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Cowl vs prop size

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Cowl vs prop size

Post  Cribbs74 on Sun Dec 25, 2011 10:59 pm

Opened up my Laird's super solution today. Very happy with the kit! However, I noticed the cowl was huge, too big for a .020 prop to clear and a 6x3 .049 prop gives about 3/4 inches of exposed prop either side of the cowl.

So..... My question is how much of the prop must clear the cowl to achieve adequate thrust? I was wanting to use my tee dee .020 but a 4.5" prop won't clear. My fear is I will have to step up to a .049 but with a span of 24" it may be too much power.

Any ideas?

Also got a DX5E transmitter! Now I need to find a receiver to fit in my mini Spit.

Hope everyone had a good Christmas or whatever you may celebrate!

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Re: Cowl vs prop size

Post  Mark Boesen on Mon Dec 26, 2011 12:17 am

I'm guessing it's a electric kit?
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uhoh

Post  Jaspur_x on Mon Dec 26, 2011 3:22 am

For example, my cox peewee 020 powered radio controlled cub trainer`s cowl only blocks about 1/3rd of the prop blast.

How much distance is there between where the prop is located and the cowl? I mean how far forward of the cowl is the teedee020`s prop going to be?
To allow it to produce thrust it will need some distance for the prop blast to be shoved rearward before it hits the cowl I would think.
24" is not too small for a 049,but is right n the ballpark for an 020. If you decide to go 049, definately run a throttle sleeve or some sort of throttle or be prepared for a pretty fast flight with way more than enough thrust. I have ran 049`s on much less(14") span planes and definately want throttles on anything below 30" for any 049 until my flying prowess returns from its break.

I just ran a teedee051 on a 26" span plane saturday morning and really wish I had throttled back. lol!
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Re: Cowl vs prop size

Post  nitroairplane on Mon Dec 26, 2011 7:21 am

For you spit I would use one of these
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Re: Cowl vs prop size

Post  Cribbs74 on Mon Dec 26, 2011 7:45 am

Mark Boesen wrote:I'm guessing it's a electric kit?

Sorry bout that, Dumas rubber powered kit. Comes with a huge 9" prop.
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Re: Cowl vs prop size

Post  nitroairplane on Mon Dec 26, 2011 7:47 am

Maybe try a 5x2 prop.
Graupner make one.
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Re: Cowl vs prop size

Post  Cribbs74 on Mon Dec 26, 2011 7:50 am

Jaspur_x wrote:For example, my cox peewee 020 powered radio controlled cub trainer`s cowl only blocks about 1/3rd of the prop blast.

How much distance is there between where the prop is located and the cowl? I mean how far forward of the cowl is the teedee020`s prop going to be?
To allow it to produce thrust it will need some distance for the prop blast to be shoved rearward before it hits the cowl I would think.
24" is not too small for a 049,but is right n the ballpark for an 020. If you decide to go 049, definately run a throttle sleeve or some sort of throttle or be prepared for a pretty fast flight with way more than enough thrust. I have ran 049`s on much less(14") span planes and definately want throttles on anything below 30" for any 049 until my flying prowess returns from its break.

I just ran a teedee051 on a 26" span plane saturday morning and really wish I had throttled back. lol!

Not sure about the distance, as It is still in pieces. I could install it with any amount of distance I suppose. Good to hear I can do an .049 if needed. Another problem is getting to the needle valve and attaching a glow clip for starting.
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Re: Cowl vs prop size

Post  nitroairplane on Mon Dec 26, 2011 7:52 am

cribbs74 wrote:
Jaspur_x wrote:For example, my cox peewee 020 powered radio controlled cub trainer`s cowl only blocks about 1/3rd of the prop blast.

How much distance is there between where the prop is located and the cowl? I mean how far forward of the cowl is the teedee020`s prop going to be?
To allow it to produce thrust it will need some distance for the prop blast to be shoved rearward before it hits the cowl I would think.
24" is not too small for a 049,but is right n the ballpark for an 020. If you decide to go 049, definately run a throttle sleeve or some sort of throttle or be prepared for a pretty fast flight with way more than enough thrust. I have ran 049`s on much less(14") span planes and definately want throttles on anything below 30" for any 049 until my flying prowess returns from its break.

I just ran a teedee051 on a 26" span plane saturday morning and really wish I had throttled back. lol!

Not sure about the distance, as It is still in pieces. I could install it with any amount of distance I suppose. Good to hear I can do an .049 if needed. Another problem is getting to the needle valve and attaching a glow clip for starting.

I dunno with a .049 it would be pretty mad so I would not use anything more powerful than a babe bee for sure.
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Re: Cowl vs prop size

Post  Cribbs74 on Mon Dec 26, 2011 7:54 am

nitroairplane wrote:For you spit I would use one of these

Good price on that one. Thanks I may give it a go!
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Re: Cowl vs prop size

Post  Cribbs74 on Mon Dec 26, 2011 7:57 am

nitroairplane wrote:Maybe try a 5x2 prop.
Graupner make one.

Maybe, the cowl is about 5" in diameter. Dumas does have electric conversions for their kit but I want nitro!
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Re: Cowl vs prop size

Post  nitroairplane on Mon Dec 26, 2011 8:01 am

Okay that is really weird.
Come to the chatbox and we can discuss it further.
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Re: Cowl vs prop size

Post  Cribbs74 on Mon Dec 26, 2011 8:15 am

nitroairplane wrote:
cribbs74 wrote:
Jaspur_x wrote:For example, my cox peewee 020 powered radio controlled cub trainer`s cowl only blocks about 1/3rd of the prop blast.

How much distance is there between where the prop is located and the cowl? I mean how far forward of the cowl is the teedee020`s prop going to be?
To allow it to produce thrust it will need some distance for the prop blast to be shoved rearward before it hits the cowl I would think.
24" is not too small for a 049,but is right n the ballpark for an 020. If you decide to go 049, definately run a throttle sleeve or some sort of throttle or be prepared for a pretty fast flight with way more than enough thrust. I have ran 049`s on much less(14") span planes and definately want throttles on anything below 30" for any 049 until my flying prowess returns from its break.

I just ran a teedee051 on a 26" span plane saturday morning and really wish I had throttled back. lol!

Not sure about the distance, as It is still in pieces. I could install it with any amount of distance I suppose. Good to hear I can do an .049 if needed. Another problem is getting to the needle valve and attaching a glow clip for starting.

I dunno with a .049 it would be pretty mad so I would not use anything more powerful than a babe bee for sure.

Well, I would have to use an un tanked engine as I want a little longer flight time. May even consider using my tach race engine. Modified back to stock specs of course. Guess I had better pick up a throttle sleeve and one of those throttled TD carbs just in case.....
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Re: Cowl vs prop size

Post  nitroairplane on Mon Dec 26, 2011 8:16 am

Tack race engine!
In a 24" floaty dumas kit.
I reckon it will rip it apart.
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049

Post  Jaspur_x on Mon Dec 26, 2011 10:45 am

I would run a small/ish prop on an 049 to keep the thrust lower,maybe a 5", or 6x3 if you don`t feel enough thrust when it is in your hand, due to the large cowl.

I wold convert to glow too if it was mine lol.

I wouldn`t thhink the dumas wing would fold up, but it may be way fast with a small/ish span.

I would think a throttled reedie would be all the thrust you will need and then some, my teedee was more than twice what I needed saturday. I should switch to a reedie instead of my teedee,but I don`t feel like it lol!

You may find that nitroaitplane is right, and it be mad fast with any 049.

Maybe go throttled texaco style,I think the texaco went like 3 minutes and used a 7" prop,somebody set me straight if I`m wrong on that Huh...
That may still be faster than you want without a throttle though Flying
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Re: Cowl vs prop size

Post  nitroairplane on Mon Dec 26, 2011 10:51 am

With an 8x4 a texaco will get a good 20 minutes.
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Re: Cowl vs prop size

Post  SuperDave on Mon Dec 26, 2011 11:39 am

Ron:

Once encountered the same problem on an CL Ambroid "Gulfhawk" bipe powered by a Fox 15 RC. Matched the prop to the engine rather than the cowl. Problem was that the larger diameter prop, IIRC, 8X4, didn't have enough ground clearance for the landing gear.

Solution: hand launch.
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Re: Cowl vs prop size

Post  Cribbs74 on Mon Dec 26, 2011 11:55 am

Hhhm not a bad idea. Throttled Texaco, I could even run it un-tanked. Besides the large head is there any diffence than a regular babe bee?
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Re: Cowl vs prop size

Post  Cribbs74 on Mon Dec 26, 2011 12:02 pm

SuperDave wrote:Ron:

Once encountered the same problem on an CL Ambroid "Gulfhawk" bipe powered by a Fox 15 RC. Matched the prop to the engine rather than the cowl. Problem was that the larger diameter prop, IIRC, 8X4, didn't have enough ground clearance for the landing gear.

Solution: hand launch.

The "solution" has nice tall landing gear, so clearance won't be an issue. It comes with a 9" prop. The Texaco just might be the ticket!
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Re: Cowl vs prop size

Post  SuperDave on Mon Dec 26, 2011 12:04 pm

Ron: Dunno, perhaps someone can tell us.
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Re: Cowl vs prop size

Post  SuperDave on Mon Dec 26, 2011 12:51 pm

Ron:

Just referenced the Super-Solution from Dumas. I noticed that it is for rubber-power rather than nitro/RC which calls into question if the airframe can carry the additional weight let alone fly well.

The Ambroid "Gulfhawk" bipe that I mentioned was for nitro/CL and, in competed form,
flew poorly and had the glide angle of a concrete cinder block. Why? Plenty of power but too much weight for the airframe.

Suspect that you might encounter the same problem with the "Solution". Even the kitchen sink can fly with enough power.
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Re: Cowl vs prop size

Post  nitroairplane on Mon Dec 26, 2011 3:35 pm

SuperDave wrote:Ron:

Just referenced the Super-Solution from Dumas. I noticed that it is for rubber-power rather than nitro/RC which calls into question if the airframe can carry the additional weight let alone fly well.

The Ambroid "Gulfhawk" bipe that I mentioned was for nitro/CL and, in competed form,
flew poorly and had the glide angle of a concrete cinder block. Why? Plenty of power but too much weight for the airframe.

Suspect that you might encounter the same problem with the "Solution". Even the kitchen sink can fly with enough power.

I have had over 7 successes converting ff rubber to RC.
Loads of companies but Dumas ones do look a bit lighter.
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Re: Cowl vs prop size

Post  Cribbs74 on Mon Dec 26, 2011 3:57 pm

The Dumas kit will need some beefing up I'm sure as would most rubber designed kits, I imagine some structural mods will need to be done on a Guillows to run an .061.

The wood in the Dumas kit is of excellent quality whereas the wood contained in my Guillows Spit kit was very brittle.

Funny thing is the only difference between rubber power and nitro power on my spit was the addition of a 1/16" plywood firewall..... That was what the guillows kit said to add.... I went a bit further.

So that being said I think the Dumas airframe would handle nitro just fine. Of course I could be wrong........... lol!


Last edited by cribbs74 on Mon Dec 26, 2011 4:12 pm; edited 1 time in total
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Re: Cowl vs prop size

Post  nitroairplane on Mon Dec 26, 2011 4:07 pm

Guillows wood is notoriously bad but all patterns are included on the plans so they can be re made with good quality wood.
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diference

Post  Jaspur_x on Mon Dec 26, 2011 8:35 pm

cribbs74 wrote:Hhhm not a bad idea. Throttled Texaco, I could even run it un-tanked. Besides the large head is there any diffence than a regular babe bee?

Double check this, but I think the diameter of the hole in the intake inside the tank was smaller and perhaps the backplate was a variance too; to stretch out tank run times and fight duration. But I am not entirely certain. Huh...

I would say the kit should be sturdy enough, a lot of the rubber powered kits also had in the instructions that it is intended for rubber power or free flight nitro powered;however you are considering a good bit more engine than would be recomended.

Structurally, you will have to make space inside for the radio equipmet so a little reinforcement to make up for the structure changes would be a good idea,I would.
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Re: Cowl vs prop size

Post  JPvelo on Tue Dec 27, 2011 10:32 pm

I say try it with the .020. Prop blast only happens when the model is standing still. Once in flight the "blast" matches forward velocity. The prop isn't pushing air backwards like a fan, it is pulling the aircraft forward due to it's airfoil cross section that creates "lift" in front of the aircraft.
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