FP 20 drive washer same as FP 25?

[Matt Brown]

I just picked up an FP 20 from eBay but it is missing the prop drive washer. Tower has FP/LA 25 drive washers in stock. I’d buy one if it will fit the 20. Never had a .20 so no idea on interchangeability. I won’t get the engine till later in the week so I can’t compare yet.

Matt

[Brad LaPointe]

Yup.

Brad

[Gary Dowler]

Matt, almost everything but the piston/crank and possibly the head will swap on the 20&25, and I'm not sure the crank won't too.

What are you going to put it on? I love my 20fp. I replaced a Fox 35 stunt with it and after sorting out an issue with the NV, I haven't looked back. At least as powerful, and at least 25% better on fuel to boot.   Mine started on a Shoestring Stunter, but after that plane died I put it on a Cosmic Wind. 400sq in, 34oz, and its plenty of power.

Gary

[Matt Brown]

Most likely, it will go on my Ringmaster arf. I can’t get a decent run that isn’t sub 4.5/lap.
May build something for it over the winter too.

Matt

[Mark Mc]

Matt, almost everything but the piston/crank and possibly the head will swap on the 20&25, and I'm not sure the crank won't too.

Gary

Crank is the same.  I just ordered a crank for my busted 25LA-S and it is the same part for the 20/25FP and 25 LA.

Mark

[Gary Dowler]

Most likely, it will go on my Ringmaster arf. I can’t get a decent run that isn’t sub 4.5/lap.
May build something for it over the winter too.

Matt

Brett Buck turned me on to the 20FP's.  He suggested a APC 9-4 prop, which I use, and its a great combination.  Launch it at 12K or so and it will run like an illegal during an ICE raid.....LOL!  How light is your Ringmaster?  Im right at 5 sec laps with a 32-34 oz plane.  A Ringmaster that's built light will likely be a bit faster, though you can richen things up and slow it down some.  I think he even suggested the 15FP on a Ringmaster that's built light.

Gary

[Tony Drago]

Gary. What length on the lines.

[Gary Dowler]

Gary. What length on the lines.

60'

[Tim Wescott]

Brett Buck turned me on to the 20FP's.  He suggested a APC 9-4 prop, which I use, and its a great combination.  Launch it at 12K or so and it will run like an illegal during an ICE raid.....LOL!  How light is your Ringmaster?  Im right at 5 sec laps with a 32-34 oz plane.  A Ringmaster that's built light will likely be a bit faster, though you can richen things up and slow it down some.  I think he even suggested the 15FP on a Ringmaster that's built light.

I was doing around 4.8 (I never measured) with a 32-ounce Ringmaster an a 20FP.  If I managed to build a 'ring at a more reasonable weight I think the 20FP would just be too much.  I'd try Brett's suggestion of a 15.

[Target]

I just haven't figured out what different weights on two (of a same design) plane has to do with level lap times...
Maybe it is just me, but once up to flying speed in level laps, I'd just assume each plane on the same length and size lines to fly at the same lap time with the same prop running the same RPM.

In other words, weight shouldn't matter at all until you maneuver, right?

So, this leads me to assume that the heavier planes have to be flown faster to avoid stalling on maneuvers, and THAT is why a heavier one might be flying with a faster level lap time.

Is this a correct assumption?

Also, clearly the lighter the plane is, the faster it will accelerate out of corners, I would suspect, and also hold speed better on vertical up lines.

Is this assumption correct?

Thanks,
Target

[Gary Dowler]

I just haven't figured out what different weights on two (of a same design) plane has to do with level lap times...
Maybe it is just me, but once up to flying speed in level laps, I'd just assume each plane on the same length and size lines to fly at the same lap time with the same prop running the same RPM.

In other words, weight shouldn't matter at all until you maneuver, right?

So, this leads me to assume that the heavier planes have to be flown faster to avoid stalling on maneuvers, and THAT is why a heavier one might be flying with a faster level lap time.

Is this a correct assumption?

Also, clearly the lighter the plane is, the faster it will accelerate out of corners, I would suspect, and also hold speed better on vertical up lines.

Is this assumption correct?

Thanks,
Target

Weight increases drag, which slows the aircraft.  A 747-800 at max take off weight of 975,000lbs simply cannot cruise at the same speed as it can taking off a couple hundred thousand pounds lighter, assuming similar throttle settings. Nor can it reach the same max speed.

[Target]

Hmmm, i guess I'm assuming that then a heavier plane is forced to fly at an increased angle of attack? That's about the only way that i can see that statement working.
Does a heavier wing in a wind tunnel make more drag?

Does a heavier jet in a vertical dive go slower than a lighter one because of increased drag?
I doubt it.

Why add ballast to a sailplane to make it fly faster then? The distance flown is the same, but you get there faster. How do you do that with the drag increase?  Hmmm.

[Dane Martin]

Does a heavier wing in a wind tunnel make more drag?

I don't think that's apples to apples. In a wind tunnel, the wing would be fixed and not propelling itself, rather the wind is being generated to flow over it.

In a sail plane, adding ballast could make the descent faster, making the sailplane fly faster. Flying only DLG, I think that's what happens, but I don't know.

My take on a heavy plane is like having a boat in the water. With everything equal, but you add more horsepower, the boat would over come the water better and go faster. Less weight in the plane is like adding power.

[Target]

But strictly speaking, drag to an airframe isn't increased by weight. The weight is balanced by lift in level flight, just as the thrust is by drag in steady speed flight. If you change one end, it effects the other.
I'm pretty sure the effect of thrust and gravity in a vertical climb will be a bigger factor than the small amount of drag added by a small increase of AoA. But I'm just a glider guy, so i could be wrong!
I'd also be more worried about the necessary increase in turn radius, and associated drag/skidding in that corner with the weight increase, than with added AoA drag in level flight.

To get back on topic, i have an FP20 that i bought from an rc guy. I hope it isn't too abused from lean runs. Should make a fine c/l engine. Sorry for the tangent all and no offense meant Gary.
I just want to make sure i understand WHY certain blanket statements are true. It helps us all to make correct building decisions, when needed.

Regards,
Target (Chris Behm)

[Matt Brown]

While the heavier plane/increased AOA is true, at the speeds and weights we are flying at, the difference in AOA would be essentially immeasurable with only a couple ounces difference in weight. Speed difference would also be negligible in level flight as there is way more parasitic drag controlling the speed compared to drag due to creating lift to maintain flight.

Matt

[Target]

That's exactly what my point was, Matt.
In level flight, probably not much difference in even 6 or 8 oz.
Once the plane starts into manuevers, that's when your towing the drag bucket behind. IMO.