Redshift Mk I (New Purchase)

[Doc James Hammond]

Glad to hear you are aware of these issues.

You have in the past admitted your errors when I complained about them. Like the Non-FAI radiuses nose. I'm not interested in the who I just would like the errors to not propagate to the next iteration.

I like the IDS friendly option.

As to being there at the design stage. All I can say is that I have the insight of 20/20 hindsight. That it I see the problems after the tooling and models are made. It takes a special eye mind to catch these priblems during the initial tooling up stages. CAD was to help with this.

All the best,
Konrad

Key points are to fix the problem first, learn from it, and then don't let it happen again.

Hopefully I'm getting somewhere with all three.

Thanks for all the great input.

Doc.

 

[Konrad]

Just got back from sport flying my new Redshift wings. I set up both wing sets to be interchangeable, you know replacement parts. The old Redshift (used purchase and major damage crash) flew almost the same between both sets of wings. This means that the repaired set is as true as the new set of wings. Or put another way I was lucky getting the broken wing box back in the same place after the repair.

But what I did find is the roll rate is a bit faster with the new set of wings. I attribute this to having cut back the aileron wipers to allow a bit more up aileron travel.

@Doc James Hammond you said that the tail planes between the Redshift Mk1 and the Spada would be interchangeable. I have to ask with the bottom actuation of the V-tail are the joiner bosses offset backwards (fore and aft) on the Sanda from those of the Redshift mk1. This is to allow the flipped Spanda tail feathers to align with the top push rods of the Redshift mk1. Being selfish I hope not as I've already swapped the V-tail joiner bosses to make my Redshift V tails bottom hinged to give me a longer effective control horn.

As there is only one more NCSS race this season should I leave my new fuselage unmolested and leave the V-tail joiners stock, in the hope that the larger Sanda V-tail will arrive before next seasons racing starts.

 

[Doc James Hammond]

Hi Konrad,
more below:

By the way its SPADA - Thats Italian for "sword" Its not Spanda, Spandex, Sparta, Splinter, Splendour or Sporter...

SPADA!

OK, as I was saying...

Just got back from sport flying my new Redshift wings. I set up both wing sets to be interchangeable, you know replacement parts. The old Redshift (used purchase and major damage crash) flew almost the same between both sets of wings. This means that the repaired set is as true as the new set of wings. Or put another way I was lucky getting the broken wing box back in the same place after the repair.

Good job. Not many would have done that.

But what I did find is the roll rate is a bit faster with the new set of wings. I attribute this to having cut back the aileron wipers to allow a bit more up aileron travel.

Possibly so.

You said that the tail planes between the Redshift Mk1 and the Spada would be interchangeable. I have to ask with the bottom actuation of the V-tail are the joiner bosses offset backwards (fore and aft) on the Sanda from those of the Redshift mk1. This is to allow the flipped Spanda tail feathers to align with the top push rods of the Redshift mk1. Being selfish I hope not as I've already swapped the V-tail joiner bosses to make my Redshift V tails bottom hinged to give me a longer effective control horn.

New tails are:
The same root chord, and same attachment rod spacing.
V-Angle is changed from 104 degrees to 100.
Tail area is increased buy adding 50mm on the span of each half.
The actuation has been changed to bottom connected.
Hinging may be either top or bottom.

As there is only one more NCSS race this season should I leave my new fuselage unmolested and leave the V-tail joiners stock, in the hope that the larger SPADA V-tail will arrive before next seasons racing starts.

The new model will be available, I hope, around the end of the year.
Some part moulding is underway and the machining of other parts will be done soon.

Cheers,

Doc.

 

[Konrad]

But what I did find is the roll rate is a bit faster with the new set of wings. I attribute this to having cut back the aileron wipers to allow a bit more up aileron travel.

That might not be accurate!

I set my wing surfaces using Mike Shellim's Open TX F3F templet. I set the surface until the servo stalled and back off a few numbers. As I recall this resulted in the ailerons still being a bit under the OEM's recommendation.

It is the old used purchase wing's wipers that I cut back not the new purchased wings. Today plugging the wing in and out it looks like both wings have close to the same max surface deflections.

So this leads me to think that the observed improvement in roll response is from the faster and stronger HS08 servo. While I'm sure I can't notice the .02 second spec'd improvement in speed. I think I'm seeing a real world speed improvement as the HS08 is noticeably stronger. Not that the X0-8 is overloaded it is just that the HS08 is using her power to maintain her speed.

If this is correct it means I'll need a second set of HS08 to refit the older set of wings.

The bad news is that I'm going to have to make a set of custom flap servo covers to clear the rear of X-10 mini used for the flaps.

 

[Konrad]

Just to be clear the Spada has the same joiner pins as the Mk1. This means that due to the Spada stabs being bottom actuated stabs they won't functionally interchange but will physically fit between both models (Spada & Mk1).

As I see it, if the Spada has the same configuration I used with the flipped stab, then the Spada stabs will fit the Mk1 fuselage and have the control horns properly oriented for both actuation scenarios.

I like the configurations to be the same. The port joiner being ahead of the starboard joiner as this will fit my flipped configuration.

 

[Doc James Hammond]

Just to be clear the Spada has the same joiner pins as the Mk1. This means that do to the Spada stabs being a bottom actuated stabs won't functionally interchange but will physically fit between both models (Spada & Mk1).

As I see it, if the Spada has the same configuration I used with the flipped stab, then the Spada stabs will fit the Mk1 fuselage and have the control horns properly oriented for the both the actuation scenarios.

I like the configurations to be the same. The port joiner being ahead of the starboard joiner as this will fit my flipped configuration.

View attachment 8039

Konrad - the stabs will be exactly the same as the MK1, except bottom actuated.

Cheers,

Doc.

 

[Konrad]

Perfect!

When flipped to top actuation they will fit my repositioned stab joiners.

So if the "normal public" wants to upgrade their Redshift Mk1 to the Spada tail they will only need to change the control horn to top actuation.

When the time comes I will want 2 sets of Spada tail in red camo to refit my Redshift Mk1's. Now don't tell anybody, but the camo scheme has grown on me to the point that I have to admit I really like it. Elsewhere in this forum you can see how nice both top and bottom look against the green hills.

 

[purview]

A new video of my old Redshift, flying on Braunsberg slope in Austria. The Mk1 with a "take my breath away" scenery. Redshift is in turbulent and choppy air pretty stable with its flying path, but not on rotational displacements. Although with up to 20 degrees offline to the ideal direction, the flying path is as the mass moves. But it can be very shaky also due to some pilot induced incorrect corrections.

The chequered bottom with bright colours is very good to see on this slope – it's a confidence issue

 

[Konrad]

Proof of life. I just finished the tail flip mod on my new RedShift. I also took the opportunity to narrow the V angle another 3 degrees. My new Redshift has the V-tail tips 12mm closer together (495mm) than on my other Redshift. My new Redshift is sporting a V-tail angle of 96 to 97 degrees. I really liked the improvement from stock (104) to 100 or 99 degrees. I’m hoping for much the same jump in performance. I hope I didn’t overshoot and improved this to the point that they don’t work!

Also I’m finding that liquid soap makes a great spot release agent. And it is easy to clean off making it much easier for paint repairs.

 

[Doc James Hammond]

Hi Konrad:

As designed the V-Tail angle was 104 degrees.

I guess you have reduced it quite a lot from the original. Take care about the elevator response.

Cheers,

Doc.

 

[Konrad]

Yep, moving from 104 down to 100 and much to my surprise I actually noticed an improvement in directional stability. I did do a bit of rebalancing the pitch and rudder mix response.

This time around, I again was looking for even more vertical fin authority. So I again took what I hope was a conservative move and dropped another 3 degrees on the V angle so this Redshift will be sporting a V angle of around 97 degrees. This is still giving me 7 degrees staying out of Horner’s less than 90 degrees high drag junction.

With the tail volume and moment arm of the stock Redshift we (I) suffered directional stability issue. Now I hope with the 7 degrees of total change I haven’t traded directional issues for pitch stability issues. But with the stock 104 degree tail I found I couldn’t really trim the Redshift mk1 for F3F use. The large V tail angle (for high aspect ratio wings) small vertical area and the small control horns appear to be the only real design issues I’ve had with the Redshift. The new Spada address these two concern and adds some other nice to have features.
Since I have at least 2 Redshifts I figure I really have nothing to loose, as one actually is flying fine as long as the loose nut on the sticks can stay out of the rear rotor!

 

[Doc James Hammond]

I think the tracking might show some change - but I'm a little worried about the elevator authority with the smaller tailplanes on the original.

Let see.

Doc

 

[Konrad]

You and I both have these concerns. This is why I’m taking this mod in slow steps. My first Redshift Mk1 has improved its control response to now actually being predictable. Most of this is due to the improved mechanics of the longer control arms. But a lot of this is from the added vertical area I got by lowering the V-angle.

I’ve said it before, I’m really surprised at how much changing the V-tail angle from 104° to 100° improved the directional stability. And yes I felt I had to make an adjustment to the elevator rudder mix ratio.

My first Redshift Mk1 with my modified V-tail still is lacking the control authority of say a cruciform tail. Now what, is for me, a large part of the hobby is being able to iteratively and empirically change the design. With this second Redshift I’m still looking for more directional control without making a set of tails with more area. So, I moved the V-tail tips 12mm to 13mm closer together. This corresponds to a V-tail angle of 97° to 96°. Based on the first angle mod I’m sure there will be some changes to the V-tail response. As long as I haven’t gone so far as to being unstable I should be able to adjust with the mix ratio and or balance.

Now I think I’ll have a get out of jail card with the fact that Aeroic is coming out with a new set of V-tails that have a lot more area. With my flipped V-tail mount on my Redshift, the new Spada V-tails should be easy to retro fit.

My limited understanding of V-tails is that any real world benefit comes in the reduction of the junction interference drag (Horner) and if designed correctly less mass. Far too many model designs are bias towards the false notion that the V-tail loweres drag by the reduction of wetted area using the projected area theory. It is my experiance that this always results in under performing V-tail control/stability, particularly in yaw. With the Redshift’s 19:1 aspect ratio this is more acute. So this is just another design study where I’m flirting with exchanging some pitch stability for directional stability?

 

[Doc James Hammond]

You and I both have these concerns. This is why I’m taking this mod in slow steps. My first Redshift Mk1 has improved its control response to now actually being predictable. Most of this is due to the improved mechanics of the longer control arms. But a lot of this is from the added vertical area I got by lowering the V-angle.

I’ve said it before, I’m really surprised at how much changing the V-tail angle from 104° to 100° improved the directional stability. And yes I felt I had to make an adjustment to the elevator rudder mix ratio.

My first Redshift Mk1 with my modified V-tail still is lacking the control authority of say a cruciform tail. Now what, is for me, a large part of the hobby is being able to iteratively and empirically change the design. With this second Redshift I’m still looking for more directional control without making a set of tails with more area. So, I moved the V-tail tips 12mm to 13mm closer together. This corresponds to a V-tail angle of 97° to 96°. Based on the first angle mod I’m sure there will be some changes to the V-tail response. As long as I haven’t gone so far as to being unstable I should be able to adjust with the mix ratio and or balance.

Now I think I’ll have a get out of jail card with the fact that Aeroic is coming out with a new set of V-tails that have a lot more area. With my flipped V-tail mount on my Redshift, the new Spada V-tails should be easy to retro fit.

My limited understanding of V-tails is that any real world benefit comes in the reduction of the junction interference drag (Horner) and if designed correctly less mass. Far too many model designs are bias towards the false notion that the V-tail loweres drag by the reduction of wetted area using the projected area theory. It is my experiance that this always results in under performing V-tail control/stability, particularly in yaw. With the Redshift’s 19:1 aspect ratio this is more acute. So this is just another design study where I’m flirting with exchanging some pitch stability for directional stability.

I'm really happy you are delving down all the possible avenues of V-Tailery! By the end of it there should be some really useful practical information to be used, instead of the "data" (read: "unfounded suppositions") bandied about by the armchair experts - so thanks for this Konrad.

My 'boiler plate' solution to the Redshift V-Tail questions was, I have to say somewhat less studied and experiementally structured than your work, as I simply opted for a blanket 'fix' with a bigger tail area and a less obtuse V-Angle. Thats where we are now, but as you know the die is not yet finally cast.

I'm happy that there might be more definitive data to work with before the MKII SPADA model gets into a production stage.

I think you are correct in thinking that the V-Tail is thought by most to have less drag than the more conventional cross tail. However, people who think this imagine that the aircraft is flying at cruising speed at its optimum glide angle, and completely forget all the control inputs that cause almost constant attitude changes (drag drag drag) in the real flying model. Due to the fact that the model has deeply angled control surfaces the actual control effectiveness in pitch and yaw are far less than its X-Tail counterpart (if it exisited) would be, and so inevitably needs larger movements and hence the intrinsic configuration causes more drag.

I have said and will continue to say that a well designed cross tail model will be faster in any given conditions than a V-Tail model of the same size, but...the caveat is that I am (whatever I like to think) a commercial model aircraft designer and so I have to follow that dreadful spectre: fashion. Its a fact that the world record is held by, and will continue to be broken by cross tailed models. If you ask the world record holder what he thinks, then possibly after a few wheaten beverages, he will tell you that cross tails are faster than V-tails.

Period.

We have to work with what we have, so in an attempt to compensate I used some research I'd done a few years ago to try to limit the drag caused by the excessive use of control surfaces needed for V-Tails. I have mentioned this before when commenting on the Redshift (and others of my designs) but as part of that study, the double-cusped high-response sections that I now use were born. The symmetrical section used for the Redshift V-Tail also flies in the face of "conventional" (mainly armchair aerodynamicists) thought in that it is 10% thick as opposed to the 8% thought (Guessed) to be necessary for low drag F3f type V-Tails. But in operation, the high-response sections at control angles from 0 to 25 degrees, exhibit better Delta-p, and the actual drag is far less than with any 8% section that I have ever seen.

I'm not sure if everyone can follow my thinking here but its actually quite logical and backed up by real data and not just "Should be, has to be, looks good on a computer simulation" rubbish. etc etc.

I'm looking forward to more Konrad experiments - wind tunnels are great but they aint anything compared to what ctually happens to the model when you let a loose nut, loose on the sticks - as you so nicely put it.

Per aspera ad astra!

Doc.

 

[Konrad]

I have nothing but the greatest admiration for those that can take a white paper and first principels and turn them into real hardware. Now the good ones know that testing will, in all likelihood, find that there are some errors in the assumptions made or that new unforeseen phenomenon has been revealed.

With racing machines a lot of this really boils down to personal preferences. Now I’m not much of a pilot but I can see things. And with most V-tails I see the fuselage taking many cycles to dampen when disrupted in yaw. This can’t be adding to speed. So I tried to add more vertical area to my Redshifts. While I “know” this helped, it really isn’t much of a test as there is a real possibility that I’m adding my confirmation bias.

So while I try to give an honest assessment , there is a strong possibility that it is biased. I know this and try to avoid the pitfalls of being both the designer and tester of the configuration change. But in the end it really is, with my ships, all about how do I like how they perform.

 

[Doc James Hammond]

With racing machines a lot of this really boils down to personal preferences. Now I’m not much of a pilot but I can see things. And with most V-tails I see the fuselage taking many cycles to dampen when disrupted in yaw. This can’t be adding to speed. So I tried to add more vertical area to my Redshifts. While I “know” this helped, it really isn’t much of a test as there is a real possibility that I’m adding my confirmation bias

Now, had you been alone in your findings on the Redshift V-Tail, then I might have put it down to personal preferences, but the fact is that you were not. At least three other non-USA pilots describe the same or similar phenomenon. As they are really very well known, highly competent and successful racers then I do respect their opinions, as well as I do yours at possibly the other end of the scale. All three of the test pilots are non-technical/theoretical types but instinctively good flyers so what they described was perhaps less informed than your observations, especially as to the potential causes of the directional stability. They reported 'breakaways' when turning at high speed maybe with a little too much yank on the stick. These were apparently not often seen but nevertheless were verifiably there. Also described were difficulties from time to time with some ballast/wind/lift combinations in making the model go 100% where they'd like it to go.

Ergo, the problem that you personally observed actually exists and is not simply due to one person's setup or flying style compared to another.

In two of these test cases, the problem more or less evaporated with a bit more area on the tailplane assembly, but no angular changes. All of the breakaway behaviour (read high-speed tip stall) was gone but possibly the 'point and shoot' behaviour still could have done with a little improvement. The third enlarged tailplane test didn't happen as the model decided to go for a swim - in the English Channel - and was lost with all hands.

However, even without any conclusive proof (as yet), I'm really tempted to think that for making the model really 'obey' then a more acute tailplane angle in addition to more area might not only help cure the present problems but may actually be a step ahead in overall control obedience. This potential prospect is extremely interesting and it's very likely (given the things I have done in this field on UAV projects) to show quite startling and very positive changes in the overall performance of the model.

In other words an advantage.

Cheers,

Doc.

 

[Konrad]

I’m so pleased that you have received, from others you trust, detailed feedback. There is little I find on the web talking in detail about F3F racing set up where the author is actually willing to cut into his ship to make it fit his needs. It is getting harder and harder to find modelers/engineers.

I have to admit I’ve yet to find a model that has too small a horizontal stabilizer. (Some canards have given me pain). In my F3D days I’ve had a few mid-airs where I’ve lost half a stab and still the ship flew fine. Ok, the landing was fast as I couldn’t flair. But had I been able to grab more elevator movement I think I could have made a slower landing. Now looking at F3A ships they have way oversized stabs to increase the margin of stability for the near and post stall aerobatics (allow for a rearward CG).

On my Redshift #1 with the as designed force arrangements I did get the wings into a high speed stall. She behaved just fine. All I noticed was the radius of the turn opening up (no tip stall). I didn’t think this was from the tail stalling. It just looked like a straight ahead stall but with the wing in the vertical. This is what I like to see. Now I have gotten the Redshift to stall spin (one wing stalled), low speed stall entry. In this case it took active input from the tail to recover. This has given me the confidence to add vertical area at the cost of horizontal area.

I think those nice high aspect ratio wings put extra demands of the vertical stabilization as the induced drag (changing lift vector) from the ailerons has the added moment arm. Also any mass out at the tips has the added inertia making it difficult to control. I know high aspect ratio wings need more vertical area than short stubby wings.

I have to say that on some thermal ships I’ve liked the 90° V-tail for how it cored the thermals.

I have to admit reading; “at possibly the other end of the scale” was an accurate reality check.

 

[Konrad]

I just read about the CCM Vantage in RCSD, thanks Doc for the link to RCSD.

I was plesently surprised to see that the V-tail angle is getting close to what I’m finding. That is that high aspect ratio wings need a shallower (more acute) V-angle.

For decades we have been seeing V-tail racers wiggling out of the turns. For a long time we suffered the Beech 110° tail. Then the 104° with a few 102° outliers being the norm. Now I see that CCM with the Vantage is sporting 97°.

Now before I find out why (read crash), can anybody tell me why designers have been loath to tailer the V-tail angle to the aspect ratio of the wing?

 

[Wayne]

I almost hate to suggest this, but think fashion works into it the equation.

 

[Konrad]

I almost hate to suggest this, but think fashion works into it the equation.

YES! And as you have seen my mug, you know I place little or no value on fashion!