Redshift; Used Purchase

[Konrad]

As a result of family issues and that the race season is coming to an end I don’t think I’ll be racing any F3F until 2020. During the 2019 season I was using the very economical (read cheap!) and well dated Strega’s. These did what I hoped they would. That is give me a chance to learn what F3F is all about. For a plethora of reasons, mainly focused on their construction, the Stregas are not well suited for F3F racing.

While I have made huge strides in being able to fly the F3F course it pains me to say, I’m not at the piloting level to justify a high dollar multi grand set up. Luck would have it that I found a ship that should allow me to progress well into the next level of competency for 2020. I found a used Redshift that was in my price range. Actually the Redshift I found will allow me to run with the top competitors. Again I won’t be equipment limited.

The reason the owner was selling the Redshift was that he was complaining that this particular model was double centering on the elevators. After a protracted negotiation period I quickly gave him the cash and ran away as fast as I could before he came to his senses! Possession is 9/10 of the law!

It just so happens that both the Strega and Redshift are designed by the same man, Doc. James Hammond. It will be fun to compare these designs that are decades apart.

I need to stress that this is a used ship and I don’t really know the history of this model in detail. When I looked at this model I thought that the very short (less than 5mm above the hinge line) elevator control horns were the culprit for the double centering elevators. I now don’t think they are responsible for the problem. When I freed the push rods I noticed that there was a huge amount of drag in their movement. I don’t know what happened to the snake but freeing up the push rods will be the first order of business.

As a result of trying to get the elevators “adjusted” the kevlar hinge has been stressed (torn). I’m going to try to relay a kevlar repair, rather than go with a silicone repair. Since I’m back there hacking away I’m going to change to standard clevis connection. I’m doing this to try to get 1mm to 2mm more leverage from the control horns.

Looking at the fuselage there has been a huge improvement. First I like the huge full radius fillet at the front of the wing to fuse part line! This adds a lot of geometric strength to this highly stressed area of the fuselage. Second if that this fuselage uses a slip on nose cone. With the way Doc. has designed the fuselage it is twice as thick at the nose cone and fuselage part line. This gives the fuselage real good hoop strength, again in the highly stressed area of the fuselage.

The one draw back I see in the fuselage, is that at the wing joint as a result of that huge front radius the part line is not perpendicular to the wing joiner. As designed this means that the wing wire connectors are not parallel to the motion of the wings when installing and removing them. As a result it is not advised to try to make up auto plug-in harnesses.

On my model the ballast tube is a top loader. I learned from my Stregas that top loaders are a real pain when needing to adjust ballast at a contest! I’ll look into seeing what can be done to change the ballast system to make it a much preferred shot gun bottom loader. The slip on nose should allow for this.

All the best,
Konrad

 

[Konrad]

Looking at the wings I was a bit surprised to find that the airfoils as measured at the wing root are 8.5% thick for the Redshift and 8.2% thick for Strega. I was thinking to myself these are going the wrong way. Then I looked at the actual measurements and realized the wings for the Redshift are 1.1mm thinner! Now that is what I was expecting from the use of the sine wave spar! This results in close to a 3000 square mm reduction in the frontal area from the wing!

I haven’t plotted it out but it looks like the Redshift has 0.3% to 0.4% more camber than Strega. Again this looks to be going counter to current trends where the camber is getting lower and lower to help with straight line speed and the designers are relying on snap flaps to up the coefficient of lift in the turn. I notice that the Redshift manual suggests 1/2 the normal snap flap. I think I know why. I should note that the chord of the Redshift is a lot smaller at 220mm vs Strega’s 240mm (this is at the root). The result is that the Redshift has a very high aspect ratio of 18.8:1. (Much of this can be attributed to the sine wave spar). This explains why the Redshift turns so well!

Well looking at the list price of these two ships even at close to double the retail price the Redshift is looking to be a far better value than the RCRCM Strega. I can’t wait to correct the few build/manufacturing issues I see in my particular Redshift and get her out on the slopes!

I'm not surprised to see that the joiners have the same outside dimentions

All the best,
Konrad

P.S.
Look at those narrow wing tips. This should result in a lot less tip losses! I need to get her on the slope!

 

[Konrad]

Time for some mind games.

I have seen some various numbers for the aspect ratio of this plane, they range from 18.8:1 to 19.2:1. To find the aspect ratio I divide the wing area (not FAI area) by the wing span to get the Mean Aerodynamic Chord (MAC). I then divide the wing span by the MAC to get the aspect ratio. From the published data I come up with an aspect ratio of 18.8:1. For marketing reasons I assume this equates to 19:1. I’d like to ask how do you measure the aspect ratio of a wing?

The other mind game is what servo should one be using for the ailerons. I say mind game as my Redshift already has the servos installed in the wings. I read that the designer states that the aileron pocket was designed for 8mm thick servos. Seeing how the 10mm thick KST 125mg’s fit I have to agree. It looks like I’ll have to make up a set of servo covers that will have a 0.5mm bump towards the trailing edge to clear the aft end of the 10mm thick servo. I know the KST X0-8+ has enough torque and that the ailerons are not usually subjected to shock loads (unlike the flaps), but I don’t see them list on Aloft’s sales page for the Redshift. What 8mm thick servo would one use for the ailerons?

Wing ballast (weight) does one want to get the weight out of the tips? I know with my thermal ships I want as light a set of wings as is practical to help signal the presents of lift. But with slope ships I see a trend to adding ballast to the wings. Is this a result of the modern F3F ship not having a fuselage cross section large enough to have a meaningful space for ballast? Or is the current theory that adding ballast to the wings will help dampen the roll in turbulent conditions? I can see both ideas having merit. The fast guys all have very smooth runs between the turns, no rocking in the straights. What I don’t know is this because they know how to set up the plane coming out of the turn and don’t need to make adjustments on their line. Or is this because the ships they are using all have wing ballast. I know there is a drag penalty with dampened wings when needing to make an aileron input for the turn. This question goes back to the aileron servo size (weight). Is it preferable to use the lighter 8mm servo for better roll rate? Or does one want the added mass of the 10mm servo to damped the roll response in turbulence?

All the best,
Konrad

 

[Konrad]

I've been spending some more time drooling over this airframe. OK, looking it over with a critical eye. After all she is a second hand model.
I notice that Aeroic has the part line of the aileron to wing tip cut to try to align with the span-wise air flow. I say "try", as the span-wise flow at any given time is highly dependent of the the coefficient of lift. If you have looked at the bottom of most full size aircraft you can see this flow pattern by how the fluid stains don't flow straight back, but rather are skewed towards the tip. I like this attention to detail!

All the best,
Konrad

 

[Hank GB Z]

Konrad,

Looks interesting. I'm signing on for the journey. As this will be your F3F ship for next season will you keep the Strega as a sport ship?

Hank

 

[Konrad]

YES, Actually Strega still has a lot to teach me about F3F. Then there is the learning to repair composite ships. I'll also use them for MOM racing such as the ISR.

All the best,
Konrad

 

[Konrad]

Ok, you guys win! I pulled the snakes! Unfortunately whom ever assembled this model did too good a job as the ballast tube is well fastened. I'll need to make up some tools and just pick away at the ballast tube until it is gone.

 

[Wayne]

Well that should be fun.

One of the interesting things about the RedShift is the airfoil itself, she uses a double cusped airfoil (is that the correct term?) and the wing does transfer air out towards the tips, so you will hear some noise from this one when she is making speed. This is a result of the airfoil, but the result should be quicker speeds. Typically noise is a sign that speed is being wasted, but in this case it is a by product of the design to make it go faster with less drag.

Enjoying your observations..

 

[Konrad]

Well that should be fun.

Not!

I recall Doc. Saying she made a unique sound.

I'm about to place an order for some composite materials. I hope to have the fuselage cleaned up by the time I get them.

 

[Motowncali]

Curious about why you are messing with the ballast tube...
Won’t 5he pushrods clear? Been a while since I looked inside one of these. As long as the rods go below the wing joiner and above or to the sides of the ballast tube, you should be good.

 

[Konrad]

Not a chance. Realize that the wing joiner lays right on top of the square ballast tube. The 5 mm push rod will need to go where the small teflon snakes are. Now in my example of the Redshift the wood side keel (spacers/ fillers) are right under the snakes as shown.

Not sure I can get the 5mm rods to clear even if I change the ballast tube from a square to a round one. There isn't much space between the alignment boss, ballast tube, side keel and fuselage sides. This may force me to go down to a 4mm push rod. With 4mm pushrods I will need to add center span supports to keep the 4mm push rods from buckeling.

All the best,
Konrad

 

[Konrad]

That went smoother than I expected!

The servo tray came out real easily. I stressed the nose (twisted it) and them shocked the glue joint with ultra sonic vibration from my, get this, Braun Series 7 beard shaver.

This did not work as well with the actual ballast tube. I had to split the ballast tube down the center of the top. This was to allow the tube to collapse upon itself as I pushed a lathe gouge down the side at the fuselage to side keel glue joints. These glue joints failed without further coercion, as only the front 30mm of the ballast tube was glued to the fuselage.

All the best,
Konrad

 

[Konrad]

Are square carbon tubes a standard spec item? Or are they made by the end user from carbon socks (sleeves)? Can Aeroic supply parts like a servo tray and ballast tube?

Not sure I want to stay with the square tube for the reason shown earlier. I'm leaning towards installing the Aloft carbon tube sized for the small tungsten. With all the money I saved buying this used ship I can splurge and get the 15 slugs I need.

I see these have been out of stock for a long time. Are they available or has the supply run dry?

Carbon Ballast Tubes and Tungsten Ballast

High quality materials for building your own ballast system.

alofthobbies.com

All the best,
Konrad

 

[Wayne]

You should be able to put a full load of ballast in the wings if you like.. That is a unique thing about the Red Shift. You could reach legal limits with either just the fuse tube, or just the wing tubes.

 

[Konrad]

Good to know! I assume this is with the brass bars. That would make life easier and a lot cheaper!

 

[Doc James Hammond]

I'm enjoying this too.
You guys are gradually, but very surely figuring out the ideas behind the design.

Plus points:
The aspect ratio I say as 19:1, as not that many people (apart from Konrad) will care about the odd .2%. It's been known since the 1940's that higher aspect ratios lend themselves to potentially higher speeds with unpowered airframes.
Right about the wingtips being left undisturbed by ailerons.
Right about the slanted aileron cut, and right about the frontal area.
Correct about about the double cusped aerofoils (Undercamber and "Overcamber"??)
The intrinsic camber is actually 1.72%.
Why double cusped?
The wind tunnel reveals all - unlike the computer simulations. Undercamber on certain aerofoils will optimise the lower airflow for a bit more lift.
"Overcamber" (Concavity on the top rear half of the section) encourages to airflow to stay attached a little longer which will give more lift for the same drag. Lift=speed.
Why more camber?
More Camber means more lift, and alternatively more ability to carry weight. Lift = speed.
Ballast can be put in the wings or in the fuslelage - just as Wayne says and the weight can be made up with rectangular brass slugs in the wings.

Minus points:
The nose radius is wrong - mistake plain and simple and comes from my incorrect reading of the FAI rules. Must have been a single malt evening!
I tried square tubes (For more weight per Cm) in the fuselage on that batch of planes and I wouldn't do it again - too much bother.
I want to change the fuselage shape - especially the nose radius. No good reason or potential advantage for this, other than it does not give me that little thrill when I look at it, like most of my designs do. The wings, however, are the exact opposite - I LOVE them.
The tailplane is on the edge of the stability envelope because I simply don't like unwanted surface areas hanging around in the airflow. For an experienced pilot this is OK, but if I did it again - and I will, then I'd make the tail surface a little larger.

Now, what else do you notice thats different in this design from the usual run of "Me too's"
There are at least three more very important points.

Keep up the good (Refurbish and analysis) work Konrad! And thanks to all for the contributions.

Oh and yes, I did design the Strega - but not as it is now. And the Sunbird, and the Tomcat, and the Typhoon, and the Dorado, and the "Gooney" (Should have been called "Goonybird")Plus a bunch of others that are out there from other companies.

I have attached a couple of file so you can see the section - but don't take too much notice of computer simulations, guys - Like the man said - it aint necessarily so...

Cheers,

Doc.

 

[Konrad]

Ok! we'll make this a game of sorts. (Note, I'm not an aerodynamicist!).

Are most customer more the artists (flyers) than engineering types? When I started out in RC you had to be an engineer type if you hoped to get any model to fly!

High AR's do wonders for engine driven pylon racers (FAI F3D). Again the issue was coming up with a strong stiff but light spar. The high AR Boeing wings while strong* do flex a lot!

In my professional life I was never the primary design engineer. Rather I had the privilege to test these ideas and products in the real world, as part of the flight test and certification teams. While the design engineers knew how to take the industry white papers, theory and make these into real hardware. They also knew that the real world would throw surprise at them. So while it is a skill getting the ink on paper it is just as important to understand that testing will often show that compromises made might have unintended consequences. After all engineering is the science of compromise!
(BTW: Most of the failed products I saw could be traced to the bean counters having far too much influence. I'm not stupid in that I know the reason for business is to make a profit. But really, far too often "Mahogany Row" is only looking at their stock options, not the end product!)

Yep, I don't like the square peg in a round hole that the square ballast tube effectively is. In practice much of the glue used to adhere the square ballast tube just ran into the bottom void . This was made even worse as the nose section step makes the void rather large. I'm still thinking of adding a round ballast tube to act as a spine stiffener through the wing mounting area. Radius to radius contact should result in a much better glueing contact area. The ship needs to survive my landings to be able to advance into the next round!

On the subject of the tail. Did the flight reports indicate a preference (bias)? Did the "A" list fliers like the speed of the small tail. I'm not an "A" list flier. While I like the speed that the lower wetted area offers when all is going well. I actually am more concerned with how the ship responds when things don't go well. Like when "I" stall the model in a turn! Generally I like to place my CofG aft to unload the stab (cut down on trim drag). This means I often get into stalls a bit faster than others. So how the stab performs in a stall Is just as important to me as how the wing responds in a stall.

I recall you saying that you use a "thicker than normal" airfoil for the stab. It also looks like they are from the double cusp family. I assume these airfoils are designed like the SD8000 family of airfoils to minimize the dead zone at very low Cl values.

What I'm getting around to asking is what is the designed V-tail angle? I'm thinking that since I'm hacking away at things I might like to bring the tail flippers up a bit. I see many designs hunting in yaw as they come out of the turns. To my way of thinking this yaw is adding a lot of fuselage drag from the slip (wiggles). With the small tails I don't want to loose pitch stability in favor of yaw stability. I'm not sure how far I want to go from the design angle. As you know I don't like the 110° V-tail with high AR wings.

*Boeing's wing exceeded the 150% load requirement for transport aircraft. Airbus's wing failed at 148%. Yes, this is just a regulatory number and has no value in the real word other than to show that there is head room for fault tolerance.

Friends don't oops, All the best,
Konrad

P.S.
That camber looks to be about 7% higher than what I see in the current trend. I assume this is to help with the narrower chord. 0.1% to 0.2% doesn't sound too radical a change from current thinking. Makes sense to me with the smaller chord. I've noticed that the aft loaded airfoil is falling out of favor. I liked the Eppler and Quabeck airfoils of old with the aft cusp.

 

[Doc James Hammond]

Ok! we'll make this a game of sorts. (Note, I'm not an aerodynamicist!).

Are most customer more the artists (fliers) than engineering types? When I started out in RC you had to be an engineer type if you hoped to get any model to fly!

High AR's do wonders for engine driven pylon racers (FAI F3D). Again the issue was coming up with a strong stiff but light spar. The high AR Boeing wings while strong* do flex a lot!

In my professional life I was never the primary design engineer. Rather I had the privilege to test these ideas and products in the real world, as part of the flight test and certification teams. While the design engineers knew how to take the industry white papers, theory and make these into real hardware. They also knew that the real world would throw surprise at them. So while it is a skill getting the ink on paper it is just as important to understand that testing will often show that compromises made might have unintended consequences. After all engineering is the science of compromise!
(BTW: Most of the failed products I saw could be traced to the bean counters having far too much influence. I'm not stupid in that I know the reason for business is to make a profit. But really, far too often "Mahogany Row" is only looking at their stock options, not the end product!)

Yep, I don't like the square peg in a round hole that the square ballast tube effectively is. In practice much of the glue used to adhere the square ballast tube just ran into the bottom void . This was made even worse as the nose section step makes the void rather large. I'm still thinking of adding a round ballast tube to act as a spine stiffener through the wing mounting area. Radius to radius contact should result in a much better glueing contact area. The ship needs to survive my landings to be able to advance into the next round!

On the subject of the tail. Did the flight reports indicate a preference (bias)? Did the "A" list fliers like the speed of the small tail. I'm not an "A" list flier. While I like the speed that the lower wetted area offers when all is going well. I actually am more concerned with how the ship responds when things don't go well. Like when "I" stall the model in a turn! Generally I like to place my CofG aft to unload the stab (cut down on trim drag). This means I often get into stalls a bit faster than others. So how the stab performs in a stall Is just as important to me as how the wing responds in a stall.

I recall you saying that you use a "thicker than normal" airfoil for the stab. It also looks like they are from the double cusp family. I assume these airfoils are designed like the SD8000 family of airfoils to minimize the dead zone at very low Cl values.

What I'm getting around to asking is what is the designed V-tail angle? I'm thinking that since I'm hacking away at things I might like to bring the tail flippers up a bit. I see many designs hunting in yaw as they come out of the turns. To my way of thinking this yaw is adding a lot of fuselage drag from the slip (wiggles). With the small tails I don't want to loose pitch stability in favor of yaw stability. I'm not sure how far I want to go from the design angle. As you know I don't like the 110° V-tail with high AR wings.

*Boeing's wing exceeded the 150% load requirement for transport aircraft. Airbus's wing failed at 148%. Yes, this is just a regulatory number and has no value in the real word other than to show that there is head room for fault tolerance.

Friends don't oops, All the best,
Konrad

P.S.
That camber looks to be about 7% higher than what I see in the current trend. I assume this is to help with the narrower chord. 0.1% to 0.2% doesn't sound too radical a change from current thinking. Makes sense to me with the smaller chord. I've noticed that the aft loaded airfoil is falling out of favor. I liked the Eppler and Quabeck airfoils of old with the aft cusp.

 

[Doc James Hammond]

Hi Konrad - I see you have written your usual short reply.

Some comments below:

Ok! we'll make this a game of sorts. (Note, I'm not an aerodynamicist!).

Are most customer more the artists (fliers) than engineering types? When I started out in RC you had to be an engineer type if you hoped to get any model to fly!

I grew up in the UK "Builder of the Model" era. That was a rule that if you had not built it, then you couldn't fly it.

Now I am the architect of my own demise, because I make models that expressly do not need actual building.

High AR's do wonders for engine driven pylon racers (FAI F3D). Again the issue was coming up with a strong stiff but light spar. The high AR Boeing wings while strong* do flex a lot!

Designed in - as you know Konrad. Better to move than to snap.

In my professional life I was never the primary design engineer. Rather I had the privilege to test these ideas and products in the real world, as part of the flight test and certification teams. While the design engineers knew how to take the industry white papers, theory and make these into real hardware. They also knew that the real world would throw surprise at them. So while it is a skill getting the ink on paper it is just as important to understand that testing will often show that compromises made might have unintended consequences. After all engineering is the science of compromise!
(BTW: Most of the failed products I saw could be traced to the bean counters having far too much influence. I'm not stupid in that I know the reason for business is to make a profit. But really, far too often "Mahogany Row" is only looking at their stock options, not the end product!)

Thus is always the way.

Yep, I don't like the square peg in a round hole that the square ballast tube effectively is. In practice much of the glue used to adhere the square ballast tube just ran into the bottom void . This was made even worse as the nose section step makes the void rather large. I'm still thinking of adding a round ballast tube to act as a spine stiffener through the wing mounting area. Radius to radius contact should result in a much better glueing contact area. The ship needs to survive my landings to be able to advance into the next round!

Partially true. What I was trying to do was to get more weight in less space and that what the "square peg" Ballast tube achieves very well. How its anchored to the inside of the fuselage or how its placed is up to the Builder.

What I do now is to make it bottom loading and provide a shaped "Keel" to the bottom of the tube to take up the curve. But having said that, my abandonment of the square tube was actually more due to the limited availability of the correct sized metric brass bar in the USA.

On the subject of the tail. Did the flight reports indicate a preference (bias)? Did the "A" list fliers like the speed of the small tail. I'm not an "A" list flier. While I like the speed that the lower wetted area offers when all is going well. I actually am more concerned with how the ship responds when things don't go well. Like when "I" stall the model in a turn! Generally I like to place my CofG aft to unload the stab (cut down on trim drag). This means I often get into stalls a bit faster than others. So how the stab performs in a stall Is just as important to me as how the wing responds in a stall.

I think you have to fly the model before making any assumptions or guesses. Each flyer has a different style and so the same model can do different things with different pilots. The plane flies fine as it is under most circumstances but like every other, if mistakenly pushed too far it will react.

I recall you saying that you use a "thicker than normal" airfoil for the stab. It also looks like they are from the double cusp family. I assume these airfoils are designed like the SD8000 family of airfoils to minimize the dead zone at very low Cl values.

The JHSYM10 used does perform in a very similar manner to the low drag S8020 - which incidentally I used for a long time.
The story of this section is a long one but suffice it to say that it was the result of a long study to find ways to get good control responses from less control input.

We found that a double cusped section allows the boundary layer to stay attached and behave in a more predictable way with this type of curvature regime. There is no requirement for intrinsic lift so I concentrated on making the aerofoil as tolerant s possible of high Alpha angles. Later it was found that thickness is not the be-all and and-all of lowering drag in symmetrical sections, so actually this one at 10% has a much lower CD than many claimed "low drag" symmetrical sections.

In short it needs less control input for the same reaction, it has a low CD and a very high alpha tolerance.

What I'm getting around to asking is what is the designed V-tail angle? I'm thinking that since I'm hacking away at things I might like to bring the tail flippers up a bit. I see many designs hunting in yaw as they come out of the turns. To my way of thinking this yaw is adding a lot of fuselage drag from the slip (wiggles). With the small tails I don't want to loose pitch stability in favor of yaw stability. I'm not sure how far I want to go from the design angle. As you know I don't like the 110° V-tail with high AR wings.

OK, right now the Redshift V tail angle is at 104 degrees. I will change it to 102 or maybe 100 for the MKII because I'm looking to improve the tracking just a little. And yes - try to reduce that "shimmying" and skidding that you sometimes see on leaving a turn with many F3f models.

*Boeing's wing exceeded the 150% load requirement for transport aircraft. Airbus's wing failed at 148%. Yes, this is just a regulatory number and has no value in the real word other than to show that there is head room for fault tolerance.

I'm not sure what the tolerance is the the SWS but it improved torsional resistance a lot, gives great tension and compression stiffness and its also less that half of the weight of the "old" square type spar I used to use.

Friends don't oops, All the best,
Konrad

P.S.
That camber looks to be about 7% higher than what I see in the current trend. I assume this is to help with the narrower chord. 0.1% to 0.2% doesn't sound too radical a change from current thinking. Makes sense to me with the smaller chord. I've noticed that the aft loaded airfoil is falling out of favor. I liked the Eppler and Quabeck airfoils of old with the aft cusp.

Well if you look at the distribution of the numbers it pretty much works. Frankly I don't know what the "Big Guys" are using on their designs, but judging from the planforms, they are miles away from what's needed.

But having said that - I look a couple of the newer planform designs, and I can see much better lift distribution and indications of a better understanding of what the airflow over the wing is actually doing. So the dawn of realisation is not confined to me alone. Unfortunately the majority of the "Big Guys" are also using 100% computer simulations to predict what they are doing and then working off that.

Question: If computer simulations would do the job, then why do people spend hundreds of millions of $$$ on those darned noisy wind tunnels?

The logic is clear to me. Using 100% computer simulation is like going to Las Vegas with a pocket full of money with the expectation of repeated winning. If you could actually win consistently - then Las Vegas simply would not be there at all.

Cheers,

Doc.

 

[Konrad]

LOL, let's see if I can keep this short.
Thanks for the V tail angle. 104° sounds a lot better to me than the classic 110°. I'll leave it alone and see if I can tune any shimmying with aileron differential before I start to hack at the back.

What were you thinking for 8mm aileron servos? My ship came with KST 125 in the aileron pocket. These are just a bit too large. I'll need to make bumped servo covers. I'd like to move the ailerons to LDS to allow the shortest servo arm possible (highest servo resolution). If going through all that work to install LDS I might a well change to a thinner servo. I like the KST X0-8+. I just don't feel comfortable with the gear train. Truth be told with the aileron in spoiler mode I shouldn't hit the ailerons on landing, so gears on the x0-8 may be fine.

All the best,
Konrad

P.S.
I really want to get this ship on the slopes! I want to see those wing tips working!