Redshift Mk I (New Purchase)

[Konrad]

Yikes, that you have to ask that question.

But I suspect this is actually a trick question. And yes there are formulas to help us work through these control and stability issues. You know this as it was part of our aeronautic training. Now I don’t have any of your engineering data. So the numbers I used were derived off of my Redshift models by myself. I can’t claim that my reverse engineered numbers are accurate. Actually, you are the one that might want to show what are the margins of stability. I’ve shown empirically (that is where it counts) that when it comes to directional stability the Redshift as delivered was lacking.

Since you, on this subject (engineering), put so much value on concepts derived from models claiming that what works for in the real world of full size and Reynolds numbers doesn’t apply. I shared with you the writing of Dr. Drela *. He has some very concise writing on the subject. He also has some simple formulas for the layman. I also recall he even has an excel worksheet that does most of the work for you.

Now there are a lot of variable (factors) that control stability. Area, moment arms, dihedral angle, surface coefficients of drag just some of the one that come to mind. One can manipulate any one, or combination of these variables to get the level of stability one wants. Note the idea of level. As mentioned earlier the problem here is finding the proper relationship between spiral stability and directional stability. The solution to one is often at odds with the other. And then there is the weight one place on each variable.

For F3F racers historically the designers have placed too high a value on drag reduction over that of directional stability. This is why “I” think we so many V-tails in the F3F class.

We all know, well I do, that the REDshift needs a lot more vertical area in the rear or a longer moment arm to counter that expanded nose. As I didn’t want to make a new fuselage or new control surfaces “I" was rather limited in what “I” could do to bias the stability towards greater directional stability.

When looking over the design I was actually shocked to see that you had used the rather pedestrian V-tail junction value of 104°. I was shocked because you often say you don’t follow the crowd in your designs. You deprecate, admonish "the me to crowd”. Now I was relieved to learn the angle wasn’t 110°!

Now in the more advanced control formulas the aspect ratio of the wing is a variable we designers manipulate. Seeing that the REDshift has those fantastic 18:1 aspect ratio wing. I was really perplexed as to why you used the 104° V-tail junction, for a clean sheet design, that is best for 15:1 aspect ratio wing.

Now with all the constraints I placed upon myself to correct the REDShift’s directional stability, basically left me with only being able to manipulate the V-tail junction angle. I ran the numbers and to get a value for directional stability that I felt was suitable for plane flying in the environment we see in the real world of racing (not in the clean air of a wind tunnel) I had to bring the V-tail angle up way past 90° ( I think it was close to 60°, yikes). Per the drag factors discussed by Hoerner I wasn’t about to go under 90° **for a racer, heck any other V-tail plane for that mater. But this did show that narrowing the V-tail angle nudged the stability in the right direction. This fit perfectly with my fix for the mechanical issue I had in the back, with leverage from the surface control arms.

Now I did take things slowly (not my F3F speeds ) and changed one thing at a time. first the mechanical fix with the tail flip and its slight aerodynamic hit. Then the 100° degree junction experiment, and based on that success the latest iteration this 96° V-tail. I could still go all the way to the Hoerner 90° limit, but then I think I’ll be flirting this pitch stability more than I’d like.

If I go any further with the REDshift design I will need to make new hardware not just make adjustments to the OEM hardware. Yes, your wing warrants that kind of work. But as I think there is a new ship just over the horizon I had high hopes. But with the few pictures (cartoons, non-engineering drawing) I’ve seen I fear the directional stability issue/solutions might not fit with "my expectations" for an F3F racer. (To be fair you aren’t claiming the next 3 meter ship to be an F3F racer).

* If you don’t like MIT professors, Don Stackhouse also has some easy formulas for finding the proper sized V-tail for a model airplane. He goes about it from a different angle (pun intended) but comes up with numbers similar to Dr Drela’s. I love the power form his V-tails and like you he too had some mechanical issues with his last design.

Both men have published these in the toy press. There is a lot of this in the real world of aviation, but I know you don’t put much validity on that part of aviation as it pertains to our toys

**I’m putting 90° as a self imposed limit

 

[Doc J]

This actually quite politely written, thanks; but neverthless is all just repetition of what has alrady been written by you, many times, Konrad.

So I have asked, and I admit, repeated, some new questions for you to think about and respond to, please.

Yikes, that you have to ask that question.

But I suspect this is actually a trick question. And yes there are formulas to help us work through these control and stability issues. You know this as it was part of our aeronautic training. Now I don’t have any of your engineering data. So the numbers I used were derived off of my Redshift models by myself. I can’t claim that my reverse engineered numbers are accurate. Actually, you are the one that might want to show what are the margins of stability. I’ve shown empirically (that is where it counts) that when it comes to directional stability the Redshift as delivered was lacking.

Please show me the NUMBERS YOU USED, and the formulas they were derived from, as applied specifically to my Redshift.

Since you, on this subject (engineering), put so much value on concepts derived from models claiming that what works for in the real world of full size and Reynolds numbers doesn’t apply. I shared with you the writing of Dr. Drela *. He has some very concise writing on the subject. He also has some simple formulas for the layman. I also recall he even has an excel worksheet that does most of the work for you.

I said that Full Sized models - especially those derived from Full Sized Powered Aircraft: MAY NOT APPLY and never mentioned that Reynolds numbers did not apply. What I want to ask you for, are your conclusions - based on Dr. Drela's or other studies.

Now there are a lot of variable (factors) that control stability. Area, moment arms, dihedral angle, surface coefficients of drag just some of the one that come to mind. One can manipulate any one, or combination of these variables to get the level of stability one wants. Note the idea of level. As mentioned earlier the problem here is finding the proper relationship between spiral stability and directional stability. The solution to one is often at odds with the other. And then there is the weight one place on each variable.

Precisely, so show me exactly how you did that in order to come to your conclusions that the Redshift model had these severe problems. As it pertains specifically to a model I designed, then I want to know what the proper relationship that you used, actually is.

For F3F racers historically the designers have placed too high a value on drag reduction over that of directional stability. This is why “I” think we so many V-tails in the F3F class.

We all know, well I do, that the REDshift needs a lot more vertical area in the rear or a longer moment arm to counter that expanded nose. As I didn’t want to make a new fuselage or new control surfaces “I" was rather limited in what “I” could do to bias the stability towards greater directional stability.

Demonstrate, please - show me your numbers.

When looking over the design I was actually shocked to see that you had used the rather pedestrian V-tail junction value of 104°. I was shocked because you often say you don’t follow the crowd in your designs. You deprecate, admonish "the me to crowd”. Now I was relieved to learn the angle wasn’t 110°!

We have been through this so many times that I have lost count.

By now I have readily admitted, so many times that:

• Yes, I could have used less angle.
• Yes, I could have used more wetted area.

Can we agree: Guilty as charged on that?

Now in the more advanced control formulas the aspect ratio of the wing is a variable we designers manipulate. Seeing that the REDshift has those fantastic 18:1 aspect ratio wing. I was really perplexed as to why you used the 104° V-tail junction, for a clean sheet design, that is best for 15:1 aspect ratio wing.

"We designers" Please show me YOUR KONRAD F3f design, Konrad.

Now with all the constraints I placed upon myself to correct the REDShift’s directional stability, basically left me with only being able to manipulate the V-tail junction angle. I ran the numbers and to get a value for directional stability that I felt was suitable for plane flying in the environment we see in the real world of racing (not in the clean air of a wind tunnel) I had to bring the V-tail angle up way past 90° ( I think it was close to 60°, yikes). Per the drag factors discussed by Hoerner I wasn’t about to go under 90° **for a racer, heck any other V-tail plane for that mater. But this did show that narrowing the V-tail angle nudged the stability in the right direction. This fit perfectly with my fix for the mechanical issue I had in the back, with leverage from the surface control arms.

Please show me those numbers.

Now I did take things slowly (not my F3F speeds ) and changed one thing at a time. first the mechanical fix with the tail flip and its slight aerodynamic hit. Then the 100° degree junction experiment, and based on that success the latest iteration this 96° V-tail. I could still go all the way to the Hoerner 90° limit, but then I think I’ll be flirting this pitch stability more than I’d like.

If I go any further with the REDshift design I will need to make new hardware not just make adjustments to the OEM hardware. Yes, your wing warrants that kind of work. But as I think there is a new ship just over the horizon I had high hopes. But with the few pictures (cartoons, non-engineering drawing) I’ve seen I fear the directional stability issue/solutions might not fit with "my expectations" for an F3F racer. (To be fair you aren’t claiming the next 3 meter ship to be an F3F racer).

You have already pointed out several "Konrad Theory" flaws in my design.
Konrad Theory flaws that I have to say I completely disgaree with.
So please show us your Konrad design, hopefully with none of these.

* If you don’t like MIT professors, Don Stackhouse also has some easy formulas for finding the proper sized V-tail for a model airplane. He goes about it from a different angle (pun intended) but comes up with numbers similar to Dr Drela’s. I love the power form his V-tails and like you he too had some mechanical issues with his last design.

I like anybody who can give me numbers - especially useable numbers, and even more so if directly applied to one of my designs - as you have said you have done.

Please show me the formulas and numbers you have used and derived.

Both men have published these in the toy press. There is a lot of this in the real world of aviation, but I know you don’t put much validity on that part of aviation as it pertains to our toys

What we are dealing with IS the real world of Aviation.

The fact that its small-scale toy aviation sometimes means that full-sized powered aviation models may not apply. I have found this to be so, many times. Often we find ourselves below the limits of scaling the full-sized data for model use, and this is why I dispute its vaildity as being useful across the board. This applies especially to older, full sized powered aircraft data.

**I’m putting 90° as a self imposed limit

I don't anyone needs another long diatribe covering yet again what has already been covered well and now repeated many times.

Lets have some new data: Therefore, I politely ask you again:

Please show me your design.
Please show me the numbers you have used, and the formulas used to derive them.

Cheers,

Doc.

 

[ORRich]

@Wayne is it possible to close threads? Lol

 

[Konrad]

This actually quite politely written, thanks; but neverthless is all just repetition of what has alrady been written by you, many times, Konrad.

So I have asked, and I admit, repeated, some new questions for you to think about and respond to, please.

Please show me the NUMBERS YOU USED, and the formulas they were derived from, as applied specifically to my Redshift.

I said that Full Sized models - especially those derived from Full Sized Powered Aircraft: MAY NOT APPLY and never mentioned that Reynolds numbers did not apply. What I want to ask you for, are your conclusions - based on Dr. Drela's or other studies.

Precisely, so show me exactly how you did that in order to come to your conclusions that the Redshift model had these severe problems. As it pertains specifically to a model I designed, then I want to know what the proper relationship that you used, actually is.

Demonstrate, please - show me your numbers.

We have been through this so many times that I have lost count.

By now I have readily admitted, so many times that:

• Yes, I could have used less angle.
• Yes, I could have used more wetted area.

Can we agree: Guilty as charged on that?

"We designers" Please show me YOUR KONRAD XXXX F3f design, Konrad.

Please show me those numbers.


You have already pointed out several "XXXXX Theory" flaws in my design.
Konrad Theory flaws that I have to say I completely disgaree with.
So please show us your Konrad design, hopefully with none of these.

I like anybody who can give me numbers - especially useable numbers, and even more so if directly applied to one of my designs - as you have said you have done.

Please show me the formulas and numbers you have used and derived.

What we are dealing with IS the real world of Aviation.

The fact that its small-scale toy aviation sometimes means that full-sized powered aviation models may not apply. I have found this to be so, many times. Often we find ourselves below the limits of scaling the full-sized data for model use, and this is why I dispute its vaildity as being useful across the board. This applies especially to older, full sized powered aircraft data.

I don't anyone needs another long diatribe covering yet again what has already been covered well and now repeated many times.

Lets have some new data: Therefore, I politely ask you again:

Please show me your design.
Please show me the numbers you have used, and the formulas used to derive them.

Cheers,

Doc.

Doc, Thank you! I think this is the first time you stated that publicly. This should go a long way to rebuilding the public confidence in the future Hammond V-tail, if there is to be one.

Doc, I never said I have designed a clean sheet F3F racer. The last model I designed from a clean sheet was 40 years ago and that was an AMA 422 (.15 cid racer). If I had to do it again I would add some of the lessons I learned in the preceding years.

As to the rest, are you asking for a consulting contract? You know that if we went into the numbers here we would have to explain how to interpret the findings. Suffice to say directional stability is lacking in the as delivered REDShift. By your own admission (see the red highlights in your post)

 

[Konrad]

At the last race, where I didn’t use a Redshift, it was mentioned that the REDshift is not the first F3F racer to be found lacking directional stability.
Some of the better pilot/engineers told me about how they rigged there F3F/F3B ships that lack some directional stability. I think the main point was also mentioned here by 2much2do?

The key was to try to minimize the disruption of the airflow over the V-tail. The best way to do that with a locked in design is to kill the flap movement with the aileron movement. This will necessitate reworking the aileron differential and aileron to rudder mixes.

Here are my set up values for the REDShift as I last flew her. These will be subject to change as I get more familiar with the new ship (96° V-tail REDshift)

Baseline a REDshift with flipped V-tail mod and V-tail junction at 96° (V-tail tips, 495mm apart) with the Center of Gravity at 96mm.

Elevator throw + 5mm
Rudder throw + 7+mm
Aileron 22mm up, 20mm down, Flap mix (if used) 10mm up, 9mm down
Snap flap 4mm down (below profile). Ailerons 0.5mm less than flaps, Reflex just shy of 3mm up.
Aileron to Rudder mix just under 2mm in normal mode, just over 2.5mm in reflex.

In Reflex the flap are suppressed as ailerons. As you can see to get a good roll rate I’m using a lot of aileron with little differential. This forces me to use a lot of active rudder input in the way of a 2.5+ mm mix to control the induced adverse yaw. This set up has more input drag than I like, but at least in the condition I last flew, the REDshift she is much more stable in her heading coming into and out of a pylon turn. This is key to a good handling F3F racer.

In the off season I’ll work on trying to lower this control drag yet maintain the control power I want.

 

[Konrad]

@Wayne is it possible to close threads? Lol

I hope not this one? I'm learning a lot as the owner of 3 redshifts.

 

[Doc J]

Doc, Thank you! I think this is the first time you stated that publicly. This should go a long way to rebuilding the confidence in the future Hammond V-tail, if there is one.

Doc, I never said I have designed a clean sheet F3F racer. The last model I designed from a clean sheet was 40 years ago and that was an AMA 422 (.15 cid racer). If I had to do it again I would add some of the lessons I learned in the preceding years.

As to the rest, are you asking for a consulting contract? You know that if we went into the numbers here we would have to explain how to interpret the findings. Suffice to say directional stability is lacking in the as delivered REDShift. By your own admission (see the red highlights in your post)

Ok, Understand.

As to the design, I did not say you have designed anything. I said I wanted to see A Konrad design to prove your gathered theories, as for the most part I can see no substance in them. I still would.

As to my request for the numbers and formulae used to derive numbers you said that you have; do you now confirm that there is absolutely no relationship that you have calculated and can be proven between the V-Tail and the nose on my Redshift model?

Lastly, I have admitted (ad infirnitum) that I could have desiged the V-tail better.

Doc.

 

[Doc J]

Doc, Thank you! I think this is the first time you stated that publicly. This should go a long way to rebuilding the public confidence in the future Hammond V-tail, if there is to be one.

Doc, I never said I have designed a clean sheet F3F racer. The last model I designed from a clean sheet was 40 years ago and that was an AMA 422 (.15 cid racer). If I had to do it again I would add some of the lessons I learned in the preceding years.

As to the rest, are you asking for a consulting contract? You know that if we went into the numbers here we would have to explain how to interpret the findings. Suffice to say directional stability is lacking in the as delivered REDShift. By your own admission (see the red highlights in your post)

Red highlights which pertain to the V Tail alone - nothing whatsoever to do with the nose.

Doc

 

[Konrad]

Then we are in agreement, well other than the nose. I'm truly hoping the next 3m is a world beater. That wing has so much potential. Even with me flying the REDshift mk1 I get a lot of positive comment on how she looks driving through the turns.

 

[Doc J]

Then we are in agreement, well other than the nose. I'm truly hoping the next 3m is a world beater. That wing has so much potential. Even with me flying the REDshift mk1 I get a lot of positive comment on how she looks driving through the turns.

No we are not in agreement, Konrad.

You have stated, very voluably, many many times that the model design is badly flawed and that there is a huge directional problem that is caused by an apparent instability-inducing relationship between nose and the V-Tail, and more importantly, that you have proved this.

Is this actually true? If so, then I would like to know what this relationship is, where did it come from, and I want to see your numerical proof.

If you can't do this, then I'd like you to admit that everything you have written is just pure unproven conjecture on your behalf.

Doc

 

[ORRich]

I hope not this one? I'm learning a lot as the owner of 3 redshifts.

I respectfully disagree. There are 7 pages of back and forth. I don’t think anyone is really reading this. It’s a circular conversation that isn’t really adding value.

You may think this is valuable info and that is part of the issue.

Doc is asking for your calculations to back your points. And there seem to be none.

That is why I asked if the thread could be closed. But in afterthought it wouldn’t matter as another post would invariably pop up and we’d back in the same boat.

 

[Doc J]

I respectfully disagree. There are 7 pages of back and forth. I don’t think anyone is really reading this. It’s a circular conversation that isn’t really adding value.

You may think this is valuable info and that is part of the issue.

Doc is asking for your calculations to back your points. And there seem to be none.

That is why I asked if the thread could be closed. But in afterthought it wouldn’t matter as another post would invariably pop up and we’d back in the same boat.

I'd add to that a bit.

1. I have been maligned so I have made my points and requests quite clear.
2. There will never be any more MK1 Redshifts.
3. I think keeping the face slapping on DM is the best idea. But in any case its only Konrad and I, and even Wayne got tired of that.

SOOOOOOOOO...For friendly, non confrontational, polite, affable, fun-loving, questions, answers, discussions, information sharing, and suggestions et al - lets go to...

The Gigantic, the Tremendous AERODYNAMICS CHANNEL! - It will get you high!

Doc.

 

[Konrad]

I respectfully disagree. There are 7 pages of back and forth. I don’t think anyone is really reading this. It’s a circular conversation that isn’t really adding value.

You may think this is valuable info and that is part of the issue.

Doc is asking for your calculations to back your points. And there seem to be none.

That is why I asked if the thread could be closed. But in afterthought it wouldn’t matter as another post would invariably pop up and we’d back in the same boat.

7 pages?

I do these build threads to show the product, to highlight the features of interest, to identify the problem I've found in the build and performance. I try to provide the solutions to those problems. It is far too easy to say XYZ is junk and runaway. Most of this thread is doing just that trying to show the assembly and flying issues and offer solutions. Maybe not the best, but what most can do from their building bench. Ok, post #38, 51, 65 not so much. But it isn't until page 6 post #114 that this thread really goes off the rails. This is where some folks are starting to get defensive, when I start comparing this model to the fantastic Freestylers.
You are correct, he chose to bring the issues discussed in another thread into this one. Where in a PM I mentioned the market's preception of his V-tails.

Now as to going into deep analytical discussion here, I see no point as I don't have the OEM engineering data. I derived my numbers for area and moment arms using the process of drawing out the features on cardboard cutting the shapes and using a milligram scale to calculate the area and center of gravity of the feature. Also there are a lot of general assumptions made taken from texts. These can easily be used to invalidate the quick and dirty findings. Also if a gave a value for stability would most folks understand it. I suspect I'd have to give a lesson on how to interpret the numbers.

But in the end the issue is how does the aircraft handle. I don't have any accelerometer on board to show how fast the ship comes back into a stable trim. or how fast she deviates from her heading. So I can't quantify the stability issue. I gave my impression of the handling and the solution I'm using within the constraints I place upon myself.

In post #56 it was admited that there wasn't adiquate work done. As result I suspect he doesn't have adiquate numbers

I hope you can see where this is a trap.

It isn't just I that has seen these stability issues. The whole British F3F team has seen it (post #56). I know the sample size is small as I think it was mentioned that only around 30 of these REDshifts where made.

And I'm sorry the designer thinks I'm picking on him. I try to show that the issues aren't unique to the REDshift. But as the thread is about the REDshift and how it performs as an F3F racer. The focus will be on the REDshift mk 1.

 

[ORRich]

Konrad- you seem to drive others mad. But I won’t be one There seems to be a certain tone deafness. And that’s ok we’re all different.

Again I don’t mean to poke or be rude or anything. It’s more of a ‘read the room’ scenario.

I only mean this perhaps to help and maybe it would be better DM’d to you. That’s fair. But perhaps instead of responding here, please move to the channel doc set up.

No one is really learning much here.

 

[Konrad]

I've learned a lot working my way through this project. Heck, all three of my REDshift builds.

Yes there are 7 pages of my findings, solutions and experience pertaining to the REDshift mk1. Not sure I see the back and forth. Yes the designer came and tried to offer some help and solutions to the issues I notice during the build. I don't see a problem with that.

If one want's to change the discussion to something else then explore the other threads. This thread was to discuss /share my findings with my second Redshift mk1.

A summary is that the wing has some potential. Unlike most high aspect ratio wings this set of wings has a benign stall. The OEM had many quality issues. The design has some mechanical short comings. And that in my experience flying the bird. Flights have shown the rear vertical area (V-tail?) was not sufficient to address the destabilizing nature of the fuselage. To end up with a nice predictable flying F3F racer, in a host of flying conditions I need to add more vertical area to the rear fin. Has the 96° junction done that? No, but it is a nudge in the right direction.

I try to show how I address many of these issues. And published some set up values that appear to help mitigate some of the stability issue but at the cost of added control input drag. This may help with other designs that show near the same control instability issues. These added control inputs were one of the main reasons the designer went with large nose. He stated that he was trying to come up with a design to try to minimize the control inputs in the crabbing F3F racer. In the end I'm having to add much more control input in the way of mixes than what I need to use, on say the Freestyler-5.

 

[Doc J]

7 pages?

I do these build threads to show the product, to highlight the features of interest, to identify the problem I've found in the build and performance. I try to provide the solutions to those problems. It is far too easy to say XYZ is junk and runaway. Most of this thread is doing just that trying to show the assembly and flying issues and offer solutions. Maybe not the best, but what most can do from their building bench. Ok, post #38, 51, 65 not so much. But it isn't until page 6 post #114 that this thread really goes off the rails. This is where some folks are starting to get defensive, when I start comparing this model to the fantastic Freestylers.
You are correct, he chose to bring the issues discussed in another thread into this one. Where in a PM I mentioned the market's preception of his V-tails.

Now as to going into deep analytical discussion here, I see no point as I don't have the OEM engineering data. I derived my numbers for area and moment arms using the process of drawing out the features on cardboard cutting the shapes and using a milligram scale to calculate the area and center of gravity of the feature. Also there are a lot of general assumptions made taken from texts. These can easily be used to invalidate the quick and dirty findings. Also if a gave a value for stability would most folks understand it. I suspect I'd have to give a lesson on how to interpret the numbers.

But in the end the issue is how does the aircraft handle. I don't have any accelerometer on board to show how fast the ship comes back into a stable trim. or how fast she deviates from her heading. So I can't quantify the stability issue. I gave my impression of the handling and the solution I'm using within the constraints I place upon myself.

In post #56 it was admited that there wasn't adiquate work done. As result I suspect he doesn't have adiquate numbers

I hope you can see where this is a trap.

It isn't just I that has seen these stability issues. The whole British F3F team has seen it (post #56). I know the sample size is small as I think it was mentioned that only around 30 of these REDshifts where made.

And I'm sorry the designer thinks I'm picking on him. I try to show that the issues aren't unique to the REDshift. But as the thread is about the REDshift and how it performs as an F3F racer. The focus will be on the REDshift mk 1.

Put up or shut up Korad.

Thanks,

Doc.

 

[Doc J]

I've learned a lot working my way through this project. Heck, all three of my REDshift builds.

Yes there are 7 pages of my findings, solutions and experience pertaining to the REDshift mk1. Not sure I see the back and forth. Yes the designer came and tried to offer some help and solutions to the issues I notice during the build. I don't see a problem with that.

If one want's to change the discussion to something else then explore the other threads. This thread was to discuss /share my findings with my second Redshift mk1.

A summary is that the wing has some potential. Unlike most high aspect ratio wings this set of wings has a benign stall. The OEM had many quality issues. The design has some mechanical short comings. And that in my experience flying the bird. Flights have shown the rear vertical area (V-tail?) was not sufficient to address the destabilizing nature of the fuselage. To end up with a nice predictable flying F3F racer, in a host of flying conditions I need to add more vertical area to the rear fin. Has the 96° junction done that? No, but it is a nudge in the right direction.

I try to show how I address many of these issues. And published some set up values that appear to help mitigate some of the stability issue but at the cost of added control input drag. This may help with other designs that show near the same control instability issues. These added control inputs were one of the main reasons the designer went with large nose. He stated that he was trying to come up with a design to try to minimize the control inputs in the crabbing F3F racer. In the end I'm having to add much more control input in the way of mixes than what I need to use, on say the Freestyler-5.

Konrad, we have all heard all of this many, many (7 pages of) times.

As Rich has said, its often not what you say, its how you say it. You say you have "no time" to be polite, yet you have ample time to repeat, rehash, and repeat, rehash and repeat the same things over and over and over again. However, I will admit that your courtesy and respect for others is apparently improving.

Technically here is only one point in dispute between us and that is this relationship that you state that you have discovered and that is entirely detrimental - a game changer in fact, that turns the Redshift into an uncontrollable beast. As you say you have the theory used, and the numbers, I have asked you to show me this.

In this case, to save your credibility, I ask you one last time to show me your work.

Doc

 

[Wayne]

@Wayne is it possible to close threads? Lol

Tempting.. Very tempting.

I no longer read this thread, just spot check to make sure people are not getting too out of shape.

 

[Konrad]

I don’t know why I allow myself to be goaded into this. These numbers would be better if pulled off the designer's engineering documents. But with the REDshift the CAD was outsourced. So I suspect these numbers aren’t available to or from the designer.

Here I’ll try to show how one can derive the numbers needed to plug into any stability program of your choice. And to give context I’ll do it do the Freestyler-5. This methodology is a tried and true technique used to find the area under a curve. The assumption is that the paper has a uniform thickness and mass.

Find the relationship between the area and the mass of the paper. Draw the outline of the shape keeping the pen 90° to the paper and tangent to the shape. Come back and redraw this shape removing the pen thickness offset. Mark the center of gravity (CG) of the model. This will be used as the datum to measure the fuselage moment arms. Cut out the shape from the paper, making the CG line one of the edges of the paper shape. Weigh the paper shape. As you know the relationship between the area and the mass of the paper you can calculate the area of the paper shape, no mater how odd the shape is.

Now to find the center of this shape you are going to try to find the balance point. This is why I use stiff paper (300g/m2). Use a straight pin as a pivot. Stick it through the shape and see how it rotates around the pin. You will have found the center of the shape when the shape stops spinning at random points. Mark this pin hole. Measure the distance from the CG line to this point and that is the moment arm for the shape. (Note, some programs use the center of pressure to calculate the moment arms. You can use the 1/3, 2/3 rule to guess at that)

Most stability programs will ask for the coefficient of drag for the fuselage shape. This will be a swag from general accepted data for given shapes. The front cross section shape of the REDshift is an ellipse with the long axis acting in the yaw plane. The tail boom is round in cross section.
The front cross section shape of the Freestyler-5 is triangular with the sides acting in yaw being approximately 60°. The tail boom is again a triangular cross section with the side at 30° to yaw.

To model the wing I think one can find published plan views and sales data for both models. Most stability programs will ask for the LE sweep. This will be difficult to accurately define with the reverse elliptical wing found on both planes. But for comparisons if using the same methodologies on both wings the comparative value should be valid.

For the Freestyler 5 here are the number I’ve derived.

Center of Gravity 105mm from the wing LE at the root.

Fuselage front side area 197cm2
Fuselage forward moment arm 223mm
Front area coefficient of drag - unknown

Fuselage rear boom side area 285 cm2
Boom area coefficient of drag - unknown

Stabilizer area 371cm2 (per surface)
Rear moment arm of the stabilizer 873mm
V-tail junction angle 102°

Wing dihedral 4.7°
Wing LE sweep - unknown (reverse ellipse)
Wing center of mass from fuse center line, 540mm @650grams


For the REDshift here are the number I’ve derived.

Center of Gravity 96 mm from the wing LE at the root.

Fuselage front side area 251cm2
Fuselage forward moment arm 241mm
Front area coefficient of drag - unknown

Fuselage rear boom side area 284 cm2
Boom area coefficient of drag - unknown

Stabilizer area 292cm2 (per surface)
Rear moment arm of the stabilizer 825mm
V-tail junction angle 104°

Wing dihedral 4°
Wing LE sweep - unknown (reverse ellipse)
Wing center of mass from fuse center line, 580mm @730grams

I was surprised to find that both the REDshift and Freestyler have the same boom side area. but the REDshift has 20% more wetter area (not a low drag concept) All the numbers point to a less stable aircraft in directional stability for the REDshift compared to the Freestyler-5

I have a high level of confidence that any stability model will show that the Freestyler is much more stable than the REDshift. I also “feel” that any program will show that the REDshift’s stability is eschewed towards being directionally unstable. I offer the numbers I used, for you all, to plug into any stability modeling program you are comfortable with and have a high level of confidence in.

This is all academic as I have no way of quantifying the response of the aircraft*. Aircraft design is difficult particularly the problem with stability. As there are a lot of competing factors. Here we are concerned with the dutch roll, spiral stability, directional stability while trying to maintain the lowest drag for a fast F3F ship.

Please note I’m not saying the REDshift is divergent. Just that the level of directional stability results in a racer that does not offer the pilot much level of confidence flying close to the cliff lip. This distracts from the pilots ability to place the ship where he wants on the race course.

All this gnashing of teeth and wringing of hands because I said; I like to see all fuselage junctions to be 90° of larger. And I mentioned in a PM that the Hammond V-tail has a sour reputation with slope pilots that know of the problems with the Strega and REDshift.

Doc. if quoting me please do it properly. I said I can't be bothered to placate ....

The problem I see as to my reputation is that some are casting doubt as to my ability to to ascertain a good flying ship from a poor flying ship. Let me state that the Freestyler is by far the superior F3F racer when looked at against the REDshift mk1. Now I want to be clear on this, the beauty of the REDshift is in the wing.

* With today’s stabilized receivers we might actually be able to pull out the accelerometer data. That data would be real nice to have.

Edit: to add per surface

 

[Doc J]

I'm abandoning it too, Wayne.

• Its just repeat, repeat, repeat.
• The model flies OK in most people's hands.
• In any case the model is obsolete and will never be made again.
• The V-tail has been replied to umpteen times by me.
• The mythical catastrophic instability relationship between the nose and the V-tail does not exist.

Cheers,

Doc.