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RE: Seidel 7-70 radial: Help me decide! - 12/13/2012 3:47 AM   
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ORIGINAL: abufletcher

I suppose it would be possible to put a T-connector in the vent line to accomplish this.



If the vent line is only connected to the tank and dangling in free air (It doesn't need to be connected to the exhaust ring) then there is no need for a T. And if you did try the T fitting, the fuel is going to take the path of least resistance and just run back through to the collector ring.

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RE: Seidel 7-70 radial: Help me decide! - 12/13/2012 8:57 AM   
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Status: offline 		Hi,

these are the setups on my Nieuport and my  (late) FW Stieglitz. A syringe, a bit of brass tube, a bit of heat shrink tube...
On my Nieport I have the setup installed in the fuse with a bit of fuel tube that leads to the Power/fuel panel underneath the hatch. See pictures. On the Stieglitz the brass tube was accessible first as you see it underneath the cowling (the old NACA cowling in first version). Later I moved it to the right side so it was accessible underneath the side panels.

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RE: Seidel 7-70 radial: Help me decide! - 12/13/2012 11:07 AM   
abufletcher



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Status: offline 		How much fuel do you typically use to prime the engine? I like the brass tube with the syringe tip, very neat and tidy.

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RE: Seidel 7-70 radial: Help me decide! - 12/13/2012 12:33 PM   
Spuetz



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Status: offline 		when I use the pump-tank-overpressure-method, I let the pump run with vent closed for about 10 to 15 seconds while giving the prop 10 to 15 turns.
when I use the syringe it's about half a normal syringe. whats that? 20 ml? (I think - havent flown the Nieuport this year...)

BTW - full size radials are very similar. I'm not sure if I told you guys that i have about 10 hours on T6 and another 10 or so on DC-3. Now the DC-3 start procedure is awsome: you have your hand on the starter engine button which is located in the center overhead panel, while sticking your head out of the side window. Now push the button, while the pump is running and count 12 blades out loud, then turn on the ignition and keep counting. The engine starts with huffs and puffs and black smoke and fire until it climaxes to a full run... almost as good as the other thing that involves climaxes...

So you see, they need a lot of priming, too... lets call it 4-play!

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RE: Seidel 7-70 radial: Help me decide! - 12/14/2012 11:25 AM   
abufletcher



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Status: offline 		I've flown IN a DC-3 (from a dirt landing strip at a remote Huichol settlement in the mountains of Mexico) but FLYING one has got to be really something special! Priming is definitely the key to getting the Seidel running. Today I ran the engine again and for the initial start I needed to inject 20ml of fuel directly into the open carb while turning the prop. Most of the subsequent starts didn't require priming. The exception was when the engine started up backwards and went to full-throttle. To stop the engine I put a clamp on the fuel line. To get it started again, I need to prime it again. With the trim all the way to the bottom it idles reliably at 1,500rpm. That's as low as I could go without adjusting the throttle servo travel.

Since we're talking about foreplay and climaxes here's seven and half minutes of "engine porn."



Note: This video was shot with a Sony HD AVCHD Handycam. To my surprise and disappointment it obviously uses a digital shutter that creates the weird "rubber propeller" effects. The video mode on my Nikon D300s does the same thing. I may have to shoot some more video with an older Sony miniDV camcorder. Basically this effect comes from the shutter "traveling" horizontally instead of vertically, and you can see the same effect in some old aircraft photos taken with some of the early cloth shutter cameras. On modern video devices there isn't a shutter in the traditional sense, rather the sensor reads horizontal "slices" to create the video.

< Message edited by abufletcher -- 12/14/2012 12:56 PM >

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RE: Seidel 7-70 radial: Help me decide! - 12/14/2012 1:18 PM   
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Status: offline 		I read that a polarizing filter can help get rid of the prop dance. I dont know how to attach one to a handycam. I wish I could try but mine got lifted from my possession.

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RE: Seidel 7-70 radial: Help me decide! - 12/14/2012 2:07 PM   
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Clearly for our purposes the CCD sensor/shutter type is preferable. But the simple solution is just to shoot video in poor light! I went to the field this morning precisely because I knew there would be good strong morning light. Turns out the video might have been better if I had waiting until dusk.

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RE: Seidel 7-70 radial: Help me decide! - 12/14/2012 2:38 PM   
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Status: offline 		Hey, Abufletcher, I really enjoyed your explanation of propeller bending with videos. I have experienced that too, and it's annoying. One time, I put a cheap HD USB cam on a Cub, and the whole image got rubberynot just the propellerwhen turning and banking. So, if I read this correctly, just reducing the available light by putting a neutral density lens over the cam would help. I assume this slows down the "shutter" speed thus preventing the fast shutter from "stopping" the propeller motion. Is that right?

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RE: Seidel 7-70 radial: Help me decide! - 12/14/2012 3:25 PM   
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Status: offline 		From what I understand the propeller works as a "second shutter" and the problem is that the two shutters aren't in sync. Putting a neutral density filter over the lens or just filming in weaker light will cause the camera to set a slower shutter speed.

What likely causes the "jello-effect" with the small video cameras we mount on our models is the combination of the "rolling shutter effect" with the vibration of the camera (from the motor). I saw that on some of the footage I shot today and then noticed that one of the tripod legs was touching the test stand. So the engine vibrations were being transmitted to the camcorder and it made everything including the test stand wobble around like jello. Moving the leg eliminated that. I suspect that if you provided more cushioning for your on-board camera you could reduce the jello-effect. Most guys seem to hard-mount the camera to their model.

< Message edited by abufletcher -- 12/14/2012 4:00 PM >

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RE: Seidel 7-70 radial: Help me decide! - 12/14/2012 4:30 PM   
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RE: Seidel 7-70 radial: Help me decide! - 12/15/2012 6:11 AM   
abufletcher



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Status: offline 		It was a lot harder to get the engine running today. Not sure why, exactly. Each day, as I get to know the engine, I'm confronted with new situations. Yesterday, I saw how easily the engine could start backwards. Today, I think I over-primed and encountered hydrolock on my first attempt. I need to remind myself always to "clear" the cylinders after priming by rotating the prop a few times clockwise (with the glow power off). This is stated in the manual. Then despite what seemed like the same priming as yesterday I needed 26 flips of the prop to get it started. And subsequent starts were also difficult and/or required priming the engine again. Also for the first time today, the prop nut came loose. It's all part of learning about a new type of engine.

It's a little disconcerting that the engine vibrates and "wobbles" so much at very low rpms. What's causing this? The engine is solidly mounted to the wooden stand, which in turn is bolted to the foldable worktable, which is anchored to the ground with four ropes. At full throttle you can see the engine "lean forward" a bit but that's not an issue; that's just the heavy ropes holding the stand stretching slightly. But that slow throttle the wobble seems to the engine itself and looks like it could be harmful to a model. Could this be caused by an out of balance prop?

Note: This wobble is visible in person and not just an artifact of the video recording.



This video was shot with an older Sony Handycam with a CCD sensor. As you can see this eliminated the rolling shutter distortion problem you get with CMOS sensors. All the neutral density filters (and polarizers have a similar darkening effect) do is make the distortion less apparent by slowing down the shutter speed, but it doesn't deal with the fundamental geometry problems caused the CMOS sensor recording "slices" of a moving object (as described in the video posted earlier).


< Message edited by abufletcher -- 12/15/2012 7:23 AM >

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RE: Seidel 7-70 radial: Help me decide! - 12/15/2012 4:10 PM   
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Status: offline 		Vibration. Interesting theory. I'm not sure, and here's the reason. When banking the airplane, the entire scene would develop a bend. The faulty image was very organised, non-random, and progressive and the camera would catch up with the faster changing image outside only a few milliseconds later. There was nothing random about it like you'd expect with simply vibration. I think the scan shutter needs to be either a lot faster, or slower. Somehow, the shutter speed is sitting in a speed range that doesn't lend itself to sports or action sequences. Just my humble opinion.

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RE: Seidel 7-70 radial: Help me decide! - 12/15/2012 4:38 PM   
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Status: offline 		NDs are not perfect but cheap fix. Most other fixes are about $2500 or more as you know.
The prop should be immaculately balanced for an expensive engine or airframe; lots of lumber spinning. Maybe design if the counterbalance weight on the inside is not heavy enough; sometimes there is not enough room inside and that can be for any engine. Radial harmonics are pretty good, and odd number of cylinders gives an even firing order, so they are inherently smooth.

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RE: Seidel 7-70 radial: Help me decide! - 12/16/2012 11:15 AM   
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Status: offline 		Another bit of video from today with the XOAR 22x10 instead of the 24X10. The 22x10 is significantly less wood and this affects both the idle and the top speed. What I learned about starting the engine today is that it's just as easy to over-prime the engine as to under-prime it. You certainly can flood the engine so that it doesn't want to start (at least with my pipette method). I've learned that if the engine doesn't start after a few flip, you're wasting your time continuing to flip and flip and flip and flip. Better to shut off all the power and do the start routine again. If you've done it right, it starts more or less immediately.

Another bit of video from today with the XOAR 22x10 instead of the 24X10. The 22x10 is significantly less wood and this affects both the idle and the top speed. What I learned about starting the engine today is that it's just as easy to over-prime the engine as to under-prime it. You certainly can flood the engine so that it doesn't want to start. But generally, the engine started easily today.



< Message edited by abufletcher -- 12/16/2012 2:11 PM >

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RE: Seidel 7-70 radial: Help me decide! - 12/16/2012 11:22 AM   
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ORIGINAL: Pull Up Now!
There was nothing random about it like you'd expect with simply vibration.


I'm not saying it was "random vibraton." I'm saying that the engine vibration has a regular "frequency" that reacts in specific ways with the speed of the rolling shutter. In some cases these two "frequencies" may be more in sync while at other times (as other speeds) the frequencies might be out of sync...with entirely predictable results.


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RE: Seidel 7-70 radial: Help me decide! - 12/16/2012 11:49 AM   
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ORIGINAL: Pull Up Now!
Somehow, the shutter speed is sitting in a speed range that doesn't lend itself to sports or action sequences. Just my humble opinion.


You're probably right.


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RE: Seidel 7-70 radial: Help me decide! - 12/16/2012 11:52 AM   
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Status: offline 		How would I determine which of these two props be more suitable for my (eventual) 1/4 scale Strutter? It seems to me that since most of the time the Seidel would be running under half-throttle, the larger prop would be more appropriate.

Anyway, I guess at this point all that remains is to get it into a model and up into the air.

< Message edited by abufletcher -- 12/16/2012 12:35 PM >

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RE: Seidel 7-70 radial: Help me decide! - 12/16/2012 1:33 PM   
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I asume both props are in the reccomended range per the ops manual. Id break it in with the smaller one and move to the larger one after well broken in. During break in, monitor the engine temperature closely and then after changing to the larger prop look for any undue increase in operating temps. Some is to be expected as the engine will have to work harder to turn the larger prop at any given rpm compared to the smaller one. Im sure the larger prop is closer to scale and would be more desireable to look at.
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RE: Seidel 7-70 radial: Help me decide! - 12/16/2012 1:47 PM   
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Status: offline 		Yeah, both are considered suitable for the 770, though the manual suggests breaking in with the 22x10 and that's what I've used for most of the run-time on the engine so far. I'm still using the 8% oil mixture also. I don't have a temp gauge but have been doing the "finger test" after the engine shuts off and it's certainly not running hot. But then I haven't been running it flat out on full-throttle for extended periods either (and wouldn't be on the eventual model either).

The 24" prop is almost exactly the correct diameter for the 1/4 scale Strutter.

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RE: Seidel 7-70 radial: Help me decide! - 12/16/2012 2:04 PM   
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ORIGINAL: abufletcher
It seems to me that since most of the time the Seidel would be running under half-throttle, the larger prop would be more appropriate.


What I meant is whether the larger prop would be aerodynamically better with the engine running primarily in the 1,800-4,000rpm range. What are the advantages of diameter vs. pitch? Since both of these props have the same pitch, is it just a matter of how much wood is spinning around?


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RE: Seidel 7-70 radial: Help me decide! - 12/16/2012 2:15 PM   
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Status: offline 		By the way, the painted tips on the XOAR props actually look pretty silly and are strictly fun-scale.

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RE: Seidel 7-70 radial: Help me decide! - 12/16/2012 4:07 PM   
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ORIGINAL: abufletcher

quote:

ORIGINAL: Pull Up Now!
Somehow, the shutter speed is sitting in a speed range that doesn't lend itself to sports or action sequences. Just my humble opinion.


You're probably right.


Stupid RC Universe had a server problem right when I sent this "you're probably right" post and cut off the rest of it. I usually hit Control C to preserve what I write, but I trusted RCU this time and got bit. Grrrr. Anyway, the gist of it is the plane I was using [when I previously referred to the "whole scene" becoming rubbery instead of just the prop] WAS AN ELECTRIC plane, with virtually no vibration. So while you're quite right (and I was wrong) that engine vibration is NOT random, that engine vibration has little to do with the rubbery propeller effect. It's the CAM CMOS sensor vertical scan rate vs how fast the scene is changing. You were right when you said to lower the available light. The scan rate decreases to give each CMOS sensor strip more time to soak up light, lessening the rubbery effects on the propeller AND the whole scene.

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RE: Seidel 7-70 radial: Help me decide! - 12/16/2012 4:56 PM   
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Status: offline 		If you multiply that 1inch difference by pi.. you get a lot more prop area. Providing the RPMS' are the same or close the larger prop will provide more thrust.

For your purposes it really doesn't matter though. Go with looks best and maybe more scale. I vote the near scale size prop.

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RE: Seidel 7-70 radial: Help me decide! - 12/16/2012 4:59 PM   
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Status: offline 		My experience is usually propeller diameter wins over pitchthat give more performance benefit. I'm not sure of this, but it seems the ever increasing diameter of jet engine intakes kind of speaks to this. Here's the results of some software I have, comparing the two propellers. In the first pic, note the larger propeller has more thrust. The results are qualified by your original question....the 4000 rpm range. Theoretically, as you move past the 4000 rpm range, the engine could run out of HP to swing that much wood. And then a small dia prop might start winning. The second picture below kind of shows a hypothetical case of HP limit being reached, making HP fall off and under-perform the smaller propeller. One other thing. This software is very basic and it's only good for making RELATIVE comparisons between two propellers and rpms. Notice the horsepower calculations seem too high. But it's a rough guide for general questions. For better software, Google PE Reivers HP calculators.

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RE: Seidel 7-70 radial: Help me decide! - 12/16/2012 7:16 PM   
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Status: offline 		Don,

Your Seidel sounds just WONDERFUL in the videos. And I suspect that it will smooth out at idle as you break it in and are able to fine tune the idle mixture. I have no experience with the Seidel, but it does have an idle mixture adjustment, doesn't it ?

Regarding selection of propellor pitch and diameter, people make it sound more magic than it really is. The starting point is to determine the correct pitch for the intended airplane speed and engine RPM. Once you have the correct pitch, then you find a diameter that loads your engine to run at the desired RPM. Once the prop is in the ballpark, you can make small adjustments in pitch or diameter to fine tune the performance of the engine and airplane. The important thing is that you don't just select a diameter and then adjust the pitch to load the engine. Think of the propellor pitch as you would the gears in a car. Just as the car gear ratios determine the relationship of engine RPM to road speed, the prop pitch does the same on the airplane.

A good starting point is to use one of the online prop calculators to get into the right range of prop pitch and then do practical experiments with diameter to get the static RPM that the engine needs. Note that the calculations are for flight RPM, not static. When you tach the engine on the ground, expect it to be 10% to 20% less than flight RPM.

As a shortcut, you can quickly estimate pitch by dividing expected airplane speed (in MPH) by engine RPM in thousands. Examples: Say you expect max airspeed to be 35 MPH. And your engine speed for max power is 5000 RPM. Divide 35 by 5 and you get 7. The desired prop pitch is 7 inches. Could you use a 6" pitch or an 8" pitch ? Yeah. You probably don't know your actual airspeed that closely anyway.

Now say you are flying the same Seidel on a warbird and expect to go 70 MPH. The prop pitch would be 70 divided by 5, or 14" pitch. In that case you would need a smaller diameter to let the engine turn up to rated RPM. The point here is that pitch and diameter are dependent not only on the engine but also on the airplane it's trying to pull. As a side point, don't forget that the warbird has to be smaller than the WWI biplane if you're going to try using the same engine. If the warbird is going to go twice as fast with the same engine, it has to be smaller. You can't just double the pitch of the prop and expect to go twice as fast.

Hope this hasn't been too much to digest all in one post. it's kind of like the sign at the airport: "Learn to fly ! Ten easy lessons or one hard one."

Dick

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