Something to consider is the "load factor". That's diameter x pitch x # of blades - D x P x N. For example, a 22x10 three-bladed prop has a load factor of 3,513,840, whereas a 23x10 two-bladed prop has a load factor of 2,798,410. The three-blader has more than 25% more load than the two-blader - that's a mighty big step up. Doesn't take into account differences between manufacturers, but it's not bad for a start. I can usually figure out the best prop for a plane after just a few tries, using the factor as a guide.

Of course, you can then use ThrustHP or the Abbott equation to estimate power & top speed, but I find those more useful after I have a static rpm. I program them into a simple spreadsheet to compare motor performance.

Another thing to remember, I have the older 7-70 and 9-90 so you guys likely have a bit more power to work with. My next project is an S2 models1/4 scale Pietenpol Scout that will use my rare 5 cylinder Seidel ST-540 of 40cc. I am using an 18x12 prop so the engine will keep the plane flying well at scale RPM!!! -Tom

Ran my Evo 160 today. It started right up! Ran it with a 32:1 mixture.
I used an electric starter as well.
My bud's engine ran for about 5 minutes and stopped. Checked the spark and there was none! So he'll have to call Horizon in the morning to see what's up. He may have to send it back?

FYI I didn't run it at full throttle. It's still being broken in. We did use Av Gas with no ill effects.

@Adrian
Awesome. Any rough idea when you might have these developed and available (the altered pickup)? If that's the case I'd love to buy it from you versus using onboard glow. Also that'd be cool to see some drawings to pick the best sizes for mounting for sure. I can comment at least as far as my application goes what size might work best (Hangar 9 60cc Corsair). I know the pickups may not look as minimized and sleek, but it's a minor annoyance for improved running characteristics and ease of use. Plus, I'm willing to bet it adds to the cool factor of the engine anyhow :)

Excited to see what you come up with Adrian! Holding off on the onboard glow until I see :)

@ redball8, thanks for that. That'll be an additional bit of help in trying to pick the right prop the "first" time.
@Maxam, both were Xoar props actually! The 77cc version seems to pull a bit harder from what I can see, so that's good news based on your prop selection knowing I'd have no problem and maybe a bit "extra" power to spare.

Adrian,
I think most of the planes are large enough to house the ignition with out a problem. Most WWI types are 1/4 scale. WWII Types would be around 1/5 scale. Same for civilian Air craft.

Just a note about care and maintenance. I dug out an old Seidel 7-70 manual and it states specifically there is no special care needed for the engine. It recommends a few drops of oil on all moving parts and some oil squirted into the carb and rotate the prop a few times.

Whats changed, and why are some being seemingly being so anal about engine after-run care? The truth usually lies between I guess

I used to have a Seidel St-7-70. I bought it used. It was severely corroded inside. What a mess. They are just as susceptible to corrosion so nothing has changed. Wolfgang Seidel has a well earned terrible reputation. I bought a Seidel ST 5-40 new. My analness keeps it slicker than snot. Have you read the thread. Go run your ST-9-99 on a hot humid day and put some oil in it. You will get a real surprise the next day. It will be crunchy when turned and if you start it, the exhaust will be rusty red. One person basically ruined one overnight. I do not fly these engines occasionally, rather like a 40 two stroke meaning all the time. My 9-90 has now over 150 flights. Your comment about truth.....well never mind. -Tom

I didn't mean the 'truth' comment as a stab Maxam! More as a general statement. I usually find with life in general, you take two extremes at either end and somewhere in and around the middle tends to be a good happy medium. I like to take care of my equipment, but I can foresee not hooking up a pump to the engine every time, or popping out the rocker every time. But definitely oiling up the rockers/valves and injecting a good amount of after-run oil in through the carb and turning over the engine. That's what I mean by somewhere in between... also if it really is as bad for rusting as you say, I still might find an ideal location to tap a hole in the crankcase and properly seal up a fuel nipple extending from the bottom of the case, and block it off while running the engine then unplug it later to drain then inject oil directly in the case with it.

OK CH, We are good. When you pull a bottom tappet after a flight on a humid day, collect the oil that drains out. You will not believe the amount of water globules in with the oil. I should get a micro-scale separatory funnel and collect the drainage. A half ml of water separating from the oil would not surprise me. There will still be a gob that has condensed all over the inside of the crankcase. The 9-90 is much more prone to this problem than the 7-70.That is the reason for the aquarium air pump, dry it out! It takes literally 5 seconds to put the aquarium tubing on the brass guide and let it run overnight. Easy piesy .(I think that is how you spell that) I recall you had a concern with removing pushrods and followers in cowled planes . My corsair is tightly cowled and it is still easy. Well anyway you will get a lot of fun and satisfaction with running these engines. They sure reinstated enjoyment for me in this hobby.

Interesting. It's a shame they haven't looked more closely at the potential for corrosion and plated some of the problem parts. It i guess you can't have a great running cool looking engine and expect to have it for a relative steal as well, though I'd rather pay another "$400" to do it "perfectly" right! Just in my nature I guess to always find a way to do something better or improve it if I can.

Youre probably right about the ease of it, so I'll stop thinking about it until I actually get the cowl on lol :) p.s- I think I'm going to go with the Biela 3 blade 'semi scale' 22x10 prop it looks awesome. Any experience with that one?

No I have no experience with that prop. Now that you know how to care for the engine I can assure you of its long life. They really do run well. Recall the 7-77 is less prone but still needs to be looked after. Make a nice test stand so you can learn the operation. They run really cool so overheating is not a problem. -Tom

I would agree with Maxam. Make a test stand and run the engine to break it in. My 7-70 was a bit fiddly when new. I had issues with it starting and running. I put it on a test stand and followed the break in procedures. Eventually it worked as it should. So now its a very nice starting, running engine. Yipeee!

Maxam and Bob, great to hear. I'm beyond excited to get this engine running and fully learn the ins and outs. Certainly is a showpiece either way. I've got a new test stand designed and in the works 'as we speak' :) definitely the best way to break-in and learn the engine. Still debating whether to do the CDI conversion route or onboard glo... I'm waiting to see what Adrian has coming out, but leaning towards CDI for the improved running characteristics.

This is the prop I think I'm set on - (http://www.aircraftinternational.com...5/Default.aspx)

I think the prop is too large for the 7-77.

Even though mine is a Xoar 22x10 three blade it works very well with my 7-70. Bit big for break-in but his 77 should do well with it if the pitch is the same as my xoar. -Tom

Hey have you guys seen the posts on RC groups planes, RCU gas engines and Flying giants airframes (all classifieds) There is a crook that has been using other persons pictures and using them as if they are his stuff and selling ripping people off. Well he stole a UMS 260 from somebody and all RCers have been collaborating and have located this crook. Pretty scary really. -Tom

Thanks to the good guys in the RC community they recovered the engine from this guy!!!

Gentlemen, I saw an hour long show on PBS about the first air war. Excellent! There are these guys in New Zealand that are doing amazing things including building new old engines! Check them out at thevintageaviator.co.nz I tell you guys this because I found it not only amazing but very motivating to raise my modeling challenges. With our interest in radial engines I felt you would all enjoy the show and what these guys are doing. -Tom

Very cool, thanks for posting that Maxam

excellent web site Maxam thanks for the info

You are very welcome. On PBS's website you can watch the show. There were many things I did not know about aviation in WW1!

So I'm planning my next project out, which I want to build the Ziroli 92" P-47 Razorback. I have read most of this thread with great interest. And the question is, is the 7-77 a good fit for the plane I'm considering? And what would be the proper prop size? The specs call for a minimum 3.4ci motor, and based on the cowl specs it should be real close to fit, maybe a couple cutouts at most.

Thanks,
John

What will the weight be as stated by Ziroli wjth the completed airframe? Over 28 pounds would get iffy. Building light would be of top priority. Very possible due the lack of vibration. A four bladed prop most likely could not be used for flying. -Tom

Per Ziroli Specs: Flying weight 30-35lbs all wood construction... Looking for a total weight using the fiberglass fuse.

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