Discusion Thread: Raceair Skylite Build and sub-kit developments

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Hasn't anybody come up with some system to unlink the two? You could put a linear bearing inside the torque tube and put the front rod end on a sliding slot, so that the elevator pushrod would always stay in the center of the torque tube as you moved the elevator. It's such a minor effect that it's not worth designing a more complicated solution, unless somebody else already has, in which case, I would copy it.😛
I thought of removing the reverser link from the main yoke and relocating it on an added cross tube in the lower fuselage. This decouples the sway of the reverser link. However I decided against it since this is an ultralight and no need to get too complicated.
 

bhooper360

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With the stick full forward or aft, there is a minuscule elevator deflection due to full aileron.

Yeah, I know this. I'm saying that there must a way to get rid of that miniscule deflection, and if it's probably not worth the effort. It's caused by the rod end swinging through an arc, so it goes up and down inside the tube in addition to going forward and aft. So when you move the ailerons it changes the distance from the rod end to the reverser.

This decouples the sway of the reverser link.

I misunderstood your design, I thought that this the rear control column for a dual seat aircraft or maybe an idler. Yeah, I guess it would be more complicated to mount the reverser when the fuselage is a triangular truss like that, it'd just be another thing to line up.

Here's a GrabCAD screenshot by a user named Michael who claims to have modeled the controls from Po-2. There's all kinds of weird mixing going on in the name of simplicity, the long EZ has something similar. Yeah, you probably would notice it if it was an aerobatic plane. But you would probably correct for it subconsciously and not notice until you switched planes. It's more of a craftsmanship thing.

Second picture from the Pitts, the axle is for an idler not the reverser.

Or just move the elevator control horn to the other side?

You'd have to move the entire stabilizer, wouldn't you?

Control sticks.jpg
IMG_4707.JPG
 

TFF

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A lot of times reversers are used to shorten the tubes so they don’t bow up in compression. If you are just using it to reverse, it’s because you want to pull the elevator up and not push it with a long tube. W8 Tailwinds have a reverser, but W10s don’t per plan. Wittman made sure the W10 elevator was pulled to give up. Not an aerobatic airplane so great down control is not necessary. The down side with the W10 is the elevator control horn is mighty close to fuselage tubes. Miscalculation and it will hit. Almost impossible for the W8 setup to have interference. Mooneys have long push pull tubes and have guides mid span to keep
Them from bowing.
 

cluttonfred

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Thanks, all, this sort of control system geometry is a detailed aspect of aircraft design that I have never really considered before.

The plans I have spent the most time studying over the years are Evans VP-2 and, not for the first time, I am learning to appreciate Bud’s knack for simplicity.

Here is the VP-2 control stick setup, the rest is just cables and fairleads and pulleys.

33CD32B9-87A6-48BE-B9C7-6E02E84BC474.jpg
 

BJC

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Look at a Pitts S-1S. With the stick centered fore and aft, full aileron can be applied with no elevator deflection. With the stick full forward or aft, there is a minuscule elevator deflection due to full aileron.
I'm saying that there must a way to get rid of that miniscule deflection, and if it's probably not worth the effort.
I’m not a good enough pilot to sense the difference. The few maneuvers with the stick at a forward or aft stop are so dynamic that any deflection due to aileron input is meaningless.

BTW, in this case, minuscule, as applied to the difference in position of the elevator trailing edge, is approximately 1/64”.


BJC
 
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Hello All,

Its been a while since I posted anything as I had been tied up with a 3 year long contract project I took on so pretty much all skylight development was on hold. Now we are on a much needed vacation and with a bit of downtime I decided to do some work. I have never been able to find a good cad model of a human close to my dimensions so I found some human ergonomic drawings and used them to draw up a very simple human model I can place in the fuselage to see how well I will fit. The 95% human is very close to my height of 76" and I used this as the data to make the model.

99-percentile-man-1-percentile-woman.png data-stature.png Standing Human 76in side.JPG Standing Human 76in.JPG

So once I inserted my simple human into the Skylite, it became clear I wont fit too well. Also the Skylite below already has the Cabane raised a 2" inches in anticipation of my being too tall. Seems I need to go at least an inch higher and possibly move the firewall forward a bit. I am a bit hesitant to stretch the cockpit area as that will increase the wing chord. I want to be able to wear a helmet and have some clearance under the lower wing so may even need to raise the Cabane to 4" over standard. If so I may want to bump up to the next wall thickness on those tubes.

Fuselage Fit - Side.JPG Fuselage Fit - Iso.JPG
I already have a Briggs 23hp and Ace Redrive ready to build up when I return from home from France, but after seeing this, part of me wants to leave the Skylite as is and jump straight to the enlarged Skylite (non Part 103) to use the larger Briggs Engine or O-100 engine. Unsure so far what percentage increase but likely between 15 & 25%.

Thoughts on fitting in a Part 103 version:
  • Push firewall forward a few inches. I likely can do this without extending the motor forward from standard since the Briggs 23 is fairly compact.
  • Raise the Cabane to give more head clearance. Also possibly raise the overall height of the fuselage a bit so that the Cabane height does not look too exaggerated and then maybe the standard wall tubing can be used since the triangulation likely remains the same. The fuselage sides are quite a bit below my shoulders so I have some room there. This added material in tubing may put me outside Part 103 unfortunately, but if I omit the cowl and nose bowl I may still be close.
Or just jump ship and build the larger version but that is an entire engineering change on a new airframe over an incremental one.

Thoughts?
 
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BJC

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Thoughts?
When considering head / wing clearance, also consider the visibility. It is possible to have headroom, but still have the visibility restricted to the point of making the airplane unpleasant to fly.

An option other that raising the wing is to lower the fuselage lower longerons, and, therefore, the seat. Opens a can of worms with strut dimensions, LG dimensions, etc., but still may be viable.


BJC
 

Pops

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On the leg room, did you allow clearance for the full throw of the rudder pedal and operation of the toe brakes and master cylinders if used ?
If you need to move the firewall forward, will you have enough room to move the engine back for W&B if needed ?
 
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An option other that raising the wing is to lower the fuselage lower longerons, and, therefore, the seat. Opens a can of worms with strut dimensions, LG dimensions, etc., but still may be viable.


BJC
This is what I meant about raising the height of the overall fuselage to make it taller so that I end up sitting lower. Also in doing so I can split the stretch half fuselage thickness and half cabane.
 

GeeZee

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I’ll bet the changes you describe won’t weigh much more. Probably less than a pound. I’ve already gone 4 lbs over due to going with thicker wall on the front spars. I’ve been pondering ways to recover some of that. One way that looks promising is to use titanium bar stock for the landing gear. I haven’t determined the dia. needed yet but if it’s 5/8” ish it looks like it would be worthwhile.
Also if you’re modding cabanes I wonder what it would take to make a torque box center section in order to eliminate the cables that runs from the firewall to the wing. I’ve been looking into the calculations a little but haven’t really figured out how to determine what the loads are.
 
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On the leg room, did you allow clearance for the full throw of the rudder pedal and operation of the toe brakes and master cylinders if used ?
If you need to move the firewall forward, will you have enough room to move the engine back for W&B if needed ?

As it is shown now the firewall is in its original place. and it seems like there would be no way I would have room to actuate the pedals as is. If I push the Firewall forward maybe 2 or 3" it should be enough to bring my knees down a bit and also leave room for activation. As for W&B the tail may need to grow too to compensate if the engine location ends up shifting. Since I will check everything in CAD I can take care of any cascading changes as they arise as I work on the design mods.

Seems I am just a bit to big for the Skylite and if I want to build one will need to make a few modifications.
 

TFF

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Build a fuselage with necessary mods. If it doesn’t work out, sell it to someone who can use it. It’s a mockup that may be useable. It is experimental aviation, and while you might stretch it too far, I don’t think so. Yes it changes the engineering, but much less of a change than if you wanted to lower the wing.

I am just going off Legal Eagle plans, but the cabane on it was just butt welded on the main fuselage. A finger patch gusset would have made me feel much better. Much more worried about that than the tube buckling.

You own the plans, hire an engineer to run numbers. Otherwise just do it.
 

Tiger Tim

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As it is shown now the firewall is in its original place. and it seems like there would be no way I would have room to actuate the pedals as is.
Can you just dish out the firewall where needed? The Tiger Moth by design had a pair of round stainless steel dish pressings riveted to the firewall to allow room for the rudder pedals to move. In a pinch a restoration could probably use a set of cheap stainless dog food dishes. Probably. I’m sure it definitely hasn’t been done that way, no sir! Not on a certified airplane. Quick, somebody change the subject.
 

b7gwap

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The cabanes are mostly in tension (strong) in flight, drag loads push them back for shear and moments too though. I would make a free body diagram of each triangle and just do a 6G load to see if it’s in the ballpark with a couple more inches. Then also do what VB said but only two inches. Keep proportions and add space. Speaking of space, this craft isn’t going there, no aerobatics either, so 6G is conservative.
 
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OK so I had a chance to modify the fuselage so a 76" tall person (myself) will fit better.

1664895121096.png

I raised the upper fuselage longeron 3" and left the already 2" extended Cabanes the same. Total stretch in height was 5". I have way more headroom now. I also pushed the firewall forward 3" as well. I have not had a chance to add the rudder pedals yet but it looks like this should work. I am traveling and my computer has decided now is a good time to crash every time I try and work in Solidworks. Its driving me nuts so may not be able to move much more forward until I return or until I can sort this out. **** windows auto update is what caused this but unsure when so I just cant go back and undo the upgrade sadly. Total change in weight for this mod to deepen the fuselage and push forward the firewall per Solidworks is 1.6lbs. Not counting weld material fuselage is 33.5 lbs but I still need to add the turtledeck.
 
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OK so I had a chance to modify the fuselage so a 76" tall person (myself) will fit better.

View attachment 130524

I raised the upper fuselage longeron 3" and left the already 2" extended Cabanes the same. Total stretch in height was 5". I have way more headroom now. I also pushed the firewall forward 3" as well. I have not had a chance to add the rudder pedals yet but it looks like this should work. I am traveling and my computer has decided now is a good time to crash every time I try and work in Solidworks. Its driving me nuts so may not be able to move much more forward until I return or until I can sort this out. **** windows auto update is what caused this but unsure when so I just cant go back and undo the upgrade sadly. Total change in weight for this mod to deepen the fuselage and push forward the firewall per Solidworks is 1.6lbs. Not counting weld material fuselage is 33.5 lbs but I still need to add the turtledeck.
I will also add a few inches to the aft fuselage just in case engine is moved forward. Especially since it’s likely to be a few pounds heavier than a Rotax 277 setup.
 
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