Axial crankshaft forces + Propeller help

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RenaatXS

Active Member
(LOOK AT POST #15, I HAVE UPLOADED A HD MOVIE WITH THE ENGINE ALL TUNED SO IT FINALLY REACHES 3000 RPM WITH A 48x17 PROPELLER)

Hello,

I know my engine isn't a half VW, but it is very similar to it.
It's a French made Citroën 2CV (subtype M28/AM2) engine.

-4-stroke opposed twin
-602cc
-9.1:1 compression ratio
-stock 32hp at 5500 rpm.
-Manufactured from 1968 to 1983

I bought two very ugly engines for €50/60at a local Citroën garage. I took them apart and combined the best of both to one engine. Also, I've installed electronic ignition and Mikuni 34mm carbs. Because I took off the flywheel, forced air cooling, etc., it weighs 37kgs/80 lbs now. I bolted my engine onto the back of my homemade kart, so I can try props "dynamically". This is my worn out crankshaft, the good one is in the engine. As you can see, the right bearing can pick up some axial forces. The left bearing is stronger for radial forces, so that's where the prop should come. But now my question is: Is the right bearing good enough to support 50kgs/100 lbs of axial thrust? Or should I add an external bearing? This seems very dificult to me, because I think the slide bearings should not be forced to run onto one side because the external bearing is not perfectly aligned... Yesterday I've made the propeller hub out of aluminum. The cap can be removed when access is needed to the 5 crankshaft bolts. After thightening those bolts, just put the cap back on with the 1" centering tap on it. Any propositions on what type of direct drive pusher propeller I should use? The engine is running counterclockwise. Last edited: Dana Super Moderator Staff member I'm not familiar with this engine, but most automotive engines cannot handle the thrust loads from a direct drive propeller without an additional thrust bearing. Also 5500 rpm is very high for direct drive; you'll be limited to a very small and/or noisy propeller, not very efficient. 32hp from an 80# 4-stroke sounds pretty good, though. -Dana Hardware: the part of the computer that can be kicked. If you can only curse at it, it's software. Dan Thomas Well-Known Member The gyroscopic loads from the propeller (when the airplane maneuvers) will be a bigger risk factor. It looks like a pressed-together crank, short main bearing and small rod journal diameters, and the prop will try to bend the crankshaft and either break it at the first journal or work the journal loose in the other crank parts. When testing it you'll want to drive that cart in circles for a while. Dan RJW Well-Known Member My question is why don’t auto engine makers make a decent airplane engine? It’s almost like a conspiracy or something. I agree with Dana. The thrust bearing is minimal even for a car motor. Don’t stand on the clutch too long or that thing will burn up. It will not work for prop thrust. On the other hand the heads and pistons are a very nice design—much better than VW or half VWs. Pressed cranks are problematic at high power. But if you keep the revs at reasonable levels it will probably be ok. Nice machine work on your prop shaft. Run everything on your cart (also very cool) and see what happens. Thanks for posting. This is the best look I’ve had yet of these nice little engines. Rob Lemans Well-Known Member Making Dana's words visible.... a 5500 rpm engine allows only small props so I took the liberty to ad a 90cm/35,4inch prop in front of the 2CV engine ( tip speed @ 5500 rpm apr. mach 0,8 ). You might consider a reduction drive or moving your propeller away from your engine. Attachments • 43.1 KB Views: 1,807 RenaatXS Active Member Hi there, Firstly, I'm not planning to rev up to those 5500 rpm. I don't want to get higher than 3700 rpm. This means that I'm not using the max power output of my engine, but I don't really need much more than 25hp. I think that I should be able to get 25 hp at 3700 rpm because of my modifications. Everything will be clear after my prop tests. I'm going to measure the max thrust force. If I'm not getting enough thrust, I can upgrade my engine with a programmable fuel injection kit. That should do the job for sure. I know that this might not sound very professional, but since this engine didn't cost me that much (<300) I don't mind if it's not powerfull enough. I can still sell it to a Citroen 2CV car owner for 1000$And I had lots of fun building this pretty engine. Just keep in mind that I know someone who has actually flown his home made pou du ciel with a standard! 2CV engine with a home made direct drive airscrew. (VIDEO) This is what it sounds like for the moment: (high idle speed because there's no flywheel + carbs need to be synchronised) [video]http://tinypic.com/m/f3yfch/2[/video] User Media - TinyPic - Free Image Hosting, Photo Sharing & Video Hosting Dana Super Moderator Staff member 80# for a 35HP 4-stroke sounds good. 80# for 25HP, not so good (when you consider a 25HP 2-stroke weighs under 30#). -Dana Don't ever think you know what's right for the other person. He might start thinking he knows what's right for you. BBerson Light Plane Philosopher HBA Supporter Just keep in mind that I know someone who has actually flown his home made pou du ciel with a standard! 2CV engine with a home made direct drive airscrew. Interesting, did that work well? What airframe are you planning for this engine? BB RenaatXS Active Member Interesting, did that work well? What airframe are you planning for this engine? BB It's slow, climb rate very slow, but at least it flies... I'm not looking for a hi performance airplane Airframe will be the much discussed spratt 103 airframe. I have good contact with the designer. Although some believe that his plans will never be published, I trust him. I have time too, since I'm only 20 YO now BBerson Light Plane Philosopher HBA Supporter The 602cc. engine is, of course, much smaller than the typical half VW with 900-1100cc. But it might work if the airframe is very LIGHT. And the prop would need to be optimized for the engine (custom made). The prop should be as long as possible with narrow chord blades and narrow tips. This would require carbon or metal tips for stiffness with such narrow tips. The pusher prop loads the entire crankshaft in compression, with the thrust face on the far end. A simple way to make an external pusher thrust bearing could be done with a thrust washer added between the prop hub and the case, as is done with model airplane engines. A small supply of drip oil would be needed. (just leaks away, same as a model engine does) BB RenaatXS Active Member I came up with this solution for the axial forces: The system is similar to the pushrod on some clutch systems. This is what the other side of the crankshaft looks like: This side is being pushed out of the crankcase. I'm thinking of welding a single steel ball of a large ball bearing on top of the center bolt. Then I'd take a piece of soft iron and push that ball as hard as I can (hydrolic) into it. This will leave an excellent seating for the ball. Since the metal on that spot has been deformed, it will be harder and more resistant to wear and tear. Then I'd make a welded adjustable bracket to mount that seating onto my crankcase. The ball-bolt will be fastened on the top of the crankshaft. Once the engine is running, the ball on the bolt will be pushed onto the seating. A drop of oil now and then should keep it lubricated. Cost of solution: <5$

What do you think? (might be difficult to visualise, but I promise to post more pics when I'm done)

It might be usefull to mention that my body weight + clothes is only 68kgs/150 lbs. The weight of the airframe without engine is 100kgs/220 lbs.

RenaatXS

Active Member
If necessary, there are 650-800cc kits on the market for my engine. Cost is very low, starting at about 150\$ for two cilynders and two pistons...
We'll see. Everything depends now on hom much lbs thrust I can get.

Dana

Super Moderator
Staff member
I came up with this solution for the axial forces: The system is similar to the pushrod on some clutch systems... I'm thinking of welding a single steel ball of a large ball bearing on top of the center bolt. Then I'd take a piece of soft iron and push that ball as hard as I can (hydrolic) into it. This will leave an excellent seating for the ball. Since the metal on that spot has been deformed, it will be harder and more resistant to wear and tear. Then I'd make a welded adjustable bracket to mount that seating onto my crankcase. The ball-bolt will be fastened on the top of the crankshaft.
Once the engine is running, the ball on the bolt will be pushed onto the seating. A drop of oil now and then should keep it lubricated.
As soon as any thrust is applied, it will squeeze the oil out and it will wear quickly. A clutch release only sees short term loads.

Why not just use a proper thrust bearing?

-Dana

Please return stewardess to original upright position.

erkki67

Well-Known Member
Hello Renaatxs

Do you have any news regarding your engine?

Bst Rgds Erkki

RenaatXS

Active Member
HD airplane engine run video

Well it's been a while since my last update: but I've got to my 3000 rpm direct drive

In order to reach that, I had to machine the engine cases so I could fit bigger cylinders from a Citroen VISA (successor of the 2CV car, even more ugly).
These cylinders are aluminum instead of cast iron (much lighter) and the bores are nicasil coated. The displacement is 650cc instead of 600cc.
Also the heads have bigger valves and the pistons are 9.5:1 compression ratio instead of 9:1.

The second change was removing the two motorcycle carbs and fitting a single Weber 34/36 carb. The idle is not good, but I can adjust that.

Here's a HD video of a test run: