Ed,

the design (shape) of the prop doesn't directly influence engine power or torque; only indirectly. It does, however, directly affect engine thrust.

Engine power is essentially a product of prop rpm and torque - omega tau. Naturally, proper units must be used according to how one wants power expressed (HP, Watts, etc.). In the absence of torque measurements, there is a way to derive crank power as a function of prop geometry (pitch and diameter) and crank rpm. Using SAE units, brake horsepower can be expressed as:

BHP = (P*D^4*RPM^3) / (1.4 * 10^17)

I won't go through the derivation as it would not only boring but also tedious to write on the forum with the kind of notation one can use. In the formula, P, D and RPM stand for prop pitch, diameter and rpm, respectively.

Using this, I calculated the crank power of the P80 based on the figures you provided.

I think that engine can produce more power than this with a little less oil, more nitro and, of course, a tuned exhaust for the prop desired.

David

Hi David,
He's already going 150mph... How much faster do you think the Arrow needs to go?
Will

Will,

I'd say not much, just another 10 mph... So long as my fingers are not at the sticks!

I'm dead curious though whether the engine can approach 3 bhp given a little more help.

Shawn might have some experience with this as he's managed to get his Rossi's to really turn on an 11x9 prop. Smaller and certainly lighter airframe he was using though for racing.

David

150 mph on the Arrow? Why so fast?

I've never seen a vintage pattern model fly so fast, ever. Not even with the 7 port, piped, OPS gold head up front on an immaculate Arrow, with everything tucked away including a full engine streamlined mask or cowling, and full gear doors. I'm not sure it's doable with the kind of power available from vintage powerplants. Perfectly happy at 110 tho

I did some improvements on the Picco today with good results. I changed the original 8.5mm carb for an OS 7D (10.5mm). This plus 5% nitro got it a up to a very stable 13100 rpm. Will fly this weekend to test it, expecting 7-10 mph more. More important, this eliminated the difficulty while tuning the engine with the Picco carb.

Guys, if you haven't flown a pattern plane at ballistic speeds, don't do it. You'll surely be hooked and unable to leave it.

By the way, getting the Arrow to 150 is not that hard. It is a very clean airframe with a thin wing. My Arrow 40 is doing (GPS on board) 135 with a YS45, 15%, 10x8, tuned pipe. Big brother should do 150 just to keep the sibling's respect!! The 60 Arrow has a Futaba GPS telemetry system on board. The GPS measures horizontal and vertical speed separately.

Any additional suggestions to make it faster are more than welcome.

The OS 7D is a great carb and with the larger throat and a bit of nitro you may be approaching David's 3bhp goal. It will be interesting to discover what the changes do to the top speed as you may be getting close to max speed. I had an Arrow .40 with an OS .40VF which was clocked (radar gun) at 122. The fastest pattern ship I ever saw was Sal Battaglia's YS powered Arrow which may have approached the 150mph figure and he loved to fly loooow!
As for further increasing your speed - more nitro and more prop pitch, less diameter. You may have to re-pitch an APC to get a 10x13 or 14.
good luck and keep us updated!

Yea!

I'm wondering though if at 10.5 mil carb bore, it might not help to fuel inject the sucker. Maybe the carb/engine doesn't need it but it might just increase power slightly. All stock "pumped" engines I'm aware of seem to have increased power spec. For example the RF-P vs the RF. No question the YS's breathe on their 11 mils and fuel metering.

OPS, former company of Mr. G. Picco, used to provide Perry backplate pumps for their engines. Now, they were often sold in conjunction with Perry carbs which we don't want but perhaps a regular separate oscillating Perry pump with backplate pressure feed would improve the 7D as well. I'm not sure how the 7D would cope with pumped fuel - Will? Unfortunately it would require tapping the backplate and if you're not happy with the results, getting a spare plate might be pretty hard. Of course, the tap could be just closed off but still.

20% nitro and drop the oil content to 13-15%. Watch the compression though as it could pre-ignite. You may need head shims.

Although I hate to admit it (Picco rocks!), you could likely also increase the speed with a Jett BSE FIRE 90L.

Here's an account:

[TABLE="width: 610"]
[TR]
[TD="colspan: 2"]Our engines speak for themselves.... and Jett pilots have a lot of good things to say too!
See the Jett Hall of Fame for great application examples
[/TD]
[/TR]
[TR]
[TD="width: 300"]"This is a photo of my Jett FIRE 90L with a 15 cc MACS quiet pipe. The Jett machined test stand is bolted to a pre-fab bookshelf which is in turn bolted to a shop stand. Both were purchased from Home Depot. The shop stand cost about 30 bucks.
The 90L turns an APC 11X7 at 16,200 on Sig Champion 15%. This is significantly better than your advertised numbers for the larger 95L.[/TD]
[TD="width: 300"]On the day I checked the 11X7 I was able to turn an APC 10X10 at 16,000 using the same fuel. On a previous test session a few weeks ago I got 16,300 with the 10X10.

For anyone interested in duplicating the setup the total length from the back of the exhaust spacer to the tip of the pipe is 23 inches. This seems to be optimum as I got no more gain from another 3/8" cut which I put back in.

The engine starts, runs, and throttles perfectly with the most instantaneous response I have ever seen in a glow engine. Overall another fantastic Jett engine!"

Gene Greatti[/TD]
[/TR]
[/TABLE]


he's just tipping the 3 bhp threshhold on the 10x10 with 3.09 [email protected]. 'nough said.

David

I've been looking into a Jett 1.00 LX. Still not sure if the $465 will be worth it. Donations accepted!!!

Regarding the Picco, I foresee no problem in flying with the 7D. I will try some 10% and 15% today on the bench. If we can hit 13,500 on the 12.5 pitch we should be doing some decent speed. I am also working on sealing the nose wheel well. The main gears can be improved a little bit too.

My Arrow 40 achieves the 135mph using several drag-reducing techniques which I will apply on the 60.

The nicest thing though, is that the Arrow is still a fully capable pattern plane. Snap rolls are a neck-breaking experience with LOUD sound effects.

I wondered about the 1.0 but I'm not sure it will be a better fit than the 90 for the intended purpose. You should talk to Dub about it. The bigger the cylinder the harder it is for it to rev so milage may vary.


Jim,

do post a picture of your 40 and do tell about those techniques!

David

Hi David,
The 7D can handle pump supplied fuel, but requires some adjustment to pump pressure. The external Perry pumps work well (at least the crankcase pressure driven ones - I have never used the oscillating variety), but take up some space in the engine compartment where there is typically not a lot available in the classic pattern designs. I am not sure you would see much, if any, increase in power. It is interesting that you mention the OS .61 RF as the unpumped version utilized a barrel type carb with a small throat diameter, but the pumped version used a butterfly type carb (like YS); the only butterfly type carb I have ever seen used on a stock OS engine. The Jett engines are very impressive in both performance and construction. It is basically a custom made engine and I think the price is quite reasonable for what you get. Great customer support for repair or rebuilding even in the event of a crash. They are also very durable even when run extremely hard. Plus they are quite light, I bet the .90l weighs less than the Picco .80.