Speed mods redux

griff390

This topic has been batted around on a number of Piper forums recently, and I see it here from time to time, so I thought I'd share my experience. I cross posted something similar on another forum.

Aircraft:

• 1978 Warrior
• 160 HP
• stock propeller
• "soda can" tail fin strobe
• step installed
• exposed (bare) landing gear
• no flap seals
• no aileron seals
• no VG's

Basically factory stock except for wing root fairings and upswept (lighted) wingtips. I don't know if the wingtips are even considered a speed mod, but I needed new wingtips and I wanted them lighted, so that's what was purchased.

Installing the factory wheel pants and strut fairings increased the cruise speed almost exactly per the Piper POH. The POH states 7 kts increase in speed. I saw a solid 6, and that was in a shallow climb, so the Piper engineers were right on the money. The wing root fairings added a knot or 2, and the wingtips seemed to help more in climb than speed, but by far, the biggest and best speed mod was rigging, hands down. Our Pipers are notorious for being out of rig, and mine was the poster child. Building the rigging tool is very simple. My IA and I found the rigging on my plane was nowhere near the factory spec. Proper rigging increased cruise speed a good 8 knots alone. When totaled up (wheel pants, wing root fairings, rigging), the airplane picked up 14-16 kts. Needless to say, I was very pleased with the speed increase, and it didn't cost me anything other than a few hours of work. That's a great return on investment.

Prior to the mods and rigging, I usually had difficulty reaching my flight plan speed of 100-105 kts. Now I flight plan for 112-115 kts and exceed it without pushing the engine at all. A few weeks ago on a cross country, I measured TAS. I was at 65% power, and cruising only 3 kts off the book speed for 75% power. I took a short video as proof. The extra knots are a nice buffer against headwinds.

Back when he was alive, I spoke with Art Mattson numerous times. He had a lot of knowledge for increasing performance in PA-28's. He admitted that many of the "speed mods" did not actually increase speed much, but helped more in control authority (aileron and flap) and climb rate. I have a number of friends who installed his mods on their aircraft, and they agree. Interesting note: the faster your plane is (prior to mods), the less of a difference the mods make in trip time.

Some of the discussions regarding this topic on other forums have become...shall we say..."animated"? Seems the 2 sides are heavily divided. I stay away from the fray and don't choose a side, I just present the numbers. I also have the break even (return on investment) equation. If anyone is interested, I'll be happy to post the numbers and the equation.

Scott Sherer

Having owned 8 planes I've had speed mods on most of them. Back in the day I had Lopresti speed mods on my Warrior and Seminole. Then I installed Knots2U mods on my Senecas. This winter I'm installing speed and other mods on my Turbo Arrow III. I'm currently guessing that I'll have mods on my plane from all three companies but we'll see how that turns out. I'm looking to raise my cruise speed to 170 knots at cruise altitude and 75 percent power. The numbers will tell later this winter.

Harley Kleemann

I've heard anectodal evidence that the aileron gap seals such as Knots2U sells are prone to freezing to the ailerons during cold weather. Scott, you've had experience here, is this indeed a fact?

griff390

What pilot doesn't like going faster or saving fuel (or both)?.

I've seen posts from both sides of the argument, and both have very valid points. The one side is not against going faster or saving fuel, but have doubts about the claims of speed for each mod or balk at the monetary break even point; e.g. if I gain 4 kts, how many hours do I need to fly to recover the cost of the mod? I've also seen arguments that state if you really want to go fast, buy a faster airplane. The choice is purely up to the owner/pilot.

What I often see is at the same time the mods were installed, the owner also found the rigging was out of spec and had it fixed, or installed a new engine or propeller because it was at TBO (which often is the reason the airplane was in the shop in the first place). Unfortunately, when additional variables which directly influence the speed of the aircraft are added, the core impact of the speed mod alone cannot be accurately measured. I'd like to see a double blind test performed with each device individually (aileron seals, flap seals, etc.) while all other variables are held constant. The effectiveness of that mod could then be determined and would be backed up by empirical data. In the real world, that can be a challenge because from one test to the next, it's rare that wx conditions such as DA, wind speed and direction, etc. all remain identical.

I'm an engineer, so I need solid proof, but I'm also a typical pilot, so I'm always in favor of additional speed and lower fuel burn!

Scott Sherer

Having had aileron gap seals on three Seneca's and one Seminole and flying in all kinds of icing conditions over 30 years, I've never had an icing issue with any of the mods that I've put on my planes. I've lost vacuum pumps (prohibiting me from popping boots), I've lost prop boots creating vibration and an engine shutdown, I've had boot timers fail, vanitrol heaters fail at 14,000 ft creating a 10 degree cabin and a myriad of other things but no mod/ice (or any other) problems over thousands of winter hours in 30 years.

Scott Sherer

As for solid proof that speed mods work: No disrespect meant to a respected engineer but your desire for measurable info isn't why speed mods exist or are sold. For those of us that buy them (and I'm one of those over many airplanes), we do it because we want to. If we get any speed out of them, so much the better. It's an emotional thing...

griff390

No disrespect taken Scott. I always appreciate your candor and honesty.

I know a number of the members here are engineers. We tend to gravitate toward aviation, much like we pilots gravitate toward hot rods, HAM radios, steak and whiskey, etc. (recalled from one of our earlier discussions).

Those of us who are engineers are too aware that we must provide calculations to prove our designs are sound, and have empirical data to back it up. We're also trained to only deal with facts and keep emotions out. I learned that lesson early on in engineering school, and I'll share it.

[Begin lifelong lesson learned] After an exam was graded and returned, one of our fellow classmates received a zero on one of the more difficult problems. After an entire page of calculations, his answer was perfectly correct, except for one literal that had a minus sign when it should have been a plus. Zero points, no partial credit. The rest of us lobbied hard to the professor on our classmate's behalf that he deserved partial credit (we also wanted it in case we were in a similar situation!). Our position was that he was only off by a minus sign. The professor stopped us and asked "Do you know what a minus sign means? It's the difference between having a million dollars and owing a million dollars." The classroom went silent because there was no arguing that logic. He went further; "Suppose when you graduate, you go and work for a company designing machines to keep people alive in hospitals, and someone dies while hooked up to one of your machines because you were off by a minus sign." Right then was when the responsibility of my chosen profession sunk in. 40+ years ago, and it was one of those life lessons that I've never forgotten. It also made us all aware to be very precise in our calculations. [End lifelong lesson learned]

So now you know why us engineers need proof and are void of emotion . Back to the subject (with no emotion ), I've flown a couple planes that have gap seals installed. They provide better control authority and climb rate. I installed the wing root fairings on my plane because they help smooth out a high drag area which adds a little speed and are a very good bang for the buck.

I agree Scott, if you base your decision to install speed mods on how long it will take to pay back, then it's going to be a long wait. If you base it on climb performance, then you're going to be happy, and if you base it on emotion, then you're going to be happy no matter what.

I've done the speed mod calculations for a number of aircraft including the absurd numbers for the SR-71 Blackbird. If anyone wants to see the numbers, I'll be happy to publish them.

Cheers!

Scott Sherer

HI Griff, so what would happen with a Blackbird? Now you have my curiosity up, lol.

Harley Kleemann

I think it's more along these lines...people like to customize their ride, be it a bicycle, motorcycle, car, boat, or aircraft.

Scott Sherer

Hi Harley, right you are! I wasn't thinking quite along that line but I think you nailed it!

griff390

Agree with the thoughts about customization.

But you also asked for the numbers, so here they are; (you may want to pour some Irish Whiskey in your coffee before reading. Make it a double).

Here are a few real world scenarios, and 1 unreal scenario. In each example, the speed mods add 4 KTS, and the calculations show the difference in time the mods make on a 300 and 500 mile trip. 500 NM is near the fuel endurance of a Warrior II (roughly Chicago to Atlanta with reserve), and beyond the endurance of most people's bladders, but the data is presented for comparison. Note the faster your stock airplane is, the less difference in time the mods make.

Scenario 1
Aircraft = Piper Warrior
Cruise speed (no mods) = 112 KT
Cruise speed (with mods) = 116 KT
Difference in time for 300 NM trip = 5 min 54 sec
Difference in time for 500 NM trip = 9 min 23 sec

Scenario 2
Aircraft = Piper Arrow
Cruise speed (no mods) = 128 KT
Cruise speed (with mods) = 132 KT
Difference in time for 300 NM trip = 4 min 26 sec
Difference in time for 500 NM trip = 7 min 10 sec

Scenario 3
Aircraft = Piper Aerostar 700P
Cruise speed (no mods) = 264 KT
Cruise speed (with mods) = 268 KT
Difference in time for 300 NM trip = 1 min 1 sec
Difference in time for 500 NM trip = 1 min 42 sec

Scenario 4
Aircraft = Lockheed SR-71 Blackbird
Cruise speed (no mods) = 2,196 MPH
Cruise speed (with mods) = 2,200 MPH (presuming our little fiberglass speed mods would stay attached at Mach 3+ and/or not be incinerated)
Difference in time for 300 SM trip = 14 thousandths of a second
Difference in time for 500 SM trip = 24 thousandths of a second

If you feel compelled, here are the equations (below) to calculate how much time and money you can save with a speed mod, and how long it will take to pay back the cost of the mod. I'm only focusing on fuel burn because items like tie down/hangar, maintenance, insurance are fixed costs and will remain the same no matter if mods are added or not.

Your current yearly fuel cost = [hours flown/yr] x [fuel burn (gal/hr)] x [avg fuel ($/gal)].

Your yearly fuel cost with mods = ([current hrs flown/yr] x [current avg cruise speed] / [cruise speed with mod]) x [fuel burn (gal/hr)] x [avg fuel ($/gal)]

Example:
You fly 60 hrs/yr
Your plane burns 9 gal/hr
You cruise at 110 kts (no mods)
You cruise at 116 kts (with mods)
Average fuel price is $3.50/gal.

Your yearly fuel cost (no mods) is 60 (hrs/yr) x 9 (gal/hr) x 3.50 ($/gal) = $1,890
Your yearly fuel cost with mods is (60 hrs/yr x 110 kts / 116 kts) x (9 gal/hr x 3.50) = $1,792
Your mods saved you $98 in fuel per year, and 3.1 hours of flight time.

The final step is to take the cost of the mod and divide it by the amount of savings/year. Example: if a mod costs $2,500.00, and you save $150.00 per year, it will take just under 17 years to break even, but the more hours you fly per year, the faster it will pay off, also the higher fuel prices are, the faster it will pay off. Your mileage will vary.

Here are some examples;

HRS FLOWN PER YR ........... 50
KTS NO MODS .................. 110
KTS W MODS .................... 116
AVG FUEL $/GAL .............. $3.75
FUEL BURN GAL/HR .......... 8.5
CURR FUEL COST/YR ........ $1,593.75
FUEL COST/YR W MODS ... $1,511.31
FLIGHT HRS SAVED/YR ..... 2 hr 35 min
FUEL SAVINGS/YR ............ $82.44

HRS FLOWN PER YR .......... 60
KTS NO MODS ................. 110
KTS W MODS ................... 116
AVG FUEL $/GAL ............. $4.00
FUEL BURN GAL/HR ......... 8.5
CURR FUEL COST/YR ....... $2,040.00
FUEL COST/YR W MODS ... $1,934.48
FLIGHT HRS SAVED/YR .... 3 hr 6 min
FUEL SAVINGS/YR ............ $105.52

HRS FLOWN PER YR .......... 60
KTS NO MODS ................. 110
KTS W MODS ................... 118
AVG FUEL $/GAL ............. $4.00
FUEL BURN GAL/HR ......... 9.0
CURR FUEL COST/YR ....... $2,160.00
FUEL COST/YR W MODS ... $2,013.56
FLIGHT HRS SAVED/YR .... 4 hr 4 min
SAVINGS/YR .................... $146.44

HRS FLOWN PER YR .......... 90
KTS NO MODS ................. 110
KTS W MODS ................... 120
AVG FUEL $/GAL ............. $4.00
FUEL BURN GAL/HR ......... 9.0
CURR FUEL COST/YR ....... $3,240.00
FUEL COST/YR W MODS .. $2,970.00
FLIGHT HRS SAVED/YR .... 7 hr 30 min
SAVINGS/YR ................... $270.00

Scott Sherer

Thanks Griff. You've done an amazing job on this and I actually enjoyed reading it! Thanks much and I'll have another double!

griff390

Opening a new bottle for you right now.

Harley Kleemann

Well, who wouldn't want to shave 24 thousandth of a second off their enroute time?

Now I have to think about a glass of 18 yr old Laphroaig...

Scott Sherer

18 years old? I'll be right there!

Harley Kleemann

Scott, if you make it to EAA Airventure in 2021, I will bring a bottle along...we could toast to the memory of Bill Piper!

Scott Sherer

That'll work1 I'll be there if there's a "there", lol.

griff390

I'll join you and will bring a nice bottle also. And I'll leave all the spreadsheets and calculations at home.

Scott Sherer

Drop up to our EAA chapter at Racine ( Chapter 838 at KRAC) sometime. We have a simulator and a bar, lol. And it's 16,000 square feet

griff390

Simulator and a bar? Sounds like 8 inches bottle to throttle.

Scott Sherer

Roger that!