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Q
Topic Author
Posts: 988
Joined: Sun Sep 24, 2000 10:29 am

Why are spoilers on some aircraft and not others?

Fri Aug 07, 2020 3:25 pm

Hi Y'All Folks,

I noticed most jets are using spoilers on the wing, It's very common. I noticed most propellers do not need spoilers exception Dash 8 has spoilers. It's rare. Why propellers do not need spoilers what was the reason. Is that propeller cause not even flying if spoilers on? I am not sure. Anyone can explanation, please?

Thanks,

Q
Last edited by atcsundevil on Fri Aug 07, 2020 5:01 pm, edited 1 time in total.
Reason: Edited title for clarity
 
VSMUT
Posts: 4428
Joined: Mon Aug 08, 2016 11:40 am

Re: Aircraft have spoilers questions

Fri Aug 07, 2020 3:44 pm

Q wrote:
Hi Y'All Folks,

I noticed most jets are using spoilers on the wing, It's very common. I noticed most propellers do not need spoilers exception Dash 8 has spoilers. It's rare. Why propellers do not need spoilers what was the reason. Is that propeller cause not even flying if spoilers on? I am not sure. Anyone can explanation, please?

Thanks,

Q


We do have spoilers on turboprops, but they are normally only used for roll-control. Turboprops land so slowly and on so short distances that it isn't relevant. High-winged aircraft also "suffer" less from ground-effect, so have less tendency to float. Finally, the variable pitch propellers: Propellers in fine pitch (as they will be on landing) create a massive amount of drag.

Although that said, the new ATR 42-600STOL will have spoilers on touchdown.
 
bigb
Posts: 1125
Joined: Fri Nov 07, 2003 4:30 pm

Re: Aircraft have spoilers questions

Fri Aug 07, 2020 3:45 pm

The need for spoilers are determined by the aircraft ability to remove lift from wing in order to create more tire friction to assist with braking. Props have a special device that assist with that ability by creating drag. That drag the the propellers create slows the aircraft down thus decreasing the need for lift. It’s the propellers themselves. Most props tend to be positioned in the most forward high settings for landings in order to help creat additional drag for the landing unless it was a engine failure then the prop would be in the lowest pitch settings (feather position) for the least amount of drag. On top of that, the wing properties on pro aircraft tend to not be as sleek as sweptwing jets unless is a SE prop like the Pc-12, Mooneys, Cirrus. I get into that in a bit.

Jets don’t have propellers to help create drag and on-top of that, their wings are much cleaner thus making very difficult to remove lift from the wings even at slower air speeds. Spoilers give jets the ability to dump all of the lift of the wings immediately.

When looking at landing speeds, most jets have approach/landing speeds about 120 knots and up depending on weight. Where as you bigger turboprops are in the 90-100 knot range. Big difference.

Finally, you will also see spoilers on props, usually those in need of roll control or is available as an option on those have clean wings (Pc-12, Bonanza, Monneys, Cirrus).
 
Redbellyguppy
Posts: 219
Joined: Sat Apr 01, 2017 3:57 am

Re: Why are spoilers on some aircraft and not others?

Fri Aug 07, 2020 8:24 pm

Jets are super super slippery, by design. We need drag devices since it isn’t always practical to slow by configuring. The turboprop I once flew had five bladed 114 inch props. If i put condition levers flight and power to idle it would slow in a real hurry. Think of how much drag a 114 inch circular piece of plywood would produce and it’s kind of like that...
 
EssentialPowr
Posts: 1702
Joined: Wed Sep 06, 2000 10:30 pm

Re: Why are spoilers on some aircraft and not others?

Sat Aug 08, 2020 4:25 am

Some rather awkward responses... props and turbo props for the last 50 years are designed for a short runway, shorter distance, lower altitude mission because they are cheaper/more flexible to operate In those situations. A 5-6 bladed propeller is essentially non functional above 28000 or so feet. As an extreme, the TU 95 shows us that blade counts have to increase with increasing altitude. So all this dictates for propeller driven aircraft an essentially straight but efficient wing, which further offers and dictates lower V speeds, cruise speeds, approach speeds, accelerate-stop distances, etc. Spoilers are generally not necessary given the flat plate drag from the propeller(s).

A jet is designed for higher altitudes with corresponding higher speeds achieved essentially with swept wings, and with the exception of the A400 and TU 95, turbofan/jet power plants. Spoilers provide drag capability for high speed swept wings efficiently, as they also assist with roll control in many applications (737). Spoilers are used in rejected take offs, landings and of course in flight regimes. When stowed they offer negligible drag.

Consider the early RJ days; for example an ATR-42-500 compared to an ERJ 135/145 IAH to CRP. The ATR burned half the fuel of the ERJ for almost identical block times. Currently, in a 737-900ER for example on visuals to LAX, controllers want 250kts until about an 8 mile final. In a no wind condition, full of people with 7500 lbs of fuel it will happily stay at 250 knots coming down, clean with the exception of the spoilers being 3/4 or so deployed. If carrying more fuel, full deployment of the spoilers will be necessary, then if the a/c is still a tick fast, gear down then flaps sequencing starting at 250kts or less. Approach speeds for a bone stock (non ER) 900 start at about 150kts. They’re fast....

Cheers
 
Max Q
Posts: 8415
Joined: Wed May 09, 2001 12:40 pm

Re: Why are spoilers on some aircraft and not others?

Sat Aug 08, 2020 7:47 pm

There are a few turboprops with spoilers that are not just used to enhance roll control but function symmetrically for lift dump after landing


These are primarily aircraft which require STOL performance


The Dash 7, A400 and I think the Dash 8 have them
The best contribution to safety is a competent Pilot.


GGg
 
Lpbri
Posts: 223
Joined: Tue Sep 27, 2016 7:18 pm

Re: Why are spoilers on some aircraft and not others?

Sun Aug 09, 2020 12:46 am

F-100s did not have wing spoilers but had a tail speed brake. Lift dumpers were wing mounted but we're ground use only.
 
Max Q
Posts: 8415
Joined: Wed May 09, 2001 12:40 pm

Re: Why are spoilers on some aircraft and not others?

Mon Aug 10, 2020 5:41 pm

Lpbri wrote:
F-100s did not have wing spoilers but had a tail speed brake. Lift dumpers were wing mounted but we're ground use only.



I think that’s the same as the DC8, you could use idle reverse in flight on the Douglas however !
The best contribution to safety is a competent Pilot.


GGg
 
jking629
Posts: 2
Joined: Thu Jun 16, 2016 5:44 pm

Re: Why are spoilers on some aircraft and not others?

Mon Aug 10, 2020 6:10 pm

EssentialPowr wrote:
A 5-6 bladed propeller is essentially non functional above 28000 or so feet. As an extreme, the TU 95 shows us that blade counts have to increase with increasing altitude.


In what sense is a 5-6 bladed propeller non functional above 28,000 feet?

It seems to me that there are plenty of aircraft with 4-5-6 blades that routinely fly above 28,000 feet. For example, the Piaggio P.180 Avanti (5 blades) has a service ceiling of 41,000 feet, and the Beech King Air 350 (4 blades) has a service ceiling of 35,000 feet. Looking at historical aircraft there's the Supermarine Spitfire Mk VII (4 blades), a high altitude reconnaissance model with a service ceiling of 45,000 feet.
 
EssentialPowr
Posts: 1702
Joined: Wed Sep 06, 2000 10:30 pm

Re: Why are spoilers on some aircraft and not others?

Mon Aug 10, 2020 9:27 pm

jking629 wrote:
EssentialPowr wrote:
A 5-6 bladed propeller is essentially non functional above 28000 or so feet. As an extreme, the TU 95 shows us that blade counts have to increase with increasing altitude.


In what sense is a 5-6 bladed propeller non functional above 28,000 feet?

It seems to me that there are plenty of aircraft with 4-5-6 blades that routinely fly above 28,000 feet. For example, the Piaggio P.180 Avanti (5 blades) has a service ceiling of 41,000 feet, and the Beech King Air 350 (4 blades) has a service ceiling of 35,000 feet. Looking at historical aircraft there's the Supermarine Spitfire Mk VII (4 blades), a high altitude reconnaissance model with a service ceiling of 45,000 feet.



Of course there are turboprops with 4 blade configurations that are certified to fly in the upper 30s to FL410 but that is not the normal operating environment for most turboprops, specifically those used as airliners. By non functional I’m implying a greatly decreased climb rate for these aircraft at the upper range of their altitude envelope; an operator routinely using a King Air 350 or P180 at FL350/410 is not typical.

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