Raptor Composite Aircraft

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BJC

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In the YouTube comments, RaptorAircraft wrote:
Raptor Aircraft
10 hours ago
It's a shame that A&Ps with all their years of experience never seem to be the ones to have enough guts to build something new and exciting. So it's left to inexperienced guys that have no idea what we're doing with somewhat predicable results.
He seems to be confusing building with designing.


BJC
 

BBerson

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That cable sheath system won't work well. I don't know why the original pushrod design wasn't used. Use proper pulleys and straight cable runs or push tubes.
 

BoKu

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Being I didn't see the "Before" what exactly is different now?
The prior system used 1/8" steel cables from the forward cockpit out to the drive bellcranks at the outboard ends of the strakes. All direction changes took place at pulleys that were poorly anchored to the airframe, and thus moved substantially on system preload and when loaded with control forces. The new system uses the same kind of 1/8" steel cable, but instead of pulleys runs it through flexible sheaths from the forward cockpit out to the ends of the strakes.
 

Rik-

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The prior system used 1/8" steel cables from the forward cockpit out to the drive bellcranks at the outboard ends of the strakes. All direction changes took place at pulleys that were poorly anchored to the airframe, and thus moved substantially on system preload and when loaded with control forces. The new system uses the same kind of 1/8" steel cable, but instead of pulleys runs it through flexible sheaths from the forward cockpit out to the ends of the strakes.
Thanks, that pulls back a blurry memory of the surfaces moving when he was moving them.

Don't really see how a floppy sheath will eliminate slack though. Watching the video, it didn't.
 

BoKu

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...Don't really see how a floppy sheath will eliminate slack though. Watching the video, it didn't.
The only thing that the new system improves is the stiffness of the forward anchors, which Peter had welded up out of 1/4" thick 4130 steel and bolted to the carbon sandwich sides of the keel box. If he had put that kind of attention into the pulley anchors, they would have been plenty stiff enough.

I'm hoping he realizes that, and goes back to the pulleys with improved anchors. Or, better yet, push-pull tubes with bellcranks. Either way, he's going to have to cut a hole into the lower part of the cabin aft bulkhead to install stiffer anchors there for the direction change up from the floor level.

If he would get in the habit of testing things like this on the bench, he'd end up with a lot fewer extra holes in his airplane. It would have been trivial to make an "iron bird" mockup out of 2x4s and plywood and use that to test the suitability of the sheathed cable system in a realistic simulation of the required length and geometry.
 

Rik-

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The only thing that the new system improves is the stiffness of the forward anchors, which Peter had welded up out of 1/4" thick 4130 steel and bolted to the carbon sandwich sides of the keel box. If he had put that kind of attention into the pulley anchors, they would have been plenty stiff enough.

I'm hoping he realizes that, and goes back to the pulleys with improved anchors. Or, better yet, push-pull tubes with bellcranks. Either way, he's going to have to cut a hole into the lower part of the cabin aft bulkhead to install stiffer anchors there for the direction change up from the floor level.

If he would get in the habit of testing things like this on the bench, he'd end up with a lot fewer extra holes in his airplane. It would have been trivial to make an "iron bird" mockup out of 2x4s and plywood and use that to test the suitability of the sheathed cable system in a realistic simulation of the required length and geometry.
So is a “push/pull” cable a good thing? We use a Morse cable in boats for everything that needs to be moved or monitored
 

BoKu

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So is a “push/pull” cable a good thing? We use a Morse cable in boats for everything that needs to be moved or monitored
That's a matter of opinion. They tend to have a lot of slop, relatively speaking, especially when there is a lot of total degrees of direction change. And they have relatively modest working loads in the push direction. And they are relatively heavy in terms of capacity * length.

I've used them in my designs, but only for secondary controls (flaps), only where the control was non-reversible, and only as a last resort. I know that there are some ultralights and LSAs that use them in primary flight controls, and they seem to work fine in those applications. But I don't know of any fast airplane that uses them for primary controls, probably because their slop makes them a flutter liability.
 

mcrae0104

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So is a “push/pull” cable a good thing? We use a Morse cable in boats for everything that needs to be moved or monitored
I have also heard that they can be susceptible to freezing if water gets inside the sheath, but I do not know about any instances of this actually happening.
 

Rik-

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That's a matter of opinion. They tend to have a lot of slop, relatively speaking, especially when there is a lot of total degrees of direction change. And they have relatively modest working loads in the push direction. And they are relatively heavy in terms of capacity * length.

I've used them in my designs, but only for secondary controls (flaps), only where the control was non-reversible, and only as a last resort. I know that there are some ultralights and LSAs that use them in primary flight controls, and they seem to work fine in those applications. But I don't know of any fast airplane that uses them for primary controls, probably because their slop makes them a flutter liability.
A "typical" Morse 33C Cable has about 1/4" of slack (slop) in the cable as you have to push the noodle inside the sheath.
 

TFF

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You also don’t want liquid lubrications in it. Might slip good when fresh, but as the solvents evaporate, they gum up. Attract dirt too.

I’m sure full push pull is not possible now. I bet it would require something like a tube having to go through the engine block or some other impossible change. Having cables in the fuselage transition to push pull in wings would be the smart thing.
 

Marc Zeitlin

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That's a matter of opinion...
Some opinions are worth more than others :).

... But I don't know of any fast airplane that uses them for primary controls, probably because their slop makes them a flutter liability.
The Velocity used to use push/pull cables for part of the aileron control system - they moved away from them as their XL's got larger and faster. I don't believe that there has ever been aileron flutter on a Velocity (or any canard aircraft of which I'm aware), but clearly Velocity eventually decided on a more robust system.

The Wheeler Express 2K (you're not going to believe this) used Cablecraft style push-pull cables FOR THE RUDDER ACTUATION. Yep - cables that were rated for 25 lb. maximum loads were being used for controlling the system in which you can leg-press both sides of the system simultaneously. I was asked to do a CI on a Wheeler Express 2K once, and after verifying that these cables were installed EXACTLY PER PLANS, so it wasn't a stupid builder error, but a stupid designer error (along with a substantial # of other design issues that were flabbergasting), I told the owner that I would not be able to sign off their CI and they'd need to find someone else to do it.

When I was at ICON, and we were trying to decide how to actuate the flaps, one of the possibilities was push/pull cables, but cables with the load capacity to actuate relatively large flaps would have weighed about 5X - 10X what a torque tube/pushrod style system would have weighed. Obviously, we didn't use them.
 

BBerson

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What if the designer didn't want full actuation at high speed?
Most small airplanes have no cable tension on the rudder at all (some have a little spring to hold the pedals back). So the rudder is just flopping in the wind if the pilot puts his feet on the floor. No flutter resistance from the loose cables.
The Grumman Goose has air activated split flaps, if I recall correctly. They won't come down if too fast.
The Raptor test pilot in the video was concerned about enough aileron motion from the springy control, I think.
 
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Rik-

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What about this. As everyone is so concerned with a 10 yrs worth of accumulation creating a problem in the very short term on a aircraft that is basically nothing more than a technology proving ground.

Install a small hydraulic cylinder that is matched to a small hydraulic cylinder on the ailerons ends. You can use those little aluminum cylinders that are used for machine processing (pneumatic control) and they can handle the forces required in this application with hydraulic fluid in them. If a power assist was needed a small Oildyne pump with an accumulator tank will handle that problem.

Each cylinder will be about 1 lb. and as to the weight of the fluid within 1/4" OD hose. It's a wash to the control cables, the sheath and the steel brackets.

This way there would be no slop as the cylinders will be positive displacement to the slave cylinder.
 
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akwrencher

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I have also heard that they can be susceptible to freezing if water gets inside the sheath, but I do not know about any instances of this actually happening.
I've had them freeze plenty of times. Used on our telehandler forklifts. One had the shifter cable freeze anytime it got cold. Fixed it by putting a tube over the end and soaking antifreeze down inside. Worked a treat. Don't think I'd like to have them for primary controls though.
 

wsimpso1

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What if the designer didn't want full actuation at high speed?
Most small airplanes have no cable tension on the rudder at all (some have a little spring to hold the pedals back). So the rudder is just flopping in the wind if the pilot puts his feet on the floor. No flutter resistance from the loose cables.
Rudders are actuated by our legs, really strong things, usually stronger than needed for flight, so we can usually stand some friction there. We can also do things like decrease the mechanical advantage or open the pedal travel to get full rudder control if system stiffness is too low. Peter is not fixing rudders here.

Peter is fixing is aileron control, where we humans are kind of weak, control response usually seems to be modest, and forces tend to be high. On top of that it is a side stick, which tends to have small throws. With system that is not stiff enough, full throw at the stick does not give full deflection at the ailerons.

One way is to open the stops at the stick enough to get full travel of the ailerons under flight loads, but there is stuff in the way like the pilot and the sidewall of the airplane, plus you lose the nice feel of side stick when you do that. Also, the system looks like he would need to more than double the travel and that is a bunch.

Another way is to cut the mechanical advantage of the system so the available stick travel will still give enough aileron travel at flight loads. Getting twice the aileron travel per unit travel at the stick means twice the stick force per unit of aileron movement. That might turn out to be acceptable here, as that would only get you back to the originally intended forces to achieve the control authority. Trouble with that is most of us have never complained of too light ailerons unless we overdid the spade sizes or where playing with servo tab ailerons.

The usual issue with soft aileron systems is that we do not get the control authority we are asking for and we get less and less control authority as speed goes up. BAAD.

Stiffness of the cable and then pushrod scheme would normally be adequate if the mounts are stiff. Fixing that inside the tunnel is going to be a BIG job once the ship has been built. Access is tough, then a bunch of stuff has to be removed, then an inherently stiffer scheme has to be installed.

Instead of that, it looks like Peter is trying to put in something that is stiffer without the major tearup of the airplane. The new cables are about the same stiffness as the old ones, the sleeves are somewhat springy but probably better than the softly supported pulleys were, but they add friction, and by the time the mushiness is taken off with some more cable preload, quite a bit of friction will be added by rubbing on all those bends in the system. If he gets lucky, he might get to enough preload in the system to get full control deflection at traffic pattern airspeeds without excessive friction. The test pilots will be they judge of that trade off. This scheme will most likely be unacceptable for customers to fly, and the inherent stiffness of the various mounts will have to be handled, but this might get the plane around the patch and through an initial test program. Or it might prove to be a dangerous handful, and Peter will have to seek stiffness other ways for flight test to proceed.

I personally like putting a brace longitudinally between the pulley axles in the tunnel. Light, simple, quick, and might make more than enough improvement in stiffness to get into flight test. Removing the existing pulley mounts, relocating them to simultaneously grab the other structures with larger bases and adding a couple more plies of cloth through those regions are all possible, as is other bracing schemes should more stiffness in other directions become useful. All of this will be difficult and time consuming to put in the existing ship, but is probably necessary to bring aileron forces and control to a place where Peter could let depositors handle the controls in flight.

Billski
 
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