ThomasMartino
Elite member
I didn’t cover it, I stained it with red India ink. I got lucky and the color matched perfectly.
Balsa DLG
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ThomasMartino
Elite member
That is an incredibly low wing loading you achieved on the wooden Apogee. It must be a dream to fly something so light and floaty. I think I will try a 1m DLG next and see if I can match such a low wing load. My 1.5m composite DLG came out somewhat heavy but I really enjoy how it flies. It is able to float very slowly but can slice through the air incredibly fast when I want it to.
This is the first project I’ve done where I’m trying to prioritize weight above all else. I’m not doing a great job of it though. There’s a voice in my head that keeps telling me to reinforce parts and the grams quickly add up. I’m certain I have built some parts of this plane much stronger than they needed to be, and I am paying for it with unnecessary weight.
Regarding the stabilizer pivot point; I have randomly guess all three times I have done a full moving stabilizer. I got it right the first two times by estimating what I thought was the center of pressure, maybe 30-40% back from the leading edge. This time I put the pivot farther forward, about 25% back from the leading edge. I am worried this was a mistake. I think it will increase the load on the servo and potentially cause flutter. Only one way to find out. Hopefully the plane will be ready to test fly by tomorrow evening. If the stab flutters or overloads the servo I will move the pivot point back some.
ThomasMartino
Elite member
All done except for the pod. Flight report coming soon.
ThomasMartino
Elite member
Here is my initial impression: WOW!!!
It’s cold and windy this morning so I have not explored the entire flight envelope yet, but what I was able to experience was very impressive. I started with a gentle hand toss on flat ground. The plane tracked straight and floated halfway across my yard with minimal control input. That seemed promising so I moved to the top of the hill (about 12 feet high) and tossed the plane. Some down trim was needed to keep the airspeed up. I quickly realized the ailerons were very sensitive. After an ugly landing (stalled it in for a belly flop) I added some aileron expo and more down trim. I like full flying stabilizers because you can adjust the incidence to trim the plane for a specific speed rather than just using elevator trim for pitch adjustments. The airfoils I’m using are more efficient when flying quickly, and the extra airspeed helped me fight the wind. I spent about ten minutes throwing the plane off the top of the hill and circling back to myself. One time I completed three circles before bringing the plane back and catching it. There was a bubble of lift helping me but it’s a testament to the “floatiness” of this plane. Once I felt comfortable with the plane I moved back to flat ground and did a very gentle discus launch. I have a flight mode programmed with up elevator for launch. The plane tracked perfectly straight for a gentle climb up to about 20 feet. I repeated this a few times, gradually increasing up elevator trim for more aggressive climbs. I never launched the plane very hard. I’m trying to play it safe until I have more experience with it. On the fourth or fifth launch (still only 25 or 30 feet high) I found some lift and began thermalling the plane up to 85 feet (by this point I had turned on my altimeter). I used this opportunity to test the other flight modes. I have three camber settings for the flaperons. Normal (for launch and cruise), reflex (for high speed cruise and wind penetration), and undercambered (for thermals and super slow floating). They all seemed to do what I wanted, but I will need more flight time to thoroughly analyze their performance. The weather is supposed to improve later today. I hope to get a lot more flight time to familiarize myself with the plane and try harder launches.
It’s cold and windy this morning so I have not explored the entire flight envelope yet, but what I was able to experience was very impressive. I started with a gentle hand toss on flat ground. The plane tracked straight and floated halfway across my yard with minimal control input. That seemed promising so I moved to the top of the hill (about 12 feet high) and tossed the plane. Some down trim was needed to keep the airspeed up. I quickly realized the ailerons were very sensitive. After an ugly landing (stalled it in for a belly flop) I added some aileron expo and more down trim. I like full flying stabilizers because you can adjust the incidence to trim the plane for a specific speed rather than just using elevator trim for pitch adjustments. The airfoils I’m using are more efficient when flying quickly, and the extra airspeed helped me fight the wind. I spent about ten minutes throwing the plane off the top of the hill and circling back to myself. One time I completed three circles before bringing the plane back and catching it. There was a bubble of lift helping me but it’s a testament to the “floatiness” of this plane. Once I felt comfortable with the plane I moved back to flat ground and did a very gentle discus launch. I have a flight mode programmed with up elevator for launch. The plane tracked perfectly straight for a gentle climb up to about 20 feet. I repeated this a few times, gradually increasing up elevator trim for more aggressive climbs. I never launched the plane very hard. I’m trying to play it safe until I have more experience with it. On the fourth or fifth launch (still only 25 or 30 feet high) I found some lift and began thermalling the plane up to 85 feet (by this point I had turned on my altimeter). I used this opportunity to test the other flight modes. I have three camber settings for the flaperons. Normal (for launch and cruise), reflex (for high speed cruise and wind penetration), and undercambered (for thermals and super slow floating). They all seemed to do what I wanted, but I will need more flight time to thoroughly analyze their performance. The weather is supposed to improve later today. I hope to get a lot more flight time to familiarize myself with the plane and try harder launches.
Congrats! It's looks great! What are you doing for the pod? Molded PET, or...?
ThomasMartino
Elite member
Thanks! It will be fiberglass
hsquier
Junior Member
Me too, congratulations !
Thanks for sharing. I mean it :
For me maiden flights (especially when you have thought, drawn and built (and sand
) your plane) have the special taste of moment of truth, the validation of your initial idea and building skills.
And when all goes well all these considerations are blown away by the only magic pleasure of flight.
I still have the same thrill and exaltation by reading every flight reports. And yours have a special echo up to my recent DLG build.
Sorry ... this personal and presumably worthless considerations but it still gives me joy.
Thanks for sharing. I mean it :
For me maiden flights (especially when you have thought, drawn and built (and sand
) your plane) have the special taste of moment of truth, the validation of your initial idea and building skills.And when all goes well all these considerations are blown away by the only magic pleasure of flight.
I still have the same thrill and exaltation by reading every flight reports. And yours have a special echo up to my recent DLG build.
Sorry ... this personal and presumably worthless considerations but it still gives me joy.
ThomasMartino
Elite member
You put it into words better than I could have. Certainly a magical moment indeed. Especially with these super light gliders that sublimely defy gravity. I had three good thermal flights yesterday despite the poor weather. That validated all the work I put into this project.Me too, congratulations !
Thanks for sharing. I mean it :
For me maiden flights (especially when you have thought, drawn and built (and sand
And when all goes well all these considerations are blown away by the only magic pleasure of flight.
I still have the same thrill and exaltation by reading every flight reports. And yours have a special echo up to my recent DLG build.
Sorry ... this personal and presumably worthless considerations but it still gives me joy.
ThomasMartino
Elite member
Here is a video of the plane cruising around in dead air. At the end I show how maneuverable it is.
ThomasMartino
Elite member
Time for the next step, a kit! I will be producing a limited quantity of kits of this plane in 2 channel and 4 channel configurations. The general design of the aircraft will be unchanged but the construction techniques will be tweaked in a few significant ways. First off, I will be using store bought carbon fiber DLG tail booms. Building my own boom was fun and it works great, but it was too labor intensive to be practical. Secondly, I will be switching the horizontal stabilizer to a solid sheet balsa construction like the vertical stab. The built up stab is beautiful but it was a pain to build. The ribs are tiny and delicate and I often resorted to using tweezers to position them. I will also make carbon fiber V mounts for the stab pivot rather than the plywood mount I used on the prototype.
If anyone has any suggestions for how to make this airplane better or easier to build I’d love to hear them.
If anyone has any suggestions for how to make this airplane better or easier to build I’d love to hear them.
hsquier
Junior Member
Wow ! For the video.
Some said a little drawing is often better than a long speech. You upgraded it with modern video tools.
Super extra Wow !! For your project.
Bet it, I'm in !
If I may share my thoughts.
Some times I watch myself getting lost in complexity. So I gave two goals to complexity (I'm not talking about reaching what structurally you want to do but how) first- weight second- Aesthetic.
Up to me the built up stab contributes undeniably to the "soul" of your glider and makes I love it.
Plain solid sheet balsa stab is unbeatable in construction simplicity (and even : shape to desired profile can be a task ) but in this case Balsa quality (density) could/will be sensitive.
In summary : If no major weight / structural stiffness discrepancy I will pay extra work for built up stab, if not balsa sheet will by the best alternative.
At last (naïve question) would a balsa trailing edge instead the cardboard ad help ?
I don't know you have thought your kit project ? If, as I understood, il will be cnc/laser-cut based why not leaving the choice ?
Would the pod be part of your kit ?
Sorry there is no direct relation with your question but I'm very curious. May I ask for some photos on your aileron commands : how they get out of the fuselage/boom and what control horn system you have used.
Let's say it (hope you won't find it out of place) it is a real pleasure to share with you, I feel sort of connexion (sorry and excuses in advance if I'm getting too far).
Some said a little drawing is often better than a long speech. You upgraded it with modern video tools.
Super extra Wow !! For your project.
Bet it, I'm in !
If I may share my thoughts.
Some times I watch myself getting lost in complexity. So I gave two goals to complexity (I'm not talking about reaching what structurally you want to do but how) first- weight second- Aesthetic.
Up to me the built up stab contributes undeniably to the "soul" of your glider and makes I love it.
Plain solid sheet balsa stab is unbeatable in construction simplicity (and even : shape to desired profile can be a task ) but in this case Balsa quality (density) could/will be sensitive.
In summary : If no major weight / structural stiffness discrepancy I will pay extra work for built up stab, if not balsa sheet will by the best alternative.
At last (naïve question) would a balsa trailing edge instead the cardboard ad help ?
I don't know you have thought your kit project ? If, as I understood, il will be cnc/laser-cut based why not leaving the choice ?
Would the pod be part of your kit ?
Sorry there is no direct relation with your question but I'm very curious. May I ask for some photos on your aileron commands : how they get out of the fuselage/boom and what control horn system you have used.
Let's say it (hope you won't find it out of place) it is a real pleasure to share with you, I feel sort of connexion (sorry and excuses in advance if I'm getting too far).
ThomasMartino
Elite member
Today I replaced the built up stab with a flat balsa sheet of the exact same size and shape. I used light balsa, but not contest grade. It only weighed 2 grams less. If I redesign the built up stab to have a balsa trailing edge instead of the cardstock I’m sure I could get the weight down below the flat sheet option.
I didn’t expect any discernible difference in flight time or handling, but I was wrong! The flat sheet performed quite poorly in comparison. Pitch control was adequate, but lacked the snappiness I felt with the built up stab. Overall flight duration in calm air also decreased. I was surprised at the noticeable difference since the Reynolds numbers are so low.
Tomorrow I will fly again then reinstall the built up stab and fly to ensure my findings are correct and not just the result of varying atmospheric conditions. The weather has been peculiar lately so all testing needs to happen on the same day.
I didn’t expect any discernible difference in flight time or handling, but I was wrong! The flat sheet performed quite poorly in comparison. Pitch control was adequate, but lacked the snappiness I felt with the built up stab. Overall flight duration in calm air also decreased. I was surprised at the noticeable difference since the Reynolds numbers are so low.
Tomorrow I will fly again then reinstall the built up stab and fly to ensure my findings are correct and not just the result of varying atmospheric conditions. The weather has been peculiar lately so all testing needs to happen on the same day.
ThomasMartino
Elite member
Once again, thank you for your insights and encouragement on this project. Regarding your last statement; I’m sharing my projects on this forum in hopes of connecting with like minded people who share this passion for building planes so I’m happy to hear you feel a connection and enjoy the discussions we have.
I will take photos of the aileron linkages in the morning. My approach to the task was very simple and did not prioritize aerodynamics. That’s something I plan to change with the second prototype and the kits.
The pod will be included with the kit. It will be a fiberglass pod with removable nose for quick battery changes. I just ordered the carbon fiber booms. Once those arrive I can measure them and start making the pod molds.
hsquier
Junior Member
May I ask a question (I'm just curious because these were question I had when drawing my DLG) :
Have you deliberately chosen the narrow (short) tail aspect ? (my 3 axes DLG sort of blend of best sellers is 139 cm wing span and 104 cm long).
And if yes why ? (anyway the video prouves the relevance of the choice - And presumably explains its vertical maneuverability).
How did you determine the size of stab and rudder ? (experience ? calculations ?)
Have you deliberately chosen the narrow (short) tail aspect ? (my 3 axes DLG sort of blend of best sellers is 139 cm wing span and 104 cm long).
And if yes why ? (anyway the video prouves the relevance of the choice - And presumably explains its vertical maneuverability).
How did you determine the size of stab and rudder ? (experience ? calculations ?)
ThomasMartino
Elite member
Here is a photo of the aileron pushrods. I glued plastic sleeves into the boom to act as pushrod guides. They exit through slots cut into the sides of the boom. The rods connect to the control horns with EZ Connectors. It’s simple, but I feel like it could be done more elegantly on the final version.
ThomasMartino
Elite member
The short tail moment was a deliberate design choice. I knew my tail boom would be a little heavy so I kept the tail short to achieve the proper CG without adding nose weight (I still had to add 10 grams to the nose). To compensate for the short tail I had to make the stabilizers larger. Luckily there are formulas for calculating tail size.
https://ocw.mit.edu/courses/aeronau...all-2005-spring-2006/systems-labs-06/spl8.pdf
That link takes you to Mark Drela’s lab notes that have the formulas for calculating vertical and horizontal tail volume. For a DLG I design for a Vv of 0.6. This is based on Mark Drela’s recommendation and it has worked perfectly for all three of my DLG designs. The notes also have the formula for calculating spiral stability, which can be used to calculate the correct dihedral angle. It’s all very helpful stuff for an amateur sailplane designer like myself.
The next version of the plane will be slightly longer. The tail booms I ordered are half the weight of my scratch built prototype. This means I can lengthen the tail and shrink the stabilizers to save weight and reduce drag. It should be a win-win.
ThomasMartino
Elite member
That article helped me immensely. The MIT YouTube channel has also been a valuable resource.
ThomasMartino
Elite member
Great hang time on that bird! Looks like cuts through the air nicely. I need to reduce drag as much as possible on version two of my design to make it more competitive with the composite DLGs.
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