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*Official* Foam Board Top Speed Challenge

#81
This is my newest build that I'm hoping to be a little quicker. Was planning to power it with a 4s setup but may go to 5s or even 6s if everything goes well. It has a 30 gram racing quad motor on it for the first few test flights but if it's a stable flyer then it will probably be equipped with an inrunner.
Looks good but for what my 2¢ are worth I’d claim pusher prop planes are more difficult to get high speeds out of. The prop never has clean air.
 
#84
I've heard the same thing but have yet to experiment enough with tractor type delta shapes to compare the differences.
The motor being the rear cuts do
Looks good but for what my 2¢ are worth I’d claim pusher prop planes are more difficult to get high speeds out of. The prop never has clean air.
I would think that with the pushers motor on the rear it enables a design to where the frontal area can be streamlined to cut down on the drag that's induced with the motor up front causing so much resistance. Then there's the turbulent disruption of airflow that the airframe has to contend with from the air being forced over the airframe at all times when the prop is turning. The only downside that I can really see is the fact that the prop is obstructed by the airframe somewhat with a pusher setup. There's ways around that also but I haven't flown anything with a motor pod attached above the airframe to compare any differences. I'm aware that the prop on a pusher makes more noise than a puller but that doesn't seem to make any less thrust in my opinion. I'm also not claiming that my opinion makes much if any difference. It's just what I have observed.
 
#85
The motor being the rear cuts do

I would think that with the pushers motor on the rear it enables a design to where the frontal area can be streamlined to cut down on the drag that's induced with the motor up front causing so much resistance. Then there's the turbulent disruption of airflow that the airframe has to contend with from the air being forced over the airframe at all times when the prop is turning. The only downside that I can really see is the fact that the prop is obstructed by the airframe somewhat with a pusher setup. There's ways around that also but I haven't flown anything with a motor pod attached above the airframe to compare any differences. I'm aware that the prop on a pusher makes more noise than a puller but that doesn't seem to make any less thrust in my opinion. I'm also not claiming that my opinion makes much if any difference. It's just what I have observed.
Another thing to consider to be an advantage with a pusher is that there doesn't need to be any thrust angles incorporated into the setup. Most puller setups need a thrust angle that isn't inline with the airframe therefore reducing the amount of thrust available and robbing the airframe of maximum speed potential.
 

Hondo76251

Legendary member
#86
Interesting points @Claym, fun thought exercise no doubt.

I would like to point out that you sort of, perhaps inadvertently, gave one important clue as to why a pusher isn't as efficient as a "puller."

The fact that it generally makes more noise is an indicator that the prop is powering its way through dirty air. It is turning a small portion of the motors power into noise instead of thrust. Less thrust, less speed, all other things being equal.

It is certainty possible to build a pusher that can perform quite well but i dont think it will ever be more efficient than a similarly designed tractor.
 
#87
Interesting points @Claym, fun thought exercise no doubt.

I would like to point out that you sort of, perhaps inadvertently, gave one important clue as to why a pusher isn't as efficient as a "puller."

The fact that it generally makes more noise is an indicator that the prop is powering its way through dirty air. It is turning a small portion of the motors power into noise instead of thrust. Less thrust, less speed, all other things being equal.

It is certainty possible to build a pusher that can perform quite well but i dont think it will ever be more efficient than a similarly designed tractor.
Pushers will probably never win an award for the most efficient of all winged aircraft and there's folks who dislike the sound of the prop tips breaking the sound barrier on them but to me that just adds to the cool factor of a fast pusher.
 
#88
Pushers will probably never win an award for the most efficient of all winged aircraft and there's folks who dislike the sound of the prop tips breaking the sound barrier on them but to me that just adds to the cool factor of a fast pusher.
To get the prop out into a clean source of incoming air then a pod could be incorporated on top of the fuse somewhere behind the cg. I haven't seen anyone with an example of this on a delta type pusher so maybe it's not worth it for the small amount of performance that it could possibly gain. Will have to look further into this.
 

Hondo76251

Legendary member
#89
Pushers will probably never win an award for the most efficient of all winged aircraft and there's folks who dislike the sound of the prop tips breaking the sound barrier on them but to me that just adds to the cool factor of a fast pusher.
To each his own i guess. Im not a fan of the extra noise myself but i have no room to talk as my daily drivers dont exactly have mufflers on them so I'm clearly not concerned about being obnoxiously noisy lol.

To get the prop out into a clean source of incoming air then a pod could be incorporated on top of the fuse somewhere behind the cg. I haven't seen anyone with an example of this on a delta type pusher so maybe it's not worth it for the small amount of performance that it could possibly gain. Will have to look further into this.
That would be an interesting one to test for sure. All of the "pushers" i have now are mounted above centerline. They certainly do seem to be sensitive to thrust angle and definitely noisy like most pushers. Maybe if you carefully designed a pod to set well above the plane in clean air it would work but, like you said, i doubt it would be a worthwhile difference.
 
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Piotrsko

Master member
#90
You do a pod, and for starters you need to figure out up thrust or down thrust. Behind CG on a rear facing pod, probably upthrust, but how much? Not enough and you guaranteed don't have enough up authority. Too much and it won't fly. You also get about twice the intersection drag, not to mention prop losses from the pod standoff and whatever it's mounted on.

Only reason to use a pod is to keep the prop from contacting something external to the airplane..a Lake seaplane is a good example and you don't see a lot of them
 
#91
You do a pod, and for starters you need to figure out up thrust or down thrust. Behind CG on a rear facing pod, probably upthrust, but how much? Not enough and you guaranteed don't have enough up authority. Too much and it won't fly. You also get about twice the intersection drag, not to mention prop losses from the pod standoff and whatever it's mounted on.

Only reason to use a pod is to keep the prop from contacting something external to the airplane..a Lake seaplane is a good example and you don't see a lot of them
I second this, putting your thrust line off axis is dangerous on high speed/high power aircraft.
 

FAI-F1D

Free Flight Indoorist
#98
Has anyone made any progress in their flying? I'm pondering putting a 7x13 prop on one of my cleaned up Speed Deamons to see what that can provide. Not sure we can get a clean doppler run with it but it's worth a try.
 
#99
Has anyone made any progress in their flying? I'm pondering putting a 7x13 prop on one of my cleaned up Speed Deamons to see what that can provide. Not sure we can get a clean doppler run with it but it's worth a try.
No I don't believe so. I did try modding Grifflyer's unreleased hotliner to have balsa ailerons but I found it very difficult to control on takeoff with a 10x10 prop. Didn't get further than 50 feet. Almost certain I just had my rates way too high though on roll it looked like PIO to me