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The Staff of SOH
Airacobra
- Thread starter Ivan
- Start date
I was pretty sure that eventually I would need a Top View of the Airacobra to determine the Fuselage Width in various places.
Attached is a reduced size version of the drawing I am using.
In this drawing, I noticed that there is a slight discrepancy: The Wing appears to be slightly further back than it should be according to calculations.
Other than that, there were the typical minor errors such as a slightly different scaling factors for Lateral and Longitudinal dimensions and a very slight shear error. Oddly enough, there was not a rotational error.
The maximum width of the Airacobra's Fuselage is 34.75 inches.
This works out to 1.4479 feet on each side of the Center Line. I will be using 1.45 feet.
The scaled dimension from this drawing works out to be 1.46 feet which is pretty close.
The next step is to take measurements to build a three dimensional Fuselage to replace the Profile Template that is in place now.
- Ivan.
Attached is a reduced size version of the drawing I am using.
In this drawing, I noticed that there is a slight discrepancy: The Wing appears to be slightly further back than it should be according to calculations.
Other than that, there were the typical minor errors such as a slightly different scaling factors for Lateral and Longitudinal dimensions and a very slight shear error. Oddly enough, there was not a rotational error.
The maximum width of the Airacobra's Fuselage is 34.75 inches.
This works out to 1.4479 feet on each side of the Center Line. I will be using 1.45 feet.
The scaled dimension from this drawing works out to be 1.46 feet which is pretty close.
The next step is to take measurements to build a three dimensional Fuselage to replace the Profile Template that is in place now.
- Ivan.
Attachments
aleatorylamp
Charter Member
Good morning, Ivan,
Thanks for the fuselage width data, which came in very handy indeed. I know that I´d already had it in the new drawings you sent, but I hadn´t checked it yet. Better late than never!
Cheers,
Aleatorylamp
Thanks for the fuselage width data, which came in very handy indeed. I know that I´d already had it in the new drawings you sent, but I hadn´t checked it yet. Better late than never!
Cheers,
Aleatorylamp
Hello Aleatorylamp,
There are a lot more issues that still remain with that AFX that you are working with.
Basically you really can't get a dimensionally correct (by AF99 standards) model using that AFX without replacing EVERY original polygon.
I did not see the point of doing that much work to end up with a model that I would have to credit to another author anyway even though nothing remained of the original, which is why I put certain limitations on the changes I would make.
That model was good enough to use for visualization while working on a Flight Model though.
I don't really know that my own Project will be all that accurate but I do know that the errors in it will be mine and not those inherited from the choices made by the original author. I have already had to make a few decisions that rely on Eyeball measurements rather than scaling from a drawing or using accurate specifications, so there are certain to be some errors.
As for references, nearly nothing is new. The documents have been around for decades and most of them date from well before the Microcomputer Era.
The Design Analysis article quoting Larry Bell is from a magazine published in 1943.
The P-39Q-1 Manual was in use during the war.
NACA Report L-602 dates from the same period. (It describes a P-39D-1)
The Russian Manual was written by them when they received their first P-39D-1 aircraft probably around 1941.
The Paul Matt Drawings were published in the 1960s.
It is really a matter of finding the references and trying to put together a consistent set of data despite the contradictions.
- Ivan.
There are a lot more issues that still remain with that AFX that you are working with.
Basically you really can't get a dimensionally correct (by AF99 standards) model using that AFX without replacing EVERY original polygon.
I did not see the point of doing that much work to end up with a model that I would have to credit to another author anyway even though nothing remained of the original, which is why I put certain limitations on the changes I would make.
That model was good enough to use for visualization while working on a Flight Model though.
I don't really know that my own Project will be all that accurate but I do know that the errors in it will be mine and not those inherited from the choices made by the original author. I have already had to make a few decisions that rely on Eyeball measurements rather than scaling from a drawing or using accurate specifications, so there are certain to be some errors.
As for references, nearly nothing is new. The documents have been around for decades and most of them date from well before the Microcomputer Era.
The Design Analysis article quoting Larry Bell is from a magazine published in 1943.
The P-39Q-1 Manual was in use during the war.
NACA Report L-602 dates from the same period. (It describes a P-39D-1)
The Russian Manual was written by them when they received their first P-39D-1 aircraft probably around 1941.
The Paul Matt Drawings were published in the 1960s.
It is really a matter of finding the references and trying to put together a consistent set of data despite the contradictions.
- Ivan.
Spinner & Propeller
Attached is a screenshot of the new Spinner and Propeller.
Note that the colour choices are somewhat odd but they are a consequence of a bug in Aircraft Factory 99.
The Spinner is split into a Forward Structure and a Rear Structure.
The Forward Structure has a "Forward Bulkhead" (Wall) specified.
While both Structures are specified as Yellow, Aircraft Factory 99 handles Structures with Bulkheads differently.
- Ivan.
Attached is a screenshot of the new Spinner and Propeller.
Note that the colour choices are somewhat odd but they are a consequence of a bug in Aircraft Factory 99.
The Spinner is split into a Forward Structure and a Rear Structure.
The Forward Structure has a "Forward Bulkhead" (Wall) specified.
While both Structures are specified as Yellow, Aircraft Factory 99 handles Structures with Bulkheads differently.
- Ivan.
Attachments
aleatorylamp
Charter Member
Hello Ivan,
Had known what you were going to reply, I would have refrained from making any comment, and it is by no means the first time you have used these arguments, or very similar ones, and in a similar tone.
"There are a lot more issues that still remain with that AFX that you are working with.
Basically you really can't get a dimensionally correct (by AF99 standards) model using that AFX without replacing EVERY original polygon."
Even if I´d built a model starting from scratch, which wasn´t my objective anyway, because I specifically wanted to upgrade an existing model, to get a chip off my shoulder from previous experiences of that kind, I would have run into the same problems of adjusting and re-adjusting the model because of the drawings I had started out with in the first place.
If there are still any mistakes in it, they will be small, and will come from all sorts of places apart from myself, and that doesn´t worry me in the least. The elements on the re-worked model are all now sufficiently correctly placed for me to classify it as a successful upgrade, and I am very satisfied indeed, especially taking into account that after all the work I put in, it has come out exceeding my expectations and looking very nice.
"As for references, nearly nothing is new. The documents have been around for decades and most of them date from well before the Microcomputer Era.
The Design Analysis article quoting Larry Bell is from a magazine published in 1943.
The P-39Q-1 Manual was in use during the war.
NACA Report L-602 dates from the same period. (It describes a P-39D-1)
The Russian Manual was written by them when they received their first P-39D-1 aircraft probably around 1941.
The Paul Matt Drawings were published in the 1960s."
Before the Microcomputer time not everyone was so fortunate as to have access the specific information for this model, and what was available on the Internet in 1998 at the time of the original AFX must have been a fraction of what there is now.
"It is really a matter of finding the references and trying to put together a consistent set of data despite the contradictions."
That is far more easily said than done for many people. I for one, am not very good at that, and in view of the devlopments, even people with more expertise can be misled initially.
Anyway, I´m sure my upgraded model will not be as exact as the one you are building, but that is not the point I was pursuing when I began this exercise. Thanks anyway for the help you have provided.
Cheers,
Aleatorylamp
Had known what you were going to reply, I would have refrained from making any comment, and it is by no means the first time you have used these arguments, or very similar ones, and in a similar tone.
"There are a lot more issues that still remain with that AFX that you are working with.
Basically you really can't get a dimensionally correct (by AF99 standards) model using that AFX without replacing EVERY original polygon."
Even if I´d built a model starting from scratch, which wasn´t my objective anyway, because I specifically wanted to upgrade an existing model, to get a chip off my shoulder from previous experiences of that kind, I would have run into the same problems of adjusting and re-adjusting the model because of the drawings I had started out with in the first place.
If there are still any mistakes in it, they will be small, and will come from all sorts of places apart from myself, and that doesn´t worry me in the least. The elements on the re-worked model are all now sufficiently correctly placed for me to classify it as a successful upgrade, and I am very satisfied indeed, especially taking into account that after all the work I put in, it has come out exceeding my expectations and looking very nice.
"As for references, nearly nothing is new. The documents have been around for decades and most of them date from well before the Microcomputer Era.
The Design Analysis article quoting Larry Bell is from a magazine published in 1943.
The P-39Q-1 Manual was in use during the war.
NACA Report L-602 dates from the same period. (It describes a P-39D-1)
The Russian Manual was written by them when they received their first P-39D-1 aircraft probably around 1941.
The Paul Matt Drawings were published in the 1960s."
Before the Microcomputer time not everyone was so fortunate as to have access the specific information for this model, and what was available on the Internet in 1998 at the time of the original AFX must have been a fraction of what there is now.
"It is really a matter of finding the references and trying to put together a consistent set of data despite the contradictions."
That is far more easily said than done for many people. I for one, am not very good at that, and in view of the devlopments, even people with more expertise can be misled initially.
Anyway, I´m sure my upgraded model will not be as exact as the one you are building, but that is not the point I was pursuing when I began this exercise. Thanks anyway for the help you have provided.
Cheers,
Aleatorylamp
Hello Aleatorylamp,
I believe it really depends on how interested one is in the subject.
In my prior post, I was just listing the primary references.
You are correct, they are much easier to find today than they were back in 1998, but the reason I made that comment was because of something you had mentioned earlier possibly in another thread about "new information". The point is that none of this information is new.
What I didn't list in the prior post was the actual physical books I have been using.
America's Hundred Thousand
Airacobra Advantage
Detail & Scale 63
WarbirdTech 17
Squadron's Airacobra in Action
Mushroom 6106 Bell P-39 Airacobra
Profile 165 The Bell P-39 Airacobra
There are probably another three or four books I flipped through for photographs very early in the process.
Not one of these books was a recent purchase.
They have been acquired over several decades of just looking around for books about WW2 aircraft in general.
The point is that if you are interested in a subject, you find information related to your interest and if you are not interested, you do not look.
Hobbyists have been doing this long before the Internet existed.
- Ivan.
Aleatorylamp said:
I believe it really depends on how interested one is in the subject.
In my prior post, I was just listing the primary references.
You are correct, they are much easier to find today than they were back in 1998, but the reason I made that comment was because of something you had mentioned earlier possibly in another thread about "new information". The point is that none of this information is new.
What I didn't list in the prior post was the actual physical books I have been using.
America's Hundred Thousand
Airacobra Advantage
Detail & Scale 63
WarbirdTech 17
Squadron's Airacobra in Action
Mushroom 6106 Bell P-39 Airacobra
Profile 165 The Bell P-39 Airacobra
There are probably another three or four books I flipped through for photographs very early in the process.
Not one of these books was a recent purchase.
They have been acquired over several decades of just looking around for books about WW2 aircraft in general.
The point is that if you are interested in a subject, you find information related to your interest and if you are not interested, you do not look.
Hobbyists have been doing this long before the Internet existed.
- Ivan.
aleatorylamp
Charter Member
Hello Ivan,
I will not argue with you anymore.
You have the ability to repeatedly turn all this into a very unpleasant experience.
Not all hobbyists deal with this hobby in the fashion that you employ, and least
of all do they take every opportunity to make it unpleasant for others if they don´t
have exactly the same attitude as yourself.
I will refrain from participating in this thread any longer. As a matter of fact,
I doubt I will continue participating on this forum.
If Smilo were around I´d ask him to scrub all my threads completely.
It is not worth while for me to continue dealing with the attitude that you continually show.
I suppose it is a matter of character.
Good luck with your model and Good Bye.
Aleatorylamp
I will not argue with you anymore.
You have the ability to repeatedly turn all this into a very unpleasant experience.
Not all hobbyists deal with this hobby in the fashion that you employ, and least
of all do they take every opportunity to make it unpleasant for others if they don´t
have exactly the same attitude as yourself.
I will refrain from participating in this thread any longer. As a matter of fact,
I doubt I will continue participating on this forum.
If Smilo were around I´d ask him to scrub all my threads completely.
It is not worth while for me to continue dealing with the attitude that you continually show.
I suppose it is a matter of character.
Good luck with your model and Good Bye.
Aleatorylamp
Hello Aleatorylamp,
Working with you on the last couple projects has been quite frustrating which is why I tried to have minimal participation when you worked on your Lockheed Electra. When you chose to begin work on the Ilyushin Il-2 Sturmovik and Petlyakov Pe-2, I tried to stay out of it entirely to the point where I stopped even reading the threads.
Instead, I started with a limited update on Eric Johnson's P-39D.
What was amazing was that you immediately stopped work on your own choice of projects to begin updates on the SAME AFX.
Have you noticed that since you started working on YOUR updates to the P-39D, I have tried to avoid doing anything in common even though we are working on the same basic Aeroplane? I have tried to help when I saw you get completely stuck such as was happening with the Nose Glue sequence and some of the business with Propeller Tables.
One very interesting observation that I had was that you were not doing your basic research could not answer even basic questions about the aeroplane you were modelling. Instead of looking for performance figures, you would instead speculate on what the specifications and performance should be from results you were getting from the simulator.
This is CRAZY! Folks with any kind of sense don't do this with a Desktop Flight Simulator especially if they don't understand what is going into the calculations.
What is also amusing is that several times, I was getting some pretty poor results with my Flight Model and saw you attempt to mimic those results. That confirmed for me that you were definitely not doing your research.
Keep in mind though that this is perhaps the fourth or fifth project that you have worked on with my assistance that involved Propeller Tables. The pattern that I have observed is that you didn't seem to grasp the basic terminology even as recently as a couple weeks ago and would ask the same question multiple times even on a single project.
It gets to be quite a chore to need to answer the same question again and again and was interfering with my ability to get anything done.
What was even MORE frustrating was spending the time to write a detailed explanation along with recommendations only to see you obviously NOT read or understand what I had written and go heading off in yet another strange direction.
When you had finally reached a viable stage in your version of the Propeller Tables and I had finished with my first version of my Airacobra's flight model, I figured it was a good time to work on something *I* am interested in rather than something you are interested in.
I didn't see the point of giving more advice that generally gets ignored anyway.
Good Bye, Aleatorylamp.
- Ivan.
Aleatorylamp said:
Working with you on the last couple projects has been quite frustrating which is why I tried to have minimal participation when you worked on your Lockheed Electra. When you chose to begin work on the Ilyushin Il-2 Sturmovik and Petlyakov Pe-2, I tried to stay out of it entirely to the point where I stopped even reading the threads.
Instead, I started with a limited update on Eric Johnson's P-39D.
What was amazing was that you immediately stopped work on your own choice of projects to begin updates on the SAME AFX.
Have you noticed that since you started working on YOUR updates to the P-39D, I have tried to avoid doing anything in common even though we are working on the same basic Aeroplane? I have tried to help when I saw you get completely stuck such as was happening with the Nose Glue sequence and some of the business with Propeller Tables.
One very interesting observation that I had was that you were not doing your basic research could not answer even basic questions about the aeroplane you were modelling. Instead of looking for performance figures, you would instead speculate on what the specifications and performance should be from results you were getting from the simulator.
This is CRAZY! Folks with any kind of sense don't do this with a Desktop Flight Simulator especially if they don't understand what is going into the calculations.
What is also amusing is that several times, I was getting some pretty poor results with my Flight Model and saw you attempt to mimic those results. That confirmed for me that you were definitely not doing your research.
Keep in mind though that this is perhaps the fourth or fifth project that you have worked on with my assistance that involved Propeller Tables. The pattern that I have observed is that you didn't seem to grasp the basic terminology even as recently as a couple weeks ago and would ask the same question multiple times even on a single project.
It gets to be quite a chore to need to answer the same question again and again and was interfering with my ability to get anything done.
What was even MORE frustrating was spending the time to write a detailed explanation along with recommendations only to see you obviously NOT read or understand what I had written and go heading off in yet another strange direction.
When you had finally reached a viable stage in your version of the Propeller Tables and I had finished with my first version of my Airacobra's flight model, I figured it was a good time to work on something *I* am interested in rather than something you are interested in.
I didn't see the point of giving more advice that generally gets ignored anyway.
Aleatorylamp said:
Good Bye, Aleatorylamp.
- Ivan.
aleatorylamp
Charter Member
Bye bye, Ivan,
Yes, you are absolutely right, it is absolutely crazy and insufferable.
Don´t worry, I´ve scrapped the P39D-2, so you will neither be seeing it uploaded, nor will you be bothered again.
This way you won´t have to repeat yourself ad-nauseam with your relentless criticism about my lack of research,
my forgetfulness, my overlooking things, my misinterpetation, my lack of interest or anything else that you may think,
and will not have to give any more explanations that you will not be sure I will understand.
Too bad, but that´s how it goes. We aren´t all perfect.
Aleatorylamp
Yes, you are absolutely right, it is absolutely crazy and insufferable.
Don´t worry, I´ve scrapped the P39D-2, so you will neither be seeing it uploaded, nor will you be bothered again.
This way you won´t have to repeat yourself ad-nauseam with your relentless criticism about my lack of research,
my forgetfulness, my overlooking things, my misinterpetation, my lack of interest or anything else that you may think,
and will not have to give any more explanations that you will not be sure I will understand.
Too bad, but that´s how it goes. We aren´t all perfect.
Aleatorylamp
Last edited:
aleatorylamp
Charter Member
Hello Ivan,
This is just to encourage you to continue with your fine building work on your Airacobra,
and I´m certain that it will come out much better than mine. The best of luck!
Cheers,
Aleatorylamp
This is just to encourage you to continue with your fine building work on your Airacobra,
and I´m certain that it will come out much better than mine. The best of luck!
Cheers,
Aleatorylamp
Airacobra Status Update
This thread has turned out to be more of a battle ground than a design discussion which is a shame.
I had tried to avoid the situation before ever starting this thread but that did not work as intended.
The Airacobra was chosen as a project because I was interested and I will not let a silly discussion interfere though I do not see the point of covering most of the development in this thread as I had originally intended.
Development is actually going along quite well though slower than expected.
Attached is a screenshot to show current status.
- Ivan.
This thread has turned out to be more of a battle ground than a design discussion which is a shame.
I had tried to avoid the situation before ever starting this thread but that did not work as intended.
The Airacobra was chosen as a project because I was interested and I will not let a silly discussion interfere though I do not see the point of covering most of the development in this thread as I had originally intended.
Development is actually going along quite well though slower than expected.
Attached is a screenshot to show current status.
- Ivan.
Attachments
The Airacobra project took a fairly long break for a couple reasons.
The first was that I wanted to get a working version of Eric Johnson's P-39D to test out all the other pieces that would be necessary for a completed package.
That project was released months ago but did not turn out as well as I would have wanted.
The flight model was done to the best of my ability but the handling just did not seem to match the descriptions given by various pilot reports: It didn't handle particularly well.
I had spent a lot of time calculating the proper Center of Gravity for the model but I suspected that it wasn't quite correct and that the poor handling had something to do with that.
A month or so ago, I adjusted the CoG of just the Flight Model and the handling noticeably improved.
I tried both a 1 inch and a 2 inch offset and found that the 1 inch shift seemed to give the best (to me) handling.
There are a couple more bugs I found in the flight model that I need to fix first but it is/was pretty good.
.......
That was a week ago.
.......
A few days ago I came across a Soviet test report of a P-39Q-10 from November 1943.
This was a series of spin tests conducted on that aircraft in various (mostly empty) load conditions along with pilot evaluations on handling. Reading the report is very slow because my Russian vocabulary is quite poor.
The interesting thing is that the load and CoG information from this report differ somewhat from what is found in the manual for the P-39Q upon which I based the CoG estimate for my versions of the Airacobra.
The next step is to determine what CoG estimate results from starting with information from this report.
Once that is done, I can adjust the current P-39F model and continue the build.
- Ivan.
The first was that I wanted to get a working version of Eric Johnson's P-39D to test out all the other pieces that would be necessary for a completed package.
That project was released months ago but did not turn out as well as I would have wanted.
The flight model was done to the best of my ability but the handling just did not seem to match the descriptions given by various pilot reports: It didn't handle particularly well.
I had spent a lot of time calculating the proper Center of Gravity for the model but I suspected that it wasn't quite correct and that the poor handling had something to do with that.
A month or so ago, I adjusted the CoG of just the Flight Model and the handling noticeably improved.
I tried both a 1 inch and a 2 inch offset and found that the 1 inch shift seemed to give the best (to me) handling.
There are a couple more bugs I found in the flight model that I need to fix first but it is/was pretty good.
.......
That was a week ago.
.......
A few days ago I came across a Soviet test report of a P-39Q-10 from November 1943.
This was a series of spin tests conducted on that aircraft in various (mostly empty) load conditions along with pilot evaluations on handling. Reading the report is very slow because my Russian vocabulary is quite poor.
The interesting thing is that the load and CoG information from this report differ somewhat from what is found in the manual for the P-39Q upon which I based the CoG estimate for my versions of the Airacobra.
The next step is to determine what CoG estimate results from starting with information from this report.
Once that is done, I can adjust the current P-39F model and continue the build.
- Ivan.
This is probably the most useful single diagram in the report.
Along with the data from tables, it should give a pretty complete picture of the aircraft the Soviets were testing.
Now how that relates to the P-39D/F that I am interested in is another story.
For folks who might want to read the diagram, CAX is the Russia abbreviation for MAC.
CAX == средний аэродинамический хорда
or
Medium Aerodynamic Chord
- Ivan.
Along with the data from tables, it should give a pretty complete picture of the aircraft the Soviets were testing.
Now how that relates to the P-39D/F that I am interested in is another story.
For folks who might want to read the diagram, CAX is the Russia abbreviation for MAC.
CAX == средний аэродинамический хорда
or
Medium Aerodynamic Chord
- Ivan.
