Speed gain from landing gear aft fairings.

[bradp]

So I had my landing gear fairings off for almost a year while I mucked with them forgot about them and had other projects.  I finally reinstalled them and I forgot what I was missing. 

Old KTAS no fairings  ~65% LOP 6500 = 148 ktas

New KTAS with fairings same setting = 153 KTAS.

Not to shabby for a couple of pieces of plastic.

 

[DonMuncy]

Just now, bradp said:

So I had my landing gear fairings off for almost a year while I mucked with them forgot about them and had other projects.  I finally reinstalled them and I forgot what I was missing. 

Old KTAS no fairings  ~65% LOP 6500 = 148 ktas

New KTAS with fairings same setting = 153 KTAS.

Not to shabby for a couple of pieces of plastic.

 

Are you talking about the inner gear doors, or the little fairing type bumps behind the wheel well. (Pardon me if my terminology is wrong.)

[bradp]

The little bumps that reside behind the gear doors.  

[DonMuncy]

1 minute ago, bradp said:

The little bumps that reside behind the gear doors.  

Wow. I would never have guessed they would make that much difference. 

[jetdriven]

The POH says that removing the lower gear doors results in, conservatively, a 5 knot speed penalty. Ive raced mine with the STC'd fiberglass gear doors and with no lower gear doors at all, and its about 3-5 kt.  I have a hard time thinking that lower doors on without fairings is responsible for the same 5kt loss.  but every plane is a little different.

[Hank]

3 hours ago, bradp said:

So I had my landing gear fairings off for almost a year while I mucked with them forgot about them and had other projects.  I finally reinstalled them and I forgot what I was missing. 

Old KTAS no fairings  ~65% LOP 6500 = 148 ktas

New KTAS with fairings same setting = 153 KTAS.

Not to shabby for a couple of pieces of plastic.

 

Wish I could bolt them onto my C . . . . I'd love to be >150KTAS!

[N201MKTurbo]

44 minutes ago, Hank said:

Wish I could bolt them onto my C . . . . I'd love to be >150KTAS!

I don't think there would be a lot of pushback to getting a field approval for that. They are kind of expensive. All you need are three little brackets and pop rivet the rear faring's on.

Oh yea, you would need to remove some material from your existing doors to clear the bump.

[Bryan]

I was just reading last night about the LoPresti speed modifications that were made on the Acclaim. They found one of the biggest speed improvements, outside of the obvious cowl, was the nose gear doors. On my K and most of the pre-Acclaim was the bubble of air it created behind the nose gear so they improved the aerodynamic design of the doors making them more flush.

[Bob_Belville]

Some of the comments above seem to be talking about main gear inner doors while the OP seems to be referring to the nose gear doors. 

Got pics? 

[jetdriven]

41 minutes ago, Bryan said:

I was just reading last night about the LoPresti speed modifications that were made on the Acclaim. They found one of the biggest speed improvements, outside of the obvious cowl, was the nose gear doors. On my K and most of the pre-Acclaim was the bubble of air it created behind the nose gear so they improved the aerodynamic design of the doors making them more flush.

M20TN as well. 

[Guitarmaster]

It seems the biggest gains are achieved by cleaning up the underside. This makes sense since it is a high-pressure area.

I'd probably gain 5 knots by getting rid of my antenna farm on the belly!

Sent from my XT1585 using Tapatalk

[bradp]

OP (me) was referring to the little fiberglass bumps that sit behind the main gear lower doors on a 1977 J.  I flew again last night - 65% LOP at 6500 feet and got the same 153 KTAS - so it’s definitely a gain of something.  

 

I made molds from these these little bumps and unfortunately have lost them in our move to NC- they’re around somewhere and when they turn up I’d be happy to make a set for whomever wants.  

 

Brad 

[Hank]

2 hours ago, bradp said:

OP (me) was referring to the little fiberglass bumps that sit behind the main gear lower doors on a 1977 J.  I flew again last night - 65% LOP at 6500 feet and got the same 153 KTAS - so it’s definitely a gain of something.  

 

I made molds from these these little bumps and unfortunately have lost them in our move to NC- they’re around somewhere and when they turn up I’d be happy to make a set for whomever wants.  

 

Brad 

Ain't moving fun? I'm in Town #22 now, many too small to call "cities." We won't go into the "home" count!   

My annual is coming up in January, I'll talk to the IA and see what he thinks. He drives a couple of hours up to the hangar or I'd ask him sooner . . .

[Skates97]

5 hours ago, bradp said:

I  made molds from these these little bumps and unfortunately have lost them in our move to NC- they’re around somewhere and when they turn up I’d be happy to make a set for whomever wants.  

 

Brad 

I would be interested in learning more about these... 

[Tommy]

10 hours ago, bradp said:

OP (me) was referring to the little fiberglass bumps that sit behind the main gear lower doors on a 1977 J.  I flew again last night - 65% LOP at 6500 feet and got the same 153 KTAS - so it’s definitely a gain of something.  

 

I made molds from these these little bumps and unfortunately have lost them in our move to NC- they’re around somewhere and when they turn up I’d be happy to make a set for whomever wants.  

 

Brad 

A picture is worth a thousand words

Just saying! 

[DXB]

 I'd swear that removing my fat cylindrical Whelen belly flasher at annual recently gave me a perceptible increase of a couple knots. Kinda goes with what people are saying about drag on the belly. It might very well be a delusion, but I had expected zero benefit from it, so at least it's not confirmation bias . 

 

[bradp]

@Tommy here you go. 

 

 

[ShuRugal]

Does anyone have a closeup of the gear retracted on Vintage models?  I met an Arrow pilot at the airport on Saturday who had a bunch of speed mods done, and in his case the trailing bumps behind the wheels were the only ones that made a significant difference.

[jetdriven]

On 11/27/2017 at 9:31 AM, bradp said:

OP (me) was referring to the little fiberglass bumps that sit behind the main gear lower doors on a 1977 J.  I flew again last night - 65% LOP at 6500 feet and got the same 153 KTAS - so it’s definitely a gain of something.  

 

I made molds from these these little bumps and unfortunately have lost them in our move to NC- they’re around somewhere and when they turn up I’d be happy to make a set for whomever wants.  

 

Brad 

How are you measuring true airspeed?  Also what is the temperature of the 146 knots and  what was the temperature at the 153 knots because these airplanes are faster in cold weather

[INA201]

I'm certainly no expert on aerodynamics but I'll go ahead and chime in.  Someone with more scientific knowledge may can help with this, but doesn't turbulence created behind an object cause a fairly significant drag to otherwise smooth airflow? 

[EricJ]

5 hours ago, ShuRugal said:

Does anyone have a closeup of the gear retracted on Vintage models?  I met an Arrow pilot at the airport on Saturday who had a bunch of speed mods done, and in his case the trailing bumps behind the wheels were the only ones that made a significant difference.

On an Arrow the wheels stick out quite a bit, more than I expected, anyway, when retracted.   It doesn't surprise me that cleaning that up a bit makes a difference.    I don't think the wheels stick out on a Mooney nearly as much, and on the J model the "spat" thingies are much narrower and mainly deal with the hub hardware rather than the whole tire sticking out in the breeze.

LoPresti makes the "spats" for the Arrow, there are some good pics here:

http://www.loprestiaviation.com/speed-spats-1.html

This is the Arrow that I used to rent, and it had them installed.   It was still kinda slow.       

Edited November 28, 2017 by EricJ

[Bob_Belville]

5 hours ago, ShuRugal said:

Does anyone have a closeup of the gear retracted on Vintage models?  I met an Arrow pilot at the airport on Saturday who had a bunch of speed mods done, and in his case the trailing bumps behind the wheels were the only ones that made a significant difference.

This is the best shot I found. '66E with the brake caliper reversal mod.
 

[bradp]

Byron - you’re right about the temperature.  The last few flights it was freezing or a couple above celcius.    It’s measured off of the good old IAS - there’s an error between that and CAS but should be precise but not accurate (the G5 is off from the IAS by 3-4 it’s).  Should be fairly apples to apples minus the temperature factor.  

[jetdriven]

57 minutes ago, EricJ said:

On an Arrow the wheels stick out quite a bit, more than I expected, anyway, when retracted.   It doesn't surprise me that cleaning that up a bit makes a difference.    I don't think the wheels stick out on a Mooney nearly as much, and on the J model the "spat" thingies are much narrower and mainly deal with the hub hardware rather than the whole tire sticking out in the breeze.

LoPresti makes the "spats" for the Arrow, there are some good pics here:

http://www.loprestiaviation.com/speed-spats-1.html

This is the Arrow that I used to rent, and it had them installed.   It was still kinda slow.       

The plastic pieces behind the landing gear doors on a J model simply fair at the door into the wing after the tire. If you were to forget these or leave them off then you have a 4 inch wide piece it’s an inch high that doesn’t touch the wing but it’s not like the same amount of drag as  if the whole door wasn’t there

[Captnmack]

My F model has one installed...I bought this F last summer and while I was prepping to ferry it home I noticed it was missing the Spad on the left side and once had the lower gear doors installed but not now and nowhere in sight. I asked the original owner but he did not recall when or even who removed them. I called Dan at Lasar and asked him about the Spad and the doors. He said that without the lower doors installed the Spad made no difference and would actually cause drag. He also mentioned that, as mentioned in other posts, unless you have an electric gear, retracting the gear must be performed ASAP as the wind loads above 80kts make it very difficult. I think that is why they were removed and forget about landing on unimproved runways. Also replacing the doors would run about $1400/pair plus the Spad.