Redshift Mk I (New Purchase)

[Konrad]

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• In any case the model is obsolete and will never be made again.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 unpteen times by me.
• The mythical relationship between the nose and the V-tail does not exist.

Cheers,

Doc.

It flies in most folks hands, but not well. Like I said it isn't divergent. Or not as well as other models on the market in the same time frame. Most would have attribute this flight stability issue to the mechanics and I would agree as a result of the double centering problem with the snakes and the control arms (those are also design issues). But once those problems were solved the ship still does not go where you point it.

The model is still available (DON'T RECOMMEND GETTING ONE FROM THAT SOURCE!) And as there are 20? others that are still flying? The 96° fix is any easy mod for most owners.

Some might want to try this experiment. Acquire one of these, and get her trimmed to fly as you like. Now take the same area we have in the form of the rear vertical fin and add it to the front (nose). Re-balance the model for the added nose weight this fin adds. And report back your findings. I'm sure most will find that the added front vertical area will result in a very unstable aircraft. As this added front fin will be a destabilizing factor over powering the yaw dampening of the rear fin. In fact it will cause a positive feedback resulting in the ship yawing even harder as a result of the upset (cross wind launch). This is what the added side area of a large nose is doing, adversely effecting the directional stability.

This is nothing that a larger rear fin can't address but at the cost of added drag from the added wet area.

Here in this thread I was showing that moving the V-tail junction angle from the OEM 104° to 96° adds some of that missing vertical fin area to over come the nose with no added drag penalty from any added wet area.

Edit: difergent to divergent

 

[Doc J]

It flies in most folks hands, but not well. Like I said it isn't difergent. Or not as well as other models on the market in the same time frame. Most would have attribute this flight stability issue to the mechanics and I would agree as a result of the double centering problem with the snakes and the control arms (those are also design issues). But once those problems were solved the ship still does not go where you point it.

The model is still available (DON'T RECOMMEND GETTING ONE FROM THAT SOURCE!) And as there are 20? others that are still flying? The 96° fix is any easy mod for most owners.

Some might want to try this experiment. Acquire one of these, and get her trimed to fly as you like. Now take the same area we have in the form of the rear vertical fin and add it to the front (nose). Re-balance the model for the added nose weight this fin adds. And report back your findings. I'm sure most will find that the added front vertical area will result in a very unstable aircraft. As this added front fin will be a destabilizing factor over powering the yaw dampening of the rear fin. In fact it will cause a possitive feedback resulting in the ship yawing even harder as a result of the upset (cross wind launch). This is what the added side area of a large nose is doing, adverly effecting the directional stability.

This is nothing that a larger rear fin can't address but at the cost of added drag from the added wet area.

Here in this thread I was showing that moving the V-tail junction angle from the OEM 104° to 96° adds some of that missing vertical fin area to over come the nose with no added drag penalty from any added wet area.

No it isn't.

Doc.

 

[Konrad]

Here are some of the issues I'm dealing with in regards to trim and stability.

As a result of the tilting lift vectors with the application of ailerons there is a lot of adverse yaw from the needed for a high roll rate in an F3F racer.

It is the function of the rear vertical side area to control this unwanted induced adverse yaw. In my cartoon that would be the blue and violet low pressure area. The area ahead of the plane's center of gravity also acts as a fin. Unfortunately, with the adverse yaw this area is now a destabilizing force (shown in olive) as it is offer positive feedback to the unwanted yaw. The rear vertical area must over come the induced adverse yaw and this destabilizing effect of the forward side area.

With properly sized rear vertical side area this is easy to correct. Unfortunately at the cost of drag. Most F3F racers have rather small noses not only for the reduction in frontal area (cross section) but also as short a nose as practical to minimize this forward side area. This is why some of the more forward thinking designers like Don Stackhouse minimize this and have the front fuselage laying down on its side.

Another issue is the leverage the ailerons have with high aspect ratio wings. Also the high aspect ratio wing place the wing's center of mass further away from the center line of aircraft. This forces the need for slightly larger vertical rear area. To keep the wetter area down most designers are now going with V-tail junctions below 100 degrees.

While the tail volume of the REDshift might be on the small side (but barely adiquate) of most F3F racers for its wing area. The fact that the REDshift has a rather high aspect ratio wing and oversized nose means that the tail volume has proven to be inadequate in my test flights.

In an effort to minimize the leverage the aileron input has with long glider wings we often mix in the flaps as aileron. Now because of landing requirements most designers place most of the rear vertical area above the fuselage. This results in the upward moving flap/aileron disrupting the airflow on one side of the vertical area more than the other. This is true for the cruciform T- tail and V-tail.

As of late I've been trying the trim set up where the flaps are dead in roll. This is done to minimize the above mentioned loss of vertical fin area effectiveness from the flap turbulence. The down side of this control set up is the need for more aileron inputs! The adverse effects of this can be addressed with aileron differential and active aileron to rudder mix, adding control input drag. Flight tests and race times will indicate what is the best setup for addressing the REDshift with its undersized tail volume. Looking at the REDshift numbers against those of the competition it is clear that the proper fix is to minimize the nose and add tail volume.

Edit: change 1 to 100 degrees

 

[ORRich]

Ok. So assuming your theory is correct (I can’t tell if it is or isn’t) what now? Will you modify this and test your hypothesis? And if that proves out then what is next? Showing other owners of this model how to modify it if they’re unhappy with it? It’s been a long discussion and trying to get to resolution? Or is this merely a thought experiment?

 

[Konrad]

Ok. So assuming your theory is correct (I can’t tell if it is or isn’t) what now? Will you modify this and test your hypothesis? And if that proves out then what is next? Showing other owners of this model how to modify it if they’re unhappy with it? It’s been a long discussion and trying to get to resolution? Or is this merely a thought experiment?

Really? But I'll assume this is a real question.

If you follow the 3 REDshift threads. It should be clear what I'm doing. First I addressed the mechanical issues with the V-tail linkage. Flipping the V-tails and taking the aerodynamic hit for having the hinge gap on the pressure side of the surface. (Generally the tail pushes down to counter the negative pitching moment of a cambered airfoil. This pitching moment as a function CL is well defined on most airfoil graphs). I addressed the need for more aileron movement with the cutting back of the OEM gap wipers. As the directional issue still prevailed I measured the V tail junction and was a bit perplexed as to why the OEM designer was using 104° with a set of wings that is sporting an 18:1 aspect ratio. As most F3F racers are on the shy side of tail volume It was expected with the small V-tail that the V-tail junction angle would have been less than 100°.

As the REDshift uses pin and posts to mount the V-tail it was easy to change the V-tail junction. I took the conservative approach with the used REDshift I made the first experiments and set the junction angle at 100°. This proved to be very productive. As I wasn't showing any adverse effects regarding pitch stability. And that my initial modeling of the required vertical area showed that I'd need to bring the V-tail junction up to well past 60° (keeping the same fins) to be close to having an acceptable value for directional stability. (That is NOT a practical junction value). I made my second iteration with this Redshift (new purchase) to 96°. I didn't see as dramatic a change as I did with the first 4° (Surface area is too small) but I still haven't seen any pitch stability issues.

The 96° REDshift is much better than the OEM 104° as far as stability but it is still severely lacking compared to the Freestyler-5 with the large V-tail.

This isn't to show the few REDshift owners how to address the directional problem with their REDshifts. But to show that with a V-tail there is another variable (tool) one can use to try to gain some directional stability, if the model one has is exhibiting some directional instability.

At the design level the solution is to minimize the front side area and/or add vertical area to the rear.

Rest assured this is not a thought experiment! I use data and empirical evidence in MY discussions and finding. None of this, if it looks good it will fly good crap. While in this case that might still be true. As it is, the REDshift mk-1 looks a bit odd and misshaped, to my eye, with her oversized nose and undersized V-tail.

I don't want to sound like I'm throwing out the baby with the bath water. The REDshift has a wing planform that shows great potential! It is that unfortunately the fuselage crippled the REDshift from ever being a great F3F racer. Having now set up and flown a Freestyler-5 I can say that the REDshift mk1 is unequivocally a sub par F3F design.

I truly hope that the designer will learn from the errors made with the REDshift mk-1 and apply all to his next attempt at a 3 meter ship. Please note that none of these stability issues are as a result of the REDshift having a V-tail. The stability issues are as a result of insufficient tail volume. This is true with cruciform tails, T-tail and V-tails.

 

[ORRich]

Ok. So basically Monday-morning quarterbacking a way old design. To be honest, your claim about hoping the designer improves his next 3m design doesn’t ring true. This has been mostly grandstanding on your part trying to show how much you know. I don’t think anyone can really tell how much you know or don’t know.

I happen to agree with doc, if you really felt the design was bad, you should proffer and manufacture and sell your design. Afterall that’s getting a good plane in peoples’ hands. Easier said than done.


Anyone can critique anything and there’s a whole websphere of people taking pot shots at the makers and doers. I don’t make or do so I don’t critique unless it’s truly constructive or its asked of me.

This whole thing started with hearsay on the slope about a bad design. I think it was your opportunity to have quashed it then and there.

 

[Konrad]

I was in contact with the designer through PM over this ship for years.

As to the slope it is not hearsay. It is easy to see and even the designer has said there are issues with his V-tailed models. I’ve told anybody that would listen that the issues they might be seeing in my Hammond V-tails has little to do with the V-tail. Rather the issue is in the fuselage.

I’m sorry to learn that you would be fine with poor handling ships. I tried to offer you a fix with longer control arms and more vertical area should you have post mounted V-tail.

I’m also showing where I’m going with set up schemes and why I’m heading that way.

I also state what I think are the strong points of the design.

I agree with you is far too easy to say something is sub standard and runaway. Here I try to isolate the issues, explain them as I understand them (maybe with supporting documentation) and offer my attempts at a real world solution to the problems.

This thread is about my experiences with this REDshift, the Good, the Bad and the Ugly.

 

[Konrad]

I’ve been looking for some very high level documents that support the statement that the fuselage has a destabilizing effect on directional stability. I don’t expect anybody to take my word for it, I’m just not that creative. I tried to give some references to some stability programs in the toy press, developed by men well respected and are more than qualified on the subject in the low Reynolds number realm (our toys). But I fear that one might actually need to understand the mathematic they used in explaining the stability issue.

Here I found some high level training documents for test pilots that don’t rely on too much math (still a lot more than I’d like for a toy airplane forum). Please make note of Chapter 7, Page 7.12, Fig 7.8, and on Page 7.15, the Graph Fig 7.10. If you keep reading the training document you can quickly see that control and stability is rather a complicated subject. Remember this document is so that the test pilot can talk to the design team intelligently, not just say the plane sucks!

Just for fun try to work out some of the problems in the back of the chapter. Remember this is just for Lateral-Directional Static Stability.

I need to be real clear, control and stability are very difficult subjects to master. These issue go way beyond any entry level discussion of flight. Even in the age of Computational fluid dynamics (CFD) flight testing often shows deficiencies in the design. In the last flight test program (full size) I was involved with the stabilizer was redesigned 2 time, with the associated tooling cost for new molds!

It is my understanding that with this model the designer had some ill conceived ideas as to how to control “crabbing" across the face of the slope. He put up the money to make the molds based on his theories. Unfortunately, I don’t think he had time to work out the stability issues. He was under a fast approaching dead line with the FAI F3F championship coming, and wasn’t able to give the new design adequate analysis or any real kind of flight test program. (I received 2 of his prototypes and can say that they weren’t flight worthy with the control issues (mechanical) as I found them double centering).

I had the luxury of time, to address the initial design issues as I see them and come up with “my" solution to those problems, both mechanical and aerodynamic. I’ve been trying to show in these threads the slow systematic approach I’m taking to try to extract some of the potential “I” see in the wing planform that the REDshift is sporting. I hope this give you some understanding as to why I’m adding rear vertical side area to the REDshift mk-1 with its Jimmy Durante nose.

 

[Konrad]

Ok. So basically Monday-morning quarterbacking a way old design. To be honest, your claim about hoping the designer improves his next 3m design doesn’t ring true. This has been mostly grandstanding on your part trying to show how much you know. I don’t think anyone can really tell how much you know or don’t know.

I happen to agree with doc, if you really felt the design was bad, you should proffer and manufacture and sell your design. Afterall that’s getting a good plane in peoples’ hands. Easier said than done.


Anyone can critique anything and there’s a whole websphere of people taking pot shots at the makers and doers. I don’t make or do so I don’t critique unless it’s truly constructive or its asked of me.

This whole thing started with hearsay on the slope about a bad design. I think it was your opportunity to have quashed it then and there.

This is called engineering (Form, Fit, and Function) not Monday Morning Quarterbacking. Yes, I think the design is fundimentally flawed (large side area to adress crabbing). It is here that I'm trying to address those issues. For example, here I after some analysis, changed the form with the flipped V-Tail to allow the fitting of much needed longer length control levers. After some flight testing I changed the form of the V-tail junction to add the need stability function from more rear side area. I also changed the form of the control actuation from snakes to rigid push rods for much stronger action (function). And this is just the rework of the fuselage. Then there was the problem with the as designed placement of the flap servo needing the flutter prone serpentine push rod as a result of the placement of the wing ballast tube. At the time I began this project the REDshift was for sale. I did/do these build threads to help any perspective and actual buyer, yes even the designer, get the most out of the airframe. Another thread in this vein is my Mefisto thread. Again see why I changed the V-tail junction from 110° to 100°. I go into pain full detail as to why and the how of what I’m doing. And I also try to show the results. It is hoped that this kind of detail will help out other who may notice similare form, fit and function issues with their latest purchase.

 

[Doc J]

This is called engineering (Form, Fit, and Function) not Monday Morning Quarterbacking. Yes, I think the design is fundimentally flawed (large side area to adress crabbing). It is here that I'm trying to address those issues. For example, here I after some analysis, changed the form with the flipped V-Tail to allow the fitting of much needed longer length control levers. After some flight testing I changed the form of the V-tail junction to add the need stability function from more rear side area. I also changed the form of the control actuation from snakes to rigid push rods for much stronger action (function). And this is just the rework of the fuselage. Then there was the problem with the as designed placement of the flap servo needing the flutter prone serpentine push rod as a result of the placement of the wing ballast tube. At the time I began this project the REDshift was for sale. I did/do these build threads to help any perspective and actual buyer, yes even the designer, get the most out of the airframe. Another thread in this vein is my Mefisto thread. Again see why I changed the V-tail junction from 110° to 100°. I go into pain full detail as to why and the how of what I’m doing. And I also try to show the results. It is hoped that this kind of detail will help out other who may notice similare form, fit and function issues with their latest purchase.

No I didn't.

Doc.

 

[Doc J]

Yes you did!

Holy Crap...its back to the drawing board...

Cheers,

Doc

PS No, I didnt.

 

[Hill Hobbit]

That should knife edge ok, or maybe not…
Lol!

 

[Konrad]

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.

Welcome back, Doc.

No you didn’t, what?
Add destabilizing side area ahead of the fuselage center of pressure just to address crabbing?

I hope not as this goes against most of the basic tenets of airframe stability. But how am I to read statements like this addressing the supposed weathercocking running the front of the slope? And much of what you post here on Aloft’s forum. It is clear somebody here isn’t clear on the relationship of the fuselage and stability. Please lift the veils of ignorance from my eyes and explain how I’m to read these statements?

I’ll tell anyone that will listen that I’m fighting these directional stability issue with the Redshift Mk-1. These are real and can be seen by anybody that has seen the REDshift in flight. Particularly with the REDshift sporting the 104° V-tail junction trim. I posted comparative data with the Freestlyer-5 and all matrix point to the Redshift being much more directionally unstable than the reference standard Freestyler-5. We now have measured data showing most the REDshift’s stability parameter and you have empirical data from me and some of the British F3F team members reports and findings, showing the stability issues. Not sure what is the issue here, the Redshift mk-1 could do with a lot more directional stability. I for my part don’t want these stability issues carried over to the next V-tail project. I’ve tried to direct you to finding from more learned men than myself on the subject of V-tail sizing. I also try to show that it is well understood that the fuselage side area ahead of the center of pressure is destabilizing. Please don’t add to your V-tail reputation with design #3.

What little you have shown of the new design it is looking like you are taking action is the correct direction. But running the number you provided and some I generated* it is looking like the Spada will still be lacking much directional stability. Surely less than what we have with the Freestyler 5 on the small tail. And most would like to see even more directional stability from the Freestyler-5 with the large tail. Please add a lot more directional stability to the Redshift's follow up designs. (The wing really deserves it). While this will add drag, the added control power from the ailerons and rudder will in all likelihood add speed to the F3F run. If your new design is aimed for just for straight line speed that might be nice to say in a statement on the sales page.


* I have no access to any design data other than what Doc has provided. I'm assuming that what wasn't called out is the same as the REDshift mk-1.

 

[Konrad]

Yes you did!

Holy Crap...its back to the drawing board...

View attachment 12741

Cheers,

Doc

PS No, I didnt.

Did the Test Pilot training manual, CH-7 link not reproduce?

That Super Guppy is a classic example of good design. The Boeing 377 Stratocruiser was the bases of this design. It was not a clean sheet design. As a result of the intended purpose of the new aircraft the fuselage was enlarged. So the designer had to deal with the destabilizing characteristics that the added front side area (green) would cause to flight stability. The first was to lengthen the fuselage to add much needed rear stabilizing area (blue)and cargo space. This added length allowed the tail to be much more effective. Then because of that disruption to the airflow from these oversized fuselage hoops dropping the vertical fin's and rudder’s effectiveness on control they added a large dorsal fin. Do you see the give and take of these advanced design elements? In the end the flight testing showed that the only performance loss was top speed as a result of the added frontal (cross section) area and added paricitic drag from all the fuselage wetted area. The designers had a solid handle on control and stability. NO NEED TO GO BACK TO THE DRAWING BOARD! Well, not for the Super Guppy! The Spada, well....

 

[Konrad]

That should knife edge ok, or maybe not…
Lol!

Knife edge flight characteristic for an F3F racer is defined by the horizontal stabilizer, decalage and CG. In knife edge we want the ship not to pull to the canopy or push to the bottom of the ship. A large part of this is controlled by the rigging of the trailing edges and by the elevator trim (effected by the center of gravity). With the mod of the REDShift to a 96° V-tail junction I still have enough pitch stability to trim for knife edge flight.

In my Alpha 2.8 thread I say that despite the REDshift's power coming back out of the turn I’d rather race the Alpha 2.8 because of how well she handles with her smaller nose and larger tail volume.

 

[Hill Hobbit]

I was merely making a humorous comment there regarding the Guppy’s massive side area, nothing more, and certainly nothing to do with any F3f model. I would think that the great majority of folks who’ve read my comment would see it as such.

 

[Konrad]

Emoticons often help with internet humor. That comment might be better suited to another thread where aerodynamics is looked at as a joke.

But the point is that the design has off setting rear side area (Tail volume). Something the REDshift is sorely lacking and contributes to the directional stability concerns note by me and others.

It is also a valid concern with changing the V-tail junction angle, that the pitch stability might be a concern. I was commenting on your knife edge comment/concern, stating that the 96° Junction REDshift still has enough pitch authority to trim for knife edge flight as one is heading towards the bases.

 

[ORRich]

That should knife edge ok, or maybe not…
Lol!

If you bolt the stuff inside it well enough, then yes

 

[Hill Hobbit]

Yay, a man with a sense of humour.
Happy days!

 

[Konrad]

Most air freight and cargo are held down by tie downs or container restaints, camming clamps. I've never seen bolts used to hold down cargo in the hold.