Author Topic: 30cc Flat Four (Puma)  (Read 19062 times)

Offline Jasonb

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Re: 30cc Flat Four (Puma)
« Reply #195 on: September 29, 2019, 07:16:28 AM »
The other method is to put a full length prop on it and measure what revs it will do, there is then a formula that will give the HP.

Offline doubletop

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Re: 30cc Flat Four (Puma)
« Reply #196 on: September 29, 2019, 08:02:16 AM »

The other method is to put a full length prop on it and measure what revs it will do, there is then a formula that will give the HP.


https://www.rcgroups.com/forums/showthread.php?1077012-Measuring-motor-power-output

Apparently no prop is required, just a stick. Although I would be a bit wary of a 6mm x 26mm plywood 'stick' spinning at 8000 rpm, I'd have visions of it parting company with the engine and launching itself at the neighbours place. However, the material used is apparently irrelavant as mass has no part to play in the calculations.


Pete
?To achieve anything in this game, you must be prepared to dabble on the boundary of disaster.? - Stirling Moss

Offline tangler

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Re: 30cc Flat Four (Puma)
« Reply #197 on: September 29, 2019, 11:48:14 AM »
There's a formula (of uncertain provenance) that gives Horse Power figures that are comparable to some engine tests that Peter Chinn used to publish.

BHP = 7.105 x 10-18 x D4 x P x R3

Where D is prop diameter, P is the Pitch (both in inches) and R is RPM

HTH,

Rod

Offline doubletop

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Re: 30cc Flat Four (Puma)
« Reply #198 on: September 30, 2019, 01:38:49 AM »
Rod

Thanks for the input, weíve started something hereÖ

I went looking for references to Peter Chinn to support the formula provided by your input. It turns out that Peter Chinn used his own set of calibrated props to get results. And if you read the articles in the links below all props are not equal. In Peter Chinnís time even the same prop from the same manufacturer wasnít equal

http://www.adriansmodelaeroengines.com/catalog/main.php?cat_id=57

http://www.modelenginenews.org/techniques/testing.html

Where does this take me? Back to letís get the engine running properly and maybe then Iíll try a Prony brake.

Pete

#Dynamometers


?To achieve anything in this game, you must be prepared to dabble on the boundary of disaster.? - Stirling Moss

Offline doubletop

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Re: 30cc Flat Four (Puma)
« Reply #199 on: October 01, 2019, 06:32:09 AM »
I gave it another run and although there was an improvement over previous runs it was clear it still needed some work. One benefit of a multi cylinder engine is that if one cylinder isnít working as well as the others it is pretty obvious.

Iíd previously noted that one of the cams on one of camshafts were not correctly aligned, I was also aware that two of the cylinders had considerably more compression than the other two.

So time to strip it all down again and this time get the camshafts out. The jacking screws certainly helped to make the strip down a lot easier.



Youíll notice the cam shaft has been disassembled and the crank is missing. With it all apart this time the problem with one of the crank pins coming out was obvious, one of the joints on the centre web had failed. So that was the first thing to get fixed.

I checked the angular location of the cams and confirmed they were out. The right hand (2,4) camshaft the two exhaust cams should have been 90deg apart they werenít. Same for the inlet cams on the left hand side (1,3)

When Malcolm wrote up the Bobcat article, he proposed a simple jig to align the cams



Youíll notice that even in this photo it is possible to get the cam incorrectly located in the V of the jig. Any error on the camshaft alignment is doubled at the crankshaft.

I re-made my jig to better fit the shape of the cam to better ensure correct alignment.



Investigating the two cylinders with lower compression was an easy change of the O rings. I guess they wore more quickly doing the run in.

Loctite is now curing and Iím cleaing up the other parts. Then its back together again

Pete


« Last Edit: October 01, 2019, 06:35:21 AM by doubletop »
?To achieve anything in this game, you must be prepared to dabble on the boundary of disaster.? - Stirling Moss

Offline doubletop

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Re: 30cc Flat Four (Puma)
« Reply #200 on: November 18, 2019, 12:25:46 AM »
Time to get back to this. After the camshafts were set I re-assembled and had had a brief attempt at running it. It wouldn't run so it got parked.

Next was a flight from NZ to the UK for a holiday which included a visit the Midlands Show. Where I manged to miss Jason and Stewart Hart by feet, not even days, hours or minutes. We were all in the cafeteria at 11:30 on the Thursday. While I was in transit the arrangements had been made to meet at the 'green X' and I missed the thread. However, I was in the same cafeteria at the same time but being unaware of the arrangement wasn't looking out for them. Maybe another time. I did manage to catch up with Roger Froud and Rex Hanman and a couple of others who, I'm sorry, I didn't catch their names.

I've been back two weeks now and got some other jobs out of the way so back to the engine. I'm currently re-setting the timing then I'll see if it runs. I just hope that I didn't stuff up the re-assembly of the camshafts....

Pete
?To achieve anything in this game, you must be prepared to dabble on the boundary of disaster.? - Stirling Moss

Offline doubletop

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Re: 30cc Flat Four (Puma)
« Reply #201 on: November 18, 2019, 11:04:09 PM »
The problem with starting was pretty soon sorted. I'd set the camshafts for 1&4 and 2&3 operation and the firing as 1,4,3,2 that clearly wasn't going to work.

Getting the cams more accurately located on their shafts and using a DTI to set the lift point certainly paid off.

On this run Iím using an RC servo to set the throttle so I have better control while I tweek the carb. It's a pity the rev counter isnít in view. But Iím getting around 1500 to 8500rpm


I did a few more starts after this and then the engine would not restart. This time the timing belt sprocket has moved on the camshaft. Clearly one 6ba grub screw is not sufficient. Iíll make provision to 2 or more. Filling flats wonít work as it would just about be impossible to get them correctly located and maintain the correct cam settings.

Pete
?To achieve anything in this game, you must be prepared to dabble on the boundary of disaster.? - Stirling Moss

Online Jo

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Re: 30cc Flat Four (Puma)
« Reply #202 on: November 19, 2019, 08:33:26 AM »
 8) Nice one Pete.

Jo
Enjoyment is more important than achievement.

Offline Admiral_dk

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Re: 30cc Flat Four (Puma)
« Reply #203 on: November 19, 2019, 11:50:58 AM »
Quote
Clearly one 6ba grub screw is not sufficient.

I can't say that this surprises me with the engine size you are doing ....
You need a total fixed mechanism (I will not exclude Locktite), like a pin or better a key.
Why - well, any kind of possible angular movement, WILL end up destroying the "fix to axle" - simply because the opening and closing slopes off the cam, will create opposite twisting forces.
I'll bet that the grubscrew created a "furrow" in the axle, from the back- and for-ward forces.

The engine runs very nicely at the start of the video + looks great :ThumbsUp:

Best wishes

Per

Offline doubletop

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Re: 30cc Flat Four (Puma)
« Reply #204 on: November 19, 2019, 07:20:40 PM »
Thanks Jo

Quote
Clearly one 6ba grub screw is not sufficient.

I can't say that this surprises me with the engine size you are doing ......


Best wishes

Per

Per

It is a result of creating an engine based on another design. With Malcolms orginal design with a single camshaft and using a geared drive there is an opportunity to get the camshaft set up, use the grub screw  to create a witness mark, take it all apart, machine a flat at the right location and get it all back together in alignment. Malcolm says 'file a small flat... it is easy to adjust this flat to ensure the gear is in the correct position'.

With this engine it is not so easy using a belt drive and filing flats and reassembling two camshafts at the correct angular relationship to the crank could be troublesome. That said writing this reply has made me stop and think and I have some ideas to try.

Pete
?To achieve anything in this game, you must be prepared to dabble on the boundary of disaster.? - Stirling Moss

Offline Admiral_dk

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Re: 30cc Flat Four (Puma)
« Reply #205 on: November 19, 2019, 08:42:06 PM »
Quote
That said writing this reply has made me stop and think and I have some ideas to try.

I have experienced this many times - either with me explaining or the other person doing this - and it often happens to reveal a useable solution when one has to explain the problem in such a fashion that the other person understand what you're facing .... often before having finished the "lecture" about the problem too  ;)

Per

Offline doubletop

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Re: 30cc Flat Four (Puma)
« Reply #206 on: November 19, 2019, 09:05:38 PM »
Quote
That said writing this reply has made me stop and think and I have some ideas to try.

I have experienced this many times - either with me explaining or the other person doing this - and it often happens to reveal a useable solution when one has to explain the problem in such a fashion that the other person understand what you're facing .... often before having finished the "lecture" about the problem too  ;)

Per

That's the benefit of these forums. The interaction makes you stop and think rather than plough on regardless.

I would tell junior project managers to write their weekly status report regardless of whether they thought anybody would read it. The action of stopping and taking stock refocuses from the reactive day to day problem solving back to the big picture.


Pete
« Last Edit: November 19, 2019, 09:09:43 PM by doubletop »
?To achieve anything in this game, you must be prepared to dabble on the boundary of disaster.? - Stirling Moss

Offline scc

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Re: 30cc Flat Four (Puma)
« Reply #207 on: November 19, 2019, 09:39:12 PM »
Nice engine Pete,       Terry

Offline Dave Otto

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Re: 30cc Flat Four (Puma)
« Reply #208 on: November 20, 2019, 01:07:57 AM »
She runs and sounds great Pete, congrats!

Dave

Offline doubletop

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Re: 30cc Flat Four (Puma)
« Reply #209 on: November 20, 2019, 08:24:55 AM »
Terry & Dave

Thanks guys. I'm pretty pleased with it, my 2 previous engines have never run as well as this. They are both up or some rework once I've sorted the minor issues with this one. I've learned a lot.

Pete
?To achieve anything in this game, you must be prepared to dabble on the boundary of disaster.? - Stirling Moss