Engine conundrum for Hummelbird

Discussion in 'General Experimental Aviation Questions' started by 12notes, Dec 11, 2018.

?

Engine for the Hummelbird (already have both)

14 vote(s)
77.8%

3 vote(s)
16.7%

15 vote(s)
83.3%
4. McCulloch 4318-72hp, 4 cylinder, 2 stroke

3 vote(s)
16.7%
1. Dec 12, 2018

12notes

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Unfortunately, I'd have to sell all the engines, the plane project, and at least one kidney to buy one of those.

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2. Dec 12, 2018

12notes

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I'd love to use one, but unfortunately I can't build an engine mount for an engine in the "someday" category. I have no doubt Pete will finish it and it will do all you say, but it may be a little out of my budget (haven't seen a starting from nothing cost, just the cost of the kit assuming you have an O-200 to pick off of, and the cheapest O-200 on Barnstormers right now is $4000 for a core with 1840 SMOH) and I don't know when it'll be available. 3. Dec 12, 2018 Pops Pops Well-Known Member Joined: Jan 1, 2013 Messages: 7,382 Likes Received: 6,342 Location: USA. The going price of 0-200 and 0-300 take-off cylinders is$125 each. Rebuild the cylinders yourself with new valve guides, intake and exhaust valves, valve springs,etc, from Fresno Airpahttps://www.fresnoairpartsco.com/product-category/continental-c90-o-200/

And other parts you might need.

4. Dec 13, 2018

KeithO

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It doesn't seem cheap to build a 1/2VW anymore.

Hummel Engines want $4-5k for a hand propped engine and add another$750 if you want Nikasil cylinders.. Great Plains is a similar deal, $4k for a 1/2 VW kit engine. By comparison, double the price of the engine kits and half the price of any Lycoming/Continental or Rotax for a commercially produced engine does not seem bad. You are getting a proven prop reduction drive in the deal with the ability to swing a much bigger prop for slower aircraft. I understand that if the money is not there, its going to have to be the lest expensive option... 5. Dec 13, 2018 bmcj bmcj Well-Known MemberHBA Supporter Joined: Apr 10, 2007 Messages: 13,083 Likes Received: 5,011 Location: Fresno, California You have the answer to your question. For that answer, ask yourself if you built the Hummel to go out and putt around for pleasure or to cover large distances fast (or maybe short distances fast since you’ll have twice the fuel flow)? Engine noise is another consideration... do you want to spend your flying time listening to a loping 4-stroke or a high-revving 2-stroke 6. Dec 13, 2018 12notes 12notes Well-Known MemberLifetime Supporter Joined: Aug 27, 2014 Messages: 886 Likes Received: 549 Location: Louisville, KY I'd like to be able to cover distances fast-ish. 105mph is fine, but 130 would be nicer. With the wing tanks, range won't be a problem either way. The McCulloch is direct drive, so 3800 RPM cruise, vs the 1/2 VW at 3200 RPM, so it's not that much higher revving. 7. Dec 13, 2018 TFF TFF Well-Known Member Joined: Apr 28, 2010 Messages: 11,917 Likes Received: 3,413 Location: Memphis, TN Except for the price, I dont think you will be doing any favors for yourself. The only plus is you can stretch Marilyn Monroe into the conversation. How old is the rebuild? I would build a stand and test run the thing. Seals may need to be changed if it was rebuilt a long time ago. Also if it was rebuilt a long time ago, you might want to tear it down just because standards of what is acceptable change. I have torn into low time engines that were rebuilt 20 plus years back and you knew exactly what they were thinking and what parts they "had" to reuse. I would rather find out all is good and it did not need tearing down verses the best bearings in there were all flat spotted, and it busts a crank. 8. Dec 13, 2018 BBerson BBerson Well-Known MemberHBA Supporter Joined: Dec 16, 2007 Messages: 12,492 Likes Received: 2,525 Location: Port Townsend WA A simple four cylinder VW can be 140 pounds. About the same as the 80 pound drone engine and the extra 10 gallons of fuel/oil needed because it is two stroke. The VW is smooth. Even a used$50 VW that is carefully inspected should be more reliable.

9. Dec 13, 2018

Dana

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2 stroke vs 4 stroke means 2X the noise frequency at the same rpm (It would be 4X but the opposing cylinder pairs on the McCulloch are simultaneous firing).

10. Dec 13, 2018

cluttonfred

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"How can you tell if a pilot who has flown behind a McCulloch drone engine?"

"SORRY, WHAAAT?!?"

;-)

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11. Dec 13, 2018

cdlwingnut

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Well heres my opinion: hang the McCullogh on the Hummel then send the VW to me for my piet I will even trade a rotax 503 for your next project.

Really its your plane do what you want but i love the "real" airplane sound of the VW and the 4 stroke air cooled is more like a "real" airplane engine.

12. Dec 13, 2018

12notes

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With a modified compression engine on a plane built with cheap hardware-store bolts and nuts, although the stock engine might cause the same problems on a well built plane, it's not a fair comparison.

Also, the max RPM of the McCulloch O-100 is 4200RPM. If you or the previous owner were running it at 6000RPM, it's either a different engine or a grossly over revved engine.

Thanks for pointing out the magneto as a source of problems, and the carb issues as well.

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13. Dec 13, 2018

12notes

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A $50 junkyard VW would have marginally more power than the 1/2 VW I already have. A full VW of similar power to the McCulloch would be$5K+, and 80 lbs (2.5 hours at cruise) of fuel in the wing tanks is much easier to deal with than 80 extra pounds on the nose.

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14. Dec 13, 2018

12notes

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Thanks to everyone who has posted so far, keep it coming In the interest of keeping this thread on track, please don't suggest other engines at this point. I have two types in hand, unless someone literally gives me a third, better type of engine, I'm going to use one of the two I have. I hate wheeling and dealing, and do not want to go through trying to squeeze every penny out of selling 3 engines in order to afford a 4th.

I've tried contacting Skeet Wyman, who built the original McCullibird (Hummelbird with the McCulloch), hopefully I can pick his brain about his experience with the engine, particularly reliability, noise and vibration.

Although it may seem that I'm trying to defend the McCulloch engine, I'm not set on using it, just trying to get specific information on failures before I decide. Does anyone know if they're prone to seizure or mechanical breakage, or is it all fuel and spark issues?

15. Dec 27, 2018

12notes

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In the interest of getting the plane done faster, I'm going to use the 1/2 VW on the Hummelbird.

But here's what I found out on the McCulloch reliability from the rotorcraft forums.

The original crank bearings are rollers and crap. These typically get replaced with solid bearings when rebuilt.
The magneto is also crap. There is (or was) a CDI available that solved this problem.
The little wobbler fuel pump is also, also crap. Never planned on using it anyway.
The is designed for tractor prop use, the front bearing location doesn't like being used as a pusher, and it would just transmit the force of the thrust through the entire crank and could eventually break them. Since these were used a lot on gyroplanes, someone did develop a modification for this area, but it's not an issue for tractors.

These modifications correct the vast majority of reliability concerns, other than carb issues. It's not going to be a 1500 hour TBO engine, but it's far from suicidal.

I didn't get a response from Skeet Wyman, I didn't find much feedback on noise and vibration.

After I finish the Hummelbird, I'll probably set this one up on a stand with a cheap Microsquirt EFI and junkyard parts and experiment with exhaust setups. If I can find an inexpensive uncompleted Rans S-9 kit, it might be a good match for a second build. But I'm not going to do anything else with it until the Hummelbird is done.

16. Dec 29, 2018

Little Scrapper

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Sounds like a wise decision. The McCulloch isn't installed on many airplanes, I'd say very very few. The rotocraft that used them are a very very small sample. The VW seems to have experienced quite a bit of success.

17. Dec 29, 2018

Dan Thomas

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Don't miss the point: The firewall glue joints were broken. The builder had drilled small holes and added #10 screws and nuts through the longerons and firewall uprights in some misguided attempt to beef up the structure. Properly made glue joints should not break; the wood should fail first. I think the combination of oil contamination of the wood (from the engine, whcih spat vast quantities out of the exhaust and all over the airplane) and the massive vibration are what broke the joints. Drilling the wood for screws didn't help.

The redline was told to me as 6000. I bought that airplane in 1973, a time when literature on the engine was really rare and the internet was an idea in somebody's mind. If it's really 4200, then I stand corrected.

In 1973 literature on anything I was interested in was rare. Libraries had next to nothing. Aviation and electronics both had only the most general info available, and one had to rely on trade-specific magazines and textbooks for anything further. If the internet ever fails, young folks today will suddenly understand what us old guys had to deal with. In fact it will be worse, since most commerce will cease as well.

Edit: Mine didn't run at 6000 RPM. I don't think I ever saw more than 3500 on the tach when I ran it up. It had a much larger prop on it than the drones did as part of the derating. The drones had a prop of around 36". IIRC. But it's been a long time since I had that thing. I never flew the airplane; it had too many other issues to be economically repairable.

Last edited: Dec 29, 2018
18. Dec 30, 2018

Bill-Higdon

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The Late Ken Brock did a lot of work on the McCulloch's to improve their reliability during his Gyro-Copter involvement, and the manuals for them specify 4200 RPM as max for the 90 hp version.

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19. Apr 23, 2019

cgifly2

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So 12note did contact me, and I find it funny after all these years how people cling to what they have heard verses what are facts. The guy who built the Taylor plane with the firewall falling out? Alls I can say to that is if you fix the firewall, you better inspect the rest of the plane for poor workmanship. It wasn’t the Mac that broke that fuselage. It’s a shame that others have found out what a good engine the Mac was if you (like any other engine) take the time to set it up correctly. All of its problems are known, and can be dealt with easily by modern tech. Because they have found that it’s really a great engine, the price has risen on them. The Mac that I flew to Copperstate and then Jean Nevada, for the fly in, was one I bought off of eBay torn down inspected and put back together for 450\$. I know one of the gentleman that bought it and flew it down the road with the same engine. It’s a YouTube video called “Glens fav” it did have a flame out eventually, but it was the ignition system after many hours. And for the guy who built it, his comment was this is only the one he’s seen. Maybe I should have run air duct straight onto it
As far as comments on the 1/2 VW ha ha ha. That’s the reason WHY I did not use that engine. EVERY VW will crack the stock cases in time. Horizontally opposed twin will have a vibration and a certain rpm that will go through altimeters and vario’s. Not an opinion FACT. Ask David Roe. He has the most hours in a VW Hummel that I know. He went through countless altimeters and after his 3rd engine he said enough. He ended up building a really bitchen 4 cylinder VW with super short stroke and put a round cowling on it. He beefed up the spar and did some 175Mph runs on it.
Can’t speak for other Macs but mine was no more noisier that any other plane. It did have a “different” sound. I would describe it as a geared auto engine airplane. If you read my article in Sport Aviation, you would understand what made my plane so reliable. Purposely designed NOT to run on the edge of its envelope. THATS what make ALL 2 strokes including you beloved Rotax so unreliable.
If you where to take a Continental 0360, and prop it and run it at 4500 rpm all the time, guess what? Planes would be falling out of the sky every day. The best way to have a reliable engine is to build in a safety margin.
The Mac is as safe as any IC engine out there, but please keep bashing it. No Really! Cause we don need the price to go any higher.
Skeet Wyman

20. Apr 24, 2019

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