"1/2 A" & "1/8 A" airplanes These are the small ones...more popular now than ever.

MDS F2A 2.5cc

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Old 06-05-2015, 11:02 PM
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combatpigg
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What do you think will be the winning prop if you put the MDS on a small delta..?
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Old 06-06-2015, 05:15 AM
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Good question - based on the speed trainer write up, somewhere around 5.5 x 5, 5.5 x 6 or so.

  1. Propeller. The best speed was achieved with a Master Airscrew 7x5 S-2 G/F Nylon Gray Propeller cut to 140 mm (5.5 inches) diameter. With this prop the engine was turning about 30,000 rpm in the air. I suggest starting with 6 inch diameter and cutting the prop until the engine pipes up. Too small propeller will turn a lot of rpm with no thrust. We also tried more pitch (up to 6.5 inches) but this did not result in faster speed.



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Old 06-06-2015, 06:00 AM
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Hi MJD,
Glad you are having fun!
As a side note, my friend Frank, who I got the engine from, has spilt the beans...
The day we tried to run that engine... How many years ago?
Was on a 'Shoppers Drug Mart' methanol and 'gummed' Castor oil mixture !

Keep us posted...
This is a really cool thread, with lots of Worldwide information...

Cheers,
Dave'crosscheck'Fallowfield
Maac 6437
Unabashed Combat Team
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Old 06-06-2015, 07:19 AM
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Originally Posted by MJD View Post
Good question - based on the speed trainer write up, somewhere around 5.5 x 5, 5.5 x 6 or so.

  1. Propeller. The best speed was achieved with a Master Airscrew 7x5 S-2 G/F Nylon Gray Propeller cut to 140 mm (5.5 inches) diameter. With this prop the engine was turning about 30,000 rpm in the air. I suggest starting with 6 inch diameter and cutting the prop until the engine pipes up. Too small propeller will turn a lot of rpm with no thrust. We also tried more pitch (up to 6.5 inches) but this did not result in faster speed.



I liked the G-2 5.5 x 5.5 and also the E-8 5.5 x 5.75 with the open exhaust Zalp .15
IIRC, one of these two props had chunky blades that resisted breakage [but your piped engine might not like as much].
I'd test them on the ground with a big fan to force air at the engine. Hose down the area to keep the engine from sucking in dust, too.
Some of the Eliminator props listed in this size range did not have enough meat at the hub to mount to a .15, so beware.
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Old 06-07-2015, 06:54 PM
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The Graupner speed 6x5.5. cut down is one possibility. I have a 5" dia version I'll try on the stand. I used that prop for setting up the pipe on the OPS .15, worked out perfectly in the air on the full 6x5.5.

Annoying the neighbours at 8:00 this evening: https://youtu.be/KqhHc34eySM

This heavy stand doesn't move on a rough surface, but these are Al bleachers, need a clamp..
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Old 06-07-2015, 06:58 PM
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Hmm.. pull plug heat on a pretty new Nelson HD and the rpm drops and it starts complaining about being rich - pull a head shim?
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Old 06-07-2015, 10:40 PM
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Yes, that is a symptom of low compression.
At some point the actual flight prop has to be bolted to the engine and fired up. This is what the compression needs to be set for.
The "bench prop" is just to get a few minutes of heat controlled parts conditioning. If the engine feels good, it's time to tune for the flight prop now. Whatever size prop is considered small for a .15 speed engine. I think a 6 x 4 that's rated for the rpm would be a safe bet to launch a small delta for the first flights.

Last edited by combatpigg; 06-07-2015 at 10:56 PM.
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Old 06-07-2015, 11:35 PM
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Hi MJD,

Put a pair of servos and elevons on the test stand... and I'll hand launch it for you !

I am pretty sure that engine came with extra head shims, and we put them in.
Thicker than beer can aluminum...
The Russian/English instuctions were confusing and hillarious at the same time!

I figured it was built for 10 second FF runs. ?
Seems to like the bigger pipe volume...

The SWAT team would be here within minutes, if I dared to bark that puppy, here in the GTA !
(GTA=GrosserTorontoArea)

Thanks for making beer come out my nose Mike!

Cheers,
Dave'crosscheck'Fallowfield
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Old 06-08-2015, 12:00 AM
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That was enjoyable Mike I read 29,492 rpm
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Old 06-08-2015, 05:02 AM
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That's about what it read when I decided to kill it. It wasn't completely at peak, you could hear it clean up and surge a little when I pulled the line.

Yep - a combat 6-4 GF prop would be a good start, pretty much what I had in mind. From there start reducing diameter and adding pitch - the 5.25 - 5.5 x 5 area sounds about right.

Dave - yeah, there are shims there. I dropped in the Profi head button designed for AMA speed (10%) and the deck clearance looked about right with one of them pulled so that's where I started. Seems there is a bit too much volume yet.
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Old 06-08-2015, 08:51 AM
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The APC 6.3 x 4 ought to be just right to break the engine [and the plane] in....[.why didn't I think of that sooner..?]
It should be good for 30,000 rpm or more.
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Old 06-08-2015, 09:29 AM
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I did think of that prop, I was thinking it might be too much blade area for a speed engine so haven't run it yet.
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Old 06-08-2015, 11:13 AM
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The more narrow blade 6.5 x 3.7 combat prop might spin up more with added thrust.

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Old 06-08-2015, 11:29 AM
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Yes, the combat prop looks even better.
APC simply does an amazing job of catering to our needs.
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Old 06-08-2015, 12:48 PM
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Since that F2D guy is nearby in Toronto, should be no problem snagging some FG combat props locally to try out. I need to place an online order with APC sometime, low on pylon props and whatnot, so I should look at some of the APC props that might be of use. I'd like to end up on a 5" or 5.5" prop running in the 30's for the cool factor.
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Old 06-08-2015, 03:36 PM
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That's the best idea yet.
Be prepared for high acceleration out of your hand though..!
If the model isn't trimmed...not much time to react. It'll be 50 feet away before you can blink.
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Old 06-08-2015, 03:50 PM
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They have nice thin blades, perfect for this type of engine. I wonder if this thing has much more, or any more, moxie than a contemporary F2D engine. Whatever.. it has a pipe on it and it sounds great.
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Old 06-08-2015, 04:00 PM
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They have nice thin blades, perfect for this type of engine. I wonder if this thing has much more, or any more, moxie than a contemporary F2D engine. Whatever.. it has a pipe on it and it sounds great.

I think those APC props would drag it down way too much, doubt it would stage. It homed in on about 27,600 - 28,000 on the old skinny MDS pipe with a huge stinger outlet, and feels like it really wants to run 30+ now.

Might be smart just to whip up a small hershey bar shoulder wing sport speed model with side mounted engine, rather than a delta. In other words, a 26-28" span version of the Profilactic with the fuselage wrapped around a Jett 4oz tank.
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Old 06-08-2015, 04:14 PM
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The delta is less work, I think.
I wouldn't get too crazy with seeing how small I could make it, 28 inches sounds good to me. A Junior Demon..Demon Jr.
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Old 06-08-2015, 05:59 PM
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The 26" Demon already exists, but it is more than enough airplane for a .15, it was a floater with the .21 case overweight OPS .15. I'd go to 23-24 for this,but needs a center bay fuselage deep enough to bury a Jett 4 oz tank.
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Old 06-08-2015, 06:38 PM
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Is there a way to use a pair of Hayes 2 oz rectangular tanks...plumbed in series...?
They would be slim enough to fit behind the engine and under the pipe.
The Twin .020 thread has me thinking like I know enough about plumbing to be dangerous.
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Old 06-09-2015, 03:29 PM
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Funny, thinking alike are we? I was laying out 3 and 2 ounce Hayes tanks the other day, considering a rear 2oz and forward 3oz in the Mini Contender I'm converting to .15 power. The 3oz drops nicely into the forward compartment, and the 2 could sit on the radio shelf behind. But I think I'll stick to 3oz.

A pair of 2's would make a nice slim fuel compartment for the MDS.
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