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Thursday at the airfield with the SS

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Thursday at the airfield with the SS

Post  RknRusty on Thu Apr 18, 2013 12:56 pm

Last night I tuned up the Shoestring. Padded the tank against vibrations and also I bolstered the engine mount with some of the Brodak 2 degree wedges. Touched up anything that wasn't still pretty and got all set to go fly today.

No flat tires or any other catastrophes, so I loaded up and went out to the field. I set it up to launch with a tailwind and rigged up the stooge. I guess they haven't started mowing yet because there were lots of dandelions.

This time I was using a 10x4 prop and proper uniflow plumbing. Got her cranked and tuned and ran out to the lines and set her free. It made a long roll. For one, I was trying to make a regulation takeoff and also I suppose the 10x4 had a bit less thrust. Finally I saw it lift and at that same instant, it turned towards me and continued to climb, right into center circle. I stood there stupified, and stepped aside to let it pass. The wings were perfectly level and it was slightly climbing but flying in an arrow straight line. I figured, okay, when it gets to the other side maybe I can get her back... either that or rip out the bellcrank. As it started to pick up the lines it started heading downward and I never got a chance to pull them tight before it hit the ground at a fairly easy angle. It broke the outboard wheel off, broke my new prop and got a minor crack where the tail fin and rudder join near the bottom.

Can't say I've ever had a flight like that before. So I packed up the car and came home. All I can figure is some dandelions snagged the lines, or maybe an anthill, there are plenty of those too. Once it was airborne, there was nothing obviously wrong, it flew right past me straight and true.

I didn't think that Dural landing gear would ever break like that.
Nothing else made it unflyable, the engine didn't even get dirty and I could have fixed the rudder crack in a minute. But I sure as hell don't carry spare LG in the box. Needles to say I left a bit discouraged.

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Re: Thursday at the airfield with the SS

Post  Cribbs74 on Thu Apr 18, 2013 1:12 pm

Mega bummer Rusty,

I promise when it finally goes right it will be a blast. Your experience sounds exactly like what was happening to my Ring. In my case I had the altitude to keep it aloft.

10x4 eh?

I am using a 9.5x6 on my Fox .35. I have no idea about TT's, but that seems like a large prop for a smaller displacement engine.

Ron
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Re: Thursday at the airfield with the SS

Post  RknRusty on Thu Apr 18, 2013 1:59 pm

It does sound large, however it comes highly recommended by the TT's previous owner, Mark. The maiden flight was fast and furious with a 9x5. so I figured I'd tame it with the 10x4. That was the only 10" prop of any kind I had, so I'll have to get another one to try. I have every pitch of 9" prop I could need, both APC and MA. When I got home I put a MA 9x4 on it so I could make sure the fuel was all burned off. It wasn't, so I'm glad I did. It's all oiled up and hanging. I have the old Dural gear from it's previous life, they're ugly but they'll work.

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Re: Thursday at the airfield with the SS

Post  Cribbs74 on Thu Apr 18, 2013 2:29 pm

Mark does have a lot of experience. So I would listen. Plus the TT with a smaller displacement is probably still more powerful than a Fox .35

Ron
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Re: Thursday at the airfield with the SS

Post  ian1954 on Thu Apr 18, 2013 2:51 pm

"I didn't think that Dural landing gear would ever break like that."

I would be interested to know how old the landing gear was.

Dural(uminium) is an aluminium alloyed with about 4% copper. It was originally developed because of its self or age hardening properties but later, with the addition of a little magnesium, It was heated and quenched to make a very light but strong (tensile strength) metal. It can, however, end up brittle and break.

I have made a few engines using dural for the con rod - light but strong. Always worry a little when I see a "snapper" like your unfortunate experience with the undercart on that very nice model.
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Re: Thursday at the airfield with the SS

Post  RknRusty on Thu Apr 18, 2013 3:03 pm

The LG was brand new. This was only the third "landing" in its life.

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Re: Thursday at the airfield with the SS

Post  ian1954 on Thu Apr 18, 2013 3:20 pm

Then I would have expected a bend and not a break.
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Re: Thursday at the airfield with the SS

Post  RknRusty on Thu Apr 18, 2013 5:05 pm

Me too. If it had bent I could have flown again. With a faster prop that plane would jump out of the weeds and fly without rolling. I learned my lesson about having a cluttered runway. It looks like I'll have more opportunities on Tuesdays and Thursdays to get out there. I'm anxious to get that plane doing what it's meant to do. All this time piddling with it is driving me nuts.

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Re: Thursday at the airfield with the SS

Post  Mark Boesen on Thu Apr 18, 2013 8:19 pm

Hi Rusty,

Sorry to hear of mishap, the 10x4 prop is going to put about the same load on engine as a 9x5, maybe even less.

It's hard to say what happened and can only throw some ideas at you, like you said it either snagged something or (I'm assuming you readjusted the needle) if not I'm wondering if you took off a little rich and with less RPM and little pull out of the 4" pitch prop it could of come around upwind wind and blew in, if it was flying really slow it may have?

How long was the roll out?

Did you get it videoed?

I'm glad to hear its ok, maybe you do need the 9x5 or at least till you get the tank set up and needle dialed in, i'd rather have too much line tension then not enough.

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Re: Thursday at the airfield with the SS

Post  Mark Boesen on Thu Apr 18, 2013 8:58 pm

The smaller pitch prop turning at a slightly higher RPM, has been the bread and butter set up for most stunt set-ups the last 15-20 years or so for R/C type engines that are ported different than the old Fox .35, ST.46, etc.

Dwelling on this I pulled out a old magazine from the early nineties: R/C REPORT ENGINE TEST BOOK I. This was a book of over 50 engine tests done during that period. The TT .25 PRO was not tested but the O.S. and Royal were and they'd be pretty close to see what's what.

_______________________9X5_____________9x6___________ 10x4
O.S. .25 FP (RPM)13,100 (thrust oz.)49___11,400/47_______11,000/54
O.S. .25 FRS__________12,600/50_______11,600/45_______11,600/50
Royal .25 FSR ABN_____11,900/48_______10,900/44_______10,800/52

For stunt we want airspeed (RPM) for line tension and power (torque) to pull thru maneuvers. This gives us at least a ballpark comparison of props/airspeed/RPM/torque relationships and can see that the load of the 9x6 is close to what the 10x4 is, but would be moving the plane a lot faster.


Last edited by Mark Boesen on Thu Apr 18, 2013 9:04 pm; edited 3 times in total
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Re: Thursday at the airfield with the SS

Post  RknRusty on Thu Apr 18, 2013 9:00 pm

Mark Boesen wrote:Hi Rusty,

Sorry to hear of mishap, the 10x4 prop is going to put about the same load on engine as a 9x5, maybe even less.
I was thinking it was probably a similar load. The old 9x5 from the maiden was a big fat heavy Master Airscrew. The 10x4 was a featherweight Topflite woody.

Mark Boesen wrote:It's hard to say what happened and can only throw some ideas at you, like you said it either snagged something or (I'm assuming you readjusted the needle) if not I'm wondering if you took off a little rich and with less RPM and little pull out of the 4" pitch prop it could of come around upwind wind and blew in, if it was flying really slow it may have?
How long was the roll out?
I set it very rich, just like when I had the other prop. That was a mistake that didn't register in my idiot brain. Thinking back, I should have just riched it down to a medium rolloff instead of a sloppy chug. It was a very long rollout, probably more than 20 feet and very very bumpy. I was beginning to wonder if it would lift off with a slight up elevator, but when I pulled full up it eased off, but at 1 or 2 feet high is when it quickly snap turned into the circle. I've convinced myself it was likely a chunk of weeds that hooked it. I did have a little less outboard thrust, but not radically different, maybe 1 deg. less.

I had it positioned to start rolling with a tailwind so when it came around the first quarter it would be blowing it tight. But... BUT, the wind was shifty and would sometimes gust inward in the bad direction. I don't know if it did at that time or not.

Mark Boesen wrote:Did you get it videoed?
No. I had the camera set up and planned to warm the engine up, pinch it off and then turn on the camera. But once I had it running and warm, I said, "Screw it, I'll video the next flight." I wish I had it, but I don't. Not only would it be helpful evaluating the incident, it would have been hilarious... for y'all. Rolling Eyes

Mark Boesen wrote:I'm glad to hear its ok, maybe you do need the 9x5 or at least till you get the tank set up and needle dialed in, I'd rather have too much line tension then not enough.
Until they cut the grass, I will go back to a 9x5. At least I know I can just jump off the ground, even rich, and be flying with no rollout. I put a 9x5 on it today when I got home so I could burn off any remaining fuel. Not the same one, this is one of the new slim MA GF series props. Not the big fat one you sent me. It probably has a little less thrust. Or maybe not, it's hard to guess considering it might turn faster.

I'll get another try either this coming Sunday, Tuesday or Thursday.

Thanks for giving me some things to think about. I was hoping someone would throw some ideas my way.
I want to fly this plane like it's meant to fly and I'm getting frustrated about it. The other day when I made the video, I just didn't feel good after the flight and packed it in rather than risking a mishap. Looking back, that was a pretty good run, I just didn't do any proper stunts.

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Re: Thursday at the airfield with the SS

Post  Mark Boesen on Thu Apr 18, 2013 9:11 pm

Mark Boesen wrote:The smaller pitch prop turning at a slightly higher RPM, has been the bread and butter set up for most stunt set-ups the last 15-20 years or so for R/C type engines that are ported different than the old Fox .35, ST.46, etc.

Dwelling on this I pulled out a old magazine from the early nineties: R/C REPORT ENGINE TEST BOOK I. This was a book of over 50 engine tests done during that period. The TT .25 PRO was not tested but the O.S. and Royal were and they'd be pretty close to see what's what.

_______________________9X5_____________9x6___________ 10x4
O.S. .25 FP (RPM)13,100 (thrust oz.)49___11,400/47_______11,000/54
O.S. .25 FRS__________12,600/50_______11,600/45_______11,600/50
Royal .25 FSR ABN_____11,900/48_______10,900/44_______10,800/52

For stunt we want airspeed (RPM) for line tension and power (torque) to pull thru maneuvers. This gives us at least a ballpark comparison of props/airspeed/RPM/torque relationships and can see that the load of the 9x6 is close to what the 10x4 is, but would be moving the plane a lot faster.

I'm thinkin your right, if you launched sloppy rich, it may have only been turning 8-9k? I'm not sure what that engine will tach out at, but i'd think you'd want to launch it 500-750 less? I'd ask the guys on stuka what they think?
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Re: Thursday at the airfield with the SS

Post  Cribbs74 on Thu Apr 18, 2013 10:00 pm

Rusty,

This is sounding more and more like the problem I had.......
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Re: Thursday at the airfield with the SS

Post  RknRusty on Thu Apr 18, 2013 10:09 pm

cribbs74 wrote:Rusty,

This is sounding more and more like the problem I had.......
I'd forgotten about that. You launched the Ringmaster too rich and the wind or something brought it in because it had too little thrust. Am I remembering correctly?

I'm sure nothing is wrong with my plane. But it definitely had too little thrust. I had it set too rich and slow.

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Re: Thursday at the airfield with the SS

Post  Cribbs74 on Thu Apr 18, 2013 10:11 pm

Sent you a PM
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Re: Thursday at the airfield with the SS

Post  crankbndr on Fri Apr 19, 2013 6:58 am

ian1954 wrote:"I didn't think that Dural landing gear would ever break like that."

I would be interested to know how old the landing gear was.

Dural(uminium) is an aluminium alloyed with about 4% copper. It was originally developed because of its self or age hardening properties but later, with the addition of a little magnesium, It was heated and quenched to make a very light but strong (tensile strength) metal. It can, however, end up brittle and break.

I have made a few engines using dural for the con rod - light but strong. Always worry a little when I see a "snapper" like your unfortunate experience with the undercart on that very nice model.


The Cameron .199 came with a Dural rod also


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Re: Thursday at the airfield with the SS

Post  RknRusty on Fri Apr 19, 2013 10:58 am

Interesting stuff. I had always heard the term "Aircraft Aluminum" and wondered what it was. This LG must have suffered an unusual stress in the bending brake. If you look at the picture I posted it's a perfect break right along the bend. Any smoother and it would look like it was sawed off. I'm glad it wasn't made into a part for a Lockheed F-35.

I think Mark and Ron are right. I didn't have enough thrust tuned in and whether the wind lifted it or a weed snagged it, or both, I think if I had been running the engine faster it would have been less likely to come in the circle. I'm just thankful the wing didn't hit the ground. I worry about the ancient old brittle glue holding it together. I'm figuring this plane only has one good impact left in it's life before it totally slags. I'm hoping I get a lot of good fun out of it before and if that bad day ever happens.

I'll try to polish up the old pre-rebuild Dural legs and put them on tonight. They've been flying and landing for decades. The stuff is supposed to get stronger with age, so it ought to be indestructible. Laughing

I appreciate the post crash analysis. That's what I was hoping for, and I think I have a better idea what happened. I really wish it was on video. I would have waved at it as it passed by me at center circle.

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