Tag Archives: flying

Adding tip tanks to a PA-28 Cherokee or PA-28R Arrow?

I receive many questions about the fuel systems of Piper PA-28 Cherokees, Arrows, and PA-28-235 Pathfinders. A common question is:

How can I modify my PA-28 to add tip tanks from the PA-28-235?

Thanks for the question. You have a good point, as the PA-28 Hershey bar wing chord is common across the PA-28R Arrow and PA-28 Cherokee variants prior to the tapered wing. Plus, the PA-28-235 and the Cherokee 6 have two 17 gallon tip tanks for a total of 84 gallons. 

Yet, for all of the advantages of these tip tanks, I’ve never seen or heard of them being retrofitted into a non-235 Cherokee or Arrow. I suspect that there are three primary reasons.

1) This modification is a major change and will require substantial engineering and flight testing work. I’m not aware of any STCs available.

2) The plumbing and fuel management systems are substantially different between the tip and non-tip PA-28 variants. Plus, the tip tanks significantly increase the fuel management decision making. The tips have capital and maintenance costs too.

3) The aircraft endurance/range performance in the stock aircraft is equal to or exceeds the normal endurance performance of the pilot and passengers. Additionally, adding 34 gallons of fuel effectively removes 1+ passenger, as you are unlikely to increase the certified gross weight for climb and structural performance reasons.

Given these negatives, how would I approach the installation of more fuel?

1) Sell the Arrow and buy a Bonanza.

2) Selling the Arrow and buying a Lance won’t work, as the larger engine burns substantially more fuel. I burned 9 gph in an Arrow and 14 in a 235. 

2) Add the PA-28-235 tip tanks but *don’t* copy the -235’s fuel system. Rather use a gravity or electrical pump into the existing fuel line, such that you one-way transfer fuel into the mostly empty main tanks. This has the potential to be an easier and safer certification path.

Now for the lawyer statements: 1) I am not advocating this process. Buy the Bonanza and be done with it. 2) I have not and will not indicate the legal, structural, or performance suitability of this process except under contract. 3) I am not presenting myself as a Designated Engineering Representative DER.

The answer really is no unless you have unlimited funds and time.

Wind Clover Airspeed Calibration

The purpose of this page is to develop and distribute a simplified airspeed indicator calibration technique and computer program tool. Calibration from indicated (KIAS) to calibrated (KCAS) is required for certified and experimental aircraft (c.f FAR 23.1323 and FAR 25.1323). There are many techniques and flight test approaches available; however, the mathematics of generating a calibration chart or card can be daunting. This page provides a FREE self-contained airspeed calibration tool for Windows computers useful for subsonic aircraft with minimal calculation and with minimal equipment.

Requirements: You need an indicated airspeed, a GPS with track and groundspeed readouts, a thermometer, and your altitude. You will need to fly three independent headings (approximately 120 degrees apart) for each data point. You will need to download and enter your data into the windclover program.

Non-requirements: You do NOT need any ground references. You do NOT need to know your precise heading or magnetic variation. You do NOT need accurate timing or any clock. You do NOT need to calculate your true airspeed. You do NOT need an aerospace engineering background or on-board flight test engineers or hardware.

Cloverleaf Flight Profile: You will need to fly three lines that are approximately 120 degrees apart (e.g. 100, 220, 320). Maintain a constant heading, altitude, and indicated airspeed. Using your GPS, record your ground speed and track. Enter these data values into heading columns #1, #2, and #3. The program determines the wind direction/speed and the calibration from KIAS to KCAS.

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