# Low budget Ultralight Aircraft

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#### BBerson

If my GX670 proves too small, I will consider the Briggs 810cc vertical crankshaft model 49T877 on sale for $959 at Northern Tool. The vertical needs conversion to horizontal, but should be doable. Briggs are good enough for aircraft, I feel. (used in France and Europe) Direct drive can only produce less power than typical use. So should be fine if crankshaft doesn't break from prop torsional dynamics. All conversions risk torsional vibration. The thrust bearing should be fine. #### Topaz ##### Super Moderator Staff member Log Member ... some of them use "splash" lubrication instead of pressure... I can't speak to your other concerns, but the Predator engine at HF is pressure-lubed, with filter. I know because I was just looking at one the other day when I was in there for some more work gloves (see photo). It also has an external oil cooler, which I thought was a nice touch in that for an ultralight installation it could be turned directly into the airflow for better cooling. My main point here is that using even the best, most expensive, highest quality industrial V-twin engine already represents a huge reduction in cost from any aircraft style powerplant. So chasing after the last$500 in cost reduction, ... is going to be a very bad bargain.
All true. And yet that argument can be carried over and over until one is right back at a $200,000 airplane. It's not like the old MC101 was the "best, most expensive, highest-quality" motor in its class "back in the day", either. And yet a lot of guys had a lot of fun struggling off the ground and into the air with one. And yes, they had failures, and yes, they glided down and took the beast back home and fixed it, and flew again in a couple of weeks. Little Scrapper's exercise in low-cost aviation, along with revisiting this thread and the earlier discussion, simply makes me wonder, "How low can you really go?" If one is expecting to do cross-country and expect to never have an engine-out, then yeah, I don't think the HF engine is the way to go. It may not be the way to go regardless. But for a guy with very little discretionary income (family obligations, etc.),$500 delta on the engine might make the difference between flying now and flying a year or two from now. If his expectations of the experience are in line with what he's spending, and those expectations might be, "go out and hop around the field a few times once a month, and if the engine quits I glide down and talk around the campfire with my friends," I really don't see the issue with that.

If the HF engine has "cheap parts", then replacement and repair parts are cheap, too, and plentiful. Tinkering with the motor used to be part of the ultralight fun, IIRC, and this is "experimental" aviation we're talking about here, after all. I keep hearing, "believe" and "probably" and "I wouldn't" on these threads as reasons not to use this or that motor. Those are opinions, not data. At this price point, it might be worth just trying it. I know Hot Wings tore into one and didn't like some of the components, but that's still different than bolting one to an ultralight airframe and trying it.

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#### pictsidhe

##### Well-Known Member
Some of the smaller horror fright engines have a great reputation. And metal cams.
I only know of plastic cams in Honda and Briggs engin'
Engineered right, plastic cams should be fine. The kind of plastic needed is likely pricier than cast iron. I doubt Honda wiuld use them to try saving a few cents.
I'm currently thinking of a pair of HF engines for my 103. At \$100 each, I can afford to just replace fhem every few hundred hours.

#### Hot Wings

##### Grumpy Cynic
Log Member
I agree with VB. Hot Wings had some problems with HF, I think.
That was some time ago. Problem was with the order process not the engines.

I've got 2 engines at the shop. I intended on converting them for my Quickie but life has chosen to delay that project for far longer than I would have expected.

One is the HF horizontal and the other is a Briggs 810cc vertical shaft. I've looked inside both in detail. Can't say anything about the materials or actual production tolerances but IMHO the HF engine is a superior unit with regard to design detail. That being noted I'll actually start with the B+S engine because it is a vertical shaft configuration. Sounds counter intuitive but it provides options that the HZ shaft engine doesn't. If I had it to do over again I'd get one of the new HF vertical shaft units to start with.

https://www.harborfreight.com/708cc-22-hp-v-twin-riding-mower-engine-epa-62879.html

#### Topaz

##### Super Moderator
Staff member
Log Member
Thanks for sharing, Hot Wings. I had looked for your earlier thread, but only briefly, and couldn't turn it up.

Could you expand on the vertical versus horizontal shaft options?

#### Hot Wings

##### Grumpy Cynic
Log Member
Thanks for sharing, Hot Wings. I had looked for your earlier thread, but only briefly, and couldn't turn it up.

Could you expand on the vertical versus horizontal shaft options?
Vertical shaft engine are produced in larger volume than the horizontal shaft due to the mower market and are generally cheaper than the equivalent HZ. For my intended use cost isn't so much of an attraction as is the ease with which the oiling system, on some vertical shaft models, can be modified. That's all I'd like to say about it right now..................

#### lr27

##### Well-Known Member
Don't they bolt mower blades onto the bottom of those vertical shafts? Seems to me that a mower blades moment of inertia might approach that of a propeller. So maybe the vertical shaft engines have an advantage that way.

As far as PSRU's go, has anyone been comparing the weight between a small engine with a PSRU and a somewhat larger engine run at lower RPMs?

Another dodge, if you design your aircraft as a twin, is that a smaller engine that runs at the same rpm as a larger one has less need of a PSRU. Consider a 60 inch prop at 3600 rpm. 942 fps at the tips, which is much too high if you're taking your ears along with you when you fly. OTOH, if you use two engines, then each can have a 42 inch prop. Tip speed is now 659 fps, which is much more bearable, and you still have the same prop disc area. Of course, a twin has all sorts of other issues, and I don't know how the weight comes out. I'm guessing the Home Depot plane might be a little tricky to fly on one engine. Maybe the aircraft needs to be configured like a Cri Cri to make it more manageable with one engine out.

#### pictsidhe

##### Well-Known Member
Riding mowers aren't used direct drive to blades.

#### lr27

##### Well-Known Member
I guess you're right. Looking at self propelled, walk behind mowers, which appear as though they have the blade on the shaft like a regular mower, they seem to top out at 5 or 6 hp and 200 cc for the really big ones. Sigh. I supposed if you used two with mild performance enhancements... Or maybe there's another application where they put something big directly on the shaft?

#### pwood66889

##### Well-Known Member
Suggested Vert. motor use for helicopters. Rebuilt a VO-435 Lyc (IIRC) for A&P school.

#### lr27

##### Well-Known Member
Looking through this thread, there's been repeated mention of the weight of flywheels. If there's room, a larger diameter flywheel can be much lighter if it's still strong enough.

Realistically, those little 2 strokes are probably the way to go. Particularly since saving weight means a smaller , lighter airframe too. But who wants to listen to them or spray oil into the air? I'll admit that one or two of the two strokes at the fly in this weekend didn't sound completely awful, and the 912's didn't sound that good. And the VW in the Sonex used a prop the size of a toothpick.

There was something else, but between dealing with internet outages and having to use my Stoopidfone® for internet, I forgot.

#### lr27

##### Well-Known Member
Or you could make a flywheel the same size, much lighter, except for all the lead weight you put at the rim. Maybe not as light as a larger one.

#### lr27

##### Well-Known Member
Some of the modestly sized Honda engines come with 2:1 reduction gears.Wonder how long they'd last with props bolted on? Some even have 6:1. You could swing a 7 foot prop and get amazing static thrust for a minute b4 it all turned to metal shards.

#### ryanjames170

##### Well-Known Member
I am going to be talking to the performance 670 guy tomarrow, I will ask him as much as I can think of and will post my findings tomarrow

#### pictsidhe

##### Well-Known Member
Unless you are using a soft redrive, you don't want a flywheel. You may be able to make your system tolerate it, but it's a lot of weight for a ring gear and somewhere to hang the ignition magnet.

#### ryanjames170

##### Well-Known Member
Unless you are using a soft redrive, you don't want a flywheel. You may be able to make your system tolerate it, but it's a lot of weight for a ring gear and somewhere to hang the ignition magnet.
not to be a dick but you do know they make billet aluminum flyhweels for alot of the popular engines.. in fact any go carting performance parts place worth its salt sells them as the cast flyhweels cannot and should never be spun faster then 3800 RPM.. as they are known to explode