While the FAA does allow flight training in ones own homebuilt it will need to have it's 40 hours flown off first and you will need to convince a CFI to do so. Most CFIs will likely decline to train in any machine they have no confidence in.
While the FAA does allow flight training in ones own homebuilt it will need to have it's 40 hours flown off first and you will need to convince a CFI to do so. Most CFIs will likely decline to train in any machine they have no confidence in.
Zzorse
Forum Supporter
October 1994, would that have been the LW-2?
Supermotive
Member
Alan. Thank you for the insight. I don’t think I was very clear about why I would move the landing gear forward. My thoughts were by moving the landing gear forward, the tail would be less likely to lift; especially when there is no elevator to counter tail lift. I would use a little longer fuselage that a LW5 in order to improve longitudinal stability and also to lessen the taper rate from the cab to tail; for the purpose of reducing boundary layer separation on the fuse. I would also use twin rudders and triple v-stabs. I think a locking tail wheel would be helpful on landings as well.
