j lauria

Bandangle,

You have me a little worried about my plans for the 7-77 in the 77 inch Stearman. I just laid out my plan with the fuse in take off attitude and measured from the center of the engine to the ground. It is about 12.5 inches. A 22 inch prop will have 1.5 inches of clearnce. The prop on my 1/6 scale Waco clears by about 2.5 inches in take off attitude and I have never had a ground strike on take off. I am hoping that the 7-77 will like a 20X12 prop.

I am also skeptical of the finished weights as advertised as they always seem to turn out a few pounds more in my hands and never less.

I have not reached the point of no return on this project yet even thoughI will soon have a full kit and plans, so I will be watching this forum closely.

Maxam

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You could use a 20x12 prop but you would need to limit the throttle so the engine would not over rev. -Tom

badangle

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j lauria...hope your kit is better than mine....I had missing plywood and parts that did not match plans.

a real stearman has an engine that's smaller in diameter than the fusealage and the cowl size for 77" stearman is 8"

my engine (7-77)  is a bit big and too long for the 77" ...I  will need to move firewall to fit properly.... look at reverends aeroworks stearman...his engine is bigger than  the fusealage.......Ya it could be made to work by altering prop and moving firewall but when the 87" kit solves all the problems AND  actually fits the engine better why even go there?

Maxam

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Engine smaller in Diameter?? Here is an original with stock engine that I flew in. -Tom

j lauria

Bandangle
What is the diameter of the 87 inch cowl? Looking at the full size photos that Maxam provided, indicates that the engine should be a bit larger in diameter than the fuselage. If it can be reliably shown that the 7-77 will fly a 30+ pound airplane with reaonable authority the 87 inch version may indeed be the way to go if the engine looks right on that size model. I really want to build a Stearman without a cowl and without a dummy engine, but if I am going to spend that much for an engine it has to look right. The BUSA 1/3 scale Stearman flies great on a five cylinder Moki and sounds very realistic but it isn't SCALE.

badangle

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j lauria sorry guys, the photo I have shows a smaller engine but after searching I found planes with engines a bit bigger than fusealage.

as realistic as rc models are im not sure if my photo is a real plane or not.. its not a close up photo.

I don't have planes for 87" yet and no cowl listed for it so I cant say as to diameter but should be closer to 9". Question...WHY is 77cc radial

not as strong as 77cc single?

will single take same prop as radial?

Maxam

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Badangle, There are many more moving parts so there are frictional losses, also a two stroke fires every rotation. Vibration levels and torque impulses are very high. Each cylinder in a 4 stroke fires every other rotation but is scavenged more completely that a two stroke. Having 7 cylinders fire every two rotations have lesser torque fluctuations. An advantage of these radials also is high torque developed at lower rpm so a big efficient prop can be used. -Tom

badangle

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maxam

can prop size be used to figure engine size? I mean, ziroli tells me 77" should be flown with 18" prop...from there you find engine that swings 18" prop and all is well? is this logic sound?

Maxam

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I am assuming 18" is the scale size (sounds small to me). For flying I would use a prop that loads the engine correctly. Say a 20 x 14 for your 7-77. For disply install a very scale prop. So many people say use a low pitch prop for slow draggy planes like a Stearman. I disagree since these props are aerodynamically ineffecient unless static thrust is used but planes are not static. The engine will pull well at lower settings and sound much more scale. I use higher pitch props even on my slow planes with great success. A 20 x 14 is not an outrageus pitch to diameter ratio. Take a 10 x 6; doubled to a 20x12 close to same blade angle at a given position on a blade. Now an extreme prop like a 20 x 16 or 18 would go ineffecient at slower speeds! Very poor thrust at slow speeds. -Tom

badangle

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Maxam

plans for 77" show quadra 35 or 40cc gas........ziroli says that equates to 18" prop. I don't know quadra so I cant say. Whoever it was I spoke to (think his name was mike) said he flew these engines  when they were sidel...he made me think 77cc put out around 20lbs thrust and was more suited to 87" stearman . 20lbs thrust in a 20lb plane does sound a bit high.. also, is there an issue with structural stress when a bigger powerplant is used than the design calls for? is throttle management all that will keep me from flying the wings off?  

Maxam

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Angle, Seriously the engine will not even remotly "fly the wings off" that plane. Those quadra's and zenoa's cannot swing big props. My 7-70 in my corsair cannot hover!!! Fly well yes! I can explain more with a phone conversation. The airframe will love the lower vibration. Check E-mail

badangle

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maxam
My modeling history is all kit built planes. they all stress not to use bigger power plants and if the plan has 7 inches to back of prop from firewall thats what it must be to perform properly and so on and so on....after calling ziroli and was told no problen in moving firewall or just go with longer engine and seeing videos of planes hopping of the ground at take-off due to big radials in front it now seems the old rules have gone out the window. Imnew at giant scale and new at building without instructions and as I couldnt find a full kit for stearman in size needed i am trying this ziroli plan with wood from national balsa, selected for it weight. I guess the worker at ziroli has me doubting my selection. check answering machine.

EQ1

Hello everybody! Hope you enjoy the easter days!

Being new to this thread I'd like to introduce myself briefly. I have been building an flying model airplanes for 36 years now, with the main interest in aerodynamic and structural design, i.e. building my own planes from scratch mostly. Because I am addicted to the "Golden Era of Air Racing" it was logical to let a long fostered dream come true and build a racer with a radial engine. Searching the internet for information about a suitable engine I stumbled over this thread and my impression was, that it is one of the rare useful ones with thorough information. This encouraged me to buy the EVO 999 recently and I am about to do my first break-in runs soon.

And here it comes: Yesterday, preparing the first run, I started adjusting the valve clearance. With the plugs removed I cranked the engine and was shocked to hear an unusual sound every eights rotation exactly at the same position. It is a clear "clonk" accompanied with a slight resistance while cranking. Now my question: Is this normal, did anyone of you experienced similar things?

Have a nice day! - Olaf

Maxam

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did you adjust a valve way too tight and it is hitting a piston? Unlikely but maybe possible.

j lauria

Maxam,
On RCSB-Show your stuff Heyluc posted on 10/9/2010 pictures of his 87 inch Stearman powered by a Sidel 7-70. The engine size looks almost perfect. It could be a little larger as with an Evolution 9-90. What do you think?
John

EQ1

No, it was before beginning to adjust the valves and the factory setting showed very much clearance in the range of .025 mm compaired to the .01 which is stated in the manual (checked on several rotations). I am wondering whether they really did a test run at UMS for 20 minutes. Now I don't know, should I start the engine or not? Didn't expect to be faced with such a problem ...

Maxam

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EQ1 Return it!!!

slskn

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EQ 1 I know this may sound like a pain in the b*** but maybe you should send it back to Horizon and let them test run for you tell them but something doesn't sound right. Or you can try starting it, and if something does not sound right they do stand behind this engine

EQ1

Thanks for your suggestions. Yes, I was also thinking of sending it back, but I am so eager to let it run and hear the sound. Looks like this sound is not usual and to be on the save side I think of sending it back. Unfortunately, this requires ALOT of patience from me ... But damaging the engine with all the hassle than is not an option. Thanks again, i will post my experience about this later on.

slskn

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Well I am going to put the 7-77 in my Stearman with a 89in. Wing it may look a little small but hope it will do the job, I am sure it is going to be around 28 lbs. Or so ,but if it flies on the wings with just enough power, then it will be just like the full scale. On a continental 220? That would be ok with me.

EQ1

But wait: maybe I should open the engine and see what the problem is. I have a lot of experience in engine dismantling, even large ones from cars, so it should be no problem. Removing the front from the crankcase should reveal the reason, because I assume it is somewhere around the cam ring. Has anyone opened an Evo before?

Reverend

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Nope, but very eager to see you do it

Maxam

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JLauria, I am not a member so they would not let me see the show your stuff! Can you link a picture? -Tom

j lauria

Maxam,
I ahve tried copying image from RCSB and pasting it into this space, it didn't work. I will try E mailing it directly to you. You really ought to belong to RCSB there is a lot on there that should be of interest to you.

I now have plans for both th 77 and 87 inch Ziroli Stearmans. Looking at your pics of the fullsize and and comparing to plans it is apparant that both th 7-77 and the9-99 extend beyond the fornt edge of the cowl. However the 9-99 extending 1/2 inch more all around is closer to scale than the 7-77. Also looking at the Ziroli plan with dummy engine, which I assume he drew to scale, it extends out further than the 9-99 by 1/2 an inch. The dummy engine is 1/4 scale and the airplane is 22.5% scale. My conclusion is the 9-99 is a near perfect fit. The7-77 looks good, but a little small. Ground clearance with the 9-99 should be no problem with any suitable prop on the 87..

I never thought I would ever be contemplating buying an engine this expensive for a model. I hope that the peoblems encountered by Olaf prove to be isolated.

Maxam

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J, I am confident that Horizon will take care of an engine that is not right. I love my 9-90 (99). It is so smooth and cool sounding. If you have read the whole thread, you will have seen that mine has well over 100 flights. Also I am pleased with the XOAR 24x12 black warbird style prop and I use a 20 ounce tank. I look forward to updates on your Stearman as well as Badangle's. Yes you are correct, I must join that scale site. Thank you for informing me of it.
-Tom