Duck
Active member
My first scratch build was the Mini Arrow from the speed build kit which was awesome and amazing. I had it balanced wrong my first flight out but the people flying at my field stepped up and helped me get it up in the air. Now I can head to the field and toss it into the air with no problems.
A few months ago I attempted my second scratch build the Sparrow and it has been quite a bit more challenging. I've finally gotten a single good stable flight but it has taken a number of attempts. I thought I would share the mistakes I made and maybe get a few recommendations on how to make it a more reliable flying machine.
Mistake #1 - Locally I can only find Elmers foam board which is stronger but heavier then dollar tree foam. This would be awesome for durability in theory but in practice it made the sparrow extremely tail heavy. The surface area behind the CG is just so much larger then in front that dealing with this resulted in a number of issues.
Mistake #2 - I started with a slightly larger motor & ESC then the A Pack EMaxx MT1806 which just made the balance issues worse.
Mistake #3 - During the build I lined up everything 3 times before gluing the servos in and I slipped once the glue was on and they wound up farther back then they should be which made the balance even worse!
Mistake #4 - The only batteries I had on hand that fit were 800mAh instead of 1300mAh so it wound up even more tail heavy. (See where this is going?)
Mistake #5 - I tried to compensate for tail heavy-ness with more weight in the front. I used steel bolts as they were the only weight I could find with enough total mass to balance it out. I don't have lead on hand.
Mistake #6 - The extra volume from steel means the weight takes more space which means they had to be closer to the CG which meant it needed even more weight to balance it out.
Mistake #7 - HAND LAUNCHING FROM UNDER THE BODY IS NOT SAFE!!! So I wound up with a neat new scar on my hand after the propeller caught my hand when the obviously overweight plane decided go down instead of up. Pro Tip: Wing tip launches 100% of the time from now on for pushers. Even accidentally folding the wing is better then a trip to the doctor.
Mistake #8 - If you are going to keep a medical kit in your car make sure the labels on the packaging is not in German. It does make it harder.
So that was maiden attempt #1 which didn't go so well. But I learned a few things so lets call it a win. Lets talk about attempt #2!
Fix #1 - I fixed the obviously overweight motor and ESC to help bring the balance back.
Fix #2 - I took inspiration from the F Pack sparrow design on the form and build a nose job for my Sparrow which fits snugly around the original nose but gives it a good 3" of extra length to put the nose weight. This helps massively reduce the weight I had to add to balance it out. I wound up with 3x 2" bolts taped to the inside of the nose for a good balance. With a battery extension cable and a strategic hole I might be able to just put the battery in the nose but I haven't attempted this.
Fix #3 - With a little help from the maiden attempt #1 I loosened the motor mount and shaved a few mm off the length. Every little bit helps right?
So with the above the plane was obviously improved and I took it out for maiden attempt #2. I didn't wind up bleeding so this was even better! What I learned:
Issue #1 - The plane takes more then half throttle to get lift from a slow launch.
Issue #2 - Friction fit is great at rest but under a nose first collision of a still heavy plane everything slides and my BBQ skewers ripped right through my new nose as it got shoved the 3" further onto the plane.
Issue #3 - I didn't double check the control surfaces and left was right. This wasn't helpful when I was also trying to recover from a too slow launch.
Issue #4 - I launched it with my right hand which meant it took a second to get my hand back on the control I needed to steer the plane. This was a second I didn't have.
Issue #5 - My ballast came loose after the first toss and wasn't quite far enough forward for proper balance on subsequent attempts. It also left pretty hex shaped indents in the foam as it bounced around.
All in all pretty good! No bleeding and these are all pretty minor tweaks. With the nose glued back together after all the seems popped under the pressure and the collapsed foam just cut off (who needs it) and the landing skid glued back on it was pretty much ready to fly again.
Fix #1 - More tape on the balast.
Fix #2 - Launches at 75% throttle.
Fix #3 - Friction fit the nose again, lets hope we don't crash.
Fix #4 - Left hand launch this time as we don't need to touch the throttle if we make it into the air just fine.
Fix #5 - Obviously fix the control surfaces. Check them again. And again. And again.
Fix #6 - A few not-flights in both the original and enhanced bonus nose were a little lumpy. I covered the nose job with packing tape to reduce future repairs.
I got a good 8 minute flight! I almost ditched a couple of times because the roll rate was pretty awful and I had to take a very long time to get turned around. The neutral control surfaces are slightly elevated and I think it also reduced my ability to pitch down. I did one or two unintentional loops. I couldn't tell how much was just my flying, the light wind or the control surface throws being off. Even on the bench the piano wire deflects quite a bit and it doesn't have the zip tie re-enforcement that the Mini Arrow has.
Overall the Sparrow has been a learning experience for me. Watching the flight test videos I've learned to at least identify the mistakes after I make then even if I don't prevent them. I came away with a few things better ingrained at least:
Lesson #1 - Propellers are dangerous. Stay away from them at all times. Think through your hand launch plan.
Lesson #2 - Think through the ramifications of substitutions. The design balances as designed, each little 'close enough' adds up.
Lesson #3 - When it seems obviously wrong, it is. Fix it before tossing it into the air.
My final sparrow balances OK but has the giant nose appendage which is an extra step to get air-worthy for each flight and has a few extra variables to worry about. The flight characteristics are sloppy. I am going to redo the linkages and see if I can get the control surfaces really neutral without trim and with less wobble.
I did have fun on my flight! It really does fly very smooth and once it is up in the air seems to want to stay there. Overall though I wish the design was just easier to balance. Even with all the reversible mistakes reversed I still had to extend the nose to get a reasonable balance. Even putting my runcam on top puts it too close to the CG to help at all.
Did anyone else have an exciting learning adventure getting the Sparrow or another FT design finally in the air?
A few months ago I attempted my second scratch build the Sparrow and it has been quite a bit more challenging. I've finally gotten a single good stable flight but it has taken a number of attempts. I thought I would share the mistakes I made and maybe get a few recommendations on how to make it a more reliable flying machine.
Mistake #1 - Locally I can only find Elmers foam board which is stronger but heavier then dollar tree foam. This would be awesome for durability in theory but in practice it made the sparrow extremely tail heavy. The surface area behind the CG is just so much larger then in front that dealing with this resulted in a number of issues.
Mistake #2 - I started with a slightly larger motor & ESC then the A Pack EMaxx MT1806 which just made the balance issues worse.
Mistake #3 - During the build I lined up everything 3 times before gluing the servos in and I slipped once the glue was on and they wound up farther back then they should be which made the balance even worse!
Mistake #4 - The only batteries I had on hand that fit were 800mAh instead of 1300mAh so it wound up even more tail heavy. (See where this is going?)
Mistake #5 - I tried to compensate for tail heavy-ness with more weight in the front. I used steel bolts as they were the only weight I could find with enough total mass to balance it out. I don't have lead on hand.
Mistake #6 - The extra volume from steel means the weight takes more space which means they had to be closer to the CG which meant it needed even more weight to balance it out.
Mistake #7 - HAND LAUNCHING FROM UNDER THE BODY IS NOT SAFE!!! So I wound up with a neat new scar on my hand after the propeller caught my hand when the obviously overweight plane decided go down instead of up. Pro Tip: Wing tip launches 100% of the time from now on for pushers. Even accidentally folding the wing is better then a trip to the doctor.
Mistake #8 - If you are going to keep a medical kit in your car make sure the labels on the packaging is not in German. It does make it harder.
So that was maiden attempt #1 which didn't go so well. But I learned a few things so lets call it a win. Lets talk about attempt #2!
Fix #1 - I fixed the obviously overweight motor and ESC to help bring the balance back.
Fix #2 - I took inspiration from the F Pack sparrow design on the form and build a nose job for my Sparrow which fits snugly around the original nose but gives it a good 3" of extra length to put the nose weight. This helps massively reduce the weight I had to add to balance it out. I wound up with 3x 2" bolts taped to the inside of the nose for a good balance. With a battery extension cable and a strategic hole I might be able to just put the battery in the nose but I haven't attempted this.
Fix #3 - With a little help from the maiden attempt #1 I loosened the motor mount and shaved a few mm off the length. Every little bit helps right?
So with the above the plane was obviously improved and I took it out for maiden attempt #2. I didn't wind up bleeding so this was even better! What I learned:
Issue #1 - The plane takes more then half throttle to get lift from a slow launch.
Issue #2 - Friction fit is great at rest but under a nose first collision of a still heavy plane everything slides and my BBQ skewers ripped right through my new nose as it got shoved the 3" further onto the plane.
Issue #3 - I didn't double check the control surfaces and left was right. This wasn't helpful when I was also trying to recover from a too slow launch.
Issue #4 - I launched it with my right hand which meant it took a second to get my hand back on the control I needed to steer the plane. This was a second I didn't have.
Issue #5 - My ballast came loose after the first toss and wasn't quite far enough forward for proper balance on subsequent attempts. It also left pretty hex shaped indents in the foam as it bounced around.
All in all pretty good! No bleeding and these are all pretty minor tweaks. With the nose glued back together after all the seems popped under the pressure and the collapsed foam just cut off (who needs it) and the landing skid glued back on it was pretty much ready to fly again.
Fix #1 - More tape on the balast.
Fix #2 - Launches at 75% throttle.
Fix #3 - Friction fit the nose again, lets hope we don't crash.
Fix #4 - Left hand launch this time as we don't need to touch the throttle if we make it into the air just fine.
Fix #5 - Obviously fix the control surfaces. Check them again. And again. And again.
Fix #6 - A few not-flights in both the original and enhanced bonus nose were a little lumpy. I covered the nose job with packing tape to reduce future repairs.
I got a good 8 minute flight! I almost ditched a couple of times because the roll rate was pretty awful and I had to take a very long time to get turned around. The neutral control surfaces are slightly elevated and I think it also reduced my ability to pitch down. I did one or two unintentional loops. I couldn't tell how much was just my flying, the light wind or the control surface throws being off. Even on the bench the piano wire deflects quite a bit and it doesn't have the zip tie re-enforcement that the Mini Arrow has.
Overall the Sparrow has been a learning experience for me. Watching the flight test videos I've learned to at least identify the mistakes after I make then even if I don't prevent them. I came away with a few things better ingrained at least:
Lesson #1 - Propellers are dangerous. Stay away from them at all times. Think through your hand launch plan.
Lesson #2 - Think through the ramifications of substitutions. The design balances as designed, each little 'close enough' adds up.
Lesson #3 - When it seems obviously wrong, it is. Fix it before tossing it into the air.
My final sparrow balances OK but has the giant nose appendage which is an extra step to get air-worthy for each flight and has a few extra variables to worry about. The flight characteristics are sloppy. I am going to redo the linkages and see if I can get the control surfaces really neutral without trim and with less wobble.
I did have fun on my flight! It really does fly very smooth and once it is up in the air seems to want to stay there. Overall though I wish the design was just easier to balance. Even with all the reversible mistakes reversed I still had to extend the nose to get a reasonable balance. Even putting my runcam on top puts it too close to the CG to help at all.
Did anyone else have an exciting learning adventure getting the Sparrow or another FT design finally in the air?
