RE: JMGlasscraft Penetrator

RE: JMGlasscraft Penetrator
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RE: JMGlasscraft Penetrator - 5/11/2008 3:00:58 PM

turbotodd

Posts: 35
Joined: 3/26/2008
From: Sunnyvale, CA, USA
Status: online

The preliminary data shows .25 less amps than the 2s set-up. 45 Watts now and projected 65w w/3s. The motor is rated for 45w continuous. It should be fine w/ some throttle control. I have run the 300w Medusas @ 500w+ and never burned one up. I will make a CG jig with a couple screws in a board. I like the cg where it is. Very neutral inverted. It's hard to say how far behind 1 1/8" I am without a more accurate method than my fingers. I will run the 2s and 3s set-up on my watt meter and post real world data soon. The prop is a stock GWS 3x3.

(in reply to RocketRob)

Post #: 101

RE: JMGlasscraft Penetrator - 5/11/2008 3:20:16 PM

turbotodd

Posts: 35
Joined: 3/26/2008
From: Sunnyvale, CA, USA
Status: online

Rob, I would estimate 75mph. Everyone at the field thought it was wicked fast, Eric and I both thought it was fast but some more would be better. It was faster with the new battery on the second flight. I wish I had the gun. I should get a speed reading w/both set-ups. I am guessing the 3s will pick up 15mph.

I don't think a heat sink is required. I have spoken w/Medusa Tech support in the past and all the specs in the book are very consrvative. My personal testing backs this up. I do have 2 vents in the cheek cowls. I kinda want another one already! The new T tail Rivets will be cool when it comes out. There is always the scale look of a smoke trail and the words.... MAYDAY MAYDAY if neccesary.

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< Message edited by turbotodd -- 5/11/2008 7:15:14 PM >

(in reply to turbotodd)

Post #: 102

RE: JMGlasscraft Penetrator - 5/11/2008 9:30:18 PM

DeviousDave

Posts: 383
Joined: 2/25/2007
From: , MI, USA
Status: offline

What do you have to an exit hole for the hot air to escape from the fuse? Area wise, it should be 3:1 outlet to inlet.

(in reply to RocketRob)

Post #: 103

RE: JMGlasscraft Penetrator - 5/12/2008 1:30:46 AM

turbotodd

Posts: 35
Joined: 3/26/2008
From: Sunnyvale, CA, USA
Status: online

Dave, 3 to 1 shaped as a triangle in the factory location. I will check motor temp right after landing through the cowl opening. Once wing is off I'll check the back side. By the way I was impressed with the centering capabilities of the 6g high speed JR servo. I don't recall the part number. I think John said he was going to try them out as well as the Hitec hs45. Is the PeeWee Penetrator much draggier then the Yellow Jacket? I love the way yours looks! John mentioned that it runs on the same Medusa set-up.

(in reply to DeviousDave)

Post #: 104

RE: JMGlasscraft Penetrator - 5/12/2008 4:39:26 AM

DeviousDave

Posts: 383
Joined: 2/25/2007
From: , MI, USA
Status: offline

quote:

ORIGINAL: turbotodd

Dave, 3 to 1 shaped as a triangle in the factory location. I will check motor temp right after landing through the cowl opening. Once wing is off I'll check the back side. By the way I was impressed with the centering capabilities of the 6g high speed JR servo. I don't recall the part number. I think John said he was going to try them out as well as the Hitec hs45. Is the PeeWee Penetrator much draggier then the Yellow Jacket? I love the way yours looks! John mentioned that it runs on the same Medusa set-up.

Great Minds think alike RE: airflow management.. Are you by chance talking about the JR241's? I've only ever used them on 400 racers, and they do indeed work well. For micro stuff, I tend to stick to what I know works well, the HS50. There are probably quite a few great smaller servos these days, I just don't have as much interaction with the electric micro guys as has been the case in the last year or two. At the time anything smaller, and just about everything under 9 grams and made in China didn't center well. Do report back on the servo type you are using!

The PWP shouldn't be a whole lot draggier than the MicroShark based airplanes (i.e. Estrellita, Yellow Jacket etc.) as it's just scaled up. The PWP does have a longer tail moment, and I like the way it flies better. I'd like to fly one with a really hot motor, glow or electric as I've only ever seen the PWP fly with 2S and a 4000KV Feigao and with my G-Mark .03. Neither will pull the skim off warm milk, but they can get out of their own way and offer non-park flier performance in a sleek package. Here's a qualifier though-the electric PWP had one of John's built up wings, and my G-Mark powered one uses his same airfoil-at my prodding (just happened to have the cores laying around and they fit the tiny wing saddles) every one of his planes was faster with an RG14 wing without a penalty in other areas of performance. John's airfoil is almost a match on top for the RG14, but the bottom is fatter.

Sooo..... did you take your Wife to the field for Mothers day to show her the new 3S battery pack you bought her?

(in reply to turbotodd)

Post #: 105

RE: JMGlasscraft Penetrator - 5/12/2008 3:28:27 PM

turbotodd

Posts: 35
Joined: 3/26/2008
From: Sunnyvale, CA, USA
Status: online

Dave, The JR servo I used was the S185. 6g and 12 oz. torque. When I set up the throws I taped a ruler to the vertical stab and whether I used up or down it always went right back to 0. I have to use digitals to get this type of accuracy usually. One thing I did have to do is mix in a small amount of down elevator with throttle so she didn't climb under power. Now she goes straight at any throttle position. I used mix6 thr/ele on my JR radio to do this. Power off at full speed she goes straight, as she slows down the nose will drop slightly as the speed is reduced. I am very happy with the flight performance. My new 3s packs were dated 06. I am returning them for 08mfg. today. There is a performance loss with storage time. So I spent the day with the no.1 wife Yesterday. We are moving on the 15 of next month. Packing has already begun. The good news is that the local electric flying field will be walking distance away or about 2 minutes drive. Before and after work flight sesions will be an order occasionally. A PWP will probably be on my list. I think I need to have 1 of each because there small.

Todd

< Message edited by turbotodd -- 5/12/2008 3:36:19 PM >

(in reply to DeviousDave)

Post #: 106

RE: JMGlasscraft Penetrator - 5/13/2008 3:37:25 PM

Schu

Posts: 259
Joined: 3/3/2002
From: Stafford , VA,
Status: offline

Guys
I made a scaled down elec racer w/ a Medusa 12mm ( 5,000 kv I think ) and used a 3 x 3 Gws black prop - is this what you guys are using?
It seemed over prop'ed to me - go to 3 cell or cut down the 3 x 3 or go to 3 x 2? I would like the hot set up - thanks for your help.
I hope to get one of the JM's soon - always loved their look.
Dale

(in reply to turbotodd)

Post #: 107

RE: JMGlasscraft Penetrator - 5/13/2008 10:14:48 PM

DeviousDave

Posts: 383
Joined: 2/25/2007
From: , MI, USA
Status: offline

We do rework the props. They get tapered back at the tips, with an occasional reduction in diameter. Definitely too much prop, there's another 10-15 mph in that prop if you get it right.

(in reply to Schu)

Post #: 108

RE: JMGlasscraft Penetrator - 5/16/2008 12:58:55 AM

turbotodd

Posts: 35
Joined: 3/26/2008
From: Sunnyvale, CA, USA
Status: online

I flew the Yellow Jacket twice today on 3 cell W/4000kv Medusa. It was 90 deg. out so this was a good test day for heat management. With a fully charged TP480mah 3s the watt meter read 85w peak, 7.9a peak, 10.6vm, with stock GWS 3x3. If I hold it for 5 seconds at full power I get 7.25a and 75w. After each flight the temps were 115F for the battery and 130F for the motor. Its difficult to get an accurate reading on the motor. I could hold my finger on the back of it for a couple seconds. I would estimate the speed to be about 15-20 mph faster than the 2-cell set up. Lets just say that it got small much quicker!

The CG is at 1.25" back from the center of the wing. I used a Dubro fuel tubing bender turned upside down held by a C-clamp to my table to check CG. It has pointed rubber caps on the ends of the handles which worked perfectly.

The next step is the Devious Dave prop mod! I'll make a couple slightly different and compare w/the radar gun to make sure the results are accurate. OH! and it's still TurboTodd. Rocket Robs flying skills are way better, even if he had 1 eye blind folded!!!

(in reply to DeviousDave)

Post #: 109

RE: JMGlasscraft Penetrator - 5/16/2008 5:01:16 AM

DeviousDave

Posts: 383
Joined: 2/25/2007
From: , MI, USA
Status: offline

Todd: you sound like you know what you are doing, but if I can be of help getting the prop right, let me know.

(in reply to turbotodd)

Post #: 110

RE: JMGlasscraft Penetrator - 5/17/2008 12:13:19 AM

turbotodd

Posts: 35
Joined: 3/26/2008
From: Sunnyvale, CA, USA
Status: online

Dave: I flew her 1 flight this morning. The prop flew off on the second test run up. Yesterday it flew off on the 3rd half way through the underhand toss.

I almost let go! She was almost a glider. I pushed the prop back on. this time it went on further. About 1/16 from the end of the shaft and it stayed on.

There were about 40 guys at the field this morning and they really got a kick out of it. It specked out on me a couple of times way out there. I need to keep her in tighter, but that wouldn't be as fun. On final approach it profiled and disappeared too. The best part is it re-appeared and I was able to make one of my best landings. I was able to flare it about 6" off the ground and it stalled about 2" up and just kinda did a high alfa swish. I called John with an update. He suggested using medium CA on the prop and then pressing it on as far as I can get. I will try this with the 2.75" prop. Maybe in the morning.
If you ever get a chance to create a spinner solution I would be interested. I have some ideas I just need to draw them out as it needs to be light and tight! I think you need to try the 3s set-up. The vertical performance is unreal! The power is only there if you want it. 1/4 stick and she's cruising right along. This thing is 5oz. of adrenalin.

Todd

If you have already figured out the best prop mod would you be willing to send me one. I will make a template of it for future use. I can send a little extra to John when I get my next plane to cover your costs. Todd

< Message edited by turbotodd -- 5/17/2008 12:17:16 AM >

(in reply to DeviousDave)

Post #: 111

RE: JMGlasscraft Penetrator - 5/17/2008 2:50:47 AM

DeviousDave

Posts: 383
Joined: 2/25/2007
From: , MI, USA
Status: offline

quote:

ORIGINAL: turbotodd

Dave: I flew her 1 flight this morning. The prop flew off on the second test run up. Yesterday it flew off on the 3rd half way through the underhand toss. I almost let go! She was almost a glider. I pushed the prop back on. this time it went on further. About 1/16 from the end of the shaft and it stayed on. There were about 40 guys at the field this morning and they really got a kick out of it. It specked out on me a couple of times way out there. I need to keep her in tighter, but that wouldn't be as fun. On final approach it profiled and disappeared too. The best part is it re-appeared and I was able to make one of my best landings. I was able to flare it about 6" off the ground and it stalled about 2" up and just kinda did a high alfa swish. I called John with an update. He suggested using medium CA on the prop and then pressing it on as far as I can get. I will try this with the 2.75" prop. Maybe in the morning.
If you ever get a chance to create a spinner solution I would be interested. I have some ideas I just need to draw them out as it needs to be light and tight! I think you need to try the 3s set-up. The vertical performance is unreal! The power is only there if you want it. 1/4 stick and she's cruising right along. This thing is 5oz. of adrenalin. Todd

If you have already figured out the best prop mod would you be willing to send me one. I will make a template of it for future use. I can send a little extra to John when I get my next plane to cover your costs. Todd

Gluing the prop on might help. John does this, I've never had to when I pushed them on far enough. (I just happen to be holding the sticks when come off of HIS airplanes) There are one of two things happening here-either the shaft is getting hot (not likely if this happens on test runs before flight) or the hub is being pulled apart by the blades due to the RPM. When we first started flying the Medusa motors we'd occasionally have a prop come off in flight-which really sucks when you are waaaay out and have to land it while it's a spec on the other side of the school. After going to the modified props, I can't remember it happening again-it's been a couple years since the Medusas came out. This tends to lend some credence to the whole hub pulling apart hypothesis- with 3 cells there may not be much you can do about it.

Do you have a set of calipers? I can give you blade width at .100 increments (it's how I make the blades symmetrical, and the marks are already there for me) so you can emulate one of the props I have on hand. Basically you put one jaw of the caliper in the shaft hole, then use the other jaw to scratch a line in the prop at .100 intervals. Then you sand the LE to a shape you like (or my numbers) and sand the other side to match. You'll do this from the leading edge because it's a lot easier to put a LE radius back on than sand the TE sharp again-and, you end up with a pitch increase on most props as the undercamber curvature is less agressive toward the LE. It's pretty easy to do once you do your first one and realize it's not rocket science-props this small work on brute force more than intelligent design. Just to prove this out, mount up a Graupner CAM 3-3 and compare it to the stock GWS... The GWS is 10-15 mph faster than the CAM 3-3 yet the GWS looks like it belongs on some ChiCom toy for a Happy Meal(TM)

One other thing that will pay benefits is that the voltage drop won't be so severe on your poor little pack. I'm guessing that 9 amps is pretty much the limit for them, and even at 1/2 volt you are looking at a free 2650rpm.

Wait a minute... Are you having a problem getting the props on the shaft far enough?? I had this problem too, and the way around it was to support the motor from the inside of the fuse with a sharpie/pen, put the prop against something solid, then push on the sharpie to get it on.

Dave

PS: I just read my post and I think I just figured out why I haven't had a date since God was a boy...

(in reply to turbotodd)

Post #: 112

RE: JMGlasscraft Penetrator - 5/18/2008 7:35:15 AM

DeviousDave

Posts: 383
Joined: 2/25/2007
From: , MI, USA
Status: offline

Rivets prototype #2 has been born, flight tests in a week or two. Weather was too bad to fly today, but I went over to John's side of town and hung out for a few hours. I took an airplane and a camera....

Leave 'em out in the rain and they'll shrink every time:

(in reply to DeviousDave)