Redshift #3 (Green glass prototype)

[Konrad]

Some of you might know that I've just acquired my 3rd Redshift. This was the airframe Aeroic used to test the molds looking for issues like negative rake and other fit concerns. As such it was laid up in glass and does NOT represent the end Aeroic product. This airframe was used as a demonstration ship by Aloft. As Aeroic and Aloft no longer field this aircraft it was surplussed to me.

I was ecstatic to get this airframe as it looked ready to fly (I had actually flown this at an ISR) and she came with a great set of 4 X10 mini and 2 KST 215mg servos. These will fit my penchant to use 2 lipos for my radio set. I plan to use her as a light lift F3F racer. I want to stay with the high aspect ratio wing at my current state of F3F development.

Now I need to learn that there is no such thing as a PNP model when it come to my expectations. I was hoping to use this Redshift in the first F3F race of the season on February 20th. Prior to setting up a radio I gave the airframe a close look over. I was happy to see that it had my tail flip mod. I figured that was going to be the rate limiting step. But no I looked at the flap movement and found that the flaps only reflexed up 5°. that is to say the flaps did NOT augment the ailerons in roll. Damn, I though all I had to do was lengthen the servo arm and program my flap curves. But NO I found that all 4 control horns caused surface binding in the upward direction!

This will force me to remove all four control horns. If doing all that work I might as well install IDS to all the wing surfaces. This is a good thing, it just that it means a lot of work and I'm facing the February 20th dead line. Damn another issue, none of the servos can be freed from the servo trays as there is no clearance provided to move the servo away from the bearing. I was forced to force the servo out of the servo tray. Because of the geometry I'm going to have to replace the flap servo trays. As I'm doing all this work I might as well go all in and change the Aileron servos to ones that are 8mm thicK. Luckily the servo trays were glued in with what looks like CA and broke free with little damage to the top skins as they don't look to have been permanently distorted by this. And damn the wiring harness does not expose the servo connector when the servo is taken out of the servo tray. So I'll have to change the wiring harness if I want to change the servo.

So two days after purchasing my PNP F3F racer, the wings are now in the condition of an as received kit.

 

[Konrad]

If the wings of this green Redshift where in the same configuration as they where at the ISR 5 years ago, I think this demonstrator did the Redshift a disservice. I flew this demonstrator for about 3 to 5 minutes (being new to fully molded 3 meter F3F ships I didn't want to crash her). As I recall the roll rate was a bit dead. I attributed it to being set up as a racer combined with the thin high aspect ratio wings, and that I wasn't flying the Redshift fast. I now think the slow roll rate was as a result of Zhou's poor horn set up, not allowing the builder to get more than 5° of up flap. My two other Redshifts have 20°+ upward flaps as aileron coupling.

While this may have hurt the reputation of the Redshift the fact that not many were sold probably was a blessing in disguise.

With all that water under the bridge I really wanted to try the Spada this season. But these 3 Redshifts should keep me moving forward in the standings.

 

[Konrad]

One of the things that is always running in my mind is root cause analysis. Earlier in my used Redshift thread I bemoaned the installation of the flap servos.

Well I think I've now found the root cause for that issue. This prototype is sporting a set of wing ballast tubes that is 10cm shorter than the production Redshift ballast tubes. With the shorter ballast tube of the green Redshift prototype there is no issue getting the servo output arm to align with the factory installed flap control horn, even the 30 x 35 servo fits.

I don't have the engineering change documents, but I suspect that it was found that using brass as ballast one couldn't reach the needed 75 grams per square decimeter limit called out by the FAI. So a change was added to lengthen the ballast tubes by another 10cm. This unfortunately violated the space for the flap servo, resulting in the fit issues with the flap servo. This caught the designer and builder of my first Redshift off guard, in his rush to get a ship ready for his trip to the ISR.

This means that the ballast set of weights I have made up for my two carbon Redshifts won't fit this glass Redshift.

 

[Konrad]

Let's see if this shows up. This is why there was so much distortion in the lower skin and so limited control movement. The control horns crossed the hinge line.

 

[Raymond Gaskins]

Konrad,
Thanks for the link to your Hobie Hawk thread. Did you ever get to fly it? I read the thread with interest and thought your 4 degree drop in the tail incidence was a unique solution. I have looked at a lot of hawks and both sloped and thermaled mine back in the day. It was a handful at times and only happy when flying fast.
Best,
Raymond

 

[Konrad]

I have owned and flown a few Hobie Hawks in my day. I think this one is waiting paint. I don’t know if I have flown her or not. (I’ll have to see if any of my radios have a Hobie Hawk in the memory).

Now my experiance is a bit different than yours. Because of all that decalage (6° plus) I found she was a bear at speed. Now when slowed, one really had to watch out for mass coupling. So smooth control inputs where the word of the day. At higher speeds the dihedral and rudder would work more as we would expect.

 

[Konrad]

Have I mentioned that I hate having to remove factory installed control horns! Oh, I also hate doorways! (I'm fit to be tied!)
(Keep hearing Wayne saying "You'll give her a good home, right?")

While I'm ranting I see that servorahmen has various configuration KST v3 servo arms! Whats the point of have revision numbers if they aren't incrementally update when there is a configuration change? You can see that the earlier v3 has a grove in the servo arm flank to allow the push rod stiffening beam to clear. The later v3 has smooth flanks that allow the push rod to bind if the servo is allowed to fully rotate!

Also why does KST have these vestigial cooling fins. They only make it harder to slide the servo into the bearing supported frame as they act like detents against the skin. FORM follows FUNCTION!

Ok, with the narrow chord of the Redshift's high aspect ratio wing we need to be careful as to how the servos are placed. I'm finding that there is less than a 1mm clearance with some of the spar structure. I'm finding it beneficial to remove the 1mm micro ledge on the servo tray that might interfere with the spar.

 

[Konrad]

When sizing your wiring harness make sure the connectors reach the servo opening to facilitate easy changing out of the servo if needed.
I also like to tie the connectors together with dental floss. I find this works a lot better than heat shrink as I can change the servo at the field without the need for a heat source.

 

[Konrad]

Wow, Just did a weight and balance and came in at 2.2 KG, with the cg and 97mm This is light in my book. What I found odd was that I took out 84 grams of lead shot out of the nose. I was thinking that the change to a denser (no voids between the shot) Woods Metal I’d be able to move the balance mass center of gravity further forward resulting in needing less balancing weight. Well to get the CG to 97mm I had to use 95grams of Woods Metal cast into the nose. I knew many folks didn’t like how this model performed. I and others had atributed it to the double centering V-tails. I’m now thinking that along with the V-tail issues this model might have been on the tail heavy side.

My Alpha 2.8 is coming in at 2.53KG with the CG at 97mm.

Now the Redshift (Green) is a glass lay up and the Alpha is a carbon. I’ll need to do a comparison between this glass Redshift and a virgin (not crashed) carbon Redshift. But as it is now I think I’m going to like the light glass Redshift. I hope to get in a few test flight before Sunday’s race. I know, I’m again allowing racing to interfere with my flight test schedule!

It is looking like at the end of the week I should have six 3m F3F type ships read to fly. No, they won’t be in paint but as they aren’t carrying sponsors logos it doesn’t matter.

 

[Konrad]

ITS A HOBBY NOT A JOB!!!

Have I said how much I hate working to a dead line, the Feb 20th F3F race?

This time everything was looking good. I started to set up Mike Shellim's templet. I'm getting rather good at this if I do say so myself. That was when I found my fatal mistake. To make matters worse I knew better from my experience with the Aeroic Gremlin. As a result of the double cusp airfoils the TE is rather thin. This results in there not being much leverage for the control spoons If one tries to bury it 100% into the control surface. On this Redshift I had placed the control spoon pin too close to the hinge line. the result was that I was only able to use about 1/3 the servo resolution. This results in a huge loss of potential power and causes centering errors to be grossly magnified.

So instead of test flying tomorrow I will be grinding out the control spoons and attempting to properly set up the IDS spoons for the dual cusp airfoils.

It is a good thing Aloft Hobbies has these spoons as separate purchased items

 

[Doc James Hammond]

ITS A HOBBY NOT A JOB!!!

Have I said how much I hate working to a deal line, the Feb 20th F3F race?

This time everything was looking good. I started to set up Mike Shellim's templet. I'm getting rather good at this if I do say so myself. That was when I found my fatal mistake. To make matters worse I knew better from my experience with the Aeroic Gremlin. As a result of the double cusp airfoils the TE is rather thin. This results in there not being much leverage for the control spoons If one tries to bury it 100% into the control surface. On this Redshift I had placed the control spoon pin too close to the hinge line. the result was that I was only able to use about 1/3 the servo resolution. This results in a huge loss of potential power and causes centering errors to be grossly magnified.

So instead of test flying tomorrow I will be grinding out the control spoons and attempting to properly set up the IDS spoons for the dual cusp airfoils.

It is a good thing Aloft Hobbies has these spoons as separate purchased items

View attachment 10013View attachment 10014

After quite a lot of thought and consideration, I am really not convinced that the advantages of the IDS system outweigh the disadvantages. The possible drag saving is so small as to be incalculable and the potential complications are many.

I did fit out one model with IDS with no problem at all, bar the fact that everything was a bit new so it needed a bit more thought and fiddling than perhaps I was used to. But nope - For me, I think it's a bit like RDS: It's the technology of the future - and always will be.

Doc

 

[Konrad]

They do have a lot of constraints.

I do love the external bearing support servo tray. Have I said how much I try to avoid cantilevered designs!

 

[Konrad]

Well, the cutting out of the spoons went well. The replacement spoons set ok with the pin boss protruding about 1mm above the top skin. This resulted in the added resolution from using about 2/3 the servo motion even with smallest servo arm. I'm still not happy with the centering of the ailerons.

I think my next molded model will use another type of surface drive.

I do love the bearing supported servo tray.

FYI: I'm also still seeing a slight double centering of the V-tail flippers. (I'm noticing more push rod drag than I recalled earlier.). All these double centering issue are about 2 to 3 numbers on the FrSky output curve. Not gross but still not what I'd like to see in a molded model.

 

[Doc James Hammond]

Its back to Carbon pushrods on the MkII Konrad.

Doc.

 

[Konrad]

This is for the V-tail, the 6 gram servos aren’t working well?

Note the carbon rods for the V-tail in the Mk1 aren’t working so well with the green glass lay up Redshift. The two red carbon Redshifts (mk1) appear to be centering just fine.

The ballast tube is placed rather high in the green Redshift. This may be the cause for the added drag on these carbon push rods.

 

[Doc James Hammond]

This is for the V-tail, the 6 gram servos aren’t working well?

Note the carbon rods for the V-tail in the Mk1 aren’t working so well with the green glass lay up Redshift. The two red carbon Redshifts (mk1) appear to be centering just fine.

The ballast tube is placed rather high in the green Redshift. This may be the cause for the added drag on these carbon push rods.

its a choice I guess - on testing the Kingmax 6mm servos are exceptionally good I have to say. They repeatedly centre well even after 12 hours non-stop testing. In any case the 6mm servos fit easily in the tails. Not sure I'd like to try a 6mm IDS fit out though!

Cheers,

Doc

 

[Hill Hobbit]

James, you really mustn’t mention Kingmax servos here, it’s a real no-no going by the reaction to my mentioning them a while back…
Cheers
Jonty

 

[Doc James Hammond]

Off with his head! I'll have no popery!
Long live the king! Confound the servo police, say I!

Doc the unabashed.

 

[Hill Hobbit]

Like it, like it! Now, let’s see if you (because of who you are) get told that a servo you describe as ‘exceptional’ is actually rubbish?
Cheers
Jonty

 

[Doc James Hammond]

Like it, like it! Now, let’s see if you (because of who you are) get told that a servo you describe as ‘exceptional’ is actually rubbish?
Cheers
Jonty

Tell you what, Jonty - I think that Kingmax sevos maybe were a bit naff in the past(?) but due to feedback from people like the guys at Aloft and others, they knew that they needed to clean up their act. The servos I have on test are all "new generation" but having said that, since I didn't see the old ones, I can't say. If Wayne said they were not so good, which he did to me on several ocasiaons, then I'm completely sure they did not impress him. But times change.

What I can say is that the ones I have on test up to now are at least as good as KST and pretty much up there with MKS.

Iain Medley-Rose is flyng one of my Alpenbrise mdoels all over the firmament - and whats inside? Kingmax! What do a lot of the The UK GPS triangle lads use?

You got it!

Buy them with confidence.

Cheers,

Doc.