ForcedAeroMotive: SuperCharged DA40

[Tommy]

Just a quick note. After experiencing several times the climb performance cold weather affords, (it's been a really cold winter this year) just the performance gain in climb alone a supercharger will provide will be a welcome change.

[Antoine]

Since we are all waiting impatiently, allow me a slight thread creep: if we could add a de-iced prop to the supercharger package, it would make a very nice "get-out-of-jail" package for that inadvertent icing -encounter. I typically escape down because there is too little climb rate to go up, but life gets really miserable under the low cloud base in rain and fog...
A strong climb rate and an ice-free prop would make the option "on-top" much more viable.

[carym]

Since we are all waiting impatiently, allow me a slight thread creep: if we could add a de-iced prop to the supercharger package, it would make a very nice "get-out-of-jail" package for that inadvertent icing -encounter. I typically escape down because there is too little climb rate to go up, but life gets really miserable under the low cloud base in rain and fog...
A strong climb rate and an ice-free prop would make the option "on-top" much more viable.

Antoine,
I understand and agree with the "get-out-of-jail" concept. That is why I chose a FIKI plane (having encountered ice that almost brought me down in my unprotected C310). However, I still hate ice and I get out of anything more than trace-light ice as soon as I can (this is just my fears and not based on rational judgement). But, at least on this side of the pond, icing tends to be more severe at the tops of the clouds than at the bases. Therefore, when I am in icing conditions that I need to escape, I will go down rather than up because I don't want to enter a situation where my de-icing can't handle the more severe ice accumulation when climbing and at a lower airspeed. Rather than prop ice, I am more worried about elevator ice and a tail stall. I use the app "SkewTLogPro" to help determine where icing is likely to occur during my pre-flight planning.

Don't take this as a criticism, but just as some additional thoughts about icing, icing encounters, and ways of avoiding the dangers. I think of that TBM who thought he could outclimb the ice late last year and ended up stalling when he neared the top of the clouds.

[CFIDave]

Cary: Thanks for the tip on the SkewTLogPro app. I didn't know about that app, so I got it and tried it out. Nice.

I've found the ability to climb in icing conditions can be quite useful. In those cases where I'm cruising up high in the bright sunshine and the clouds rise up to put the aircraft into cloud tops full of ice, I immediately ask ATC for higher to climb back into the sunshine.

Of course in this situation you may eventually have to descend through potentially icy conditions, so in a DA40 (without de-ice) I'd be more likely to descend instead of climb if I know there's warmer or clear air below. But having a supercharged DA40 gives you more of an option to climb out of icing.

[BRS]

Since we are all waiting impatiently, allow me a slight thread creep: if we could add a de-iced prop to the supercharger package, ....

Hi Antoine (and everyone),

Wow, so you want deice too? Ha, aren't dreams wonderful. Never stop dreaming that's how this project got started. Someone else will have to tackle the deice issue though. If we were to add deice I think the collective patience of the diamond community and the FAA would be quickly exhausted. Perhaps something like "never-wet" (never-ice?) will be invented.

Our next round of testing should start the first week of April. It is possible that all of our flight testing (except one) could be completed. But past experiences tells me not to hold my breath. So many things must happen with out glitch. Our longest delays, but in all fairness not all, continue to be bureaucratic. The exception, and last flight test, will be the climb-cool-test which Rod forgot to mention in his last communication. For this we are going to have to wait until the ambient temperature is near 100ºF. It is an interesting test where we will have to climb using only 4 qts of oil with T/O flaps at 67KIAS up to 16,400. It's a real challenge.

During the last flight test I learned some things. We did engine shut downs, throttle slams, and operations at reduced power. Engine shut downs at 16,400' (and below) were a non-event. We (FAA test pilot and I) turned off the fuel selector until the EGT's showed the engine was not making any power. Recovery only required turning on the fuel selector. Didn't even need the fuel pump. Next we cycled the throttle from Max power to idle then back to max power. This, like all the other tests was done at various altitudes. Lycoming specifies not to do this at a rate faster than 4-5 seconds (stop to stop). What was interesting is that we found that going from idle to max power faster than this rate could cause a prop over-speed. Lesson learned - be gentle on go-arounds when punching in the power. This can also happen when restarting the engine in flight (ie. if you run a tank dry), it's best to pull the throttle back some before restarting. The last test was to pull the power back to 13" while at full rich at 16,400'. We had figured that without the help of the supercharger at this altitude that the engine would flood out. To our delight it ran just fine, though at reduced power.

Disclaimer: These tests were all done under controlled conditions. Don't try these on your own as they are not normal procedures.

I'm sharing this information, for your encouragement to continue to be patient, and for you to benefit some from what we have learned.

Keep dreaming.

[Antoine]

cary: no bad feelings at all - I can only bow to your experience and wisdom. We are fundamentally NOT de-iced and going for the "on top" option should be a very carefully weighed decision, hot prop or not.

Now that Brock has jumped in, I will limit this debate to get back on topic.

Thank you for the update Brock. I can imagine that the climb test will stress the hell out of the system. 4 qts of oil !?! I never ever fly with less than 6. But OK, I understand what the FAA wants you to prove.

(And no - I was not expecting you/ Rod to do the prop de-ice thing. I have good contacts at MT and maybe they would look at it...). Let's just start a separate thread if someone wants to continue debating this.

Keep the good work coming. And thank you for being one of very very few people who are actually doing something for the enhancement of 1'000 + DA40s out there. (Yes this was a call to Diamond).

[BRS]

Now that we are "back on topic" (thanks Antoine) I'll give you an update.

After what seems like months of effort we finally got back to flight testing. I'm excited to report that we had a very productive few days last week. In fact we managed to fly ALL of the remaining flight tests. However, that does not mean that we are finished, so try not to get too excited. The test data is being evaluated, reports created, and the data must be submitted to the FAA. When / IF the FAA accepts all the data then I'll (or Rod) will be sure to let you know. That will be time to celebrate.

Even still, after the flight tests are accepted we still have more work. Detonation testing must be done, as well as, possibly, such things as noise and vibration analysis. There are other tasks as well.

I'm looking forward to getting the final numbers especially the performance related stuff. I will share with you "unofficially" that during our take-off tests, which were done at 2800 feet, the full gross take off test seems to be 4 to 500' shorter than the AFM charts indicate. We expect to be closer to the AFM charts at sea level but increasingly better than the AFM charts as the takeoff DA increases.

All this to say, our little supercharger project is very much alive, and though there will still be a few hurtles, the finish line is in sight. Thanks for your continued encouragement.

[BRS]

Do you have any color on how difficult it is to keep CHT under control with the supercharger? On warm days I struggle to keep CHTs under 390F even with the mixture full rich and IAS >100 kts. When there is a strong inversion layer that basically becomes impossible at any decent climb rate. So my concern is how the stock DA40 cooling will handle the normalized HP >5k DA. Does the added power enable higher IAS cruise-climb? What is your experience so far?

Here is what I have learned about keeping CHTs cool. First of all my CHTs stay <400 on this plane, depending on FF, it's the oil temps that are the limiting factor. Our worst case "FAA torture test" was to drain the oil then add back 4 qts (minimum oil). Next we took off with an OAT of 100˚F (actually 102˚ in our case) and climb to 16,400' (or until temps stabilize) with T/O flaps and 67 knots the whole way. We were not allowed to exceed any mfr redlines. Don't try this at home. The max CHT (30" & 2400 rpm) was about 420˚ and the Max oil temp was 237˚. This is about as hot as I ever want to get but then again this was a torture test and I doubt anyone would fly like this. This is done full rich up to 8500' which is about 20 gph. I believe the Stock DA40 will push up to 17 gph max. BTW - as I recall, our temps stabilized well before 9000' and started decreasing but we continued the test to 10,500.

The key to cool cylinders in climb are two fold. First, make sure you have plenty of fuel flow. I believe some DA40s might be lacking here. I use enough fuel to keep the EGTs around 1150 on climb. That's cool but it works. Of course in cruise you can use much less fuel because you are fast and not loaded in a climb. Second there are a lot of air leaks in most planes. Start by removing your top cowl and looking carefully at the marks left from the baffle material. Where it is black it is sealing. Where it is not black or worse you see kind of a faint spray pattern then you have a leak. You can also look at the baffle material. It will be worn where it touches the cowl - this is good. Where the seal is new looking is where it is not sealing. It takes very little leakage to make a significant difference so be a little OCD about it. Most front and aft baffles have a wavy scalloped shape and don't touch on the low points. We took RTV and filled in the low spots, covered it all with plastic wrap and put the cowl back on while it dried. The sides baffles are made up of two overlapping pieces (on my plane). I found that in the middle above the cylinders one was a bit taller than the other keeping the lower one from sealing. Have your A&P carefully trim them so they both make good contact with the top cowl. Next there are many leaks where the fiberglass touches the engine especially near the case halves fore and aft as well as around and in grommets etc. Seal all that stuff up. You get the idea. Lastly (bonus point) I have learned there is a considerable difference between running 2700 rpm and 2400 rpm. So consider 2400 rpm for cruise climb on hot days.

My personal limits are 400˚&< on Climbs and 380˚ &< in cruise and more than 240˚ in descents. This is based on my reading etc. I have no trouble keeping within these limits.

[Antoine]

Here is what I have learned about keeping CHTs cool. First of all my CHTs stay <400 on this plane, depending on FF, it's the oil temps that are the limiting factor.

Second there are a lot of air leaks in most planes. Start by removing your top cowl and looking carefully at the marks left from the baffle material. Where it is black it is sealing. Where it is not black or worse you see kind of a faint spray pattern then you have a leak. You can also look at the baffle material. It will be worn where it touches the cowl - this is good. Where the seal is new looking is where it is not sealing. It takes very little leakage to make a significant difference so be a little OCD about it. Most front and aft baffles have a wavy scalloped shape and don't touch on the low points. We took RTV and filled in the low spots, covered it all with plastic wrap and put the cowl back on while it dried. The sides baffles are made up of two overlapping pieces (on my plane). I found that in the middle above the cylinders one was a bit taller than the other keeping the lower one from sealing. Have your A&P carefully trim them so they both make good contact with the top cowl. Next there are many leaks where the fiberglass touches the engine especially near the case halves fore and aft as well as around and in grommets etc. Seal all that stuff up.

Brock I am just finished doing the above per your advice. It took maybe 4 hours in a relatively dark hangar, using a flashlight light to locate the leaks. The gaps were so numerous and huge that I am now convinced that ALL DA40s have the same limitation. I plugged everything but stopped at the level of the pushrods. because the RTV would have messed up the CHT sensor assembly. So I still have big gaps as of this "level". Did you also plug those?

One other thing I have not done is the filling of the scalloped shapes.
The problem exists, but frankly I am trying to figure out a way of making a cover. Looking for ideas here:
- How to make it and
- How to fasten it in an airtight fashion.
- It must be easily removable for the A&P so that he can sign off the annuals without it in place.

Maybe fill the area with some material and lay a pre-impregnated fiberglass cloth on top to start with?

Oil temperature issue:
I would like to draw your attention to an issue with the oil cooling setup in case you have not noticed it yet.
At least in my plane, the duct that brings the air to the cooler does not contact the cooler. The gap is about 1/2" all around. This means that there is no pressure differential on the air side of the oil cooler. In other words: the cooler is not working as it was designed to and it is providing a small fraction of its nominal performance.
I never have excessive oil temps so I will only worry about this when my plane gets the Supercharger. Just wanted to share the info.

[BRS]

I plugged everything but stopped at the level of the pushrods. because the RTV would have messed up the CHT sensor assembly. So I still have big gaps as of this "level". Did you also plug those?

Not sure where you mean - got a picture? I did seal around at least one control cable which is just left (toward co-pilot side) of center.

One other thing I have not done is the filling of the scalloped shapes.
The problem exists, but frankly I am trying to figure out a way of making a cover. Looking for ideas here:

Antoine, I don't think you can legally make a cover like that. Not in the USA anyway. That would probably fall under a major modification. I'd stick with sealing the scallops, it's easy to do and works well. Not to mention legal. A cover would be nice but perhaps a bit overkill.

Oil temperature issue:
I would like to draw your attention to an issue with the oil cooling setup in case you have not noticed it yet.
At least in my plane, the duct that brings the air to the cooler does not contact the cooler. The gap is about 1/2" all around. This means that there is no pressure differential on the air side of the oil cooler. In other words: the cooler is not working as it was designed to and it is providing a small fraction of its nominal performance.

Do you have the powerflow exhaust? I remember when installing it I got a plate the mounts to the oil cooler for the seal to rest upon. Can't remember if it was part of the Powerflow STC or another one just bundled with the powerflow. I believe it is on the current production aircraft though. In any case, we did have some leakage in this area but not a 1/2". We adjusted the fit with RTV like the baffles. Cover the oilcooler with plastic wrap, put rtv on the seal where it might be leaking then reinstall the bottom and top cowl. Let sit overnight. DONT FORGET to remove the plastic wrap before flying.