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size of plane versus engine size - 12/8/2012 6:40 PM   
robster1


 

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From: las vegas, NV, USA
Status: offline 		 Hi Guys. This question is for you guys who know engine size to plane size and weight. I scratch built a Hal Krier Great lakes special, she came out at 22lbs. Tried hard to keep the weight down and this is what I got. BUT, you can lift the plane by its top wing and hold the fuse with the tail upward vertical!! Its built great, but I installed a Ryobi 31cc with a 16/8 prop. Is this plane gonna get off the runway and fly for me. I really don't want to replace the engine, as I will have to reconstruct the firewall, as the Ryobi required a recessed fire wall. Can you guys who are up on this guide me as I don't wanna crash her on her maiden flight. Should I go to a 18 or 19/6 on the prop and does the Ryobi have enough grunt to at least do some rolls and loops. She has quad ailerons. help me out here folks, if you would please. I do have a brand new Turnigy TR-50HP waiting in the box if I absolutely have to swap engines. It is white with red trimm and sunburst on top of top  and bottom wing and red and white checkered on the bottom of the wing and tail....man is sshe a beaut!! Motor runs strong and I bought a tach to check the RPM's which will happen later today.


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RE: size of plane versus engine size - 12/8/2012 6:54 PM   
av8tor1977



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Status: offline 		Well, the bad news is 22 lbs. is just a whole lot of weight for a Ryobi to haul around. Since the airplane should have a good amount of wing area, it will probably fly, but don't expect stellar performance.

It also depends on what has been done to the Ryobi. If it is stock, no way. Some of the Ryobis came with very low exhaust port timing, and they all came with a restrictive muffler and a very small carburetor. If the exhaust port timing has been raised to about 150 degrees, an 11mm carb installed, and a free breathing exhaust, AND the ring is in very good condition, you might have a chance. A 16 x 8 prop will be too small if it is a good running Ryobi. Normally an 18 x 6 prop would be indicated, or an 18 x 8 if it is a really good Ryobi. You want to prop it to turn no more than 7500 rpms on the ground, as the Ryobis, while a useful engine, should not turn more that 7500 rpms static because they have a weak rod. But they'll run forever if you just don't over rev them.

Ultimately, you are most likely going to want more power, even if your Ryobi is properly modified and putting out good power. If your Ryobi is stock, I wouldn't even try to fly it in your application.

AV8TOR

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RE: size of plane versus engine size - 12/8/2012 7:03 PM   
robster1


 

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From: las vegas, NV, USA
Status: offline 		man, that is what I was afraid of. This is a stock girl with stock muffler and carb. I geuss I wont be buying a prop but insted install ing the 50 cc as I have already bought  two 20/10's for it a the low price of 5.00 a piece. (sigh)

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RE: size of plane versus engine size - 12/8/2012 8:37 PM   
All Day Dan


 

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Status: offline 		Robster, more bad news. Here’s a biplane I designed for a Brison 3.2(52cc). It came in at 20 pounds. The Brison pulls it around just fine with a Zinger 20X10 prop at 7200 RPM. It is not over powered. av8tor is right. You’re going to need some more power. Dan.

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RE: size of plane versus engine size - 12/8/2012 10:05 PM   
pe reivers



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Status: offline 		The ryobi will fly the plane if you put an 18x10 prop on it. It will fly, but not very convincing. Using the 16" prop I doubt your runway is long enough to get airborn.


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RE: size of plane versus engine size - 12/9/2012 12:58 AM   
earlwb


 

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Status: offline 		I would agree with pe Reivers in that the Ryobi probably likes a 18x10, 19x8 or a 20x8 prop. The engines tend to run best when loaded down good. They behave like they are a four stroke engine with lots of torque at lower RPMs.


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RE: size of plane versus engine size - 12/9/2012 1:07 AM   
flyinwalenda


 

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Status: offline 		Agree here as well. The Ryobi in stock form will be on the bleeding edge if it manages to get it in the air at all. I have several Rybois and all have been modified to some degree (port timing, carb, exhaust) and at that point they are a decent engine.  I would either do some work to the engine or install another rear carb engine so you don't have to do much more mods to the firewall.


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RE: size of plane versus engine size - 12/11/2012 5:06 AM   
robster1


 

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From: las vegas, NV, USA
Status: offline 		Well guys, I redesigned the firewall and mounted the Turnigy TR-50HP. I have no idea on how to modify my Ryobi. While I have the new motor in hand, it would be a shame to fly  theplane underpowered and have a good motor on the shelf. Problem is now, the muffler that came with it is gonna have to sit this one out cause I lack 3/16ths of an inch to mount the muffler. I geuss I will have to look up B&B Specialties. But thats cool... cause I wanted to put a smoke system in it any how. You can't a
have a 1930's era correct plane with out smoke!!!!! Any hints on a pocket book friendly  smokesystem out there?

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