AlexL

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Dear All,

I have recently inherited a Ziroli PT17 built by an old friend. It was done in RCAF colour, hence, with the desigator of Boeing PT27.

Anyway, a true TOC quality, but when I put the plane on a scale, that's where the trouble surfaced. It weights 23 lbs, way above the recommended 16-17 lbs as detailed in the plan set. It has a Zenoah G38 with spring starter upfront, and dummy rotary engine.

I have since removed the dummy engine and the lead weight secured in the tank depart, and it now weighs 19+lbs, but my problem now is the tail-heavy balance. I had moved the G38 and extended it 1/2 inch forward, but it is not helping, it is still very tail heavy.

It might after all, remain a hangar queen, I hope not. It is a piece of Canadian history when Canada committed to train all the CommonWealth pilots, using the PT27 before they transition to Spitfire, Hurricane, or other warbirds.

Any thought on this? Anyway to lighten the tail a bit without major operations, or just fly the damn thing at 23lbs. I just hate to loose it on the first landing which I imagine, would be at a very high speed so that I wouldn't stall it.

Thx in advance,

Alex

geoardsog5

My Feedback: (31)

Hi, Al. It may not be the lead sled that you think it is. Figure out the wing area and wing loading, with it balanced so that it is slightly nose heavy. These big scale bi-planes have a lot of wing area to carry the extra weight. John R.

www.rcaircraftworks.com

AlexL

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Dear John, Thanks for the motivation. The plane has 1725 square inches of wing area equals 11.98 square feet.

With a weight of 23 lbs equals 368 oz. That is 30.7 oz per square foot, very heavy wing loading. I will be comfortable flying it under 20 oz per square which is still high by a lot of flyers in my Club.

Any other suggestions?

Thx,

Alex

The_Wreck

My Feedback: (40)

It will be fine at 23 lb. The cubic loading is 8.9 oz/ft3. This is the same as a 50cc aerobatic plane that weighs 17 lbs. Slightly better than a 28lb aeroworks 35% extra 260.

Do some research on Cubic loading, it is a much better indicator of how light a plane flies.

I bet it is a floater, might be a little light on power with a 38 but it should fly scale.

AlexL

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Dear John,

That's a huge encouragement, will try to put everything back together, and hopefully fly it before the falls. Are we at falls now, I think we are, I remember they announced the over of the Summer couple of weeks back, what can I say, senior moment.

Thanks for the info. Will report back.

Alex

XTRA230

My Feedback: (10)

Hi Alex
Nice plane to inherit definitely well constructed would be a shame to have it as a hangar queen I Have been looking at getting one down here in Aus for some time now But no luck yet missed one by a day but I will keep looking I also agree with John A bit bigger engine would be nice Maybe G62 It would also eliminate some of the lead you have in the front.
Rob ...

Chad Veich

My Feedback: (60)

I would just like to concur with what has already been posted regarding the weight. On a model this size 30.2 oz/sq foot wing loading is not bad at all and I believe the model will perform very nicely at 23 pounds. I certainly would not hesitate to fly it at that weight. I also think the G38 will provide plenty of power for better than scale performance. Just my .02 cents of course.

AlexL

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Thank you guys, really appreciate the kind encouragement. It is getting cold up the true North, so it probably be next year before I mainden it. I guarantee you that it will not be sitting around.

Take care,

Alex

Edwin

My Feedback: (2)

Dont worry about the weight. I'm assuming its the 77" ws. Mine weighs 20lbs. I switched engines from the one in the picture to a DLE30. I had to use a 1/4" x 8"dia steel plate (plus a little more) on the firewall to get it to balance. It flys fine and is actually a little over powered. Mine is balanced on the top wing where the lower wing leading edge lines up with the top wing. Flys great at that CG. I also changed the incedence on the top wing to -1.5deg. Ziroli uses +1.5deg. I flew it Ziroli's way and to tell the truth, if flys fine that way. I'm just annal about how I set up my biplanes. They all are -1.5 on the top wing. The only difference is which wing stalls first.
Edwin

AlexL

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Edwin,

Amazing, that is how my PT17 looks like now, without the dummy radial engine. The DL30 is a good choice, but for now, I will try to fly it stock without altering too many things.

The negative incidence is a plus (no pun intended) for me. My Pitts Python has similar set up too, and now it doesn't pitch up when I throttle up, will check my upper wing incident and will report back.

Happy landing,

Alex

gafur

I built a 77 inch pt17 from Ziroli plan. It is 19 pound, but it is tail heavy. Engine is DLA 32 with a prop. 18*8. I made just one flight. Engine is very suitable for the plane. But because of the wrong c.g. flight was a bit difficult. This sunday I am planning another flight with correcting the c.g. I will also change the incidence of the top wing, according to the advice of Edwin, thanks
ihsan gafuroglu

AlexL

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Dear Gafur,

Very interesting post. Keep us posted.

Thx,

Alex

Edwin

My Feedback: (2)

Gafur,
One other thing to keep in mind when trimming, my elevator has about 1/4" down elevator trim to fly straight and level. I've had two other biplanes trim that way and they both (being scale) flew fine that way. Just something to watch out for.

Mine is finally complete. I have a cowl on it which really dresses it up. Since I'm running a single cylinder engine it just didnt look right with the engine exposed like that. Putting the cowl on changed the tune on the carb so I had to drill an access hole for the carb needles and move the ignition switch. I didnt want to do that, but, oh well. She's flying very good now, nice and slow, very predictable. I have dual rates setup, but I really dont need the low rates. It slows down a LOT when you go to idle so I would carry about 1/4 throttle or so until you're about ready to touch down, (at most about a foot or so above the ground). You'll love it, once trimmed, its very predictable.
Edwin

AlexL

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Edwin,

Does that make it a Super Stearman?

I was actually thinking of doing that. I mean putting a cowling upfront, so that it still looks somewhat scale, hiding the extension of the engine - to help balancing without adding too much nose weight.

Alex

Edwin

My Feedback: (2)

No not really. A Super Stearman has ailerons on both wings. This one was still in military colors. Naturally I cant find the picture. I'll post it when I find it.
Edwin

dadragon

I have never seen a ziroli PT 17,I know he has a PT 19 stearman,was the 17 a much earlier kit that he had?

Edwin

My Feedback: (2)

Ziroli doesnt list a PT-19 on his current web site. The PT-19 is a mono wing trainer. Hostetler does a good one. The PT-17 is the biplane trainer.
http://www.ziroliplans.com/zirolipla..._frameset.html
http://www.hostetlersplans.com/fairchild.html
Edwin

s3nfo

My Feedback: (14)

PT-17 Stearman
PT-19 Fairchild

dadragon

Yep;Got my numbers mixed up,either change glasses or change drinks on weekends.

Edwin

My Feedback: (2)

Yeah, my wife is always riding me about getting my tang all tonguled up.
Edwin

s3nfo

My Feedback: (14)

Haven't started on my PT-17 yet, but it was a cold, rainy weekend here in San Diego, so I did whip out the Ziroli Continental 670 engine kit

Edwin

My Feedback: (2)

Wow, that looks nice.
Edwin

geoardsog5

My Feedback: (31)

Edwin, Great advice on the top wing incedence set-up. Jack Strickland, who designed a 1/4 scale Stearman & competed in aerobatic contests with it, advocated the neg top wing set-up and I supported him. We were both run off of another Stearman build thread by the Thread owner, a "cyber" charactor - who insisted that the top wing incedence had to be positve as per the full size Stearman.
I set up all my bipe builds with neg. top wing incedence - they fly great in this configuration. Regards; John R.

smkrcflyer

I got a 77" wing Ziroli PT17 kit that I will be starting soon. I will be using a Saito 325R5 for power. I'll be watching this thread for tips and ideas. This will be my first build without instructions.

aeroscale

Here's mine. It's actually Nick's prototype from years ago which I stripped and recovered. 21 lbs, originally flown with a 5 cylinder O.S. 300 radial. Currently G38 powered. No fireball but very scale looking in flight, actually flies very much like the full scale....lazy aileron rolls, slight dive required for loop entry.
Fun airplane!

Rich