Saito 82. You dont have to use the power; but when you need it to save your can, it is nice to have. Plus you get to have a bigger prop.

Part of my hesitance about putting the 82 in is that it has a poor reputation among Saito enthusiasts. It uses the same case as the 72 but has a larger bore. People (including the past president of Saito) have said this causes vibration. I've run the engine on a stand but never had it in a model. In terms of running it on the stand, I recall having problems keeping the idle steady.

But I'll put it back on the stand and have another look. I like the idea of having a larger prop (which is more weight up front). As you can see on this chart, the Saito 72 and the Saito 82 are very close in most ways.

http://www.saito-mfg.com/Adobe/singl...ifications.pdf

BTW, I still haven't had a chance to fly my ARF. The wind kept everyone on the ground except for one guy who decided to fly his large Corsair (with a Saito 180). The model just barely made it down on one piece. A couple of minutes into the flight something happened and once it was on the ground we could see that the both blades of the (wooden) prop had shattered and that the violence of this seemed to have done something to one of the spars (on the opposite side of the wing seen striking the ground on landing). It would have been foolish for me to maiden my ARF in this wind.

Oohhh that stinks. At least he made it down though. I had a saito 82 and don't recall much in the way of vibration. It ren great for me for quite a while. No complaints. If it were me, I'd give it a shot. I certainly wouldn't have done a maiden in that wind either.good luck when you do get her in the air.

Frankly, I'm amazed the prop didn't rip the engine out. One blade was missing a large chunk and the other blade was split all the way from the hub to the tip. I should add that the pilot did a great job and was even able to recover the model after the wind nearly flipped it on landing and was able to achieve a nice roll out.

Anyone ever heard of a prop just coming apart in the air?

Back to the topic of power for my Snipe, after a number of repairs my Puppeteer actually weighed almost exactly the same as the Snipe and had just about the same wing area. Initially the Puppeteer had a Saito 56 and that was very sluggish...or rather I should say, it was always just barely flying. When I upgraded to the Saito 62 it was great. I'd even say perfect. But the Snipe has a lot more drag to it.

Only prop I ever saw come apart in the air was a guy who was so cheap, he thought he could glue a prop back together. Note to self; NEVER, AND I MEAN NEVER, GLUE A BROKEN PROP . You would think everyone knew this, but that guy didn't.LOL.

Gluing a prop; what a horror.
Reliable is better than pure power. If the 72 is a better runner, use it. Out of the box engines and scale models should not meet. That is why planes like Ugly Sticks are so valuable. A new engine needs a couple of gallons before it is seasoned. There should be no questions about an engine to make it a quality airplane like the Snipe.

Just wondering if you have tried any other prop pitches to see how they might affect overall performance? If you're flying at full throttle with a low pitch it might be worth trying. Of course this could result in faster landing speeds than your used to on the first few attempts...a very reliable low idle would be desired.
I read in one of the threads here lately that good starting point is to make sure the engine has at least 20-25% pull in pounds of the "all up weight" of the aircraft.
Now this may just mean to "get airborn" ( not sure) I would think your 72 has enough pull it as it obviously does...But as Doc says "more than enough power" is great to have.

Put the 82 on the stand (again) and had uneven success. It initially started right away with the top end roaring away at 10,900 which I adjusted down to 9,700prm. Then I brought it down toward idle and only managed to get down to the mid-3,000s before it died. I had started with the idle set screw in the "factory default" position, which for the Saito is supposed to be flush with the exterior. I had to screw this in a least another full two turns (well below the flush position) before I could get an idle around 2,700.

During the run there is certainly a lot of visible vibration at full rpms. The whole engine is a blur. And I noticed the tip of the glow plug vibrating even more. After I shut it down, I tightened the plug but when I tried to restart I found there was no compression at all! So I took out the old plug and put in another. The compression returned. This engine has a LOT of compression. Far more than any other Saito I've owned. In fact, even after clearing for possible hydrolock, when I tried to start it again the starter motor wouldn't turn the prop.

So far this does not inspire a lot of confidence.

*****

Good news is that it turns out the Rx battery wasn't dead after all. I just needed to bind the new Tx with the Snipe's Rx. The previous Tx was the one with the broken wire that led to the destruction of my Puppeteer. I had transferred all of the Snipe settings from the old Tx to the new Tx. But I think I messed up the alieron/flaperon settings for differential. I'll have to redo that.

It is meant to be a powerful motor. Saitos have a nack for vibrating when not 100% broken in; especially on the low end. They have to be broken in well, so the low end can be as lean as tolerable; the only way to get rid of the low vibe. Running the 72 along with it could not hurt; it should be much better than the smaller engine no matter what.

The 82 is not exactly "new from the box." I've had it on the stand before...quite a lot. But is it fully broken in? Who knows. The vibration seems much worse at the top end than the bottom end. I'll keep working with it. I stopped today, because it just wouldn't start anymore. I couldn't get the propeller to turn over with the starter motor (using a brand new 12 volt car battery).

There's really no hurry on the Snipe. It's been sitting around for several years. A few more months won't make any difference. BTW, regarding the bubbles on the lower wing undersurface, it occurred to me that I might be able to carefully iron these flat and then put on a fresh layer of clear coat. If not, then I'll carefully cut off the bubbled "paint" (actually UV+stain) and try to match the color as best I can.

*****

Just tried that and, no, it won't "iron down" but applying the iron does a good job of removing the bubbled areas, revealing the white solartex underneath.

I went ahead and removed the 72, in part because I need to put some wood screws into the engine mount. The mount consists of ply slotted into the firewall and epoxied to the beams (also slotted through the firewall) but the epoxy has cracked and there's some wiggle room, which is never good on an engine mount. So I'll see if I can slip some new epoxy into the crack and then put two wood screws in on each side to secure the ply to the beams. The engine is mounted to the ply plate.

Also, now that the 72 is out, I can compare it directly with the 82 on the stand.

Wing area on the original Snipe was 271sq.ft. Therefore 1/6th scale is 271X4=1084sq.in. or about 7 1/2 sq.ft

Martin

Martin, that looks close to my calculation on the last page (of about 1,200). Your number is probably right, which means that my wing loading is closer to 20oz per sf.

That's a floater by anyones standards.
Doc

I was wondering about that. These wing loading numbers mean nothing to me. What counts as a lightly loaded WWI model?

A little better success to failure ratio on today's engine tests. The good news is that the 72 performed admirably on the stand (high 9800, low down below 2500). It's lucky that I decided to pull the engine because all four of the backplate bolts were loose and one had actually vibrated almost all the way out.

I'm starting to think that the extreme vibrations I'm seeing during runs may be partly due to weaknesses in my (commercially produced) wooden stand.

Next I put the 82 back on the stand. I noticed that the idle set screw on the 72 sticks out and so I set the idle screw on the 82 to approximately the same position. The engine started right away (as it did yesterday, albeit with a few backfires) and revved up to 10500 at full throttle. Again I adjusted this downwards to 9600 but it seemed to drift upwards into the 9700-9800 range. Then I brought it down and it was holding an idle at 3000 but would die below that.

I made another small adjustment to the idle set screw but than couldn't get the engine to turn over again. I think this is a problem with my starter and the rubber cone...and maybe heat on the thrust washer. It's like it loses all traction after a few starts and at that point, I just called it quits.

Wing loading on your average trainer like say an Avistar or similar will generally be in the 16 to 18 oz range. On my 1/4 N 28c1 it weighs 16.5 lb and the wing loading is right at 23 oz psf. the 1/4 SE 5a weighs 23.5 lb and the wing loading is 23.54 oz psf. The 1/3 scale N28 c1 weighs 39 lbs fueled and the wing loading is 29.95 oz psf. Lots of "heavy iron" WWII models wing loading goes as high as 40 oz psf or even more. The bigger a model is the more it will tolerate before it becomes a snap risk at slow speeds. The volume of a 1/3 scale model is greater than twice the volume of a 1/4 scale model where 1/3 is only about 8.5% larger than 1/4 in simple terms. There are things called Reynolds numbers that I dont pretend to understand but they are relative to airfoil efficiency and ability and as scales change so do the Reynolds numbers and the change is logrythmic. It's all very mathmatical and as I said beyond my ken but at 20 oz rest assured your airplane is quite lightly loaded and would prolly fly very slowly. Got washout? That helps with slow flight also as the tips of the wings stall later that the roots and soften the break. Oh yeah and biplanes actually dont get to use all of thier wing area because of the effect of the two wings being close together and the upper wing causes the lower wing to be less effective. I dont usually give that too much consideration but some say only consider 80% of the area on a biplane. It's all part of the show.lol But like I said the Snipe is a floater. Next time you have it flying find some altitude and slow it down and fly around doing level manoevers, turns, banks, maybe a soft wingover at a low throttle setting and see how well it handles at slow speeds you may find out it's really fun to fly. Just do all this a couple of mistakes high. Also knowing an airplane handles well at slow speeds makes landing MUCH less traumatic. Enjoy.
Doc

"It initially started right away with the top end roaring away at 10,900 which I adjusted down to 9,700prm. "

That sound to me like not enough prop. I have never had a 4 stroke that would top out at much above 9000.

Les

Les, I've never had a Saito that didn't turn at least 9,800. In fact, they all turn 10,000+ but that's totally maxed out. Nevertheless, you might be right about needing a larger prop. There's a 13/7 (I think) on there now but I could go to a 14/6 or even 14/8.

Luckily, I have a 14/6 APC sitting around. The additional 75g up front doesn't hurt either. :)

A real Snipe Replica in Australia is ready to fly. The one chronicled on The Aerodrome.

With scale projects I usually go for the biggest prop that does not seem to lug. 14/6 seems about right.

I've repaired wood props for both models and man carrying planes with no failures yet.

More break-in/testing of the Saito 82a. This time using the 14x6 APC prop, which is definitely better. At full throttle I was getting around 9,300-9,400rpm. It wouldn't go higher...which is maybe OK. I'm still having trouble getting a stable idle below 3,000.

Mostly, I just ran fuel through the engine with the throttle set in the mid-ranges. Lots of smoke, lots of oil...and the engine cooled down quickly after the run. I also checked the fuel consumption/run time for one full tank at 6,200rpm and that turned out to be just a bit over 5 minutes. The tank I use on the stand is maybe about 1/5 smaller than the tank in the Snipe (which I can't remove without removing the wings and no larger tank would fit anyway). So that gives maybe 6 minutes at 6,000+ if I use the 82...with no safety margin. I should compare the fuel consumption with the 72 with the same setup.

The other minor step forward was to repair the loose engine mounting beams with a bit of epoxy and a couple of screws.