Engine test stand (Show and tell)
11-07-2009, 05:14 PM
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Engine test stand (Show and tell)
Well it was nice out today so I started tuning my OS .25 VFDF, and I got to try out my new stand so I thought I would share some pics, Its very easily adjusted for different size engines by loosening one bolt in "T" slots, same goes for the tank height adjustment, then two slotted toe clamps on each mounting flange. Still deciding what to do for linkage, made a handle so far. Also for added safety I drilled a reamed a .125 dowel hole on each side of the mount blocks in front of the engine mounting flanges.
The whole unit is just clamped to whatever...picnic table etc...
That OS .25VFDF is LOUD[:@] with a pipe, "DEAF"inately wearing earmuffs is a must!
The whole unit is just clamped to whatever...picnic table etc...
That OS .25VFDF is LOUD[:@] with a pipe, "DEAF"inately wearing earmuffs is a must!
11-07-2009, 11:00 PM
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RE: Engine test stand (Show and tell)
That OS .25VFDF is LOUD[:@] with a pipe, ''DEAF''inately wearing earmuffs is a must!
I got a shock at the sound level from the .65. I popped the earmuffs off for a sec standing maybe 5-6 feet away, holy mackerel.
Nice stand. Machinists.. spoiled brats, they just make whatever they need.
MJD
11-08-2009, 08:49 AM
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RE: Engine test stand (Show and tell)
I'm still trying to figure out what prop size to run for 25 sized demon (26" wingspan), type airframe, so I can tune the pipe to that size and to get it into the 23-24 000 range.
I was running a trimmed down 7x8 apc to 6x8, also tried a trimmed down 7x6apc to 6.5x6, till the tips started to come apart, which seem to spark it up quite a bit.
I was running a trimmed down 7x8 apc to 6x8, also tried a trimmed down 7x6apc to 6.5x6, till the tips started to come apart, which seem to spark it up quite a bit.
11-08-2009, 10:37 AM
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RE: Engine test stand (Show and tell)
[link]http://www.nclra.org/Supply/SteveWilk/[/link]
I've got a .15 on a delta just a hair smaller that uses a 6.5 x 5 prop and it's a good combo.
Your .25 should be able to use a 6.5 x 6 or so? I'll bet Steve Wilk will have a better idea.
I've got a .15 on a delta just a hair smaller that uses a 6.5 x 5 prop and it's a good combo.
Your .25 should be able to use a 6.5 x 6 or so? I'll bet Steve Wilk will have a better idea.
11-08-2009, 11:17 AM
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RE: Engine test stand (Show and tell)
MJD: Might you have a recommendation, out of the props in the 7x7 range or smaller, for a .25 DF engine (OS VF-DF .25)? There are a lot of props of similar diameter and pitch, so I need some help there. There's G-6, T-10, P-2 etc., but I don't know which are popular, or better designs than others, etc.. you know. The idea is to run it in the 22-24k regime. This is for 150+ (hopefully) small RC delta flying.
Steve Wilk: T-10 is a Top flight speed prop. P-2 RC Pylon prop big hub, G-6 Graupner electric prop thin blade area. SC-3 Supercool, T-4 Tiapan prop re pitched.
I think the T-4 and T-5 Taipan copies, and the P-5 look right. Or a trimmed SC-5. T- are Taipan copies, P- are pylon props with largish hubs, and SC- are Supercool designs.
Round numbers:
7" pitch at 24k = 159
7.5" pitch = 170
8" pitch = 182
Maybe there's more top speed to be had but I'd start in the 7" - 7.5" pitch range.
MJD
11-08-2009, 11:18 AM
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RE: Engine test stand (Show and tell)
Thanks for the link, I notice he has a bunch of sizes I might be interested in, Exp... Webra 80 DF RIRE.
11-08-2009, 11:23 AM
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RE: Engine test stand (Show and tell)
Here is the new list, that link goes to an older copy. Anyone who wants the original Excel file that he hands out, please PM me.
The 8.25x10 is the only D speed prop that looks useful for 10cc+ DF engines, at the moment. That's what I have on the OPS .65, but trimmed 15% for break-in and set-up.
MJD
The 8.25x10 is the only D speed prop that looks useful for 10cc+ DF engines, at the moment. That's what I have on the OPS .65, but trimmed 15% for break-in and set-up.
MJD
11-08-2009, 04:52 PM
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RE: Engine test stand (Show and tell)
ORIGINAL: smoknrv4
Not sure what the compression is , its stock, no head shims.
Not sure what the compression is , its stock, no head shims.
...more room for more combustible mixture to occupy
...properly timed combustion instead of preignition that happens while piston is still on it's way up.
...detonation that is just generally a destructive blow that hammers parts out of round.
11-09-2009, 07:35 PM
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RE: Engine test stand (Show and tell)
After looking at sound wave charts and seeing those revs per second results it helps to put the task of fine tuning the ignition timing into perspective. Your 25 will run best at about 400 revs per second. The portion of a single cycle where hitting the piston produces power is just after it moves past TDC by some degrees and the striking force should be pretty much absorbed by the piston and sent to the crank by the time the exhaust port opens. So this portion of the cycle, this window of opportunity takes a millionth of a second. Looking at it like this, what are the chances that the factory compression setting and liner height is dead on perfect? A millionth of a second either way from perfect is........less than perfect.
Adjusting prop load [usually by shaving those blades] also tunes the engine in a way by allowing higher timing and more compression to work for you. It is like balancing a balloon on a stick.
Adjusting prop load [usually by shaving those blades] also tunes the engine in a way by allowing higher timing and more compression to work for you. It is like balancing a balloon on a stick.
11-09-2009, 08:34 PM
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RE: Engine test stand (Show and tell)
Those soundwave charts and stuff you guys are always talking about sound interesting, what is that all about breifly.
Also CP how do you make your shims, I was thinking about my next small side project would be to see if I could sneak onto the Jig grinder at work and fashion a small shim punch set with about .0015 clearance per side of punch, for making small precise shims, not very difficult really, and what do you use , brass or steel.
Also CP how do you make your shims, I was thinking about my next small side project would be to see if I could sneak onto the Jig grinder at work and fashion a small shim punch set with about .0015 clearance per side of punch, for making small precise shims, not very difficult really, and what do you use , brass or steel.
11-09-2009, 08:48 PM
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RE: Engine test stand (Show and tell)
The sound wave chart is the difference in pitch and the time it takes for the pitch to change. Each wave on the chart has a left edge and a right edge that you set a measuring stick on and the program gives you a mph readout, plus 2 different frequency numbers to look at. The difference between the 2 numbers is the revs per second.
Brass sheet works well for shims. Most are .005" down to .001". I've made some by scribing a tracing and cutting with cuticle scissors. The liner shim in the FAI engine I made by hand. It's a better idea to order them from the factory or dealer, but if you can punch them out, that's pretty cool. Aluminum works, too...but not if they are too thin.
Brass sheet works well for shims. Most are .005" down to .001". I've made some by scribing a tracing and cutting with cuticle scissors. The liner shim in the FAI engine I made by hand. It's a better idea to order them from the factory or dealer, but if you can punch them out, that's pretty cool. Aluminum works, too...but not if they are too thin.
11-09-2009, 09:47 PM
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RE: Engine test stand (Show and tell)
Shim Punch. The top plate guides the punch. The bottom plate is the hardened die plate. Punch the inside diameter first. The outside diameter punch should have a pilot fitted.
Ed S
Ed S
11-09-2009, 10:55 PM
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RE: Engine test stand (Show and tell)
This is a Wav-o-scope output. The leftmost line is the fundamental frequency - if the high and low markers were on that line, it would give the apaprent frequency of the engine in both directions same as you see here but numbers in the 300-500 Hz range. If you average the high and low readings you get cycles per second, so multiply by 60 to get rpm. As you move to the right you get upper harmonics and/or other noises or whatever they are.
MJD
MJD
11-10-2009, 05:50 PM
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RE: Engine test stand (Show and tell)
ORIGINAL: Ed Smith
Shim Punch. The top plate guides the punch. The bottom plate is the hardened die plate. Punch the inside diameter first. The outside diameter punch should have a pilot fitted.
Ed S
Shim Punch. The top plate guides the punch. The bottom plate is the hardened die plate. Punch the inside diameter first. The outside diameter punch should have a pilot fitted.
Ed S
Thats right a pilot definitely helps with concentricity, especially with these types of shims.
11-13-2009, 07:56 PM
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RE: Engine test stand (Show and tell)
Anybody else want to post their set-ups for testing their engines, I know a basic set-up will work fine, but some people come up with some neat ideas I'm sure.
11-13-2009, 08:04 PM
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RE: Engine test stand (Show and tell)
Mine is a PSP test stand bolted to an 18"x30" chunk of 1-1/2" plywood (3/4" x 2 screwed and glued). It could hold up the corner of a truck. So far has proved itself holding a pulsejet, a turbine, and an OPS .65, among assorted other engines. I just clamp it to whatever, we have metal bleachers out back in the ball diamond with a big oily patch and clamp marks on one seat.
MJD
MJD