I think these are the statements that actually bother me - these are merely your opinion Konrad yet you say them as if they're fact- could you provide some video evidence of your claims? ie show the less-than-desirable characteristics that you claim about this model - also where are the other opinions on the forums? usually there is consensus around ideas, or tribal knowledge but no one is backing these claims up -
@Wayne this is just getting ludicrous - instead of citing engineering manuals that none of us have the time or inclination to decipher why don't we see video evidence of how this machine flies vs other models - if indeed there was spiral instability as is claimed, pilots would really a) not bother with a plane with these characteristics and opt for the 100 other options in the market or b) add mixers in their radios to compensate for this behavior - are either of these things been done by the owners? I just don't see the problem -
It's too bad Konrad because for all the good that you post and help out in the forum you take as many +1 steps backwards with this issue - and that's a shame - do you recall this forum thread?
https://forum.alofthobbies.com/index.php?threads/konrads-departure.2310/
Rich. I post what I experienced in hopes that it will help others. Reading your posts I don't think you understand what static directional stability is. Comments like the one's Doc. makes, claiming unstable flight are not seen, just shows to me that you and he still don't understand the stability part of a design.
All of Doc's V-tails are flyable. I have never said they models are divergent unstable in flight. Just that they all need MORE directional stability. This is shown by their wandering in yaw, the extra need for excessive control inputs (large rudder mixes and large amounts of aileron differential [slow roll response]). I reference the setup of the Freestyler-5 a contemporary design to the REDshift as a base line.
I've provided most of the data you would need to compare the results should you run the numbers using any formulas you are comfortable with. I don't publish a value here because I have stated that even with the the data I provide there are still too many assumptions I had to make. Besides If I gave you a stability quotient of say 1.12 would you know what that means? I also don't have any accelerometer data to show the yaw rates (this is what you would want as proof of some level of stability, not videos, to validate my observation.
I try to show that stability is very difficult to predict and model (mathematically) by showing that many many full size designs have had to add much area after flight testing. Even some modern designs using computational fluid design models had to be re-designed after flight testing. ( I have not run any of my toy airplane values through these).
In the end this is all about my experience observations. Early on I asked Doc, about the oversized nose. He came back with an honest admission that he had misunderstood the FAI nose radius requirement. That and looking at what a nose needs to do (house the radio ballast tube) I didn't think there was a big problem. I did notice early on that the tail volume looked rather small, actually very small. Again Doc claimed that his airfoils were more effective (higher control power) than what others used. So I again took him at face value. I did see a fatal design issue (very low servo resolution and double centering surfaces) with the linkage and flipped inverted the flippers.
So far so good. Then came the flight testing and trying to race the F3F REDshift racer. I was surprised at how poorly the REDshift acted with regards to directional stability. But I wasn't surprised as all F3F designs are biased towards some directional instability (note this not a problem unique to Doc's designs). I was shocked to learn that the V-tail junction angle was a typical 104°. This (for design reason I won't go into here) is very shallow for a design that has such a high aspect ratio wing. I came up with an easy dirty fix of bringing up the V-tail junction to 96°. This proved by flight testing to validate my understanding of the V-tail theories and the tail volume findings early on. I think I stated that the modified REDshift can now finally run with the big boys.
I've been doing my re-design work in a bit of a vacuum until I acquired my Freestyler-5. Having set up and flow the Freestyler I was shocked at how stable it was. I was expecting much the same directional stability issues as I saw with the REDshift. I expected the Freestyler-5 to again be fighting the same physics trying to keep the wetted are down to a minimum. This drove me to actually derive the data for both models. Working with the same assumption I came up with the REDshift having approximately 60% the directional stability of the FreeStyler. This aligned with my flight test findings.
I started to wonder why the REDshift has some much front side area and moment arm. I had assumed that the nose was so long to compensate for the mass of the tail boom. But doing some research I cam across this statement. This make it clear to me that designer misunderstood the relationship between vertical area and stability. I tried to show that this isn't my idea but well documented in most texts about directional stability.
I then saw that the designer is coming out with a new 3 meter ship the Spada. And again with what little he has shown it is looking to me that the design will continue to have directional stability issues as the V-tail as shown will again be undersized and the nose will again be too long. While the Spada does show a marked reduction in side area, it stall has too long nose moment arm. This can be a problem with spin recovery. Also while the Doc say he has narrowed the V-tail junction to 100° this is in the right direction. But with the high aspect ratio wing and the under sized tail volume "I" think the V-tail junction needs to be much closer to 90°, like 94°.
I was hoping that with all the experience we have gained with the REDshift that we might benefit from it with the new model. I fear this won't be the case.
While I know Doc won't or can't change the design, I hope you and others have been exposed to the design issues and features surrounding directional stability. These Issues are the core reason V-tail have their poor reputation. It has nothing to do with being a V-tail rather most V-tails don't have enough effective rear vertical area. These issues unique to any of Doc's designs. I was just expecting more of Doc.
Yes, this is all from my experience and observation, I also try to offer supporting documentation. I hope I've given anyone who is looking some background to dig deeper. But I leave it up to you to determine if you can using it in your understanding and purchases.
In conclusion the REDshift is a vey poor design with a wing that show great potential. I hope the Spada can bring this out.
