Cowl vs prop size

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.

For you spit I would use one of these

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

Sorry bout that, Dumas rubber powered kit. Comes with a huge 9" prop.

Maybe try a 5x2 prop.
Graupner make one.

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.

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.

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.

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.

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

Good price on that one. Thanks I may give it a go!

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!

Okay that is really weird.
Come to the chatbox and we can discuss it further.

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.

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.....

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

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

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
That may still be faster than you want without a throttle though

With an 8x4 a texaco will get a good 20 minutes.

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.

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?

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!

Ron: Dunno, perhaps someone can tell us.

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.

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.

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...........

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

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.

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.

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.