Discusion Thread: Raceair Skylite Build and sub-kit developments

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Have a look at the Weller Rebell Uli, this about the size of aircraft you are looking for, 120kg incl. Safety chute and a Parazoom 4 stroke engine installed!

I nearly bought a 3 cylinder Verner Engine before they stopped production, but decided against it since no point my building a version of the skylite for an engine that was going out of production. I see this airplane also can be built with the Briggs 627cc with redrive as well.
 
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Here is what I have with the test fit of the Briggs 627cc. This has a parazoom redrive, but I am planning to use an Ace since that is what I have. Ace was a bit of a pain to deal with so in the end I may make my own at some point but for now will use the Ace I bought.

1664921412407.png

I need to have a look at my plans to see where the prop mounting plate is on a Rotax 627 and then see how that compares to what I have here. Best guess is my engine will be a bit forward than normal and may require lengthening the aft fuselage a bit. Also it looks a bit stubby now with the addition of the thicker fuselage mod. I am liking how the engine fits though. I could likely enclose the engine fully if needed..

1664921626981.png

I still have the original fuselage CAD model as well and can do a simple CG comparison between the two and see how much forward the CG shifted with the fuselage mods only. Then figure in a rough estimate of the difference in FWF weights and then that should tell me how much I need to lengthen the aft fuselage to get back to original CG location., or see if its even worth it to do.
 
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Here is what I have with the test fit of the Briggs 627cc. This has a parazoom redrive, but I am planning to use an Ace since that is what I have. Ace was a bit of a pain to deal with so in the end I may make my own at some point but for now will use the Ace I bought.

View attachment 130537

I need to have a look at my plans to see where the prop mounting plate is on a Rotax 627 and then see how that compares to what I have here. Best guess is my engine will be a bit forward than normal and may require lengthening the aft fuselage a bit. Also it looks a bit stubby now with the addition of the thicker fuselage mod. I am liking how the engine fits though. I could likely enclose the engine fully if needed..

View attachment 130538

I still have the original fuselage CAD model as well and can do a simple CG comparison between the two and see how much forward the CG shifted with the fuselage mods only. Then figure in a rough estimate of the difference in FWF weights and then that should tell me how much I need to lengthen the aft fuselage to get back to original CG location., or see if its even worth it to do.
Having already gone through this exercise, I have to wonder how flexible you are! I abandoned these changes because even with a 3" cabane height increase I could not get over the Longeron in a mockup...that was getting in at leisure...even tougher to get out, even more in an emergency exit!
 

TFF

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Entry is one difference with the legal eagle if compared. Not as strong as a longeron across the top, but you do have to get in. Baby Aces had to add a side door.
 
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Entry is one difference with the legal eagle if compared. Not as strong as a longeron across the top, but you do have to get in. Baby Aces had to add a side door.
The upper longeron on the rught side is cut and a cub type fold down door helps with access. Some omit tge door entirely. The fuselage is beefed up on that side since the longeron is removed. In my cad model i still show it in since its cut out after welding.
 

Pops

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On the JMR I moved the lower firewall forward an extra 2 " for the clearance of the rudder pedals. Can't remember for sure but I think the firewall was slanted 7 degrees.
 
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Just an update of where I am now with the fuselage mods.

The length of the cabanes have been increased as well but only by 2". So the fuselage is a bit taller then the cabanes increased in height by 2" making the overall change from seat to wing attach point by 5" in total. I did not want to raise the wing with just the cabanes by doing it with the fuselage as well, the cabane geometry only changed by 2" and I wanted to keep the cabane geometry as close to stock as possible. This would be too much of a change and would require thicker wall tubing than stock at a minimum. With myself (230lbs) and the engine modeled in CAD my CG is circled in red. I have not added any of the tailplane yet so it will shift back as I do and also the wheels and gear legs will then shift it back forward. I can then move the engine fore and aft to get the CG close to where I want for me. The yellow CG symbol is the CG of just the fuselage not counting the pilot and engine.

1665180603560.png
1665180626102.png

I also ended up pushing the firewall forward 3" since my legroom was too tight. The pedals shown are in the same place on the floorboards per plans in relation to the firewall which is 5". Yet by pushing out, the new firewall location is 3" farther away from the back of the seat which lowers my knees quite a bit. I may be able to pull it in an inch and still be OK with my legroom and then the firewall will only be 2" forward of plans. However with the rudder pedals mounted per plans 5" from the firewall it does not give a lot of rudder pedal travel before the pedal hits the firewall support cross tube. See pic below. Total weight gain per Solidworks in adding 3" depth to fuselage and pushing out firewall 3" is 1.6lbs,

1665180663520.png


As you can see the rudder pedal hits the blue cross tube at 116 degrees. That is only 16 degrees off perpendicular to the grey floorboard. I suppose I can have the rudder pedal start a bit less than 90 degrees but unsure if the range of motion in my ankles can deal with that as the pedal rotates toward the cockpit with opposite deflection. Since I may have a bit more room than needed I may bring the pedals closer to the cockpit by 1" to give more deflection range toward the firewall. I can also add 3 positions of nut plates just in case I feel I need to relocate them after the first flight. Also since I will likely use my ankles instead of moving my legs to actuate the rudders, what do you think about trimming back the main rudder plate to make room for a roller on the top where my shoes contact. This way as the rudders actuate, the roller will give less friction and roll with my shoe. I can make the roller out of nylon or Carbon Fiber tube so it won't weigh much.

I am hoping to flesh out any of the issues I have with making myself fit in the next few weeks and be ready to start building a jig and laying out a fuselage when I return home from France.

Your thoughts?

Marc
 

b7gwap

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Marc

It looks great. You are a talented CAD jockey and a thoughtful designer as well.

I think everything you’ve done here looks good high level. And it sounds like you are going to do some checks on tube wall thickness/diameter, so that’s goodness.

I would expect the failure mode on any of these tubes to be buckling or crippling, Euler and Bruhn have formulae for both.

It may also be worthwhile to study what Milholland did to make the Legal Eagle XL vs the original.

Cheers! Keep it up!

Austin
 

Lucky Dog

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Just an update of where I am now with the fuselage mods.

The length of the cabanes have been increased as well but only by 2". So the fuselage is a bit taller then the cabanes increased in height by 2" making the overall change from seat to wing attach point by 5" in total. I did not want to raise the wing with just the cabanes by doing it with the fuselage as well, the cabane geometry only changed by 2" and I wanted to keep the cabane geometry as close to stock as possible. This would be too much of a change and would require thicker wall tubing than stock at a minimum. With myself (230lbs) and the engine modeled in CAD my CG is circled in red. I have not added any of the tailplane yet so it will shift back as I do and also the wheels and gear legs will then shift it back forward. I can then move the engine fore and aft to get the CG close to where I want for me. The yellow CG symbol is the CG of just the fuselage not counting the pilot and engine.

View attachment 130597
View attachment 130598

I also ended up pushing the firewall forward 3" since my legroom was too tight. The pedals shown are in the same place on the floorboards per plans in relation to the firewall which is 5". Yet by pushing out, the new firewall location is 3" farther away from the back of the seat which lowers my knees quite a bit. I may be able to pull it in an inch and still be OK with my legroom and then the firewall will only be 2" forward of plans. However with the rudder pedals mounted per plans 5" from the firewall it does not give a lot of rudder pedal travel before the pedal hits the firewall support cross tube. See pic below. Total weight gain per Solidworks in adding 3" depth to fuselage and pushing out firewall 3" is 1.6lbs,

View attachment 130599


As you can see the rudder pedal hits the blue cross tube at 116 degrees. That is only 16 degrees off perpendicular to the grey floorboard. I suppose I can have the rudder pedal start a bit less than 90 degrees but unsure if the range of motion in my ankles can deal with that as the pedal rotates toward the cockpit with opposite deflection. Since I may have a bit more room than needed I may bring the pedals closer to the cockpit by 1" to give more deflection range toward the firewall. I can also add 3 positions of nut plates just in case I feel I need to relocate them after the first flight. Also since I will likely use my ankles instead of moving my legs to actuate the rudders, what do you think about trimming back the main rudder plate to make room for a roller on the top where my shoes contact. This way as the rudders actuate, the roller will give less friction and roll with my shoe. I can make the roller out of nylon or Carbon Fiber tube so it won't weigh much.

I am hoping to flesh out any of the issues I have with making myself fit in the next few weeks and be ready to start building a jig and laying out a fuselage when I return home from France.

Your thoughts?

Marc
 

Victor Bravo

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An old-school "rudder bar" (vertical pivot bolt in the middle) instead of pedals looks like it would allow more rudder cable movement for a given deflection. This changes the pilot's actuation method from ankle movement to leg extension of course. But having the cable attach points outboard of your footrests (rudder bar) will result in more cable travel (per foot movement) than the cable attach bolt location shown in your rendering, which looks like halfway up the side of the pedal. The price you pay for this is reduced mechanical advantage; the rudder forces will be a little higher. This may not matter if the Skylite rudder has an aero balance.
 

Pops

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I'm not satisfied with the rudder pedals on the JMR. I may change them in the future. IF I change then I will mount them from above. Gives more movement before hitting the firewall. Also more space in the flat flood for placing your feet while in cruise if wanted. Always liked the rudder pedals and brakes on my Piper Cherokee .
 
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Maybe swing the rudder pedals from above. That will give you a bit longer and more consistent cable pull in the same space.
I was considering this as well but it adds a bit more complexity since the gas tank may be in the way. Also no structure to hang the pedals and that would need to be added. In the meantime, I am working on the Rudder Assembly and once done will add it to the main assembly and connect the pedals to see how much rudder movement I get before the pedals hit the firewall. If needed I can add multiple cable connection holes and move the cable up or down until I get the rudder deflection I want even with limited rudder pedal travel.
 
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Marc

It looks great. You are a talented CAD jockey and a thoughtful designer as well.

I think everything you’ve done here looks good high level. And it sounds like you are going to do some checks on tube wall thickness/diameter, so that’s goodness.

I would expect the failure mode on any of these tubes to be buckling or crippling, Euler and Bruhn have formulae for both.

It may also be worthwhile to study what Milholland did to make the Legal Eagle XL vs the original.

Cheers! Keep it up!

Austin
Thanks for the kind words Austin. I have been meaning to buy some legal eagle XL and the 2 lace plans to see what diameter tubes are used in the fuselage. Jus never got around to it and may do so when I return home from vacation. I can do a lot of virtual testing in Solidworks to flesh out the cascading changes since I am modifying so much but sadly I am not an FEA guy in the least. I would like to learn FEA one day. Or even look at the formulas you mention above for buckling but I am even less a math guy. I may ask for help or another more trained set of eyes before I finalize anything. I have run each mod by Ed and so far he has given me the thumbs up with a bit of advice each time. If anyone on here is well versed in structures and willing to have a look let me know. Also any good resources would be great as well, but I know with FEA if the problem is not set up right the results will be incorrect.
 
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More updates. No pics since we are on the road in the car. Anyhow I finished up the rudder and have attached it to the fuselage in the CAD model. Tonight I hope to connect the ridder pedals to the rudder to see how much deflection I get. The fuselage ended up increasing in length by 2” due to needing to maintain the 35 degree swept tailpost. After the fuselage was increased in depth the tailpost angle went to 30degrees due to solidworks constraints. Pushing out the upper longerons brought it back to 35 degrees. Also with the mods the tailpost length increases a bit as well as did the rudder to accommodate. So just by putting things back where they needed to be the fuselage lengthened a bit over 3” to help offset the Heavier Briggs engine.

I feel things are progressing nicely. I considered redoing the rudder in Aluminum like an Aerodrome Biplane but decided to draw it up in 4130 first. Glad I did because its way lighter than I expected it would be. Even slightly enlarged its under 4 lbs so will keep it Steel.
 

TFF

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The Legal Eagle has an aluminum tail. Some of the choice had to have been weight; some was probably about bending tubes. Maybe cost. 4130 varies greatly in price by size, by popularity more than weight of steel like normal steel. I would have rather built a steel tail.
 

Victor Bravo

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There could be dynamic considerations too. The mass of the (steel) rudder trailing edge tube being far enough away from the hinge line that it becomes more prone to flutter? Or that this small difference in mass - times the distance - would require a lot more weight added at the front of the aero balance... to get the overall rudder mass balance within limit?
 
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