F-22 90mm HobbyTopGun - Build Log - Page 2 - RC Groups
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Jul 21, 2012, 07:00 AM
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OK.... CS12/ESC mounting time....

The CS12 is a slightly larger outer diameter than the stock FlyFly fan unit. So a bit of "foam machining" was required. Basically to make a larger diameter, but also to make the "foam EDF bay" a fraction longer - 3mm - because I cut down all my CS12's to near 'normal' length, but it was still a bit too long to fit.

I was going to mount the CS12 to the top of the fuselage, and make a bottom removabe cover - mainly so as not to mess up the look of the top, seeing that is what anyone sees mainly. But for numerous reasons that was not ideal, so I mounted it into the bottom shell and there will be a large removable top cover for maintenance access.

The ESC will mount into a rectangular hole in the fuselage bottom, with motor wires in an external fuselage channel, and battery/RX leads going up internally.

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Jul 21, 2012, 07:05 AM
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ESC hole and internal cover plate made and fitted. ESC to motor, and ESC to battery/RX wiring done also.....

There will be a wiring cover of thin plastic from the ESC rearwards. And some form of plate/cover for the ESC itself and the bit of gap ahead of it. To all end up pretty 'natural' for the underbody.
It was all designed to allow easy enough ESC removal and wiring access, seeing that once the fuselage top and bottom are joined you won't be getting inside there anymore!

I have to do some ducting "tidying up", at the rear of the motor area, and also up front in the ducting path as it has a few oddities ahead there.
Then I should be able to clamp the upper and lower together and run up the CS12 to test thrust. On the bench this setup get 2.7Kg from 6S 77Amps (initial peak just under 3.0Kg).
So it will be interesting to see what comes OUT of the F-22 rear end!! The bifurcated exhaust system actually looks very well suited to match the output path around the motor - it doesn't look too restrictive really - and having the EDF so close to the very rear means there is not a lot of distance for drag addition.
I would hope it will actually run quite well as it is..... but for sure a straight shot thrust tube setup still has to be better.

Last edited by PeterVRC; Jul 21, 2012 at 07:11 AM.
Jul 21, 2012, 10:21 AM
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A bit of diversion to the elevators.....

Anyone who has seen FyFly kits will know the pretty much standard elevator hinging/pivot system they use. I think it is pretty well rubbish! If you see one, or have built one up, you will quickly see how sub-standard it is.
So, that needs improving.... which luckily is very easy to do.

I replace it with a 5mm carbon fibre rod system.
Use a philips (cross head) screwdriver - with a 5mm shaft in this case - to drive a hole into the elevator where the FlyFly 3mm L-bend piece would go. Making sure it is square in both directions - fore/aft and up/down. Epoxy a length of 5mm CF into that hole in the elevator - you will need about 60mm, or more, sticking out. Cut it off to suit the aircraft (F-22 tail end here).... not just enough for the pivot block, but a lot more into the fuselage.
See the pics.

Drill out the pivot blocks to 5mm and then the CF rod can feed through the block and pivot in that, as per the stock system did. Mount the pivot block and use the 5mm screwdriver to "drill" deeper into the fuselage - but not to come out the inner side of it. This is just so you can have a much longer CF rod than just to go through the pivot block, thus offering a bit better support for the whole assembly too. An option to do, if required, is that you can then also add a plywood pivot piece more inboard of the main pivot block, for extra support - and doing this 'amplifies' the pivot system strength many times! To fit that, just cut a 2.5mm ply rectangle that you will feed into a knife-cut-slot that you make 20mm or so further inboard of the pivot block. Epoxy that in, then drill through the pivot block and through the ply - thus creating another pivot point a fair way inboard of the main pivot block.

I put 5mm Collars either side of the pivot block. The elevator side one is just to give a gap between the fuselage and the elevator. The other side of the block collar is clamped with its two grub screws, to the CF rod. This is the collar that locks the CF rod into the pivot block. And it gets recessed into the foam that is inboard of the pivot block - Cut a bit of foam away by knife and the collar will 'eat' its own nice hole to live in, lol.

This 5mm CF rod system is rock solid.... versus the very wishy-washy, wobbly, FlyFly stock pivot rubbish! So if you want elevators (elevons) that obey commanded accuracy to perfection, then this is what you want to be doing! If you don't mind wobble.... fluttering at speed.... use the stock supplied stuff!! LOL

The rest of the elevator control system - control horn and servo etc - are done as per the stock system.

Last edited by PeterVRC; Jul 21, 2012 at 10:27 AM.
Jul 22, 2012, 03:43 AM
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More elevator mods.....

After looking at the quite pathetic elevator control horns and how they are mounted, and even how they operate, I decided there is no way I am going to use those!
Any horn mounted on, or through, foam is always going to be a weak point for some failure to one day occur at. Then there is the geometry of the stock system - that is terrible and gives you a form of "negative expo" in its motions.

So the best solution was pretty obvious, and even easy to do.....
A plywood horn and mounts onto the elevator pivot rod (5mm) and is also glued to the face of the elevator. Thus a 100% rock solid and reliable device. Plus it then allows a more 'traditional' servo to control horn geometry.

I actually didn't make enough effort to make it geometrically perfect - I didn't quite think enough in advance about the elevator horn needing to be tilted more rearwards really, DOH - and which is somewhat because I "could not" make it all perfect anyway. This is because the servo full range is way too much to be usable as elevator deflection, thus you need to have some ratio of reduction. And with the servo range being so large (180deg?) that means if you use the full resolution - range - then you must move into non-linear motion areas as it nears the end of its travel and around the arced path it takes. Or, you could opt to reduce the endpoints (resolution range) and then have dead linear motions.
I will decide on that later, but for now it is all done and the elevators are rock solid without even 0.5mm of play, thanks to the highly rigid pivot mount system (after improving them) and the 5mm elevator rods. Plus all pushrod holes being 2mm, just as the fittings are. So there is no play at all... for now. One day the plywood will wear a bit, and maybe I will put a bush in then.....

I think if I were to hit full deflection in an instant, when going too fast, the elevators would just do as told but the rear end would rip out of the plane first!! LOL.

The elevator assembly is all made so the elevators can be removed once the plane is assembled fully.
I am still pondering over how to make the servos removable.... Because they and their wiring get covered, and locked in, by the lower fuselage when you assemble that (glued) - which is sort of a good thing for strength, but not for future servo replacement!

I chose to use 12g Corona MG servos for the elevators.
Ailerons and rudders will use 9g HXT900's.

Last edited by PeterVRC; Jul 22, 2012 at 03:54 AM.
Jul 22, 2012, 10:26 AM
Should've, Would've, Could've
v8truckin's Avatar
Man Pete you've got a lot of work going on in this plane. That what makes this hobby so fun is ppls will to mod and make airframes better. Some ppl like to just thow it together, fly, crash, & buy another. While others are true modelers. Keep it coming.
Last edited by v8truckin; Jul 22, 2012 at 03:53 PM.
Jul 22, 2012, 10:47 AM
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After investigating the structure - how the top deck meets the bottom half, and what is "done" by each half - I am pretty sure I can make the whole upper deck removable instead of glued on! Originally I was just going to cut a section for the fan area, to be removable.
This removable top deck would allow total, and easy, maintenance of everything! EDF, ESC and wirings, servos...
It can definitely be done, but the main issue is HOW to bolt it down in a visually nice way!! So I will work on that idea, and pretty sure I can get that done.

Idea number one is to mount plywood plates in strategic spots on the top deck (hidden), with captive nuts (prob 4mm) and then use allen head bolts from underneath the lower fuselage. The bottom positions will need plywood plates also, but they can be hidden in the foam - by slotting them in from the side, internally - and then the bolt will he hidden in the foam, down where it reaches the ply plate.

The main issue is whether the key points that need strength, can be locked down adequately and 'properly'.
I think it can, because I have been making all the major strength items locked to the lower fuselage half, so the top deck doesn't need to do much 'work' at all. Mainly just the very rear end elevators and rudders area, which has a lot of mounting area to affix them together very well.

It sounds complicated I guess, but really it (seems so far) that it should be fairly easy to achieve.

I cut out my Ailerons and flaps, and fit their servos into the wing. No pics for now (should be tomorrow). And the Rudders also cut. So tomorrow is finish off all those surfaces day (evening).
I had to cheat a bit on the flaps/ailerons, because the size of the real ones are too small to even be worth having. I made them just a bit bigger.

The wing has a 6mm spar now that runs a fair way into the wing pieces, and the wings will be locked down solidly to the lower fuselage permanently and that helps form the rigid lower structure that then reduces the top decks mutual strength needs.
The F-22 wingspan is small enough to be manageable if it can't come off.

Today was the first day it was sat together all 'complete' (all pieces mounted) and was a full F-22. It looked really nice, even in its 'Plain Jane' FlyFly spray job! I am not going to do anything to visually finish it once it is complete - filler, paint, sealer etc - because I want to test fly it before that, to see if it even flies! LOL.
Jul 24, 2012, 06:01 AM
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When I cut all the new control surfaces and trimmed and sanded their bevelled edges, I had an idea.....
I normally leave them and do nothing else, then paint them later. But I thought it might be a good idea to coat them in a thin coat/smear of epoxy to make them a toughened edge/surface that will cope with their situation better. Certainly better than raw foam, or foam with a bit of paint on it.
So I did that, and now just need to resand them nice and smooth (those epoxy edges) then hinge and fit them.

I will do a run of pics soon, but I want all the work for this section done, and I will get pics of all the pieces before and after fitting (surfaces, servos etc).
I should also be able to fit the wings and spar to the lower fuselage - which will all be permanent. Then work out the servo wiring runs.
The totally removable top deck still looks POSSIBLE, but I am not sure if it is a really necessary or 'great' idea. Still humming and harring over that.... until I get to needing to do it.
Jul 25, 2012, 02:22 PM
Hawk Fanatic
SkylineFlyer's Avatar
Subbed, I love the F-22. Nice job so far!
Jul 26, 2012, 11:22 AM
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capt soap's Avatar
Pete, I love f-22's... What kind of performance are you exspecting out of this jet?
With the size, i would quess around 95 on 6 cells. Cant wait to see it go. Lee
Jul 26, 2012, 06:57 PM
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I have no idea what speed (or thrust) it will do. I will static test it with its stock bifurcated exhaust first. It looks a good area of opening, and good pathing - for bifurcated. And a very short path. But for sure it can't match a straight out thrust tube. Thus there is no way it could do the same speed.
The main 'nuisance' of going straight out is that it means cutting away the centre 'tail' of the F-22, which is a fairly distinguishing feature of them. Though who will know? LOL. Not many people who see it.

That will be easy to do later anyway, thus why I will leave it until I think it is required.

I have read that the 'chunky' wing leading edges, and even trailing edges, are a speed eater (drag). So if you wanted more speed you would sand the LE and TE to finer radius/edges.
I have hummed and harred over that too.... It would then need soem replacment, or strength, added. Eg balsa edges, or CF strip imbedded. Balsa would be a better finish.
But what I am going to do is not paint anything on it at all and fly it for tests... then decide what it might need changing, then paint it once I am totally satisfied.

Even painting it, and WBPUing it, would help with speed a lot. As the stock plane is quite a coarse finish - pock marked foam and the paint they use doesn't really do a thing for smoothness. It must be an anti-radar stealth finish! LOL
But anyway, it is a waste to paint it until all ideas/mods a re done.

I had to do some other plane's for a few days, so will be back on the F-22 tonight almost certainly.....
Jul 29, 2012, 12:45 AM
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Quite a lot done over a few days, so.....

First were the Flaps and Ailerons.
A tiny bit of poetic licence taken, to make the ailerons a little bit deeper than the moulded outlines, seeing they would be so small you may as well not have them - almost! And even being a bit larger now, that is still a very small aileron. But it should be enough to be of good use.

The "Flaps", well they will be Flaps, Flaperons, Spoilerons, and 'elevons' or whatever it is called when the all-moving tailplane and the main wing 'flaps' work in unison. (one day I will look that up!)

The servos and wiring were embedded into the wing (as is usual) and the wing spar suppoort/guide block glued in also.

With the wings and their mounting:
They were obviously designed to be removable, by using "clamping blocks" - like wheel collets, but square - that go into the black support/guide blocks that mount in the wing and on the fuselage each side. So that is a possible choice to use, if you want removable wings. But then you have to sort out the wiring so it can all be plugged in - though the stock design has no wing surfaces, so removing a wing then is simple.

I am not so sure their flimsy half-plastic/half-carbon-fibre.... or whatever it is... wing joiner rod that they supply is that good. It is about 4mm or 5mm, but very short and it really on designed for the wing attachment, not as a spar also.
I guess it would all work... but would not be an overly strong or safe idea!

I drilled out the blocks to 6mm and used a long 6mm CF spar that goes out will into the wing. 14cm into each wing. (Seen later in the build.. soon)

Jul 29, 2012, 12:50 AM
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So the rudders were cut out and servos mounted in the OUTER sid eof the fins.
That was actually a dum boo-boo, as I meant to do them on the inner side. But really, on either side is fine and they will be painted, and/or covered anyway.

The wiring goes down through the top deck, which the fins glue onto, and some amount goes into a recessed cavity so that if you ever need to replace a servo then when it is pulled out there is 50mm or so of servo lead that can feed out to allow rejoining the new one.
The same is done for the elevator servo leads. To make them easily replaceable if that need ever arises. (more pics of all that later on).

Jul 29, 2012, 12:55 AM
Hawk Fanatic
SkylineFlyer's Avatar
Then don't go that route if you think its unsafe for the plane. Why do the wings need to be detachable? I'd make them permanent and use a solid CF rod. JMHO.

EDIT: I see that I missed that last sentence. Your going with a longer CF rod. Great!
Jul 29, 2012, 12:58 AM
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Wings and spar:
The 6mm wing spar was made and fed through the fuselage mounting blocks. With those block epoxied in, and then the spar also epoxied just inboard of the block so it can't move.
The wings I skewered with a philps head screwdriver of 5mm shaft diameter, which was almost long enough to do that job fully. Then some 4mm piano wire for the remainder. This made the 6mm CF spar a snug/tight fit when fed in (14cm of it per wing). The wing were only glued to the foam surfaces of the fuselage, not the spar or into the block at all. This means the wings can be cut off along the fuselage if there is ever a need for that in the future. eg Maybe a change of mind to make them a removable system.

The wiring was run in through some new channels made for them. I used fibre tape to cover them and make it all flush. I generally do that, but was toying with the idea of using some glue and filler instead - to make it a perfect surface again. Though fibre tape sticks extremely well and it almost as good as flush. So I am feeling a bit lazy about glue and filler!!

Jul 29, 2012, 01:05 AM
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I made a larger plywood mount than the stock ones supplied were. Just for a first 'layer' to then mount the stock one onto. This was just to get more surface area to bond to the foam with.
Later on, all the area from the front outer edge of the plywood mount will be filled out and down so that it is all streamlined. And I will also fill in the fuselage wing mounting block area to be flush also.

The wiring was run through yet more new channels in the lower fuselage, and the retract lead was all coiled and stored in under the retract so that the retract can be removed fine, and replaced if need be.

The metal trunion retracts from PW-RC (Typical PZ's) work fantastic. No slop what-so-ever, and sound nice. And with a bit of grease the stock FlyFly oleos are also pretty good. They are a bit cheap and the HobbyKing recent oleo additions are very high quality units, so if you want to spend another $45 approx for perfection then they are a great choice. I will stick with the stock ones as they really are adequate for the job.

Note that I also changed the crappy FlyFly wheels to rubber tired wheels, but a bit smaller diameter so they can store away nicely when retracted. And they also look ok in proportion to the plane too.

Last edited by PeterVRC; Jul 29, 2012 at 01:21 AM.

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